TPS22954: Power rating of internal protection diodes

Sam Shishimvearba

Part Number: TPS22954

Hello everyone.

I use this power switch to feed a resistive load connected through very long wire - basically an LR load.

During shutdown via the EN pin, the switch needs to discharge the energy in the wire's inductance. Because the disconnection is very fast, the inductor pushes the output voltage below zero and discharges through the output's internal protection diode. The result is a pulse of -380mV, roughly 5usec long, during which a current of 1A discharges linearly to zero. On average, that is about 150mW of power for 5usec.

I wanted to ask if there is any danger to the device because of this pulse.

Thank you!

over 4 years ago

0 Shreyas Dmello over 4 years ago

TI__Mastermind 32650 points

Hi Sam,

Unfortunately, our load switch devices are not meant to drive any inductive loads. The voltage of -0.38V is below the absolute minimum specification for the device.

Over time and across devices, this could cause damage to the device.

I would recommend either implementing some sort of external inductive clamp to clamp the voltage at a value higher than -0.3V or using a High Side Switch (https://www.ti.com/power-management/power-switches/high-side-switches/overview.html) which is capable of handling off board and inductive loads.

Thank you for choosing TI Power Switches in your designs.

0 Sam Shishimvearba over 4 years ago in reply to Shreyas Dmello

Prodigy 70 points

Thank you for the reply.

Do you recommend any kind of clamp that would fit this design? Ideally some sort of high-current Schottky diode with minimal recovery time.

Assume I have no mechanical/space constraints.

0 Shreyas Dmello over 4 years ago in reply to Sam Shishimvearba

TI__Mastermind 32650 points

Hi Sam,

The clamp would depend on your system considerations. For the purposes of the switch, the only reccomendation is to make sure the inductive negative spike is not more negative than -0.3V.

It may be possible to add a low fwd voltage shottkey from GND to VOUT if the load resistance is large enough.

The other option is to use a high side switch which is capable of handing these inductive spikes.

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TPS22954: Power rating of internal protection diodes