Datasheet

LTC3442
12
3442fa
Figure 5. Soft-Start Circuitry
–
+
12
11
V
IN
ERROR AMP
1.22V
14µA
FB
R1
R2
C
P1
V
C
V
OUT
1
SHDN/SS
C
SS
1V
ENABLE SIGNAL
R
SS
SOFT-START
CLAMP
TO PWM
COMPARATORS
CHIP
ENABLE
3442 F05
–
+
V
CI
OPERATIO
U
response, Type 3 compensation is also recommended to
broad band the control loop and roll off past the two pole
response of the output LC filter. (See Closing the Feedback
Loop.)
Soft-Start
The soft-start function is combined with shutdown. When
the SHDN/SS pin is brought above 1V typical, the IC is
enabled but the EA duty cycle is clamped from V
C
. A
detailed diagram of this function is shown in Figure 5. The
components R
SS
and C
SS
provide a slow ramping voltage
on SHDN/SS to provide a soft-start function. To ensure
that V
C
is not being clamped, SHDN/SS must be raised
above 2.4V. To enable Burst Mode operation, SHDN/SS
must be raised to within 0.5V of V
IN
.