TPS54302: Is it necessary to add any bypass diode (fron VOUT to VIN) for avoiding reverse current flowing when input voltage is powered down?

Kazuya Nakai59

Guru 20100 points

Part Number: TPS54302
Other Parts Discussed in Thread: TPS54202

Hello guys,

One of my customers is evaluating TPS54302 for their new products.

They have a question as the follow. Could you please give me your reply?

Q. They think that some currents flows from VOUT to VIN when VIN is powered off because VOUT is larger than VIN in the situation.

Is it necessary to add any bypass diode (fron VOUT to VIN) for avoiding reverse current flowing into TPS54302 when input voltage is powered down?

TPS54302 datasheet recommends to use 44uF~66uF as the output capacitor. But they are using about 100uF output capacitor due to some reasons.

So they think the reverse current will be larger than 44uF~66uF output capacitor case.

Is it necessary to add the bypass diode?

Your reply would be much appreciated.

Best regards,

Kazuya.

over 3 years ago

0 Gerold Dhanabalan - Online Design Tools over 3 years ago

TI__Genius 14455 points

The reverse current flowing from Vout into Vin, when Vin is powered down can happen with any converter. Is there any specific concerns in your application?

regards,

Gerold

0 Kazuya Nakai59 over 3 years ago in reply to Gerold Dhanabalan - Online Design Tools

Guru 20100 points

Hello Gerold,

Thank you very much for your reply.

The customer thought bypass diode would be needed for DCDC too because some linear regulators need the bypass diode.

Is the bypass diode not needed for TPS54302 regardless output capacitor value?

Thank you again and best regards,

Kazuya Nakai.

0 Vincent Zhang(BSR) over 3 years ago in reply to Kazuya Nakai59

TI__Expert 4795 points

Hi Kazuya,

My understanding is if VIN power off very fast and there is large output capacitance, the diode is needed. But normally there is pre-regulator(has output cap) before TPS54202, as normally pre-regulator won'r drop off rapidly, so the VIN of TPS54202 couldn't power off rapidly as well.

Back to customer's usecase, For 100uF out cap, if VIN drop slew rate is between 0.1V/ms ~ 10V/ms, there no need to add this diode based on our validation results.

Hope it helps.

0 Kazuya Nakai59 over 3 years ago in reply to Vincent Zhang(BSR)

Guru 20100 points

Hi Vincent,

Thank you very much for your reply.

It is very helpful for the customer and me.

Thank you again and best regards,

Kazuya Nakai.

Power management

Power management forum

TPS54302: Is it necessary to add any bypass diode (fron VOUT to VIN) for avoiding reverse current flowing when input voltage is powered down?