SC1102(2000) Ver la hoja de datos (PDF) - Semtech Corporation
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componentes Descripción
Fabricante
SC1102
(Rev.:2000)
(Rev.:2000)
Semtech Corporation
SC1102 Datasheet PDF : 10 Pages
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SYNCHRONOUS DC/DC CONTROLLER FOR
SC1102
DISTRIBUTED POWER SUPPLY APPLICATIONS
September 5, 2000
THEORY OF OPERATION (CON’T)
An over-current condition occurs when the high-side
drive is turned on, but the PHASE node does not
reach the voltage level set at the OCSET pin. The
PHASE node is sampled only once per cycle during the
valley of the triangular oscillator. Once an over-current
occurs, the high-side drive is turned off and the low-
side drive turns on and the SS/SHDN pin begins to
sink 2uA. The soft-start voltage will begin to decrease
as the 2uA of current discharges the external capaci-
tor. When the soft-start voltage reaches 0.8V, the SS/
SHDN pin will begin to source 10uA and begin to
charge the external capacitor causing the soft-start
voltage to rise again. Again, when the soft-start volt-
age reaches the level of the internal oscillator, switch-
ing will occur.
If the over-current condition is no longer present, nor-
mal operation will continue. If the over-current condi-
tion is still present, the SS/SHDN pin will again begin to
sink 2uA. This cycle will continue indefinitely until the
over-current condition is removed.
In conclusion, below is shown a typical “12V Applica-
tion Circuit” which has a BSTH voltage derived by boot-
strapping input voltage to the PHASE node through
diode D1. This circuit is very useful in cases where only
input power of 12V is available.
In order to prevent substrate glitching, a small-signal
diode should be placed in close proximity to the chip
with cathode connected to PHASE and anode con-
nected to PGND.
APPLICATION CIRCUIT
Typical 12V Application Circuit with Bootstrapped BSTH
+5V
R1
R2
1k
1.74k
PWRGD
OVP
C1
0.1
C2
0.1
R4
10
U1
SC1102
1 VCC
GND 14
2 PWRGD
SS/SHDN 13
R3
1k
3 OVP
VREF 12
4 OCSET
SENSE 11
5
D1
MBR0520
6
PHASE
DRVH
BSTH 10
BSTL 9
7 PGND
DRVL 8
D2
MBRA130
C3
0.1
SHDN
VREF
C4
1.0
R5
3.9
R6
2.2
Q1
STP40NE
Q2
STP40NE
+
C5
C6
C7
C8
Vin 12V
10.0
270/16V
270/16V
270/16V
_
R8
127
C9
L1
1.0
4uH
D3
MBRD1035
Optional
C10
180/4V
R9
205*
C11
180/4V
C12
180/4V
C13
180/4V
+
C14
180/4V
Vout=3.3V*
_
NOTE:
*) Vout = 1.265 x (1+R9/R8)
© 2000 SEMTECH CORP.
8
652 MITCHELL ROAD NEWBURY PARK CA 91320
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