LT1970A - 500mA Power Op Amp with Adjustable Precision ... · The LT®1970A is a ±500mA power op...

LT1970A

11970afc

For more information www.linear.com/LT1970A

2V/DIV

0V

1970A TA01b

100µs/DIV

CURRENT LIMIT = 500mA

VLOAD, RLOAD = 100Ω

VLOAD,RLOAD = 10Ω

VIN, 5V/DIV

Typical applicaTion

DescripTion

500mA Power Op Amp withAdjustable Precision Current Limit

The LT®1970A is a ±500mA power op amp with precise externally controlled current limiting. Separate control voltages program the sourcing and sinking current limit sense thresholds with 1% accuracy. Output current may be boosted by adding external power transistors.

The circuit operates with single or split power supplies from 5V to 36V total supply voltage. In normal opera-tion, the input stage supplies and the output stage sup-plies are connected (VCC to V+ and VEE to V–). To reduce power dissipation it is possible to power the output stage (V+, V–) from independent, lower voltage rails. The amplifier is unity-gain stable with a 3.6MHz gain-bandwidth product and slews at 1.6V/µs. The LT1970A can drive capacitive and inductive loads directly.

Open-collector status flags signal current limit circuit activation, as well as thermal shutdown of the amplifier. An enable logic input puts the amplifier into a low power, high impedance output state when pulled low. Thermal shutdown and a ±800mA fixed current limit protect the chip under fault conditions.

The LT1970A is packaged in a 20-lead TSSOP package with a thermally conductive copper bottom plate to facilitate heat sinking.

Device Power Supply (DPS) with ±500mA Adjustable Current Limit

FeaTures

applicaTions

n ±500mA Minimum Output Currentn Independent Adjustment of Source and

Sink Current Limitsn 1% Current Limit Accuracyn Improved Reactive Load Driving Stabilityn Operates with Single or Split Suppliesn Shutdown/Enable Control Inputn Open-Collector Status Flags: Sink Current Limit Source Current Limit Thermal Shutdownn Fail-Safe Current Limit and Thermal Shutdownn 1.6V/µs Slew Raten 3.6MHz Gain-Bandwidth Productn Specified Temperature Range: –40°C to 85°Cn Available in a 20-Lead TSSOP Package

n Automatic Test Equipmentn Laboratory Power Suppliesn Motor Driversn Thermoelectric Cooler Driver

VCC

COMMONVEE

V+

EN

V–

10k

100pF

VCSRCVCSNK

ISNKISRC

SENSE–SENSE

SENSE+

TSD

IOUT

OUT

RCS1Ω

1/4WTRACE R100mΩ

TRACE L200nH

6k

+IN

20V

LT1970A

–5V

20V

–IN

LOADESR0.1Ω

4.7µF

1970A TA01

VLIMIT0V TO 5V

VIN

VLIMIT10 • RCS

IOUT(MAX) = ±

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

http://www.linear.com/LT1970A


LT1970A

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absoluTe MaxiMuM raTings

Supply Voltage (VCC to VEE) ..................................... 36VPositive High Current Supply (V+) ................... V– to VCCNegative High Current Supply(V–) ....................VEE to V+

Amplifier Output (OUT) ..................................... V– to V+

Current Sense Pins (SENSE+, SENSE–, FILTER) ........................... V– to V+

Logic Outputs (ISRC, ISNK, TSD) ....... COMMON to VCCInput Voltage (–IN, +IN) ............ VEE – 0.3V to VEE + 36VInput Current ......................................................... 10mACurrent Control Inputs (VCSRC, VCSNK) .............. COMMON to COMMON + 7VEnable Logic Input .............................. COMMON to VCC COMMON ....................................................... VEE to VCC Output Short-Circuit Duration ......................... IndefiniteOperating Temperature Range (Note 2)....–40°C to 85°CSpecified Temperature Range (Note 3) LT1970AC ................................................ 0°C to 70°C LT1970AI.............................................. –40°C to 85°CMaximum Junction Temperature.......................... 150°CStorage Temperature Range ................... –65°C to 150°CLead Temperature (Soldering, 10 sec) .................. 300°C

(Note 1)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITSPower Op Amp Characteristics

VOS Input Offset Voltage 0°C < TA < 70°C –40°C < TA < 85°C

l

l

200 600 1000 1300

µV µV µV

Input Offset Voltage Drift (Note 4) l –10 –4 10 µV/°C

IOS Input Offset Current VCM = 0V l –100 100 nA

IB Input Bias Current VCM = 0V l –600 –160 nA

Input Noise Voltage 0.1Hz to 10Hz 3 µVP-P

elecTrical characTerisTics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. See Test Circuit for standard test conditions.

pin conFiguraTion

FE PACKAGE20-LEAD PLASTIC TSSOP

1

2

3

4

5

6

7

8

9

10

TOP VIEW

20

19

18

17

16

15

14

13

12

11

VEE

V–

OUT

SENSE+

FILTER

SENSE–

VCC

–IN

+IN

VEE

VEE

V+

TSD

ISNK

ISRC

ENABLE

COMMON

VCSRC

VCSNK

VEE

+–

21

TJMAX = 150°C, θJA = 40°C/W (NOTE 8)

EXPOSED PAD (PIN 21) IS CONNECTED TO VEE

orDer inForMaTionLEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE

LT1970ACFE#PBF LT1970ACFE#TRPBF LT1970AFE 20-Lead Plastic TSSOP 0°C to 70°C

LT1970AIFE#PBF LT1970AIFE#TRPBF LT1970AFE 20-Lead Plastic TSSOP –40°C to 85°C

Consult LTC Marketing for parts specified with wider operating temperature ranges.For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.


http://www.linear.com/leadfree/

http://www.linear.com/tapeandreel/

LT1970A

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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITSen Input Noise Voltage Density 1kHz 15 nV/√Hz

in Input Noise Current Density 1kHz 3 pA/√Hz

RIN Input Resistance Common Mode Differential Mode

500 100

kΩ kΩ

CIN Input Capacitance Pin 8 and Pin 9 to Ground 6 pF

VCM Input Voltage Range Typical Guaranteed by CMRR Test

l

–14.5 –12.0

13.6 12.0

V V

CMRR Common Mode Rejection Ratio –12V < VCM < 12V l 92 105 dB

PSRR Power Supply Rejection Ratio VEE = V– = –5V, VCC = V+ = 3V to 30V

VEE = V– = –5V, VCC = 30V, V+ = 2.5V to 30V VEE = V– = –3V to –30V, VCC = V+ = 5V VEE = –30V, V– = –2.5V to –30V, VCC = V+ = 5V

l

l

l

l

90 110 90

110

100 130 100 130

dB dB dB dB

AVOL Large-Signal Voltage Gain RL = 1k, –12.5V < VOUT < 12.5V

l

100 75

150 V/mV V/mV

RL = 100Ω, –12.5V < VOUT < 12.5V

l

80 40

120 V/mV V/mV

RL = 10Ω, –5V < VOUT < 5V, V+ = –V– = 8V

l

20 5

45 V/mV V/mV

VOL Output Sat Voltage Low VOL = VOUT – V–

RL = 100, VCC = V+ = 15V, VEE = V– = –15V RL = 10, VCC = –VEE = 15V, V+ = –V– = 5V

l

1.9 0.8

2.5

V V

VOH Output Sat Voltage High VOH = V+ – VOUT RL = 100, VCC = V+ = 15V, VEE = V– = –15V RL = 10, VCC = –VEE = 15V, V+ = –V– = 5V

l

1.7 1.0

2.3

V V

ISC Output Short-Circuit Current Output Low, RSENSE = 0Ω Output High, RSENSE = 0Ω

500 –1000

800 –800

1200 –500

mA mA

SR Slew Rate –10V < VOUT < 10V, RL = 1k 0.7 1.6 V/µs

FPBW Full Power Bandwidth VOUT = 10VPEAK (Note 5) 11 kHz

GBW Gain-Bandwidth Product f = 10kHz 3.6 MHz

tS Settling Time 0.01%, VOUT = 0V to 10V, AV = –1, RL = 1k 8 µs

Current Sense Characteristics

VSENSE(MIN) Minimum Current Sense Voltage VCSRC = VCSNK = 0V

l

0.1 0.1

4 7 10

mV mV

VSENSE(4%) Current Sense Voltage 4% of Full Scale VCSRC = VCSNK = 0.2V l 15 20 25 mV

VSENSE(10%) Current Sense Voltage 10% of Full Scale VCSRC = VCSNK = 0.5V l 45 50 55 mV

VSENSE(FS) Current Sense Voltage 100% of Full Scale VCSRC = VCSNK = 5V

l

495 480

500 500

505 520

mV mV

IBI Current Limit Control Input Bias Current VCSRC, VCSNK Pins l –1 –0.2 0.1 µA

ISENSE– SENSE– Input Current 0V < (VCSRC, VCSNK) < 5V l –500 500 nA

IFILTER FILTER Input Current 0V < (VCSRC, VCSNK) < 5V l –500 500 nA

ISENSE+ SENSE+ Input Current VCSRC= VCSNK = 0V VCSRC = 5V, VCSNK = 0V VCSRC= 0V, VCSNK = 5V VCSRC = VCSNK = 5V

l

l

l

l

–500 200

–300 –25

250

–250

500 300

–200 25

nA µA µA µA

Current Sense Change with Output Voltage VCSRC = VCSNK = 5V, –12.5V < VOUT < 12.5V ±0.1 %

Current Sense Change with Supply Voltage VCSRC = VCSNK = 5V, 6V < (VCC, V+) < 18V 2.5V < V+ < 18V, VCC = 18V –18V < (VEE, V–) < –2.5V –18V < V– < –2.5V, VEE = –18V

±0.05 ±0.01 ±0.05 ±0.01

% % % %


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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITSCurrent Sense Bandwidth 2 MHz

RCSF Resistance FILTER to SENSE– l 750 1000 1250 Ω

Logic I/O Characteristics

Logic Output Leakage ISRC, ISNK, TSD V = 15V l 1 µA

Logic Low Output Level I = 5mA (Note 6) l 0.2 0.4 V

Logic Output Current Limit 25 mA

VENABLE Enable Logic Threshold l 0.8 1.9 2.5 V

IENABLE Enable Pin Bias Current l –1 1 µA

ISUPPLY Total Supply Current VCC, V+ and V–, VEE Connected l 7 13 mA

ICC VCC Supply Current VCC, V+ and V–, VEE Separate l 3 7 mA

ICC(STBY) Supply Current Disabled VCC, V+ and V–, VEE Connected, VENABLE ≤ 0.8V l 0.6 1.5 mA

tON Turn-On Delay (Note 7) 10 µs

tOFF Turn-Off Delay (Note 7) 10 µs

Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reli-ability and lifetime.Note 2: The LT1970AC is guaranteed functional over the operating tem-perature range of –40°C and 85°C.Note 3: The LT1970AC is guaranteed to meet specified performance from 0°C to 70°C. The LT1970AC is designed, characterized and expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LT1970AI is guaranteed to meet speci-fied performance from –40°C to 85°C.

Note 4: This parameter is not 100% tested.Note 5: Full power bandwidth is calculated from slew rate measurements: FPBW = SR/(2 • π • VP)Note 6: The logic low output level of pin TSD is guaranteed by correlating the output level of pin ISRC and pin ISNK over temperature.Note 7: Turn-on and turn-off delay are measured from VENABLE crossing 1.6V to the OUT pin at 90% of normal output voltage.Note 8: Thermal resistance varies depending upon the amount of PC board metal attached to the device. If the maximum dissipation of the package is exceeded, the device will go into thermal shutdown and be protected.

Warm-Up Drift VIO vs Time

Input Bias Current vs VCM

Total Supply Current vs Supply Voltage

Typical perForMance characTerisTics

TIME (100ms/DIV) 1970A G01

0VV OS

• 100

0 (5

0mV/

DIV)

COMMON MODE INPUT VOLTAGE (V)–15 –12 –9 –6 –3 0 3 6 9 12 15

INPU

T BI

AS C

URRE

NT (n

A)

–100

–120

–140

–160

–180

–200

–220

–240

–260

1970A G02

VS = ±15V

–IBIAS

+IBIAS

SUPPLY VOLTAGE (±V)0

–14

TOTA

L SU

PPLY

CUR

RENT

(mA)

–10

–6

–2

14

6

4 8 10 18

1970A G03

10

2

–12

–8

–4

12

4

8

0

2 6 12 14 16

ICC + IV+

IEE + IV–

25°C

25°C

–55°C

–55°C

125°C

125°C


LT1970A

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Gain Bandwidth vs Supply Voltage

Gain vs Frequency

Gain vs Frequency with C LOAD

Output Impedance

Disabled Output Impedance

Slew Rate vs Supply Voltage

Supply Current vs Supply Voltage

Open-Loop Gain and Phase vs Frequency

Phase Margin vs Supply Voltage

SUPPLY VOLTAGE (±V)2 4 6

0

SUPP

LY C

URRE

NT (m

A)

0.5

1.5

2.0

2.5

14 16 18

4.5IV

+

IV–

1870A G04

1.0

8 10 12 20

3.0

3.5

4.0

TA = 25°CVCC = V+ = –VEE = –V–

IVCC

IVEE

FREQUENCY (Hz)100 1k

10OP

EN-L

OOP

GAIN

(dB)

PHASE MARGIN (DEG)

20

30

40

50

10k 100k 1M 10M 100M

1970A G05

0

–10

–20

–30

60

70

40

50

60

70

80

30

20

10

0

90

100

PHASEGAIN

TOTAL SUPPLY VOLTAGE (V)0

40

PHAS

E M

ARGI

N (D

EG)

42

46

48

50

60

54

8 16 20 36

1970A G06

44

56

58

52

4 12 24 28 32

AV = –1RF = RG = 1kTA = 25°CVOUT = VS/2

TOTAL SUPPLY VOLTAGE (V)0

0

GAIN

BAN

DWID

TH (M

Hz)

1

3

4

5

8 16 20 36

1970A G07

2

4 12 24 28 32

AV = 100

FREQUENCY (Hz)

VOLT

AGE

GAIN

(dB)

10

–30

0

–10

–20

10k 1M 10M

1970A G08

–40100k

VS = ±5V

AV = 1

VS = ±15V

FREQUENCY (Hz)

VOLT

AGE

GAIN

(dB)

10

–30

0

–10

–20

10k 1M 10M

1970A G09

–40100k

30nF 10nF

1nF

0nF

VS = ±15VAV = 1

FREQUENCY (Hz)1k 10k

0.001

OUTP

UT IM

PEDA

NCE

(Ω)

0.1

100

100k 1M 10M 100M

1970A G10

0.01

1

10

VS = ±15V

AV = 100

AV = 1

AV = 10

FREQUENCY (Hz)1k

1

OUTP

UT IM

PEDA

NCE

(Ω)

100

100k

600k

10k 100k 1M 10M 100M

1970A G11

10

1k

10k

VS = ±15VVENABLE = 0.8V


SLEW

RAT

E (V

/µs)

1.7

10

1970A G12

1.4

1.2

6 8 12

1.1

1.0

1.8

1.6

1.5

1.3

14 16 18

FALLING

RISING

AV = –1RF = RG = 1kTA = 25°C


LT1970A

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Small-Signal Response, AV = 1

Small-Signal Response, AV = –1

Output Overdriven

% Overshoot vs CLOAD

Undistorted Output Swing vs Frequency

Full Range Current Sense Transfer Curve

Slew Rate vs Temperature

Large-Signal Response, AV = 1

Large-Signal Response, AV = –1

TEMPERATURE (°C)–50 –25

0

SLEW

RAT

E (V

/µs)

1.0

2.5

0 50 75

1970A G13

0.5

2.0

1.5

25 100 125

VS = ±15V FALLING

RISING

20µs/DIV 1970A G14

0V

10V

–10V

5V/D

IV

RL = 1k 20µs/DIVRL = 1kCL = 1000pF

1970A G15

0V

10V

–10V

5V/D

IV

500ns/DIV 1970A G16

20m

V/DI

V

RL = 1k 2µs/DIV 1970A G17

20m

V/DI

V

RL = 1kCL = 1000pF

200µs/DIV 1970A G18

VOUT5V/DIV 0V

0VVIN

5V/DIV

VS = ±5VAV = 1

CLOAD (pF)10

0

OVER

SHOO

T (%

) 40

50

60

100 1k 10k

1970A G19

30

20

10

VS = ±15V

AV = 1

AV = –1

FREQUENCY (Hz)100

0

OUTP

UT S

WIN

G (V

P-P)

20

25

30

1k 10k 100k

1970A G20

15

10

5 VS = ±15VAV = –51% THD

VCSNK = VCSRC (V)0

V SEN

SE (m

V) 100

300

500

4

1970A G21

–100

–300

0

200

400

–200

–400

–5001 2 3 5

SOURCINGCURRENT

SINKINGCURRENT


LT1970A

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Safe Operating Area

Output Stage Quiescent Current vs Supply Voltage

Control Stage Quiescent Current vs Supply Voltage

Supply Current vs Supply Voltage in Shutdown

Low Level Current Sense Transfer Curve

Logic Output Level vs Sink Current (Output Low)

Maximum Output Currentvs Temperature

VCSNK = VCSRC (mV)0

V SEN

SE (m

V) 5

15

25

200

1970A G22

–5

–15

0

10

20

–10

–20

–255025 10075 150 175 225125 250

SOURCINGCURRENT

SINKINGCURRENT

SINK CURRENT (mA)0.001

0.4LO

GIC

OUTP

UT V

OLTA

GE (V

)

0.5

0.6

0.7

0.8

0.01 0.1 1 10 100

1970A G23

0.3

0.2

0.1

0

0.9

1.0V+ = 15VV– = –15V

125°C25°C

–55°C

TEMPERATURE (°C)–75

OUTP

UT C

URRE

NT (m

A)

800

1200

125

1970A G24

400

0–25 25 75–50 0 50 100

1600

600

1000

200

1400

V+ = 15VV– = –15V

SOURCE

SINK

SUPPLY VOLTAGE (V)0

0

I OUT

PEA

K (m

A)

200

400

600

800

10 20 30 40

1970A G25

1000

1200

5 15 25 35

IOUT AT 10% DUTY CYCLE


OUTP

UT S

TAGE

CUR

RENT

(mA)

–10

–6

–2

6

4 8 10 18

1970A G26

10

2

–8

–4

4

8

0

2 6 12 14 16

IV+

IV–

25°C

25°C

–55°C

–55°C

125°C

125°C


SUPP

LY C

URRE

NT (m

A)

–5

–3

–1

3

4 8 10 18

1970A G27

5

1

–4

–2

2

4

0

2 6 12 14 16

ICC

IEE

25°C

25°C

–55°C

–55°C

125°C

125°C

SUPPLY VOLTAGE (V)0

TOTA

L SU

PPLY

CUR

RENT

, ICC

+ I V

+ (µ

A)

400

500

600

16

1970A G28

300

200

04 8 122 186 10 14

100

800

70085°C

25°C

–55°C

VENABLE = 0V


LT1970A

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pin FuncTionsVEE (Pins 1, 10, 11, 20, 21): Minus Supply Voltage. VEE connects to the substrate of the integrated circuit die, and therefore must always be the most negative voltage ap-plied to the part. Decouple VEE to ground with a low ESR capacitor. VEE may be a negative voltage or it may equal ground potential. Any or all of the VEE pins may be used. Unused VEE pins must remain open.

V– (Pin 2): Output Stage Negative Supply. V– may equal VEE or may be smaller in magnitude. Only output stage current flows out of V–, all other current flows out of VEE. V– may be used to drive the base/gate of an external power device to boost the amplifier’s output current to levels above the rated 500mA of the on-chip output devices. Unless used to drive boost transistors, V– should be decoupled to ground with a low ESR capacitor.

OUT (Pin 3): Amplifier Output. The OUT pin provides the force function as part of a Kelvin sensed load connection. OUT is normally connected directly to an external load cur-rent sense resistor and the SENSE+ pin. Amplifier feedback is directly connected to the load and the other end of the current sense resistor. The load connection is also wired directly to the SENSE– pin to monitor the load current.

The OUT pin is current limited to ±800mA typical. This current limit protects the output transistor in the event that connections to the external sense resistor are opened or shorted which disables the precision current limit function.

SENSE+ (Pin 4): Positive Current Sense Pin. This lead is normally connected to the driven end of the external sense resistor. Sourcing current limit operation is activated when the voltage VSENSE (VSENSE+ – VSENSE–) equals 1/10 of the programming control voltage at VCSRC (Pin 13). Sink-ing current limit operation is activated when the voltage VSENSE equals –1/10 of the programming control voltage at VCSNK (Pin 12).

FILTER (Pin 5): Current Sense Filter Pin. This pin is normally not used and should be left open or shorted to the SENSE– pin. The FILTER pin can be used to adapt the response time of the current sense amplifiers with a 1nF to 100nF capacitor connected to the SENSE– input. An internal 1k resistor sets the filter time constant.

SENSE– (Pin 6): Negative Current Sense Pin. This pin is normally connected to the load end of the external sense resistor. Sourcing current limit operation is activated when the voltage VSENSE (VSENSE+ – VSENSE–) equals 1/10 of the programming control voltage at VCSRC (Pin 13). Sink-ing current limit operation is activated when the voltage VSENSE equals –1/10 of the programming control voltage at VCSNK (Pin 12).

VCC (Pin 7): Positive Supply Voltage. All circuitry except the output transistors draw power from VCC. Total supply voltage from VCC to VEE must be between 3.5V and 36V. VCC must always be greater than or equal to V+. VCC should always be decoupled to ground with a low ESR capacitor.

–IN (Pin 8): Inverting Input of Amplifier. –IN may be any voltage from VEE – 0.3V to VEE + 36V. –IN and +IN remain high impedance at all times to prevent current flow into the inputs when current limit mode is active. Care must be taken to ensure that –IN or +IN can never go to a volt-age below VEE – 0.3V even during transient conditions or damage to the circuit may result. A Schottky diode from VEE to –IN can provide clamping if other elements in the circuit can allow –IN to go below VEE.

+IN (Pin 9): Noninverting Input of Amplifier. +IN may be any voltage from VEE – 0.3V to VEE + 36V. –IN and +IN remain high impedance at all times to prevent current flow into the inputs when current limit mode is active. Care must be taken to ensure that –IN or +IN can never go to a volt-age below VEE – 0.3V even during transient conditions or damage to the circuit may result. A Schottky diode from VEE to +IN can provide clamping if other elements in the circuit can allow + IN to go below VEE.


LT1970A

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pin FuncTionsVCSNK (Pin 12): Sink Current Limit Control Voltage In-put. The current sink limit amplifier will activate when the sense voltage between SENSE+ and SENSE– equals –1.0 • VVCSNK/10. VCSNK may be set between VCOMMON and VCOMMON + 6V. The transfer function between VCSNK and VSENSE is linear except for very small input voltages at VCSNK < 60mV. VSENSE limits at a minimum set point of 4mV typical to ensure that the sink and source limit amplifiers do not try to operate simultaneously. To force zero output current, the ENABLE pin can be taken low.

VCSRC (Pin 13): Source Current Limit Control Voltage Input. The current source limit amplifier will activate when the sense voltage between SENSE+ and SENSE– equals VVCSRC/10. VCSRC may be set between VCOMMON and VCOMMON + 6V. The transfer function between VCSRC and VSENSE is linear except for very small input voltages at VCSRC < 60mV. VSENSE limits at a minimum set point of 4mV typical to ensure that the sink and source limit amplifiers do not try to operate simultaneously. To force zero output current, the ENABLE pin can be taken low.

COMMON (Pin 14): Control and ENABLE inputs and flag outputs are referenced to the COMMON pin. COMMON may be at any potential between VEE and VCC – 3V. In typical applications, COMMON is connected to ground.

ENABLE (Pin 15): ENABLE Digital Input Control. When taken low this TTL-level digital input turns off the ampli-fier output and drops supply current to less than 1mA. Use the ENABLE pin to force zero output current. Setting VCSNK = VCSRC = 0V allows IOUT = ±4mV/RSENSE to flow in or out of VOUT.

ISRC (Pin 16): Sourcing Current Limit Digital Output Flag. ISRC is an open-collector digital output. ISRC pulls low whenever the sourcing current limit amplifier assumes control of the output. This pin can sink up to 10mA of

current. The current limit flag is off when the source current limit is not active. ISRC, ISNK and TSD may be wired “OR” together if desired. ISRC may be left open if this function is not monitored.

ISNK (Pin 17): Sinking Current Limit Digital Output Flag. ISNK is an open-collector digital output. ISNK pulls low whenever the sinking current limit amplifier assumes control of the output. This pin can sink up to 10mA of current. The current limit flag is off when the source current limit is not active. ISRC, ISNK and TSD may be wired “OR” together if desired. ISNK may be left open if this function is not monitored.

TSD (Pin 18): Thermal Shutdown Digital Output Flag. TSD is an open-collector digital output. TSD pulls low whenever the internal thermal shutdown circuit activates, typically at a die temperature of 160°C. This pin can sink up to 10mA of output current. The TSD flag is off when the die tem-perature is within normal operating temperatures. ISRC, ISNK and TSD may be wired “OR” together if desired. TSD may be left open if this function is not monitored. Thermal shutdown activation should prompt the user to evaluate electrical loading or thermal environmental conditions.

V+ (Pin 19): Output Stage Positive Supply. V+ may equal VCC or may be smaller in magnitude. Only output stage current flows through V+, all other current flows into VCC. V+ may be used to drive the base/gate of an external power device to boost the amplifier’s output current to levels above the rated 500mA of the on-chip output devices. Unless used to drive boost transistors, V+ should be decoupled to ground with a low ESR capacitor.

Exposed Pad (Pin 21): The exposed backside of the pack-age is electrically connected to the VEE pins on the IC die. The package base should be soldered to a heat spreading pad on the PC board that is electrically connected to VEE.


LT1970A

101970afc


block DiagraM anD TesT circuiT

applicaTions inForMaTionThe LT1970A power op amp with precision controllable current limit is a flexible voltage and current source module. The drawing on the front page of this data sheet is representative of the basic application of the circuit, however many alternate uses are possible with proper understanding of the sub circuit capabilities.

CIRCUIT DESCRIPTION

Main Operational Amplifier

Sub circuit block GM1, the 1X unity-gain current buf-fer and output transistors Q1 and Q2 form a standard operational amplifier. This amplifier has ±500mA current output capability and a 3.6MHz gain-bandwidth product. Most applications of the LT1970A will use this op amp in the main signal path. All conventional op amp circuit configurations are supported. Inverting, noninverting, filter, summation or nonlinear circuits may be implemented in

a conventional manner. The output stage includes current limiting at ±800mA to protect against fault conditions. The input stage has high differential breakdown of 36V minimum between –IN and +IN. No current will flow at the inputs when differential input voltage is present. This feature is important when the precision current sense amplifiers “ISINK” and “ISRC” become active.

Current Limit Amplifiers

Amplifier stages “ISINK” and “ISRC” are very high transcon-ductance amplifier stages with independently controlled offset voltages. These amplifiers monitor the voltage between input pins SENSE+ and SENSE– which usually sense the voltage across a small external current sense resistor. The transconductance amplifiers outputs con-nect to the same high impedance node as the main input stage GM1 amplifier. Small voltage differences between SENSE+ and SENSE–, smaller than the user set VCSNK/10

3

19

7

9

8

17

16

18

15

12

13

–

+

–

+

–

+

ISNK

1970ATC

RFIL1k

RCS1Ω

RLOAD1kISRC

D2

D1

1×

Q1

Q2

4

5

6

2

GM1

ENABLE

COMMON

VCSRCVCSRC

VCSNK5V

15V

VCSNK

ISRC

ISNK

–IN

VIN

RG1k

+IN

ENABLE

TSD

14

VCC

V+

15V

–15V

OUT

SENSE+

FILTER

SENSE–

V–

VEE

1, 10, 11, 20

10k

10k

10k

RF1k

VSRC+–

VSNK+–

+–


LT1970A

111970afc


applicaTions inForMaTionand VCSRC/10 in magnitude, cause the current limit ampli-fiers to decouple from the signal path. This is functionally indicated by diodes D1 and D2 in the Block Diagram. When the voltage VSENSE increases in magnitude sufficient to equal or overcome one of the offset voltages VCSNK/10 or VCSRC/10, the appropriate current limit amplifier becomes active and because of its very high transconductance, takes control from the input stage, GM1. The output current is regulated to a value of IOUT = VSENSE/RSENSE = (VCSRC or VCSNK)/(10 • RSENSE). The time required for the current limit amplifiers to take control of the output is typically 4µs.

Linear operation of the current limit sense amplifier occurs with the inputs SENSE+ and SENSE– ranging be-tween VCC – 1.5V and VEE + 1.5V. Most applications will connect pins SENSE+ and OUT together, with the load on the opposite side of the external sense resistor and pin SENSE–. Feedback to the inverting input of GM1 should be connected from SENSE– to – IN. Ground side sensing of load current may be employed by connecting the load between pins OUT and SENSE+. Pin SENSE– would be connected to ground in this instance. Load current would be regulated in exactly the same way as the conventional connection. However, voltage mode accuracy would be degraded in this case due to the voltage across RSENSE.

Creative applications are possible where pins SENSE+ and SENSE– monitor a parameter other than load current. The operating principle that at most one of the current limit stages may be active at one time, and that when active, the current limit stages take control of the output from GM1, can be used for many different signals.

Current Limit Threshold Control Buffers

Input pins VCSNK and VCSRC are used to set the response thresholds of current limit amplifiers “ISINK” and “ISRC”. Each of these inputs may be independently driven by a voltage of 0V to 5V above the COMMON reference pin. The 0V to 5V input voltage is attenuated by a factor of 10 and applied as an offset to the appropriate current limit amplifier. AC signals may be applied to these pins. The AC bandwidth from a VC pin to the output is typically 2MHz. For proper operation of the LT1970A, these control inputs cannot be left floating.

For low VCC supply applications it is important to keep the maximum input control voltages, VCSRC and VCSNK, at least 2.5V below the VCC potential. This ensures linear control of the current limit threshold. Reducing the current limit sense resistor value allows high output current from a smaller control voltage which may be necessary if the VCC supply is only 5V.

The transfer function from VC to the associated VOS is linear from about 0.1V to 5V in, or 10mV to 500mV at the current limit amplifier inputs. An intentional nonlinear-ity is built into the transfer functions at low levels. This nonlinearity ensures that both the sink and source limit amplifiers cannot become active simultaneously. Simul-taneous activation of the limit amplifiers could result in uncontrolled outputs. As shown in the Typical Performance Characteristics curves, the control inputs have a “hockey stick” shape, to keep the minimum limit threshold at 4mV for each limit amplifier.

Figure 1 illustrates an interesting use of the current sense input pins. Here the current limit control ampli-fiers are used to produce a symmetrically limited output voltage swing. Instead of monitoring the output current, the output voltage is divided down by a factor of 20 and applied to the SENSE+ input, with the SENSE– input grounded. When the threshold voltage between SENSE+ and SENSE– (VCLAMP/10) is reached, the current limit stage takes control of the output and clamps it a level of ±2 • VCLAMP. With control inputs VCSRC and VCSNK tied together, a single polarity input voltage sets the same + and – output limit voltage for symmetrical limiting. In this circuit the output will current limit at the built-in fail-safe level of typically 800mA.

ENABLE Control

The ENABLE input pin puts the LT1970A into a low sup-ply current, high impedance output state. The ENABLE pin responds to TTL threshold levels with respect to the COMMON pin. Pulling the ENABLE pin low is the best way to force zero current at the output. Setting VCSNK = VCSRC = 0V allows the output current to remain as high as ±4mV/RSENSE.


LT1970A

121970afc


applicaTions inForMaTion

Figure 2. Using the ENABLE pin

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

12V

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+IN

5V

0V

5VENABLE

DISABLE

VIN

LT1970A

–12V

–IN

RS1Ω

RL10Ω

1970A F02

RG10k

RF10k

EN10V/DIV

0V

VOUT

1V/DIV

5µs/DIV

0VVIN = 0.5V VIN = –0.5V

In applications such as circuit testers (ATE), it may be preferable to apply a predetermined test voltage with a preset current limit to a test node simultaneously. The ENABLE pin can be used to provide this gating action as shown in Figure 2. While the LT1970A is disabled, the load is essentially floating and the input voltage and current limit control voltages can be set to produce the load test levels. Enabling the LT1970A then drives the load. The LT1970A enables and disables in just a few microseconds. The actual enable and disable times at the load are a function of the load reactance.

Operating Status Flags

The LT1970A has three digital output indicators; TSD, ISRC and ISNK. These outputs are open-collector drivers referred to the COMMON pin. The outputs have 36V ca-pabilities and can sink in excess of 10mA. ISRC and ISNK indicate activation of the associated current limit amplifier. The TSD output indicates excessive die temperature has caused the circuit to enter thermal shutdown. The three digital outputs may be wire “ORed” together, monitored individually or left open. These outputs do not affect circuit operation, but provide an indication of the present operational status of the chip.

Figure 1. Symmetrical Output Voltage Limiting

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

12V

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+IN

R33k

80mVTO

10V

–80mVTO

–10V±CLAMPREACHED OUTPUT CLAMPS

AT 2× VCLAMP

VCLAMPOV TO 5V

VIN

LT1970A

–12V

–IN

R121.5k RL

1970A F01

R21.13k

RFRG

For slow varying output signals, the assertion of a low level at the current limit output flags occurs when the current limit threshold is reached. For fast moving signals where the LT1970A output is moving at the slew limit, typically 1.6V/µs, the flag assertion can be somewhat premature at typically 75% of the actual current limit value.

The operating status flags are designed to drive LEDs to provide a visual indication of current limit and thermal conditions. As such, the transition edges to and from the active low state are not particularly sharp and may exhibit some uncertainty. Adding some positive feedback to the current limit control inputs helps to sharpen these transitions.

With the values shown in Figure 3, the current limit thresh-old is reduced by approximately 0.5% when either current limit status flag goes low. With sharp logic transitions, the status outputs can be used in a system control loop to take protective measures when a current limit condition is detected automatically.


LT1970A

131970afc



Figure 3. Adding Positive Feedback to Sharpen the Transition Edges of the Current Limit Status Flags

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

12V

ISOURCE FLAG

WHEN CURRENT LIMITIS FLAGGED, ILIMITTRESHOLD IS REDUCEDBY 0.5%

ISINK FLAG

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+INVIN

LT1970A

–12V

–IN

RS1Ω

RL

1970A F03

RG RF

R2100Ω

R1100Ω

CURRENTLIMIT

CONTROLVOLTAGE

(0.1V TO 5V)

R420k

R320k

The current limit status flag can also be used to produce a dramatic change in the current limit value of the ampli-fier. Figure 4 illustrates a “snap-back” current limiting characteristic. In this circuit, a simple resistor network initially sets a high value of current limit (500mA). The circuit operates normally until the signal is large enough to enter current limit. When either current limit flag goes low, the current limit control voltage is reduced by a factor of 10. This then forces a low level of output current (50mA) until the signal is reduced in magnitude. When the load current drops below the lower level, the current limit is then restored to the higher value. This action is similar to a self resettable fuse that trips at dangerously high current levels and resets only when conditions are safe to do so.

THERMAL MANAGEMENT

Minimizing Power Dissipation

The LT1970A can operate with up to 36V total supply volt-age with output currents up to ±500mA. The amount of power dissipated in the chip could approach 18W under worst-case conditions. This amount of power will cause die temperature to rise until the circuit enters thermal

Figure 4. “Snap-Back” Current Limiting

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

12V

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+INVIN

LT1970A

–12V

–IN

RS1Ω

RL

1970A F04

RG10k

RF10k

R32.55k

R239.2k

R154.9k

IMAX500mA

–500mA

50mA0IOUT

ILOW

VCC • R2(R1 + R2) • 10 • RS

IMAX ≈

VCC • (R2||R3)[R1 + (R2||R3)] • 10 • RS

ILOW ≈

shutdown. While the thermal shutdown feature prevents damage to the circuit, normal operation is impaired. Thermal design of the LT1970A operating environment is essential to getting maximum utility from the circuit.

The first concern for thermal management is minimizing the heat which must be dissipated. The separate power pins V+ and V– can be a great aid in minimizing on-chip power. The output pin can swing to within 1.0V of V+ or V– even under maximum output current conditions. Using separate power supplies, or voltage regulators, to set V+ and V– to their minimum values for the required output swing will minimize power dissipation. The supplies VCC and VEE may also be reduced to a minimal value, but these supply pins do not carry high currents, and the power saving is much less. VCC and VEE must be greater than the maximum output swing by 1.5V or more.


LT1970A

141970afc


applicaTions inForMaTionWhen V– and V+ are provided separately from VCC and VEE, care must be taken to ensure that V– and V+ are always less than or equal to the main supplies in magnitude. Protection Schottky diodes may be required to ensure this in all cases, including power on/off transients.

Operation with reduced V+ and V– supplies does not affect any performance parameters except maximum output swing. All DC accuracy and AC performance specifications guaranteed with VCC = V+ and VEE = V– are still valid with the reduced output signal swing range.

Heat Sinking

The power dissipated in the LT1970A die must have a path to the environment. With 100°C/W thermal resistance in free air with no heat sink, the package power dissipation is limited to only 1W. The 20-pin TSSOP package with exposed copper underside is an efficient heat conductor if it is effectively mounted on a PC board. Thermal resis-tances as low as 40°C/W can be obtained by soldering the bottom of the package to a large copper pattern on the PC board. For operation at 85°C, this allows up to 1.625W of power to be dissipated on the LT1970A. At 25°C operation, up to 3.125W of power dissipation can be achieved. The PC board heat spreading copper area must be connected to VEE.

Figure 5 shows examples of PCB metal being used for heat spreading. These are provided as a reference for what might be expected when using different combina-tions of metal area on different layers of a PCB. These examples are with a 4-layer board using 1oz copper on each layer. The most effective layers for spreading heat are those closest to the LT1970A junction. Soldering the exposed thermal pad of the TSSOP package to the board produces a thermal resistance from junction-to-case of approximately 3°C/W.

As a minimum, the area directly beneath the package on all PCB layers can be used for heat spreading. However, limiting the area to that of the metal heat sinking pad is not very effective. Expanding the area on various layers significantly reduces the overall thermal resistance. The addition of vias (small 13 mil holes which fill during PCB

plating) connecting all layers of metal also helps reduce the operating temperature of the LT1970A. These are also shown in Figure 5.

It is important to note that the metal planes used for heat sinking are connecting electrically to VEE. These planes must be isolated from any other power planes used in the PCB design.

Another effective way to control the power amplifier operat-ing temperature is to use airflow over the board. Airflow can significantly reduce the total thermal resistance as also shown in Figure 5.

DRIVING REACTIVE LOADS

Capacitive Loads

The LT1970A is much more tolerant of capacitive loading than most operational amplifiers. In a worst-case con-figuration as a voltage follower, the circuit is stable for capacitive loads less than 2.5nF. Higher gain configurations improve the CLOAD handling. If very large capacitive loads are to be driven, a resistive decoupling of the amplifier from the capacitive load is effective in maintaining stability and reducing peaking. The current sense resistor, usually connected between the output pin and the load can serve as a part of the decoupling resistance.

Inductive Loads

Load inductance is usually not a problem at the outputs of operational amplifiers, but the LT1970A can be used as a high output impedance current source. This condition may be the main operating mode, or when the circuit enters a protective current limit mode. Just as load capacitance degrades the phase margin of normal op amps, load inductance causes a peaking in the loop response of the feedback controlled current source. The inductive load may be caused by long lead lengths at the amplifier output. If the amplifier will be driving inductive loads or long lead lengths (greater than 4 inches) a 500pF capacitor from the SENSE– pin to the ground plane will cancel the inductive load and ensure stability.


LT1970A

151970afc



Figure 5. Examples of PCB Metal Used for Heat Dissipation. Driver Package Mounted on Top Layer. Heat Sink Pad Soldered to Top Layer Metal. Metal Areas Drawn to Scale of Package Size

STILL AIR θJA

TSSOP100°C/W

TSSOP50°C/W

TSSOP45°C/W

PACKAGE TOP LAYER 2ND LAYER 3RD LAYER BOTTOM LAYER

1970A F05a

AIRFLOW (LINEAR FEET PER MINUTE, lfpm)

–50

–60

REDU

CTIO

N IN

θJA

(%)

–30

–10

0

–40

–20

200 400 600 800

1970A F05b

10001000 300 500

Typical Reduction in θJA withLaminar Airflow Over the Device

700 900

% REDUCTION RELATIVETO θJA IN STILL AIR


LT1970A

161970afc



Figure 6. Current Modulation of a Magnetic Transducer

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

12V

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

D21N4001

C1500pF

R195.3K

LT1634-2.5

+IN

5V

VIN

0V

LT1970A

–12V

–IN

12V

5V

SOURCING

SINKING

2.5V

RS1Ω

±500mA

MAGNETICTRANSDUCER

1970A F06

D11N4001

Figure 7. Digitally Controlled Analog Pin Driver

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

18V

R63k 10µF 0.1µF

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+INR210.2k

R13.4k

0V

5V

APPLY LOADDRIVE

OPTIONAL TEST PINON/OFF CONTROL

Hi-Z

LT1970A

–18V10µF 0.1µF

SENSE

–IN

RS1Ω FORCE

TEST PINLOAD

1970A F07

R410.2k

VCC VREF

5V

CLR

DAC A

DAC B

CS/LDSCK

DI

DAC C

DAC D

R33.4k

LTC1664QUAD 10-BIT DAC

DECODER

3-WIRESERIAL

INTERFACE

+

R53k

+

VOUT = 15V

ISOURCE(MAX) = ≈ –4mA TO –500mA

≈ ±15VCODE C – CODE D1024( )

0.5 • CODE B1024 • RS

ISINK(MAX) = ≈ 4mA TO 500mA0.5 • CODE A1024 • RS


LT1970A

171970afc


applicaTions inForMaTionFigure 6 shows the LT1970A driving an inductive load with a controlled amount of current. This load is shown as a generic magnetic transducer, which could be used to create and modulate a magnetic field. Driving the current limit control inputs directly forces a current through the load that could range up to 2MHz in modulation. Clamp diodes are added to protect the LT1970A output from large inductive flyback potentials caused by rapid di/dt changes.

Supply Bypassing

The LT1970A can supply large currents from the power supplies to a load at frequencies up to 4MHz. Power supply impedance must be kept low enough to deliver these currents without causing supply rails to droop. Low ESR capacitors, such as 0.1µF or 1µF ceramics, located close to the pins are essential in all applications. When large, high speed transient currents are present additional capacitance may be needed near the chip. Check supply rails with a scope and if signal related ripple is seen on the supply rail, increase the decoupling capacitor as needed.

To ensure proper start-up biasing of the LT1970A, it is recommended that the rate of change of the supply volt-ages at turn-on be limited to be no faster than 6V/µs.

Application Circuit Ideas

The digitally controlled analog pin driver is shown in Figure 7. All of the control signals are provided by an LTC®1664 quad, 10-bit DAC by way of a 3-wire serial interface. The LT1970A is configured as a simple differ-ence amplifier with a gain of 3. This gain is required to produce ±15V from the 0V to 5V outputs from DACs C and D. To provide voltage headroom, the supplies for the LT1970A are set to the maximum value of ±18V. As ±18V is the absolute maximum rating of supply voltage for the LT1970A, care must be taken to not allow the supply voltage to increase. DACs A and B separately control the sinking and sourcing current limit to the load over the range of ±4mA to ±500mA. An optional on/off control for the pin driver using the ENABLE input is shown. If always enabled the ENABLE pin should be tied to VCC.

In some applications it may be necessary to know what the current into the load is at any time. Figure 8 shows an

LT1787 high side current sense amplifier monitoring the current through sense resistor RS. The LT1787 is biased from the VEE supply to accommodate the common mode input range of ±10V. The sense resistor is scaled down to provide a 100mV maximum differential signal to the current sense amplifier to preserve linearity. The LT1880 amplifier provides gain and level shifting to produce a 0V to 5V output signal (2.5V DC ±5mV/mA) with up to 1kHz full-scale bandwidth. An A/D converter could then digi-tize this instantaneous current reading to provide digital feedback from the circuit.

The LT1970A is just as easy to use as a standard opera-tional amplifier. Basic amplification of a precision reference voltage creates a very simple bench DC power supply as shown in Figure 9. The built-in power stage produces an adjustable 0V to 25V at 4mA to 100mA of output current. Voltage and current adjustments are derived from the LT1634-5 5V reference. The output current capability is 500mA, but this supply is restricted to 100mA for power dissipation reasons. The worst-case output voltage for maximum power dissipated in the LT1970A output stage occurs if the output is shorted to ground or set to a voltage near zero. Limiting the output current to 100mA sets the maximum power dissipation to 3W. To allow the output to range all the way to 0V, an LTC1046 charge pump inverter is used to develop a –5V supply. This produces a negative rail for the LT1970A which has to sink only the quiescent current of the amplifier, typically 7mA.

Using a second LT1970A, a 0V to ±12V dual tracking power supply is shown in Figure 10. The midpoint of two 10k resistors connected between the + and – outputs is held at 0V by the LT1881 dual op amp servo feedback loop. To maintain 0V, both outputs must be equal and opposite in polarity, thus they track each other. If one output reaches current limit and drops in voltage, the other output fol-lows to maintain a symmetrical + and – voltage across a common load. Again, the output current limit is less than the full capability of the LT1970A due to thermal reasons. Separate current limit indicators are used on each LT1970A because one output only sources current and the other only sinks current. Both devices can share the same thermal shutdown indicator, as the output flags can be ORed together.


LT1970A

181970afc



Figure 8. Sensing Output Current

VCSRC

COMMONVEE

VCSNK

V–FILTER

V+

12V

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+IN

VCC0V TO 1V

LT1970A

–12V

–IN

RS0.2Ω

RLOAD

1970A F08

RG RF

VS–

VEE

20k

BIAS–12V

–12V

R160.4k

R4255k

VOUT2.5V±5mV/mA

1kHz FULL CURRENTBANDWIDTH

R210k

R320k

VS+

LT1787

–

+LT1880

12V

–12V

0V TO 5V A/D

OPTIONAL DIGITAL FEEDBACK

Figure 9. Simple Bench Power Supply

VCSRC

CURRENT LIMITADJUST

COMMONVEE

VCSNK

V–FILTER

V+

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

C210µF

C1 10µFRG

2.55k

LT1634-5

+IN

LT1970A

–5V

–IN

RS1Ω

R55.49k

30V DC

LOADFAULT

VOUT0V TO 25V4mA TO 100mA

C310µF

GND

1970A F09

+

++

LTC1046

RF10.2k

R310k

R4 10kOUTPUTVOLTAGEADJUST

R12.1k

R2 40k


LT1970A

191970afc



Figure 10. Dual Tracking Bench Power Supply

VCSRC

COMMONVEE

VCSNKR513k

V–FILTER

V+

15V

R618.2k

R73k

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

–IN

LT1970A

–15V

R1110k

15V

C11µF

–15V

+IN

RS11Ω

+OUTCURRENTLIMIT

THERMALFAULT

R83k 0.1 10µF

R1325.5k

GROUND

OPTIONAL SYMMETRYADJUST100Ω

+

C210µF

+OUT0V TO 12V4mA TO 150mA

–OUT0V TO –12V4mA TO 150mA

1970A F10

+

VCSRC

COMMONVEE

VCSNKR14

10.7k

V–FILTER

V+

15VR153k

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

–IN

LT1970A

–15V

+IN

RS21Ω

–OUTCURRENTLIMIT

TO TSD PINOF +OUT

C310µF

R1010k1%

10µF 0.1µF+

+

–

+–

+R1210k

1/2 LT1881

1/2 LT1881

R910k1%

VOUTADJUST

CURRENTLIMITADJUST

R16.19k

R210k

R410kLT1634-5

R323.2k

5VREF

18V


LT1970A

201970afc


VCSRC

COMMON

R449.9k

15V

–15V

REVERSE

FORWARD

R210k

VEE

VCSNK

V–FILTER

V+

15V

ENVCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+IN

LT1970A

–15V

–IN

RS1Ω

12V DCMOTOR

TACHFEEDBACK3V/1000rpm

GND

1970A F11

C11µF

R549.9k

R31.2k

R11.2k

OV TO 5VTORQUE/STALL

CURRENT CONTROL

Figure 11. Simple Bidirectional DC Motor Speed Controller

applicaTions inForMaTionAnother simple linear power amplifier circuit is shown in Figure 11. This uses the LT1970A as a linear driver of a DC motor with speed control. The ability to source and sink the same amount of output current provides for bidirectional rotation of the motor. Speed control is managed by sensing the output of a tachometer built on to the motor. A typi-cal feedback signal of 3V/1000rpm is compared with the desired speed-set input voltage. Because the LT1970A is unity-gain stable, it can be configured as an integrator to force whatever voltage across the motor as necessary to match the feedback speed signal with the set input signal.

Additionally, the current limit of the amplifier can be ad-justed to control the torque and stall current of the motor. For reliability, a feedback scheme similar to that shown in Figure 4 can be used. Assuming that a stalled rotor will generate a current limit condition, the stall current limit can be significantly reduced to prevent excessive power dissipation in the motor windings.

For motor speed control without using a tachometer, the circuit in Figure 12 shows an approach. Using the enable feature of the LT1970A, the drive to the motor can be removed periodically. With no drive applied, the spinning motor presents a back EMF voltage proportional to its rotational speed. The LT1782 is a tiny rail-to-rail amplifier with a shutdown pin. The amplifier is enabled during this interval to sample the back EMF voltage across the motor. This voltage is then buffered by one-half of an LT1638 dual op amp and used to provide the feedback to the LT1970A integrator. When re-enabled the LT1970A will adjust the drive to the motor until the speed feedback voltage, com-pared to the speed-set input voltage, settles the output to a fixed value. A 0V to 5V signal for the motor speed input controls both rotational speed and direction.

The other half of the LT1638 is used as a simple pulse oscillator to control the periodic sampling of the motor back EMF.

Figure 13 shows how easy it is to boost the output current of the LT1970A. This ±5A power stage uses complemen-tary external N- and P-channel MOSFETs to provide the additional current. The output stage power supply inputs, V+ and V–, are used to provide gate drive as needed. With higher output currents, the sense resistor RCS, is reduced in value to maintain the same easy current limit control.

This Class B power stage is intended for DC and low frequency, <1kHz, applications as crossover distortion becomes evident at higher frequencies.

Figure 13 shows some optional resistor dividers between the output connections and the current sense inputs. They are required only if the load of this power stage is removed or at a very low current level. Large power devices with no load on them can saturate and pull the output voltage very close to the power supply rails. The current sense amplifiers operate properly with input voltages at least 1V away from the VCC and VEE supply rails. In boosted current applications, it may be necessary to attenuate the maximum output voltage levels by 1V before connecting to the sense input pins. This only slightly deceases the current limit thresholds.


LT1970A

211970afc



Figure 12. Simple Bidirectional DC Motor Speed Controller Without a Tachometer

VCSRC

COM

VEE

VCSNK

V–FILTER

V+

FAULT/STALL

R32k

12V

EN

VCC

ISNKISRC

SENSE–SENSE+

TSDOUT

+IN

LT1970A

–12V

12V

–12V

12V

12V

–12V

–IN

RS1Ω

12V DCMOTOR

1970A F12

C14.7µF

R15100Ω

C20.01µF SHDN

R1410k

OV TO 5VTORQUE/STALL

CURRENT CONTROL

R220k

R110k

R4100k

R5120k

R710k

R1210k

R1310k

R820k

R920kR10

82.5k

C30.1µF

D11N4148

D21N4148

–12V

R119.09k

–

+

–

+–

+

R649.9k

1/2 LT1638

1/2 LT1638

LT1782

5V

0V

MOTOR SPEEDCONTROL

REV

FWD

STOP

1µF

2.5V AT 10mA


LT1970A

221970afc


package DescripTionPlease refer to http://www.linear.com/product/LT1970A#packaging for the most recent package drawings.

FE20 (CA) TSSOP REV K 0913

0.09 – 0.20(.0035 – .0079)

0° – 8°

0.25REF

RECOMMENDED SOLDER PAD LAYOUT

0.50 – 0.75(.020 – .030)

4.30 – 4.50*(.169 – .177)

1 3 4 5 6 7 8 9 10

DETAIL A

DETAIL A

111214 13

6.40 – 6.60*(.252 – .260)

4.95(.195)

2.74(.108)

20 1918 17 16 15

1.20(.047)MAX

0.05 – 0.15(.002 – .006)

0.65(.0256)

BSC0.195 – 0.30

(.0077 – .0118)TYP

2

2.74(.108)

0.45 ±0.05

0.65 BSC

4.50 ±0.10

6.60 ±0.10

1.05 ±0.10

6.07(.239)

6.07(.239)4.95

(.195)

MILLIMETERS(INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.150mm (.006") PER SIDE

NOTE:1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE

SEE NOTE 4

4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT

6.40(.252)BSC

1.98(.078)REF

FE Package20-Lead Plastic TSSOP (4.4mm)

(Reference LTC DWG # 05-08-1663 Rev K)Exposed Pad Variation CA

0.56(.022)REF

DETAIL A IS THE PART OFTHE LEAD FRAME FEATURE

FOR REFERENCE ONLYNO MEASUREMENT PURPOSE


http://www.linear.com/product/LT1970A#packaging

LT1970A

231970afc


revision hisToryREV DATE DESCRIPTION PAGE NUMBER

A 06/12 Corrected D1, D2 orientation in Block DiagramChanged supply voltage in Figure 12

1021

B 09/14 Corrected TSD pin description 9

C 11/15 Updated Package Drawing 22

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.


LT1970A

241970afc

For more information www.linear.com/LT1970A LINEAR TECHNOLOGY CORPORATION 2011

LT 1115 REV C • PRINTED IN USA

relaTeD parTs


PART NUMBER DESCRIPTION COMMENTS

LT1010 Fast ±150mA Power Buffer 20MHz Bandwidth, 75V/µs Slew Rate

LT1206 250mA/60MHz Current Feedback Amplifier Shutdown Mode, Adjustable Supply Current

LT1210 1.1A/35MHz Current Feedback Amplifier Stable with CL = 10,000pF

LT1999 High Voltage Bidirectional Current Sense Amplifier –5V to 80V Input Voltage Range

Figure 13. AV = –1 Amplifier with Discrete Power Devices to Boost Output Current to 5A

VCC

VEE

ENABLE

V–

VCSRCVCSNK

SENSE–

COMMON

SENSE+

V+

OUT

+IN

R11k

RG2.2k

RF2.2k

*

*

* *

RCS0.1Ω5W

R5100Ω

R4100Ω

LT1970A

–IN

LOAD

1970A F13

CURRENT LIMITCONTROL VOLTAGE

0V TO 5V

VCC15V

VEE–15V

VIN

10µF

IRF9530

IRF530

0.1µF

0.1µF10µF

R3100Ω

*OPTIONAL, SEE TEXT

R2100Ω

Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LT1970A


http://www.linear.com/LT1010





LT1970A - 500mA Power Op Amp with Adjustable Precision ... · The LT®1970A is a ±500mA power op...

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