SIP32434

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Vishay Siliconix

S22-0384-Rev. B, 02-May-2022

15

Document Number: 63147

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SLEW RATE CONTROL

An inrush current happens when the switch turns on into a large output capacitance. If the inrush current is not controlled, it

can damage the input connectors and / or cause the system power supply to droop, leading to unexpected restarts elsewhere

in the system.

The SIP32434A and SIP32434B provide integrated output slew rate control to manage the inrush current during start-up. This

is achieved by forcing the VOUT to follow the voltage on a soft start capacitor. A constant current source of 5 μA charges the

CSS, generating a linear ramp up voltage on CSS.

The inrush current is proportional to the load capacitance and rising slew rate. The following equation can be used to calculate

the slew rate required to limit the inrush current (IINRUSH) for a given load capacitance (COUT):

An external capacitor can be connected to the soft start (SS) pin to control the rising slew rate and lower the inrush current

during turn-on. The output voltage follows the required CSS capacitance to produce a given slew rate, which can be calculated

using the following formula:

The fastest output slew rate is achieved by leaving the soft start pin open.

SR (V/ms) =

I

INRUSH (mA)

C

OUT (μF)

---------------------------------

T

SS =

V

IN

SR

-------- = V

IN x

C

OUT (μF)

I

INRUSH (mA)

---------------------------------

C

SS =

I

SS x 9



SR

-----------------------