Datasheet

LTC3400/LTC3400B
4
3400fa
UU
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor between SW
and V
IN
. Optional Schottky diode is connected between
SW and V
OUT
. Keep these PCB trace lengths as short and
wide as possible to reduce EMI and voltage overshoot. If
the inductor current falls to zero, or SHDN is low, an
internal 100Ω antiringing switch is connected from SW to
V
IN
to minimize EMI.
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the (–) side of the output
capacitor(s).
FB (Pin 3): Feedback Input to the g
m
Error Amplifier.
Connect resistor divider tap to this pin. The output voltage
can be adjusted from 2.5V to 5V by:
V
OUT
= 1.23V • [1 + (R1/R2)]
SHDN (Pin 4): Logic Controlled Shutdown Input.
SHDN = High: Normal free running operation, 1.2MHz
typical operating frequency.
SHDN = Low: Shutdown, quiescent current <1µA.
100Ω connected between SW and V
IN
.
Typically, SHDN should be connected to V
IN
through a 1M
pull-up resistor.
V
OUT
(Pin 5): Output Voltage Sense Input and Drain of the
Internal Synchronous Rectifier MOSFET. Bias is derived
from V
OUT
. PCB trace length from V
OUT
to the output filter
capacitor(s) should be as short and wide as possible. V
OUT
is held at V
IN
– 0.6V in shutdown due to the body diode of
the internal PMOS.
V
IN
(Pin 6): Battery Input Voltage. The device gets its
start-up bias from V
IN
. Once V
OUT
exceeds V
IN
, bias
comes from V
OUT
. Thus, once started, operation is com-
pletely independent from V
IN
. Operation is only limited by
the output power level and the battery’s internal series
resistance.
1.23V
REF
Burst Mode
OPERATION
CONTROL
SHUTDOWN
CONTROL
SLOPE
COMP
PWM
CONTROL
START-UP
OSC
MUX
A
B
A/B
RAMP
GEN
1.2MHz
FB
3400 BD
3
V
OUT
OPTIONAL
SCHOTTKY
L1
4.7µH
5
SW
1
V
IN
SINGLE
CELL
INPUT
6
SHDN
4
GND
2
–
+
g
m
ERROR
AMP
–
+
V
OUT
GOOD
–
–
+
PWM
COMPARATOR
R
C
80k
SHUTDOWN
C
C
150pF
C
P2
2.5pF
R2
604k
1%
(EXTERNAL)
R1
1.02M
1%
(EXTERNAL)
SLEEP
Σ
SYNC
DRIVE
CONTROL
0.35Ω
0.45Ω
2.3V
C
OUT
4.7µF
3.3V
OUTPUT
C
IN
1µF
+
CURRENT
SENSE
C
FF
(OPTIONAL)
BLOCK DIAGRA
W