13
LT3433
3433f
Input Voltage Transient Suppression
Not only does a LT3433 converter operate across a large
range of DC input voltages, it also maintains tight output
regulation during significant input voltage transients. The
LT3433 automatic transitioning between buck and buck/
boost modes of operation provides seamless output regu-
lation over these input voltage transients. In an automotive
environment, input voltage transients are commonplace,
such as those experienced during a cold crank condition.
During the initiation of cold crank, the battery rail can be
pulled down to 4V in as little as 1ms. In a 4V-60V to 5V DC/
DC converter application (shown on the first page of this
data sheet) a cold crank transient condition, simulated
with a 1ms 13.8V to 4V input transition, yields regulation
maintained to 1% with a 125mA load.
APPLICATIO S I FOR ATIO
WUUU
4V-50V to 5V Converter Input Transient Response
1ms 13.8V to 4V Input Transition
V
IN
5V/DIV
V
OUT
0.1V/DIV
1ms/DIV
3433 AI04
TYPICAL APPLICATIO S
U
V
BST
SW_H
V
IN
BURST_EN
V
C
V
FB
SW_L
PWRGND
V
OUT
V
BIAS
SHDN
SS
SGND
LT3433
D2
1N4148
C5
1µF
10V
C3 330pF
R5
309k
1%
R2
100k
1%
R3
100k
DZ1
20V
R1
68k
R4
20k
C2
1nF
V
BATT
4V TO 60V
SHDN
V
BATT
(SWITCHED)
3433 TA03a
C6
0.1µF 10V
C1
0.01µF
D1
1N4148
L1
100µH
COEV DU1352-101M
D
S2
B120A
C4
2.2µF
100V
D
S1
B160A
C7
47µF
10V
MODE SWITCH:
V
IN
H-L: 7.9V
V
IN
L-H: 8.3V
V
OUT
5V
4V < V
IN
< 8.5V: 125mA
8.5V < V
IN
< 60V: 350mA
+
4V-60V to 5V Converter with Switched Burst Enable and Shutdown
OUTPUT CURRENT (mA)
40
EFFICIENCY (%)
60
80
90
0.1 10 100 1000
3433 TA03b
20
1
70
50
30
V
IN
= 4V
V
IN
= 13.8V
V
IN
= 13.8V
BURST
V
IN
= 4V
(BURST)
Efficiency
