LTC3400-1
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
. V
IN
is connected
to V
OUT
through the internal P-channel MOSFET syn-
chronous rectifier and external inductor.
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 connected to V
IN
in shutdown through the internal
P-channel MOSFET synchronous rectifier.
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.
BLOCK DIAGRA
+
SINGLE
CELL
INPUT
6
V
IN
V
OUT
GOOD
START-UP
OSC
A
B
A/B
MUX
PWM
CONTROL
RAMP
GEN
1.2MHz
PWM
COMPARATOR
SHUTDOWN
SYNC
DRIVE
CONTROL
SLOPE
COMP
Σ
SLEEP
Burst Mode
OPERATION
CONTROL
C
C
150pF
C
P2
2.5pF
SHDN
4
SHUTDOWN
CONTROL
SHUTDOWN
2
GND
34001 BD
4
+
R
C
80k
g
m
ERROR
AMP
–
–
+
–
–
+
W
U
U
U
L1
4.7µH
C
IN
1µF
1
SW
OPTIONAL
SCHOTTKY
2.3V
0.45Ω
V
OUT
5
3.3V
OUTPUT
0.35Ω
C
FF
(OPTIONAL)
R1
1.02M
1%
(EXTERNAL)
CURRENT
SENSE
FB
3
1.23V
REF
C
OUT
4.7µF
R2
604k
1%
(EXTERNAL)
34001f
LINER [ LINEAR TECHNOLOGY ]
