TPS5430: 2 V overshoot at the output

andrea sighinolfi1

Prodigy 220 points

Other Parts Discussed in Thread: TPS5430

Hi,

I am using a TPS5430 with the following parameters:

Vin = 24Vdc

Vout = 12Vdc

Iout = 0,5A

The components surrounding the regulator are the ones suggested by Webench simulation, and the schematic is attached below.

My problem is: when the input voltage is provided (at the startup), the Output experiences an overshoot (about 2 V, see attached image): Vout reaches 14 V, and after that, it sets to desired 12 V. Please see the attached image below.

Please, could anyone give me some suggestion on how to eliminate that undesired 2 Volts overshoot at the startup?

Thanks so much in advance,

best regards.

Andrea Sighinolfi

over 11 years ago

0 JohnTucker over 11 years ago

TI__Guru**** 191445 points

That start up waveform looks unusual. See the two rise rates. What is the time scale of the waveform? The inductor value looks large also. Can you share your design equations? You may also need 10 uF ceramic X5R or better located directly across Vin and GND.

0 andrea sighinolfi1 over 11 years ago in reply to JohnTucker

Prodigy 220 points

Hi John,

first, thanks for your answer. Yes, I saw the two rise rates, it is strange, but I really don't understand that behavior. The time scale of the waveform I attached is 5 ms/div. I tried to add a 10uF ceramic capacitor across Vin and GND, but that overshoot remains. Do you have any idea, please?

Thanks,

Andrea.

0 andrea sighinolfi1 over 11 years ago in reply to andrea sighinolfi1

Prodigy 220 points

I solved my problem: I added a 100nF capacitor on the ENABLE pin of the TPS5430; in this way I added a small delay for letting the Vin to reach a good voltage level in order to produce a good Vout.

Thanks.

Andrea

0 JohnTucker over 11 years ago in reply to andrea sighinolfi1

TI__Guru**** 191445 points

So the reason was too slow of rise time on VIN to support 12 V output at the end of the internal slow start time (VIN still less than 12 V)?

0 andrea sighinolfi1 over 11 years ago in reply to JohnTucker

Prodigy 220 points

Yes, that seems to be the main reason..

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TPS5430: 2 V overshoot at the output