TPS7A94: Output short circuit protection and its impact on input rail

Trushal Alshi

Part Number: TPS7A94

Tool/software:

Is there output short circuit protection like brickwall etc on TPS7A94. Datasheet does not clearly mention about impact on V_in in case of short/overload on V_out. Section 8.1.1 Output Voltage Restart (Overshoot Prevention Circuit) has some mention about output short, but the figure shows little drop in input voltage. In my application, we don't intend to hurt input in case of output short circuit.

8 days ago

0 Hannah Grace 8 days ago

TI__Genius 9960 points

Hello,

Thank you for your question.

Short circuit was tested on this device, and there wasn't found to be any issues with this test. The conditions that were used were as follows:

Vin=3.8V

Ven=2V

Vout=3.3V

Cin=1uF

CNR/SS=4.7uF

Cout=4.7uF

IOUT=open, short, open

The validation engineer took a scope shot of this short circuit condition and this test did not damage the device and stabilized after a couple micro-seconds. The device should not damage as long as abs max conditions are not exceeded.

Do you have specific input/output/other conditions that we can test with to ensure that short circuit will not damage your device?

Best,

Hannah

0 Trushal Alshi 8 days ago in reply to Hannah Grace

Prodigy 60 points

Thanks Hannah. We plan to use it in RF application where input will be 5.5V with V_out 5V. Any worse transient load or short circuit on 5V should not cause dripping major dripping ripple on Vin 5.5 as same source rail used as input for few more similar LDOs.

0 Hannah Grace 8 days ago in reply to Trushal Alshi

TI__Genius 9960 points

Okay, I can ask if one of our validation engineers can take a look into performing a short circuit test for you.

0 Hannah Grace 8 days ago in reply to Hannah Grace

TI__Genius 9960 points

I will keep you posted on the progress of this test.

Thanks,

Hannah

0 Trushal Alshi 8 days ago in reply to Hannah Grace

Prodigy 60 points

Thanks for the efforts! Will wait for the results.

0 Hannah Grace 8 days ago in reply to Trushal Alshi

TI__Genius 9960 points

Is the input connected to a power supply, or what is the source supply connected to?

0 Trushal Alshi 8 days ago in reply to Hannah Grace

Prodigy 60 points

It comes from a dc-dc buck which has 12V_in and 5.5V_out, 20A with 400 Khz switching frequency. This 5.5V will be driving 10 nos of TPS7A94 to get 10 separate 5V rails. Hope this is what you are asking for.

0 Hannah Grace 8 days ago in reply to Trushal Alshi

TI__Genius 9960 points

Thank you for this additional information. Please allow me another business day to see what resources we have available.

Best,

Hannah

0 Hannah Grace 7 days ago in reply to Trushal Alshi

TI__Genius 9960 points

Hello,

I am sorry to inform you that after talking with a peer, we do not believe that we have the resources to take a short circuit test for your specific conditions.

Additionally, we do not think it will be necessary.

The short circuit current limit is similar to this:

From the perspective of the source supply, the LDO looks like a constant current source. If a sudden short appears on the output of the device, the LDO will see the short until the short circuit current limit loop engages. The current limit looks takes approximately 20-50us to engage, but after further testing we found that the current limit loop engages faster than 20us for this hard short, therefore preventing the device from becoming damaged.

I hope this helps explain some things better and again I am sorry about the limited resources!

Best,

Hannah

0 Trushal Alshi 7 days ago in reply to Hannah Grace

Prodigy 60 points

Thanks Hannah. No issues. So do you mean that there will be a little unavoidable drip on supply rail longing for less than 20 us just after the hard short.

+1 Hannah Grace 7 days ago in reply to Trushal Alshi

TI__Genius 9960 points

Yes, there will be an unavoidable dip on the supply rail as the LDO is trying to go into its protection mode, but typically even though this is the case, we do not see any damage occur to the device.

0 Trushal Alshi 7 days ago in reply to Hannah Grace

Prodigy 60 points

OK I got it. Thanks for the keen support!

0 Hannah Grace 7 days ago in reply to Trushal Alshi

TI__Genius 9960 points

Happy to help. Please let me know if you have any additional questions.

I will go ahead and close out this thread now.

Best,

Hannah

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TPS7A94: Output short circuit protection and its impact on input rail