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UCC27324: Drive MOSFET in parallel

user4811888
Intellectual 530 points
Part Number: UCC27324

Hi expert,

As this device is a dual channel driver, would like to learn below:

1. Are these two channels fully independent to operate? No any logic limitation for PWM input and output, right?

2. If two channels are used in parallel, wonder if below is allowed or not.

In my opinion, if two channels match well, it is okay; But what would happen if dis-matching is serious? Will OUTA and OUTB have circulating current(faster high output will send current to slow one)?

3. If I have two MOSFET in parallel ideally(ignore paralleling parasitic between two MOSFET),

Do you recommend to connect OUTA and OUTB separately to each gate of MOSFET, or tie OUTA and OUTB together, tie gate A and gate B together, and then connect them?

In my opinion,  no.2 will be better because MOSFET switching always behave at the same time, no matter if dis-matching is serious or not. Correct?

4. Based on no.3, if two MOSFET are not in ideal parallel, what's the conclusion then?

I prefer no.1 connection then, would like to learn from your analysis.

  • 0
    TI__Mastermind 23015 points

    Hello,

    For the driver concerns, the circuit you show in diagram one is OK if that is the preferred connection at the system level. If you are driving two MOSFETs the connection you show in second diagram, each driver driving separate FET with have the advantage of there not being a direct mosfet gate connection which may be a concern.

    If connecting the driver in either case, the internal channel to channel delay matching of each device is very good. It will help to drive the driver inputs with fast slew rates to minimize any very small difference in delays.

    This driver has been used driving the two channels in parallel in previous applications.

    Regards,

  • 0 in reply to Richard Herring
    Intellectual 530 points

    Hi Richard,

    Roughly get your points to some degree.

    I know it's important to make input slew rate as fast as possible, and make routes short to avoid dis-match of two channels, but still not clear:

    IF dis-matching is serious, will OUTA and OUTB have circulating current(faster high output will send current to slow one)?

    And one more extra question, do you recommend pull-down resistor at input pins to avoid uncertain states of output?

  • 0 in reply to user4811888
    TI__Guru**** 189401 points

    Hi, 

    Richard is out today, he will respond when he is back. 

  • 0 in reply to user4811888
    TI__Mastermind 23015 points

    Hello,

    The UCC27324 has been used in applications where the driver outputs are in parallel. The channel to channel delay matching is not serious when using the two channels in the same driver IC. 

    We do recommend pull down resistance on the driver inputs if the controller driving the driver may have a high impedance condition such as during startup.

    Regards,