SC1183 Semtech Corporation, SC1183 Datasheet - Page 11

• Manufacturer Part Number: SC1183
• Description: PROGRAMMABLE SYNCHRONOUS DC/DC CONVERTER/ DUAL LOW DROPOUT REGULATOR CONTROLLER
• Manufacturer: Semtech Corporation

August 25, 1998
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:
For the example above:
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
40
readily achievable. The corresponding temperature rise
is detailed below:
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.
FET type
BUK556H 22
IRL2203
Si4410
FET type
BUK556H 22
IRL2203
Si4410
FET type
BUK556H 49.6
IRL2203
Si4410
(1) With 20
o
C/W for the D
P
COND
o
C/W Heatsink
R
7.0
13.5
R
7.0
13.5
Temperature rise (
Top FET
31.6
122.4
DS(on)
DS(on)
2
PAK and 80
(1)
I
2
O
(m ) P
(m ) P
R
DS
(
2.48
0.79
1.53
1.95
0.62
1.20
Bottom FET
39.0
24.8
96
on
D
D
)
(W)
(W)
o
C/W for the SO-8 are
(1)
1 (
o
C)
Package
TO220
D
SO-8
Package
TO220
D
SO-8
)
2
2
PAK
PAK
PROGRAMMABLE SYNCHRONOUS DC/DC
CONVERTER, DUAL LOW DROPOUT
REGULATOR CONTROLLER
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.
652 MITCHELL ROAD NEWBURY PARK CA 91320
SC1182/3
11