LTC3425 Linear Technology, LTC3425 Datasheet - Page 9

• Manufacturer Part Number: LTC3425
• Description: 5A 8MHz 4-Phase Synchronous Step-Up DC/DC Converter
• Manufacturer: Linear Technology

PI FU CTIO S
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)
I
from I
for the N-channel MOSFETs, according to the formula
(note that this is the peak current in each inductor):
where I is in Amps and R is in k . Do not use values less
than 75k.
R
plane) to program the oscillator frequency, according to
the formula:
where f
V
supply and decouple with 1 F minimum low ESR
ceramic capacitor.
LIM
IN
T
I
U
(Pin 28): Connect a resistor from R
f
f
LIM
OSC
SWITCH
(Pin 29): Input Supply Pin. Connect this to the input
(Pin 27): Current Limit Adjust Pin. Connect a resistor
LIM
OSC
130
to SGND to set the peak current limit threshold
R
60
U
R
is in MHz and R
T
f
OSC
4
U
R
15
T
T
is in k .
T
to SGND (or SGND
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:
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
SS (Pin 32): Soft-Start pin. Connect a capacitor from this
pin to ground to set the soft-start time, according to the
formula:
The nominal soft-start charging current is 2.5 A. 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
function of load and output capacitance.
Exposed Pad (Pin 33): Additional Power Ground for the
IC. Connect directly to the power ground plane.
1V to enable. Once enabled, the pin only needs to be
0.65V.
t(ms) = C
V
RC Network to Ground
OUT
2
BURST PIN
High
High
Low
SS
( F) • 320
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CCM PIN
LTC3425
High
Low
Low
Low
OUT
will be a
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