LTC3425_15 Datasheet, PDF (9/24 Pages) Linear Technology – 5A, 8MHz, 4-Phase Synchronous Step-Up DC/DC Converter

LTC3425
PI FU CTIO S
I_LIM (Pin 27): Current Limit Adjust Pin. Connect a resistor
from I_LIM to SGND to set the peak current limit threshold
for the N-channel MOSFETs, according to the formula
(note that this is the peak current in each inductor):
SYNCIN (Pin 30): Oscillator Synchronization Pin. A clock
pulse width of 100ns minimum is required to synchronize
the internal oscillator. If not used, SYNCIN should be
grounded. The typical logic threshold for this input is:
I_LIM
=
130
R
where I is in Amps and R is in kΩ. Do not use values less
than 75k.
R_T (Pin 28): Connect a resistor from R_T to SGND (or SGND
plane) to program the oscillator frequency, according to
the formula:
f_OSC
=
60
R_T
f_SWITCH
=
f_OSC
4
=
15
R_T
where f_OSC is in MHz and R_T is in kΩ.
V_IN (Pin 29): Input Supply Pin. Connect this to the input
supply and decouple with 1µF minimum low ESR
ceramic capacitor.
V_OUT
2
The SYNCIN is ignored in Burst Mode operation.
SHDN (Pin 31): Shutdown Pin. Grounding SHDN (or
pulling it below 0.25V) shuts down the IC. Pull pin up to
≥1V to enable. Once enabled, the pin only needs to be
≥ 0.65V.
SS (Pin 32): Soft-Start pin. Connect a capacitor from this
pin to ground to set the soft-start time, according to the
formula:
t(ms) = C_SS (µF) • 320
The nominal soft-start charging current is 2.5µA. The
active range of SS is from 0.8V to 1.6V. Note that this is the
rise time of SS. The actual rise time of V_OUT will be a
function of load and output capacitance.
Exposed Pad (Pin 33): Additional Power Ground for the
IC. Connect directly to the power ground plane.
OPERATING MODE
Automatic Burst (Operating Mode is Load Dependent)
Forced Burst
Forced Fixed Frequency with Pulse Skipping at Light Load
Forced Fixed Frequency, Low Noise (No Pulse Skipping)
BURST PIN
RC Network to Ground
Low
High
High
CCM PIN
Low
Low
Low
High
3425f
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