1dc1825af

DEMO MANUAL DC1825A

Description

LT8300 100VIN Micropower Isolated Flyback Converter with 150V/260mA Switch

Demonstration circuit 1825A is an isolated flyback con-verter featuring the LT®8300. This demo circuit outputs 5.0V, and maintains tight regulation with a load current from ~1mA to 250mA and over an input from 22V to 75V, with a nominal 48V. The output current capability increases with the input voltage.

The DC1825A needs a very small minimum load (~1mA) to regulate the output voltage, thanks to the accurate current limit capability and ultra low switching frequency of the LT8300 at very light load. The standby input current of the demo circuit is less than 400µA (typical) because of the low quiescent current design of the IC and very small minimum load requirement.

The Performance Summary table summarizes the perfor-mance of the demo board at room temperature. The demo circuit can be easily modified for different applications with some pre-designed transformers.

performance summary

The LT8300 is a simple-to-use high voltage monolithic iso-lated flyback converter. No third winding or opto-isolator is required for regulation. The part sets the isolated out-put voltage with a single external resistor and integrates compensation and soft start circuitry inside. Boundary mode operation provides a small magnetic solution with improved load regulation. Low ripple Burst Mode® opera-tion maintains high efficiency at light loads while minimizing the output voltage ripple. A 260mA, 150V DMOS power switch is integrated along with all high voltage circuitry and control logic into a 5-lead ThinSOT™ package.

The LT8300 data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this quick start guide for DC1825A.

Design files for this circuit board are available at http://www.linear.com/demoL, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Voltage 22 48 75 V

VIN Quiescent Current IOUT = 0mA, VIN = 75V 400 µA

Output Voltage VIN = 22V – 75V IOUT = 1mA – 250mA

4.75 5 5.25 V

Maximum Output Current VIN = 22V 250 mA

Output Voltage Ripple (Peak to Peak) VIN = 22V – 75V, IOUT = 250mA 50 mV

Typical Switching Frequency VIN = 48V, IOUT = 250mA 330 kHz

Minimum Switching Frequency IOUT = 0mA 8 kHz

Efficiency VIN = 48V, IOUT = 250mA 80 %

Specifications are at TA = 25°C

2dc1825af

DEMO MANUAL DC1825A

Quick start proceDureThe DC1825A is easy to set up to evaluate the performance of the LT8300. Refer to Figure 1 for proper equipment setup and follow the procedure below.

1. With power off, connect the input power supply to the board through VIN (E1) and GND (E3) terminals. Connect the load to the terminals VOUT+ (E4) and VOUT– (E2) on the board.

2. Turn on the power at the input. Increase VIN slowly to 22V.

NOTE: Make sure that the input voltage is always within spec. To operate the board with higher input/output voltage, input capacitor, output capacitor and output diode with higher voltage ratings are needed.

NOTE: To run overload tests on the demo board with VIN higher than 40V, a RC snubber (200Ω, 150pF) or Schottky plus Zener clamp circuit is recommended to make sure the voltage spike at the switching node is always less than 150V.

3. Check for the proper output voltages. The output should be regulated at 5.0V (±5%).

NOTE: The LT8300 requires very small minimum load to maintain good output voltage regulation. A Zener diode is placed on the output to clamp the voltage to ~5.0V. This Zener is optional, and can be replaced with a 5.1k resistor.

4. Once the proper output voltage is established, adjust the input voltage and load current within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters.

NOTE: When measuring the input or output voltage ripples, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the VIN (E1) and GND (E3), or VOUT+ (E4) and VOUT– (E2) terminals. See Figure 2 for proper scope probe technique.

3dc1825af

DEMO MANUAL DC1825A

Figure 1. Proper Measurement Equipment Setup

Quick start proceDure

Figure 2. Proper Scope Probe Placement for Measuring Input or Output Ripple

INPUT OR OUTPUT CAPACITOR

Figure 3. Typical Efficiency and Regulation Curves

LOAD CURRENT (mA)

50

EFFI

CIEN

CY (%

)

60

70

85

55

65

75

80

100 200

DC1825A F03a

250500 150

VIN = 22V

VIN = 48V

LOAD CURRENT (mA)

4.50

V OUT

(V)

4.60

4.70

5.00

4.55

4.65

4.75

4.90

4.85

4.95

4.80

100 200

DC1825A F03b

250500 150

VIN = 48V

VIN = 22V

4dc1825af

DEMO MANUAL DC1825A

parts ListITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 C2 CAP., X7R, 2.2µF 100V, 10% 1210 MURATA, GRM32ER72A225KA35L

2 1 C3 CAP., X5R, 100µF 6.3V, 20% 1210 AVX, 12106D107MAT2A

3 1 C4 CAP., X7R, 4700pF 1000V, 10% 1210 VISHAY/VITRAMON, VJ1210Y472KXGAT5Z

4 1 D1 DIODE, SCHOTTKY, 30V 1A PWRDI123 DIODES INC., DFLS130-7

5 1 D2 SMT ZENER DIODE, 5.6V SOD-523 DIODES INC., BZT52C5V6T-7

6 1 R1 RES., CHIP, 806k, 1%, 0805 VISHAY, CRCW0805806KFKEA

7 1 R2 RES., CHIP, 53.6k, 1%, 0603 VISHAY, CRCW060353K6FKEA

8 1 R3 RES., CHIP, 365k, 1%, 0603 VISHAY, CRCW0603365KFKEA

9 1 T1 TRANSFORMER 7:1 WÜRTH ELECTONIK, 750312366

10 1 U1 I.C., LT8300ES5, TSOT-23 LINEAR TECH., LT8300ES5#PBF

Additional Demo Board Circuit Components

1 0 C1 CAP., 0805 OPT

2 0 R4 RES., 0805 OPT

5dc1825af

DEMO MANUAL DC1825A

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.

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6dc1825af

DEMO MANUAL DC1825A

Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2012

LT 0912 • PRINTED IN USA

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:

This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.

If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.

The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or agency certified (FCC, UL, CE, etc.).

No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.

LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.

Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and observe good laboratory practice standards. Common sense is encouraged.

This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC applica-tion engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

Copyright © 2004, Linear Technology Corporation