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DS90UB953-Q1: 20Hz Ripple on POC

Hao Wang14
Expert 4415 points
Part Number: DS90UB953-Q1

Hi Team,

It's found that there is 20Hz 300mV ripple on POC in 953 side, the frequency is the same as the frame rate, but the ripple will disappear when frame rate synchronization is removed.

My questions are:

1. Is it normal for the ripple?

2. Is there any solution to remove the ripple?

Thanks and Best Regards!

Hao

  • 0
    TI__Expert 5480 points

    Hi Hao, 

    The pulse is due to the switching of the sensor. During periods of blanking, the current draw from the sensor is significantly lower than during active periods, which causes the voltage to spike. There are a few suggestions that you may try to reduce the peak noise. 

    - Replace your switching regulator with an LDO

    - Increase the PoC voltage

    - Use a switching regulator with higher switching frequency 

    - Increase decoupling capacitance

  • 0 in reply to Sally Cheung95
    TI__Expert 4415 points

    Hi Sally,

    PMIC TPS650333 is used here, PoC voltage is 9V, the highest 2.3MHz frequency is used, and the input decoupling capacitor is already 20uF...

    May I know if there is any other potential suggestions which can also reduce the peak noise?

    Thanks and Best Regards!

    Hao

  • 0 in reply to Hao Wang14
    TI__Expert 5480 points

    Hi Hao, 

    The suggestions I provided earlier are all the recommended suggestions. Not sure, but did you mean TPS650330? If so, I see that the Vin max is up to 18.3. You may look into increasing the PoC voltage. 


    Thanks, 
    Sally 

  • 0 in reply to Sally Cheung95
    TI__Expert 4415 points

    Hi Sally,

    Due to the power supply limitation, the PoC voltage cannot increase any more...

    So is it possible to add PoC filter circuit such as inductors or set some of the registers to reduce the ripple? Thanks!

    Best Regards!

    Hao

  • 0 in reply to Hao Wang14
    TI__Guru** 103215 points

    Hello Hao,

    ~300mVpp at the input to the switcher before the PoC network is not necessarily an unreasonable measurement since the high frequency content will get filtered out before reaching the sensitive node which is at the input to the serializer AC coupling cap after the PoC network as long as the PoC network itself is designed well. Here are a couple recommendations:

    - Measure the slew rate of these noise pulses at 20Hz. Our general recommendation is that they should have a slew rate of > 100us/V. If the slew rate is faster than this, then add more decoupling cap at the input to the regulator to slow down the voltage spike slew rate 

    - Please send your PoC network for us to review including the specific passive components used 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Expert 4415 points

    Hi Casey,

    The pictures below are the schematic and the inductor part number, thanks!

    Best Regards!

    Hao

  • 0 in reply to Hao Wang14
    TI__Expert 5480 points

    Hi Hao, 

    Did you measure the slew rate? 

    Thanks 

    Sally