LTC3443 Datasheet, PDF (10/16 Pages) Linear Technology – High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter

LTC3443
U
OPERATIO
SOFT-START
The soft-start function is combined with shutdown. When
the SHDN/SS pin is brought above typically 1V, the IC is
enabled but the EA duty cycle is clamped from the V_C pin.
A detailed diagram of this function is shown in Figure 5.
The components R_SS and C_SS provide a slow ramping
voltage on the SHDN/SS pin to provide a soft-start
function.
PV_IN
9
V_OUT
8
A
dI
dt
≈
V_IN
L
D
+
–
4
5
L
SW1
SW2
B
C
800mA
0mA
T1
6
GND
3443 F03
PV_IN
9
V_OUT
8
A
dI
dt
≈
–
V_OUT
L
D
–
+
4
5
SW1
L
SW2
B
C
800mA
0mA
6
GND
T2
3443 F04
Figure 3. Inductor Charge Cycle During Burst Mode Operation Figure 4. Inductor Discharge Cycle During Burst Mode Operation
V_IN
SOFT-START
CLAMP
TO PWM
V_CI
COMPARATORS
14µA
ERROR AMP
1.22V
FB
12
V_C ^CP1
11
V_OUT
R1
R2
CHIP
ENABLE
SHDN/SS
1
R_SS
C_SS
ENABLE SIGNAL
3443 F05
1V
Figure 5. Soft-Start Circuitry
10
sn3443 3443fs