LM7480-Q1: LM7480-Q1: Reason for bidirectional vs unidirectional TVS diode on the input side

Manoj Turpati

Part Number: LM7480-Q1
Other Parts Discussed in Thread: TPS73801

Hello TI,

I was looking at this thread LM7480-Q1: Reason for bidirectional vs unidirectional TVS diode on the input side - Power management forum - Power management - TI E2E support forums regarding usage of uni directional diode where both negative and positive transients are expected.

I am looking for an LDO which can withstand both positive and negative transients at its output pin. Usually lot of TI LDOs specifies higher voltages on positive side and diode drop on negative voltage typically -0.3V as absolute maximum ratings. So what will happen if i use a unidirectional TVS diode instead of bidirectional TVS on the output ? since it will clamp to higher voltage (lets say +30V) during positive transients and it acts as forward diode for negative transients. will this work for me ? did i miss something ?

Best Regards,

Manoj.

6 months ago

0 Shiven Dhir 6 months ago

TI__Mastermind 21160 points

Hi Manoj,

Welcome to e2e.

Positive side works fine but on the negative side you are basically shorting it through a diode. Hence LDO abs max will be violated.

This is just to show, I understand you are not using this controller.

Regards,

Shiven Dhir

0 Manoj Turpati 6 months ago in reply to Shiven Dhir

Prodigy 230 points

Hello Shiven,

Thanks for the response. If I understand you correct, during negative transients the LDO sees -0.7V where as its abs max is -0.3V. This is how it violates abs max ratings. Is my understanding correct ?

Best Regards,

Manoj.

0 Shiven Dhir 6 months ago in reply to Manoj Turpati

TI__Mastermind 21160 points

Hi Manoj,

The understanding is correct.

Regards,

Shiven Dhir

0 Manoj Turpati 6 months ago in reply to Shiven Dhir

Prodigy 230 points

Hello Shiven,

Thanks for the clarification. In that case i would like to use TPS73801 LDO for my application, since its OUT pin has +/-20V abs max rating. There i can use uni-directional TVS diode at the output. please refer to the below thread to understand my requirement. suggest whether my approach is correct or not.

TPS73801: Low Power LDO with Transient protection. - Power management forum - Power management - TI E2E support forums

Best Regards,

Manoj.

0 Shiven Dhir 6 months ago in reply to Manoj Turpati

TI__Mastermind 21160 points

Hi Manoj,

I can see you have gotten your answer from the right team.

Closing this thread now.

Regards,

Shiven Dhir