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Original question:

UCC27511: UCC27511 SPEC

UCC27511: Power consumption of UCC27511 driving 2 pcs CSD18532Q5B

Will Wang47
Expert 5470 points
Part Number: UCC27511
Other Parts Discussed in Thread: CSD18532Q5B

Hi team,

Customer is using our reference design PMP9656 to in their project. This design use 2 pcs UCC27511 drive 4 pcs MOSFET at the secondary side. And the MOSFET use CSD18532Q5B, it's gate charge at 6V is 25nC; switching frequency is 200kHz, so the total current of two pcs UCC27511 would be:

25nC*200kHz*4 = 20mA; 

But now, customer measure the average current pass through the Q8, the waveform shows as below, and it's average value is 29.32, could you help comments if this is a reasonable value? Thanks.

Best Regards,

Will 

  • 0
    TI__Genius 13460 points

    Hi,

    Our office is closed for the US Memorial Day holiday. My colleague will get back to you mid week. Thanks for your patience!

  • 0
    TI__Genius 13445 points

    Hi Will,

    Thanks for reaching out.

    The current you calculated is essentially the average current required to charge/discharge the capacitive load at the frequency of interest. Higher gate charge will obviously mean higher average current at the gate for which you measure ~9mA higher than your calculations. 

    What is the IDD current during this time? Can you share waveforms around the driver: OUT, VDD and IN+?

    Thanks.

    -Mamadou

  • 0 in reply to Mamadou Diallo
    TI__Expert 5470 points

    Hi Mamadou,

    Thanks for your feedback.

    First, want to confirm with your that the calculation of supply current is 20mA, does this correct?

    Second, the total IDD current right now shows 29.32mA average current.

    Could you help us understand what could cause the current higher than calculation?

    Best regards,

    Will

  • 0 in reply to Will Wang47
    TI__Genius 13445 points

    Will,

    What you're determining from the formula above is the average gate current during charging and discharging sequences of the gate capacitance. Because it is an average over these cycles, the actual values captured may fluctuate. 

    For this driver, Ig = 29mA at the gate seems reasonable assuming your power consumption (VDD and IDD on VDD pin) is within acceptable range. 

    -Mamadou