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UCC28950: VDD current

Eze Bayer
Prodigy 150 points
Part Number: UCC28950
Other Parts Discussed in Thread: UCC27324
Hello, i saw from the datasheet that the max current in VDD pin is 10mA. But in my circuit I have it limited to 50mA and still the voltage drops. 
Is it okay to consume more than 50mA? my circuit is very similar to the one in the datasheet. 
Thanks
  • 0
    TI__Guru* 86266 points

    Hello,

    The UCC28950 should not be drawing more than 10 mA.  Have you measured the IDD current?  

    Regards,

  • 0
    Prodigy 150 points

    Thanks Mike, yes, I only power VDD pin with a lab supply limmiting it to 50mA, and the voltage drops, could be something from the rest of the connections that causes more consume? I attach my control circuit. Thanks

  • 0 in reply to Eze Bayer
    TI__Guru* 86266 points

    Hello,

    The device should not be drawing 50 mA.  There is something loading down the circuit.  Please check to make sure VDD is not exceeding the maximum rating.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 150 points

    Ok, thanks, i'm going to review the PCB. Do you know if could be a peak of consumption at startap?

  • 0 in reply to Mike O'
    Prodigy 150 points

    Hello Mike, I was reviewing the PCB but i didn't find issues. I saw that putting the SS/EN pin to GND makes VDD not drop. Is there a particular pin that you recommend me to review? I connect the outputs directly to the driver. Thanks

  • 0 in reply to Eze Bayer
    TI__Guru* 86266 points

    Hello,

    If your current is higher than expected the current could be loaded by VREF.  Also make sure you are not driving FETs directly with the outputs and are using drivers.  If you are not using drivers that could also be the place for excessive current.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 150 points

    Hello Mike,
    1_ I reviewed the PCB and with SS/EN to GND direct there is 5V in VREF pin, and very low current from VDD. When I put 5V direct in SS/EN pin the consume is low too in VDD. But when I connect SS/EN pin with the CAP to GND, VDD drop
    2_ The outputs are connected to UCC27324 like the figure attached above.
    I am testing the design without Power Voltage so "Vsense" and "CS" are 0V
    Do you know anything else that could i test? Could you check my design that i attached please?
    Thanks

  • 0 in reply to Eze Bayer
    TI__Guru* 86266 points

    Hello,

    Connecting a capacitor to the soft start pin should not cause VDD to drop.  Unless there is no capacitance on VDD.

    The only thing that could excessive current is something on the device exceeding the maximum or minimum voltage ratings.

    Check the abs max table and each pin on the device to make sure nothing is exceeding the abs max or going more than -0.45V below ground.

    Regards,

  • +1 in reply to Mike O'
    TI__Guru* 86266 points

    I noticed in your schematics that Vbias is powering the UCC28950 and the driver U2.  This high current that you are seeing out of your bias supply may be doing to the driver and not the UCC28950.

    You should be able to use measure the current by looking differentially across R6.

  • 0 in reply to Mike O'
    Prodigy 150 points

    Thanks Mike, effectively the high current came from the drivers. Now i have to review if is possible to reduce this consume