High Efficiency, High Density PSM μModule Regulator with Programmable Compensation Haihua Zhou, Jian Li, and Simon Tian Analog Devices, Inc.

FPGA boards, as well as prototype, testing, and measurement applica-tions demand versatile and high density power solutions. The LTM4678 is a dual 25 A or single 50 A µModule® regulator with digital power system management (PSM) in a small 16 mm × 16 mm footprint. It features:

X Dual digitally adjustable analog loops with a digital interface for control and monitoring

X Wide input voltage range: 4.5 V to 16 V

X Wide output voltage range: 0.5 V to 3.3 V

X ±0.5% maximum dc output error over temperature

X ±5% current readback accuracy

X Sub-mΩ DCR current sensing

X Integrated input current sense amplifier

X 400 kHz PMBus-compliant I2C serial interface

X Telemetry polling rates up to 125 Hz

X An integrated 16-bit Σ-Δ ADC

X Constant frequency current mode control

X Parallel operation with balanced current sharing

X 16 mm × 16 mm × 5.86 mm CoP-BGA

I2C-Based PMBUS Interface and Programmable Loop CompensationThe LTM4678 is a member of ADI’s power system management (PSM) µModule family, so it can be configured and monitored through a PMBus/SMBus/I2C digital interface. The PC-based LTpowerPlay® tool enables visual monitoring and control of power supply voltage, current, power use, sequencing, margining, and fault log data. The LTM4678 is the first

µModule regulator with programmable loop compensation: gm and RTH, which greatly reduces design time, since dynamic performance tuning is done without the hassle of iterative PCB board builds or modifications.

CoP-BGA Package for Enhanced Thermal Performance, Small Size and High Power DensityA thermally enhanced component on package (CoP) BGA package enables the high power LTM4678 to fit a small 16 mm × 16 mm PCB footprint. Inductors are stacked and used as a heat sink to enable efficient cooling.

Easily Scale to Higher Current with Current Mode ControlThe LTM4678 uses peak current-mode control. Current is monitored and controlled cycle by cycle. This enables equal current sharing among phases.

Other Unique Features X Dual remote output sensing compensates for the voltage drop on

traces in high current application

X ±0.5% maximum dc output error over temperature provides additional regulation margin

X Direct input current sense measures the precise input current and power

X Dedicated PGOOD pins provide signal for downstream systems when output voltage is in regulation range

X EXTVCC pin maximizes efficiency at high VIN conditions

Visit analog.com

Design Note

Share on Twitter LinkedIn Facebook Email

2 High Efficiency, High Density PSM μModule Regulator with Programmable Compensation

Dual-Output Converter (1 V at 25 A and 1.8 V at 25 A)Figure 1 shows a typical 5.75 V to 16 V input, dual-output solution. The LTM4678’s two channels run with a 180° relative phase shift, reducing the input rms current ripple and capacitor size.

As shown in Figure 2, the total solution efficiency in forced continuous current mode (CCM) is 85.8% at 1.0 V/25 A output, and 90.4% at 1.8 V/25 A.

250

95

705 10 15 20

90

85

80

75

Effi

cien

cy (%

)

ILOAD (A)

VOUT1 = 1.8 V VOUT0 = 1 V

VIN = 12 VfSW = 500 kHz

Figure 2. Efficiency of the two outputs.

Figure 3 shows the thermal performance of the LTM4678 running at VIN = 12 V, VOUT0 = 1.0 V/25 A, and VOUT1 = 1.8 V/25 A with 200 LFM. The hot spot (inductor on CH1) temperature rise is 63°C, where the ambient temperature is about 24°C.

°C25.0

120125.0

116112108104100969288848076726864605652484440363228

Figure 3. Thermal performance of the dual output converter.

PGOOD0

PGOOD1

VDD33

VDD33

1 mΩ

22 µF×5

100 µF×3 ×2

470 µF

×2470 µF

150 pF150 pF

4700 pF4700 pF

2.2 µF

150 µF+

10 kΩ 10 kΩ

FAULT0

FAULT1

VD

D33

VDD33

VD

D25

WP

SYNC

VIN0

INT

VC

C

SCL

SDA

RUN0

RUN1

EX

TV

CC

SW0

SW1

CO

MP

1a

CO

MP

1b

PG

OO

D0

PG

OO

D1

CO

MP

0a

VIN1

CO

MP

0b

VT

RIM

1_C

FG

VOSNS1+

VT

RIM

0_C

FG

VO

UT

0_C

FG

VOUT1

VOUT0

ALERT

SHARE_CLK

VO

UT

1_C

FG

GND

SVIN

VOSNS1–

VOSNS0+

VOSNS0–

TS

NS

0a

TS

NS

0b

SGND

TS

NS

1a

TS

NS

1b

FSW

PH

_CFG

AS

EL

IIN–

IIN+

LTM4678

10 kΩ

10 kΩ

10 kΩ

10 kΩ

10 kΩ

10 kΩ

4.99

kΩ

10 kΩ

CSNUB0

RSNUB0

RSNUB1

CSNUB1

22.6

kΩ

LOAD0

LOAD1

I2C/SMBus Interface with PMBus Command SetTo/From IPMI or Other Board Management ControllerConfigure Resistors To Be 1%, 50 ppm

VOUT1 1.8 V, 25 A

VOUT0 1 V, 25 A

5.75 V to 16 V

ON/OFFCONFIG

FAULT INTERRUPTS

VIN

5.23

kΩ

1.65

kΩ

6.34

kΩ

32.4

kΩ

32.4

kΩ

• Slave Address = 1001110_r/w (0x4e)• 500 kHz Switching Frequency• No GUI Configuration and No

Part-Specific Programming Required• In Multimodule Systems, Configuring

Rail_Address Is Recommended

100 µF×3

+

+

10 kΩ

Figure 1. 1V and 1.8 V outputs at 25 A with I 2C serial control and monitoring interface.

Visit analog.com 3

Polyphase, Single-Output High Current (12 V to 1 V at 250 A)The LTM4678 can be configured as a polyphase single-output converter for higher current solutions. Figure 4 shows a block diagram for con-necting multiple LTM4678s. To increase output current, just add additional LTM4678s and connect the respective VIN, VOUT, VOSNS+, VOSNS−, PGOODs, COMPa/b, RUN, FAULT , SYNC, and GND pins together.

Figure 5 shows the current from each phase when five LTM4678 (10 phases) are paralleled. The maximum current difference among 10 phases is 0.75 A (3% based on 25 A), representing balanced current sharing.

Pha

se C

urre

nt (A

)

Total Output Current (A)

VIN = 12 VVOUT = 1 V

2500 50 100 150 200

26

0

22

24

2

4

6

8

10

20

18

16

14

12

10 Channels

3% Accuracy

Figure 5. Current sharing among 5 LTM4678 devices with 10 phases in parallel.

Figure 6 shows the thermal image for the five parallel LTM4678s at 220 A output with 450 LFM air flow applied. Maximum thermal difference between the five µModule regulators is 10°C. Figure 7 shows the full schematic for an 8-phase solution.

°C

120125.0

115110105100959085807570656055504540353025.0

Figure 6. Thermal performance of multiphase converter.

Conclusion The LTM4678 µModule regulator is a versatile high performance power solution that delivers high efficiency and high power in a small 16 mm × 16 mm footprint. The small form factor and ease of use make the LTM4678 ideal for space-constrained designs, such as FPGA boards. Multiple LTM4678s can be operated in parallel polyphase operation for higher current applications, such as those required in telecom and data-com systems, as well as industrial and computer system applications.

Cthp

Cth

VOUT

VIN

VOSNSn+

RUNn

PGOODn

COMPnb

COMPna

FAULTn

SYNC

VOSNSn−

VOSNSn+

RUNn

PGOODn

COMPnb

COMPna

FAULTn

SYNC

VOSNSn−

VOUT

VIN

LTM4678Phase 1

LTM4678Phase n

Figure 4. Block diagram showing the simplicity of multiphase operation.

4 High Efficiency, High Density PSM μModule Regulator with Programmable Compensation

PGOOD

COMPb

COMPa

22 µF×4

18 nF 220 pF

2.2 µF 2.2 µF

150 µF

10 kΩ

10 kΩ

10 kΩ

FAULT0

FAULT1

VD

D33

VD

D33

VDD33U1V

DD

25

VD

D25

WP

SYNC

VIN0IN

TVC

C

INTV

CC

SCL

SDA

RUN0

RUN1

*EX

TVC

C

*EX

TVC

C

SW0

SW1

CO

MP

1a

CO

MP

1b

PG

OO

D0

PG

OO

D0

PG

OO

D1

PG

OO

D1

CO

MP

0a

VIN1

CO

MP

0b

VTR

IM1_

CFG

VTR

IM0_

CFG

VO

UT

0_C

FG

VOUT

VOUT0

ALERT

SHARE_CLK

SYNC

SHARE_CLK

SYNC

SHARE_CLK

VO

UT

1_C

FGGND

SVIN

VOSNS1–

VOSNS1+

VOSNS0–

VOSNS0+

TS

NS

0a

TS

NS

0a

TS

NS

0b

TS

NS

0b

SGND

SCL

SDA

SW1

VOUT

VOUT0

SW0

ALERT

GND

VOSNS1–

VOSNS1+

VOSNS0–

VOSNS0+

SGNDT

SN

S1a

TS

NS

1a

TS

NS

1b

TS

NS

1b

FSW

PH

_CFG

AS

EL

IIN–

IIN+

FAULT0

FAULT1

WP

SYNC

VIN0

RUN0

RUN1

VIN1

SHARE_CLK

SYNC

SHARE_CLK

SVIN

IIN–

IIN+

U1LTM4678

4.99 kΩ

4.99

kΩ

10 kΩ

10 kΩ

10 kΩ

22.6

kΩ

787 Ω

1.21 kΩ

I2C/SMBus I/F with PMBus CommandSet To/From IPMI or Other BoardManagement Controller

5.75 V to 16 V VIN

ON/OFF

FAULTS

Configure ResistorsTo Be 1%, 50 ppm

Configure Resistorsto be 1%, 50 ppm

COMPb COMPa

22 µF×4

3.24 kΩ2.43 kΩ1.21 kΩ

VIN

AS

EL

FSW

PH_

CFG

VO

UT

1_C

FG

VO

UT

0_C

FG

VTR

IM0_

CFG

VTR

IM1_

CFG

CO

MP

0b

CO

MP

0a

CO

MP

1b

CO

MP

1a

U3LTM4678

FAULTS

PGOOD

1 V at200 A

ON/OFF

*Optional 5.5 V Bias ≥ 200 mA Totalfor Efficiency and Thermal Improvement

Note: Text in this Color Denotes a Label.

+

VDD33U1

PGOOD

COMPbCOMPa

22 µF×4

2.2 µF

FAULT0

FAULT1

VD

D33

VD

D25

WP

SYNC

VIN0

INTV

CC

SCL

SDA

RUN0

RUN1

*EX

TVC

C

SW0

SW1

CO

MP

1a

CO

MP

1b

PG

OO

D0

PG

OO

D1

CO

MP

0a

VIN1

CO

MP

0b

VTR

IM1_

CFG

VTR

IM0_

CFG

VO

UT

0_C

FG

VOUT

VOUT0

ALERT

SHARE_CLK

VO

UT

1_C

FG

GND

SVIN

VOSNS1–

VOSNS1+

VOSNS0–

VOSNS0+

TS

NS

0a

TS

NS

0b

SGND

TS

NS

1a

TS

NS

1b

FSW

PH

_CFG

AS

EL

IIN–

IIN+

U2LTM4678

1.65

kΩ

1.65

kΩ

1.21 kΩ

ON/OFF

FAULTS

VDD33U1

VIN

100 µF×6

+

×4470 µF

100 µF×6

+

×4470 µF

2.2 µF

VD

D33

VD

D25

INTV

CC

*EX

TVC

C

PG

OO

D0

PG

OO

D1

TS

NS

0a

TS

NS

0b

SCL

SDA

SW1

SW0

VOUT

VOUT0

ALERT

GND

VOSNS1–

VOSNS1+

VOSNS0–

VOSNS0+

SGND

TS

NS

1a

TS

NS

1b

FAULT0

FAULT1

WP

SYNC

VIN0

RUN0

RUN1

VIN1

SHARE_CLK

SYNC

SHARE_CLK

SVIN

IIN–

IIN+

COMPb COMPa

22 µF×4

3.24 kΩ 2.43 kΩ1.21 kΩ

VIN

AS

EL

FSW

PH_

CFG

VO

UT

1_C

FG

VO

UT

0_C

FG

VTR

IM0_

CFG

VTR

IM1_

CFG

CO

MP

0b

CO

MP

0a

CO

MP

1b

CO

MP

1a

U4LTM4678

FAULTS

PGOOD

ON/OFF

SCL

SDA

ALERT

SCL

SDA

ALERT

SCL

SDA

ALERT

SCL

SDA

ALERT

100 µF×6

+

×4470 µF

100 µF×6

+

×4470 µF

Figure 7. 8-phase operation with four LTM4678s producing 1 V at 200 A.

Visit analog.com 5

Analog Devices, Inc. Worldwide Headquarters

Analog Devices, Inc. One Technology Way P.O. Box 9106 Norwood, MA 02062-9106 U.S.A. Tel: 781.329.4700 (800.262.5643, U.S.A. only) Fax: 781.461.3113

Analog Devices, Inc. Europe Headquarters

Analog Devices GmbH Otl-Aicher-Str. 60-6480807 München Germany Tel: 49.89.76903.0 Fax: 49.89.76903.157

Analog Devices, Inc. Japan Headquarters

Analog Devices, KK New Pier Takeshiba South Tower Building 1-16-1 Kaigan, Minato-ku, Tokyo, 105-6891 Japan Tel: 813.5402.8200 Fax: 813.5402.1064

Analog Devices, Inc. Asia Pacific Headquarters

Analog Devices 5F, Sandhill Plaza 2290 Zuchongzhi Road Zhangjiang Hi-Tech Park Pudong New District Shanghai, China 201203 Tel: 86.21.2320.8000 Fax: 86.21.2320.8222

©2019 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.Ahead of What’s Possible is a trademark of Analog Devices.DN21073-0-3/19

analog.com

About the AuthorsHaihua Zhou is a senior applications engineer at ADI. Her work covers µModule buck regulator and step-down regulator IC applications. Before joining ADI, she worked with Infineon/International Rectifier on GaN applications. She has a Ph.D. from the National University of Singapore. She can be reached at haihua.zhou@analog.com.

Jian Li received his M.S. degree in control theory and control engineering from Tsinghua University, China, in 2004, and his Ph.D. degree in power electronics from Virginia Tech, United States, in 2009. At present, he is an applications engineering manager for power products at Analog Devices. He holds nine U.S. patents and over 20 transaction and conference papers. He can be reached at jian.li@analog.com.

Simon Tian is a μModule design engineer at ADI and was an applications engineer at ADI prior to this position. He received his Ph.D. degree in electrical engineering from Virginia Tech in 2015 and has published more than 20 technical papers. He can be reached at simon.tian@analog.com.

Online Support CommunityEngage with the Analog Devices technology experts in our online support community. Ask your tough design questions, browse FAQs, or join a conversation.

Visit ez.analog.com