LTC3632 datasheet(7/26 Pages) LINER

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LTC3630

3630fb

PIN FUNCTIONS

SW (Pin 1): Switch Node Connection to Inductor. This

pin connects to the drains of the internal power MOSFET

switches.

NC (Pins 2, 4, 13, 15 DHC Package Only): No Internal

Connection. Leave these pins open.

VIN (Pin 3): Main Input Supply Pin. A ceramic bypass

capacitor should be tied between this pin and GND.

RUN (Pin 5): Run Control Input. A voltage on this pin

above 1.21V enables normal operation. Forcing this pin

below 0.7V shuts down the LTC3630, reducing quiescent

current to approximately 5μA. Optionally, connect to the

input supply through a resistor divider to set the under-

voltage lockout. An internal 2M resistor and 2μA current

source pulls this pin up to an internal 5V reference. See

Applications Information.

VPRG2, VPRG1 (Pins 6, 7): Output Voltage Selection. Short

both pins to ground for an external resistive divider pro-

grammable output voltage. Short VPRG1 to SS and short

VPRG2 to ground for a 5V output voltage. Short VPRG1 to

ground and short VPRG2 to SS for a 3.3V output voltage.

Short both pins to SS for a 1.8V output voltage.

GND (Pins 8, 14, 16, Exposed Pad Pin 17): Ground. The

exposed backside pad must be soldered to the PCB ground

plane for optimal thermal performance.

VFB (Pin 9): Output Voltage Feedback. When configured

for an adjustable output voltage, connect to an external

resistive divider to divide the output voltage down for

comparison to the 0.8V reference. For the fixed output

configuration, directly connect this pin to the output supply.

SS (Pin 10): Soft-Start Control Input. A capacitor to

ground at this pin sets the output voltage ramp time. A

50μA current initially charges the soft-start capacitor until

switching begins, at which time the current is reduced to

its nominal value of 5μA. The output voltage ramp time

from zero to its regulated value is 1ms for every 16.5nF

of capacitance from SS to GND. If left floating, the ramp

time defaults to an internal 0.8ms soft-start.

ISET (Pin 11): Peak Current Set Input and Voltage Output

Ripple Filter. A resistor from this pin to ground sets the

peak current comparator threshold. Leave floating for the

maximum peak current (1.2A typical) or short to ground

for minimum peak current (0.12A typical). The maximum

output current is one-half the peak current. The 5μA current

that is sourced out of this pin when switching, is reduced

to 1μA in sleep. Optionally, a capacitor can be placed from

this pin to GND to trade off efficiency for light load output

voltage ripple. See Applications Information.

FBO (Pin 12): Feedback Comparator Output. Connect

to the VFB pins of additional LTC3630s to combine the

output current. The typical pull-up current is 20μA. The

typical pull- down impedance is 70Ω. See Applications

Information.

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