LTC3631 Datasheet, PDF(6/22 Page) Linear Technology – High Effi ciency, High Voltage 100mA Synchronous Step-Down Converter

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LTC3631 Datasheet, PDF (6/22 Pages) Linear Technology – High Effi ciency, High Voltage 100mA Synchronous Step-Down Converter

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LTC3631

TYPICAL PERFORMANCE CHARACTERISTICS

Soft-Start Waveform

Load Step Transient Response

Short-Circuit Response

OUTPUT

VOLTAGE

1V/DIV

OUTPUT

VOLTAGE

50mV/DIV

LOAD

CURRENT

50mA/DIV

OUTPUT

VOLTAGE

2V/DIV

INDUCTOR

CURRENT

100mA/DIV

CSS = 0.047Î¼F 5ms/DIV

3631 G19

VIN = 24V

VOUT = 5V

1ms/DIV

3631 G20

VIN = 10V

VOUT = 5V

200Î¼s/DIV

3631 G21

PIN FUNCTIONS

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

pin connects to the drains of the internal power MOSFET

switches.

VIN (Pin 2): Main Supply Pin. A ceramic bypass capacitor

should be tied between this pin and GND (Pin 8).

ISET (Pin 3): Peak Current Set Input. A resistor from this

pin to ground sets the peak current trip threshold. Leave

ï¬oating for the maximum peak current (225mA). Short

this pin to ground for the minimum peak current (50mA).

A 1Î¼A current is sourced out of this pin.

SS (Pin 4): Soft-Start Control Input. A capacitor to ground

at this pin sets the ramp time to full current output dur-

ing start-up. A 5Î¼A current is sourced out of this pin. If

left ï¬oating, the ramp time defaults to an internal 0.75ms

soft-start.

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

above 1.2V enables normal operation. Forcing this pin

below 0.7V shuts down the LTC3631, reducing quiescent

current to approximately 3Î¼A.

VOUT/VFB (Pin 6): Output Voltage Feedback. For the ï¬xed

output versions, connect this pin to the output supply. For

the adjustable version, an external resistive divider should

be used to divide the output voltage down for comparison

to the 0.8V reference.

HYST (Pin 7): Run Hysteresis Open-Drain Logic Output.

This pin is pulled to ground when RUN (Pin 5) is below

1.2V. This pin can be used to adjust the RUN pin hysteresis.

See Applications Information.

GND (Pin 8, Exposed Pad Pin 9): Ground. The exposed

pad must be soldered to the printed circuit board ground

plane for optimal electrical and thermal performance.

3631fb

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