Datasheet

LTC3422
7
3422fa
BLOCK DIAGRA
W
–
+
––
+
Σ
+
BULK
CONTROL
SIGNALS
CURRENT
SENSE
ANTIRING
OPTIONAL
L1
4.7µH
CURRENT
SENSE
–
+
I
ZERO
COMP
BURST
COMP
AWAKEN
COMP
g
m
ERROR
AMPLIFIER
PWM
COMP
PWM
LOGIC
AND
DRIVERS
BURST SLEEP
BURST
MODE
CONTROL
V
IN
SW
1
R
T
8
SYNC
R
T
28k
9
BURST
3422 BD
3
SS
4
FB
6
V
C
7
V
OUT
V
IN
10
EXPOSED
PAD
11
2
SHDN
C
IN
10µF
5
SHUTDOWN
AND
V
BIAS
SHDN
0.88V
–
+
–
+
1.216V
1.5A
+
+
START-UP
CURRENT
RAMP
–
+
–2%
REFERENCE
THERMAL
SHUTDOWN
START-UP
SOFT-START
AND
THERMAL
REG
1.216V
0.88V
SLOPE
COMPENSATION
OSCILLATOR
I
MAX
COMP
R
B
301k
C
B
2.2nF
C
SS
0.1µF
R1
C
OUT
22µF
R2
R
Z
15k
C
C1
1nF
C
C2
22pF
V
OUT
2.25V TO 5.25
V
IN
1V TO 4.5V
OPERATIO
U
LOW VOLTAGE START-UP
The LTC3422 includes an independent start-up oscillator
designed to start up at input voltages of 0.88V typical.
During start-up, the peak current limit is gradually
increased in conjunction with the soft-start ramp. Switch-
ing frequency is also internally controlled during start-up.
The device can start up under some load (see graph of
Start-Up Voltage versus Output Current). Soft-start and