SC1183(1998) 查看數據表（PDF） - Semtech Corporation

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SC1183
(Rev.:1998)

PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER, DUAL LOW DROPOUT REGULATOR CONTROLLER

Semtech Corporation 

August 25, 1998

PROGRAMMABLE SYNCHRONOUS DC/DC

CONVERTER, DUAL LOW DROPOUT

REGULATOR CONTROLLER

SC1182/3

FET type RDS(on) (mΩ) PD (W) Package

BUK556H 22

IRL2203 7.0

2.48 TO220

0.79 D2PAK

Si4410 13.5

1.53 SO-8

BOTTOM FET - Bottom FET losses are almost entirely

due to conduction. The body diode is forced into con-

duction at the beginning and end of the bottom switch

conduction period, so when the FET turns on and off,

there is very little voltage across it, resulting in low

switching losses. Conduction losses for the FET can be

determined by:

PCOND = I2O ⋅ R DS (on ) ⋅ (1 − δ)

For the example above:

INPUT CAPACITORS - since the RMS ripple current

in the input capacitors may be as high as 50% of the

output current, suitable capacitors must be chosen ac-

cordingly. Also, during fast load transients, there may

be restrictions on input di/dt. These restrictions require

useable energy storage within the converter circuitry,

either as extra output capacitance or, more usually,

additional input capacitors. Choosing low ESR input

capacitors will help maximize ripple rating for a given

size.

FET type

BUK556H

IRL2203

Si4410

RDS(on) (mΩ) PD (W)

22

1.95

7.0

0.62

13.5

1.20

Package

TO220

D2PAK

SO-8

Each of the package types has a characteristic thermal

impedance, for the TO-220 package, thermal

impedance is mostly determined by the heatsink used.

For the surface mount packages on double sided FR4, 2

oz printed circuit board material, thermal impedances of

40oC/W for the D2PAK and 80oC/W for the SO-8 are

readily achievable. The corresponding temperature rise

is detailed below:

Temperature rise (oC)

FET type Top FET Bottom FET

BUK556H 49.6(1)

39.0(1)

IRL2203 31.6

24.8

Si4410 122.4

96

(1) With 20oC/W Heatsink

It is apparent that single SO-8 Si4410 are not adequate

for this application, but by using parallel pairs in each po-

sition, power dissipation will be approximately halved and

temperature rise reduced by a factor of 4.

© 1998 SEMTECH CORP.

11

652 MITCHELL ROAD NEWBURY PARK CA 91320

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