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UCC37324: Functioning of UCC37324

Syed Inamullah
Prodigy 61 points
Part Number: UCC37324

Hello

We are using UCC37324 to drive an array of parallel N-channel MOSFETs on the low side. The IC is supplied by 12V at VDD. Logic high at INA and INB is at 3.3V.
The distance between output terminals (OUTA and OUTB) and the first  N-MOSFET in the array is about 45mm. Does this affect the IC operation?
Issues we are facing:
1. OUTA and OUTB show 12V when INA and INB are given logic high signals.
2. Voltages across INA and INB are fluctuating between 1.5V to 0V.
3. MCU operations are being halted.

Whent the IC is depopulated off the board, MCU operations are normal. Could the distance, as mentioned above, cause these problems?
Your help is highly appreciated.

Thanks & Regards 

  • 0
    TI__Genius 11770 points

    Hello Syed,

    45mm is a lot of distance, but it depends a lot on the trace width also. One of the issues that can cause for the driver is overshoot/undershoot on the output pins due to parasitic inductance. As for the issues:

    Syed Inamullah said:
    1. OUTA and OUTB show 12V when INA and INB are given logic high signals.

    This is expected; UCC37324 is a non-inverting driver, so OUTA and OUTB should be 12V when given logic high on the inputs. 

    Syed Inamullah said:
    2. Voltages across INA and INB are fluctuating between 1.5V to 0V.
    3. MCU operations are being halted.

    This sounds like it may be the issue. Are you sure the driver is not damaged? It sounds like the input pins are drawing a much larger current than expected and causing issues for the MCU. The easiest way to check is to check the quiescent current draw of the driver and compare that to the datasheet. When a driver is damaged, pins will often short to ground, which may have happened to the IN pins here. 

    Also, what is the switching frequency, and is there an RC filter on the inputs?

    Thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 61 points

    Hi Alexander, 

    Thanks for the reply. 

    Track width is 0.2 mm. 

    The driver isn't damaged as we tested the same part on a different test board. One difference on the test board is that the driver is placed 10 mm from the gate resistors. 

    On test board the driver seems to work as necessary. 

    N-MOSFETs are used for a load switching application based on a decision taken by the MCU. 

    There are no RC filters on the input.

  • 0 in reply to Syed Inamullah
    TI__Genius 11770 points

    Hi Syed,

    Does the input use an open drain pulldown on MCU with external pullup resistor? I'm not sure why the output trace length should affect the behavior of the inputs. Also, does this test board improve the behavior of INA and INB?

    In any case, a 40mm trace length with 0.2mm width is not good for the driver; it will add a lot of parasitic inductance that can cause issues. The exact issue may be due to ground bounce, but that depends on how the grounding was done. It would be very helpful if you could share waveforms. If you don't want to share schematics/layout publicly, you can add me as a friend on E2E. 

    Thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 61 points

    Hi Alexander,

    Thanks for the reply.

    Problem solved and now it is running as expected.

    Problem occurred due to Ground connection only.

    Thanks for your valuable suggestions.