Linear Technology DC1544 User manual

LT3957

DESCRIPTION

Demonstration circuit 1544 is a Boost, SEPIC, Flyback

and Inverting Converter ith 5A, 40V S itch featuring

the LT3957. The LT3957 can be configured as a boost,

flyback, SEPIC, and inverting converter, but the demon-

stration circuit is assembled as a boost. The input volt-

age range is 4.5V to 20V and the output voltage is 24V

ith 600mA over the entire input voltage range.

The LT3957 has an internal n-channel 5A, 40V po er

s itch for high voltage, po er, and efficiency. The dual

paddle package provides excellent heat dissipation for

the internal po er s itch. The LT3957 current-mode

dc/dc converter features adjustable s itching frequency,

soft-start, compensation, shutdo n and undervoltage

lockout ith hysteresis, and a feedback pin (FBX) that

can be used in both positive and negative applications. A

SYNC input can be used to synchronize the s itching at

a frequency higher than the IC is programmed.

The demonstration circuit features small 1210 case size

ceramic input and output capacitors. The internal n-

channel po er s itch provides efficiency as high as 95%

in typical boost applications ith 14.4W output.

The LT3957 datasheet gives a complete description of

the part, operation and applications information. The

datasheet must be read in conjunction ith this Quick

Start Guide for demonstration circuit 1544A. The LT3957

is assembled in a 36-lead plastic UHE package ith t o

thermally enhanced pads for SW and GND. Proper board

layout is essential for both proper operation and maxi-

mum thermal performance. See the datasheet section

‘Layout Considerations’.

Figure 1.

DC1544A 12VIN Efficiency

Design files for this circuit board are a ailable. Call

the LTC factory.

, LT are trademarks of Linear Technology Corporation.

PARAMETER CONDITIONS UNITS

Minimum Input Supply Voltage

4.5 V

Maximum Input Supply Voltage 20 V

Output Voltage Programmed V

= 4.5V-20V, I

LOAD

≤

600mA 24 V

S itching Frequency R

= 41.2k

300 kHz

Guaranteed Maximum Output current V

= 4.5V-20V

600 mA

Input Undervoltage Lockout (falling) R1=200k, R2=95.3k 3.8 V

Input Turn-on Voltage (rising) R1=200k, R2=95.3k

4.2 v

Efficiency V

= 12V, I

LOAD

600mA 95 %

DEMO CIRCUIT

1544

QUICK START GUIDE

LT3957

Boost, SEPIC, Fly ack and Inverting Converter with 5A,

40V Switch

LT3957

QUICK START PROCEDURE

Demonstration circuit 1544 is easy to set up to evaluate

the performance of the LT3957. Refer to Figure 2 for

proper measurement equipment setup and follo the

procedure belo :

NOTE.

When measuring the input or output voltage ripple, 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 or Vout and GND terminals.

Place jumpers in the follo ing positions:

NO SYNC

With po er off, connect the input po er supply to

VIN and GND.

NOTE.

Connect po er to GND, not SGND.

Connect a load of 600mA or less to VOUT and GND

terminals (not SGND).

Turn on the po er at the input.

NOTE.

Make sure that the input voltage does not exceed 20V.

Check for the proper output voltage (24V).

NOTE.

If there is no output, temporarily disconnect the load to make

sure that the load is not set too high.

Once the proper output voltage is established, adjust

the load and input ithin the operating ranges and

observe the output voltage regulation, ripple voltage,

efficiency and other parameters.

Figure 2.

Proper Measurement Equipment Setup

JP1

LT3957

TERMINAL OPTIONS

DC1544A has both

GND

and

SGND

terminals. The sche-

matic sho s that the GND and SGND pins of the IC are

not tied together outside the IC. They are internally con-

nected. It is important that po er ground currents do not

run on the SGND components. SGND is used to termi-

nate the signal ground components such as compensa-

tion and feedback. Input and output po er as ell as

input and output caps, catch diodes, etc. should all con-

nect to the GND plane. The SGND terminals are provided

in case the customer ould like to make signal ground

measurements, but they do not need to be used. Im-

properly connecting input po er to the SGND terminal

results in noisy behavior of the IC.

EN/UVLO

(enable / undervoltage lockout) is provided as

a terminal so that the part can quickly be placed in shut-

do n by tying EN/UVLO to GND. The EN/UVLO pin is

already being used as an undervoltage lockout threshold

for the VIN ith resistors R1 and R2. Undervoltage lock-

out stops the IC from s itching hen VIN is too lo , but

shutdo n further reduces the VIN pin quiescent current

hen EN/UVLO is tied directly to GND. It is okay to leave

the EN/UVLO terminal floating.

INTVCC

is provided as a terminal to be able to po er

INTVCC externally or to tie INTVCC directly to VIN hen

VIN remains belo 8V. It is okay to leave the INTVCC

terminal floating.

SYNC

is provided as a terminal to be able to externally

synchronize the internal po er s itching frequency. If

SYNC is not used, the terminal should be left floating and

the JP1 position should be set at ‘NO SYNC’. If SYNC is

used, the s itching frequency of SYNC should be 20%

higher than the programmed s itching frequency of the

IC and the JP1 position must be set at ‘SYNC’. Please

see the datasheet for details regarding the use of SYNC

and the s itching frequency range.

LT3957

C11

OPT

0402

1210

PDS360

1210 1210

22nF

95.3k

2.2uF

50V

1210

C13

OPT

15.8k

R4 41.2k 1%

0402

4.7uF

50V

0603

0402

0402 0402

06030402

0402 0402 0402

0402

CDRH104RNP-100NC

1210

2.2uF

50V

GND

INTVCC

4.7uF

10V

4.7uF

50V

VOUT

24V @ 600mA

SYNC

NOTES: UNLESS OTHERWISE SPECIFIED,

1. ALL CAPACITORS AND RESISTORS ARE 0402.

2. ALL CAPACITOR VALUES ARE IN MICROFARADS.

3. ALL RESISTOR VALUES ARE IN OHMS.

VIN

4.5V - 20V

SGND

C10

OPT

4.7uF

50V

4.7uF

6.8k

226k

0402

SGND

GND

E10

GND

LT3957EUHE

FBX 31

GND

SYNC

GND

INTVCC

SW 38

VIN 27

EN/UVLO

SG N D

SW 21

GND

SG N D

SW 8

SENSE2 3

SENSE1 6

SW 9

SW 20

NC 10

NC 35

NC 36

NC 1

NC 2

SG N D

300kHz

C12

OPT

INTVCC

L1 10uH

EN/UVLO

JP1

SYNC

NO SYNC

0.33uF

200k

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