LTC3400B_15 Datasheet, PDF (4/12 Pages) Linear Technology – 600mA, 1.2MHz Micropower Synchronous Boost Converter in ThinSOT

LTC3400/LTC3400B
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.
BLOCK DIAGRA
+ ^SINGLE
CELL
INPUT
6 V_IN
START-UP
OSC
C_IN
1µF
A A/B
MUX
B
L1
4.7µH
1 SW
V_OUT
GOOD
2.3V
0.45Ω
OPTIONAL
SCHOTTKY
V_OUT
5
3.3V
OUTPUT
RAMP
GEN
1.2MHz
PWM
CONTROL
PWM
COMPARATOR
SLOPE
COMP
SLEEP
Burst Mode
OPERATION
CONTROL
SYNC
DRIVE
CONTROL
Σ
0.35Ω
CURRENT
SENSE
C_FF
(OPTIONAL)
R1
1.02M
1%
(EXTERNAL)
R_C
80k
C_C
150pF
C_P2
2.5pF
g_m
ERROR
AMP
FB
3
1.23V
REF
C_OUT
4.7µF
R2
604k
1%
(EXTERNAL)
4
SHDN
4
SHUTDOWN
CONTROL
SHUTDOWN
2 GND
3400 BD
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