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The datasheet for the HIP4081A bridge driver references a limit of 2.5 A "pull up"/"down" current.

I thought the maximum load current in a bridge is limited by the FETs themselves, and not the driver.

What am I misunderstanding?

The reason I ask, is that I need to drive a 12 VDC motor with a 10 A stall current with a PWM.

I confirmed the 10 A stall current by connecting it directly to a car battery with a meter, and a vice-grip to stall the axle.

When I put the 4081a circuit in between, it stalls at a peak 4 A (which is way above the 2.5 A spec). Note that I built the reference circuit in the datasheet (page 3), but pull DISABLE low so that it is 100% duty cycle.

I'm using IRF530 FETs which can handle 10 A, 88 W, so they should at least get me to 10 A @ 12 VDC before smoking. (I'll replace these later with something > 120 W.)

Is there a better full-bridge driver I should be using? I waded through DigiKey but had trouble finding a DIP package driver with that level current.

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    \$\begingroup\$ I strongly recommend you start using parts in other packages; DIP is increasingly unpopular, and you would have more success if you were open to using SOIC or TSSOP. They really aren't that hard to solder, especially SOIC. \$\endgroup\$
    – Hearth
    Nov 30, 2023 at 5:31
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    \$\begingroup\$ Please add a schematic to your question: gate drivers are NOT intended to drive loads directly, and when used as intended, does not affect the load or switching characteristics that are determined by the output transistors themselves; therefore we cannot determine an answer to your question. \$\endgroup\$ Nov 30, 2023 at 10:39
  • \$\begingroup\$ @Hearth - your comment is meaningless. DIP has perfectly fine electrical characteristics for the application, and that's not even what I asked. \$\endgroup\$
    – Freeman
    Nov 30, 2023 at 15:47
  • \$\begingroup\$ @TimWilliams - As I said in my question, I used the reference the schematic, it is on page 3 of the link. I also stated that I am using IRF530 FETs to drive the motor, which means I am not driving the motor directly. The datasheet says you can drive the FET directly with bridge. Also, I am not even switching in my test circuit. \$\endgroup\$
    – Freeman
    Nov 30, 2023 at 15:49
  • \$\begingroup\$ @PeterT I know it's not what you asked, that's why it's a comment and not an answer. It was in response to you saying that you're having trouble finding a suitable part in DIP. My comment is not about the package electrical characteristics, but about the availability of parts--very few new parts come out in DIP these days, so you're going to be limited to working with old parts. I used to be scared of working with SMD parts too! But it's a very valuable skill, and not as difficult as it seems. \$\endgroup\$
    – Hearth
    Nov 30, 2023 at 16:50

1 Answer 1

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In the datasheet, the current limits you refer to are in the "GATE DRIVER OUTPUT PINS" section. They therefore refer to the gate drive capacities (i.e. ability to source/sink current to the gate), not the "load" current in the drain-source channels of the FETs.

The drive currents are relevant when working out the switching speed of your FETs, given their gate capacitances.

In general slower switching will lead to greater resistive losses in the FET during transitions, and depending on the PWM rate, these losses could lead to significant FET heating.

However, if you are only running at 100% duty cycle, then you will only have an occasional ON/OFF transition, so 2A of gate drive will almost certainly be more than enough for your application.

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  • \$\begingroup\$ Even if the frequency is zero, as I stated in my question? The circuit is wired with disable off (and A and B control at 0 and 1), so there should be no switching losses, and this is not a self-oscillating driver. \$\endgroup\$
    – Freeman
    Nov 30, 2023 at 15:51
  • \$\begingroup\$ Answer extended to clarify impact of the gate drive \$\endgroup\$
    – colintd
    Nov 30, 2023 at 17:30

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