LT3430 Linear Technology, LT3430 Datasheet - Page 23

• Manufacturer Part Number: LT3430
• Description: High Voltage/ 3A/ 200kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
BUCK CONVERTER WITH ADJUSTABLE SOFT-START
Large capacitive loads or high input voltages can cause
high input currents at start-up. Figure 13 shows a circuit
that limits the dv/dt of the output at start-up, controlling
the capacitor charge rate. The buck converter is a typical
configuration with the addition of R3, R4, C
As the output starts to rise, Q1 turns on, regulating switch
current via the V
output. Output rise time is controlled by the current
through C
is in regulation, Q1 turns off and the circuit operates
normally. R3 is transient protection for the base of Q1.
SS
defined by R4 and Q1’s V
C
REMOVABLE
pin to maintain a constant dv/dt at the
U
INPUT
INPUT
U
40V
54k
25k
30BQ060
D3
Figure 12. Dual Source Supply with 25 A Reverse Leakage
W
Figure 13. Buck Converter with Adjustable Soft-Start
C3
4.7 F
50V
CER
BE
C3
4.7 F
. Once the output
V
SHDN
SYNC
0.022 F
IN
BOOST
SS
LT3430
C
3.3k
U
V
SHDN
SYNC
GND
GND
C
0.022 F
R
IN
C
and Q1.
BIAS
LT3430
BOOST
3.3k
C
C
R
V
SW
C
FB
C
C
220pF
F
BIAS
0.68 F
V
SW
C
FB
C2
C
220pF
D1
30BQ060
OR B250A
Q1
F
Using the values shown in Figure 10,
The ramp is linear and rise times in the order of 100ms are
possible. Since the circuit is voltage controlled, the ramp
rate is unaffected by load characteristics and maximum
output current is unchanged. Variants of this circuit can be
used for sequencing multiple regulator outputs.
MMSD914TI
Rise Time
Rise Time
33 H
D2
D1
30BQ060
R4
47k
L1
100 F
R3
2k
C2
0.68 F
10V
33 H
L1: CDRH104R-220M
C1
15nF
C
+
SS
MMSD914TI
R1
15.4k
R2
4.99k
D2
R
47 10
R1
15.4k
R2
4.99k
4
3430 F13
+
•
C
V
5V, 2A
SS
C1
100 F
10V
3
BE
OUTPUT
5V
2A
0 7
15 10
V
.
OUT
•
ALTERNATE
SUPPLY
–
9
3430 F12
5
5
LT3430
ms
sn3430 3430is
23