ATL431: Problems using ATL to control P-MOSFET with connected load

Bradley Johnson

Part Number: ATL431
Other Parts Discussed in Thread: TL331, TL431

Tool/software:

Hello,

I am having troubles using the ATL431 to control a P-channel power mosfet, as shown in the diagram below. In hindsight I wouldn't use the ATL431 again for this application, but looking for advice on how to remedy an issue as the project moves forward. The issue is Q1 is partially turned on and overheats due to gradual turn on behavior of the ATL431. When the input is below threshold R5 is keeping Vgs~0. As the input voltage rises slowly (1V/min), the 2.50V threshold is approached, the ATL431 beings to conduct, which lowers Vgs (VR1out - Vinput), Q1 begins to conduct. There is finite input current (R6), R4 is much lower than R7, so the current into the ATL431 is limited, so it cannot regulate down to 2V and fully turn on Q1.

Any advice on how to resolve this issue?

over 1 year ago

0 Jackson Wightman over 1 year ago

TI__Expert 8590 points

Hello,

Thank you for the detailed description of the behavior of the device. To help with the debug, can you answer these questions?

1. Can you please provide scope captures of Vinput as well as Vout?

2. Can you let me know what the current across R7 is when Vinput starts to meet/exceed the threshold?

3. Is this happening with every ATL431 device, a few, or just one?

Thanks,

Jackson

0 Jackson Wightman over 1 year ago in reply to Jackson Wightman

TI__Expert 8590 points

Hello again,

I haven't seen any response to this thread in the past few days, so I am going to close it. To re-open the thread, simply reply to this message, and I can continue to help with the issue you are describing.

Thanks,

Jackson

0 Bradley Johnson over 1 year ago in reply to Jackson Wightman

Prodigy 40 points

Hi Jackson, Sorry for the late response. The source of the problem is the very slow ramp rate of the input voltage, which has insufficient 'overdrive' voltage for the ATL431 to switch from floating to pull-down (~2V). This is discussed in the datasheet. I changed the design to use the TL431 to generate a reference voltage, and then added TL331 to perform the voltage comparison and MOSFET control. The new approach works as expected.

0 Jackson Wightman over 1 year ago in reply to Bradley Johnson

TI__Expert 8590 points

Glad this new approached worked with TL431.

Thanks,

Jackson

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ATL431: Problems using ATL to control P-MOSFET with connected load