This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS92692-Q1: Input current ripple issue when doing input ripple test

Part Number: TPS92692-Q1
Other Parts Discussed in Thread: TPS92692

Hi team,

My customer is doing input voltage ripple test on TPS92692-Q1(buck-boost), and the frequency of ripple is range from 50Hz-25kHz, Upp=4V. Now they find that when the ripple frequency increases, the input current ripple will increase badly and violate their test standard limitation, and the output current is normal. The test waveform is attached below. The yellow waveform is the input voltage, and the blue waveform is the input current, which is measured at the input supply wire.

Now I have 2 assumptions:

1. Maybe the response is too slow and make the input ripple current much higher;

2. Maybe 15uH inductor is not big enough;

Apart from this assumption, is there some other possibility we can try to make the input current ripple smaller?

And before they use 220nF connected to COMP, now we changed to 33nF connected to COMP, which is calculated by the calculator, and there is nothing better either.

Please give us some advice to solve the problem. Thanks.

Gary

  • Hello,

    We would need a schematic along with your requirements for us to check.

    Thanks Tuan

  • Hi Tuan,

    Yesterday I did some test, and I found that when I removed the power inductor in the buck-boost circuit of TPS92692, there was still a large AC current  flowing into the customer's board. And finally I found it's the EMC filter circuit which induces this large AC input current. So I suppose when we do the input voltage ripple test, the resonance frequency of EMC filter may locates in the input ripple frequency range, which is 50Hz to 25kHz. 

    Can you help me calculate if the resonance frequency locates in the range of 50Hz to 25kHz?

    If not, why the large AC current vanishes when I remove the capacitor of EMC filter circuit and short the inductor of the filter?

    If so, can you provide a set of L,C value which resonance frequency is far beyond the range of 50Hz to 25kHz?

    Besides, I use TPS92692EVM to do the same test, and the same happens. The customer's EMC filter circuit is attached below.

    Thank you!

  • Hi Taoran,

    The filter is not damped so the resonant frequency of the filter is causing what you are seeing.

    You can read up on damping of input filters to help you out on this,

    Thanks Tuan