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UCC27537: What is the imput impedance of UCC27537 VIN+

Wayne Wang20
Expert 4360 points
Part Number: UCC27537
Other Parts Discussed in Thread: UCC27523

Hi team,

My customer is using UCC27537. The schematic is as below: VDD=12V, EN is floating and IN+ is from a opto-coupler. 

We found that:

1. When we remove R6 and measure opto-coupler output Pin7, the voltage of Pin7 is a 12V/0V square wave

2. When we soldered R6 to connect opto-coupler Pin7 to UCC27537 IN+, in theory, UCC27537 IN+ should also have a 12V/0V square wave. But we found that the 12V signal is pulled down to some lower voltage. 

So could you please help check if this is a normal status? What is the input  impedance of UCC27537 IN+ pin and will it draw some large input current at IN+ pin? Thanks.

Best regards,

Wayne

  • 0
    TI__Expert 4070 points

    Hi Wayne,

    Thanks for reaching out!

    Our offices are currently closed due to US holiday.  We will address your questions early next week when we are back in the office.

    Thanks for understanding!

    Aaron Grgurich

  • 0
    TI__Intellectual 2061 points

    Hi Wayne, Your understanding is correct. I don't think it is normal either.

    Can you please help remove UCC27537 from board and measure from Pin3 to pin2 (not from pin2 to pin3) impedance of UCC27523? if it is within a few hundred range, the driver may be dead and please replace a new one.

    I also didn't found the bypassing cap for UCC27537 and bypassing cap for the buffer stage. It is better to have one for each.

    If EN is not used, please tie it to VDD.

    Wish it helps.

  • 0 in reply to Wei Zhang
    TI__Expert 4360 points

    Hi Wei,

    Thanks for your reply.

    We remove UCC27537 from board and measure from Pin3 to pin2 (not from pin2 to pin3) impedance. The result is ~230kohm. Then we find another totally new device and measure it again. The impedance from Pin3 to Pin2 of this new device is also ~230kohm.

    So it seems the device on the board is not damaged. Do you have any other advice on this issue? Thanks.

    Best regards,

    Wayne

  • 0 in reply to Wayne Wang20
    TI__Guru**** 189399 points

    Hi, Wayne,

    Our office is now closed for the US Thanksgiving holiday. Mamadou will respond to your latest question on Monday.

  • 0 in reply to Wayne Wang20
    TI__Genius 13445 points

    Hello Wayne,

    I've sent you an email meanwhile I will mark this thread as "resolved"

    Regards,

    -Mamadou