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DCR010505: Question about DCR010505 large start up current

Wayne Wang20
Expert 4390 points
Part Number: DCR010505


Hi team,

My customer is using DCR010505 to generate a isolated 5Vout with a 5Vin. But we found that during the start up process, there will be a delay on 5Vout and the start up current is very large.

Test condition: Vin=5V, Vout=5V, Iload=0A.

In  the test result, we could see:

1. When the 5Vin is just applied, input current Iin shows a negative current pulse(~1A) and  then a positive current pulse(~700mA)

2. after ~5ms, input current Iin shows a large positive current pulse(~2A)

3. After the 2A current pulse, then Vout starts to ramp up.

So my question is :

1. Why there is a negative current pulse when the 5Vin is applied?

2. Why there is a ~5ms delay between Vout ramping up and Vin is applied.

3. Because the 2A positive current pulse is too large, the 5Vin will have a obvious drop so it will affect other rails powered by the same 5Vin. So is this 2A positive current pulse a normal phenomenon? Can it be avoided? 

Thanks

Best regards,

Wayne 

  • 0
    TI__Expert 8130 points

    Hi Wayne,

    Can you provide a little more information on your application, such as a circuit schematic? I'm curious to know what is causing such abnormal behavior.
    I have a suspicion that whatever is connected at the input might be causing the negative current. Also, Is something attached on the load?

    Thanks,
    Alejandro

  • 0 in reply to iAlejandro
    TI__Expert 4390 points

    Hi Alejandro,

    Please see the DCR010505 schematic as below. When I did the test to capture the waveform, there is nothing on the load. Can you help do the test in your lab to see if you could reproduce the start up waveform? Thanks.

    Best regards,

    Wayne

  • 0 in reply to Wayne Wang20
    TI__Expert 8130 points

    Hi Wayne,

    Unfortunately, due to COVID-19, lab access is limited. Before attempting going into the lab, we would like to make sure if this can be resolved through communication.
    The schematic looks okay. Can you provide information on what is connected at the input?

    Thanks,
    Alejandro

  • 0 in reply to iAlejandro
    TI__Guru 50120 points

    Hi Wayne,

    Can you provide an update to Alejandro's question?

    Regards,

    Jimmy 

  • 0 in reply to iAlejandro
    TI__Expert 4390 points

    Hi Alejandro,

    When I captured the waveform in previous reply, the input is from a 5V DC power source. So I think the input should be OK. Please help provide more information on how much input current will be drew when DCR010505 just start up. Thanks.

    Best regards，

    Wayne

  • 0 in reply to Wayne Wang20
    TI__Guru 50120 points

    Hi Wayne,

    As Alejandro mentioned, with the current COVID19 situation, lab access has been limited so it may take some time for him to be able to get lab results for you. As such I'd like to try to resolve the issue as best as I can on this forum. I have a few additional questions below:

    1. As it stands, is it safe for me to assume that you have a stable 5V DC power supply powering the DCR010505 based on the schematic image you've provided previously? There is nothing else connected to P5V that could potentially cause an input current spike during startup?
    2. Have you tried attaching a dummy resistor to have a "preload" at the output to see if this issue is still there? Usually it is recommended to have some dummy resistor for these isolated power modules. 
    3. On your end, how many boards do you see have this failure?
    4. If possible please provide your PCB layout soI can help review it to see if there may be anything that could be causing this issue.

    Regards,

    Jimmy 

  • 0 in reply to Wayne Wang20
    TI__Expert 8130 points

    Hi Wayne,

    Any updates on this occurrence? Can you provide an update to Jimmy's questions?

    Thanks,
    Alejandro

  • 0 in reply to iAlejandro
    TI__Guru 50120 points

    Hi Wayne,

    We have not heard back from you for some time and will assume you were able to resolve the issue on your end. This thread will be closed. If you have any remaining questions, you can reply back to this thread to continue the discussions.

    Regards,

    Jimmy