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The MAX16126/MAX16127 load-dump/reverse-voltage protection circuits protect power supplies from damaging input voltage conditions, including overvoltage...
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Reverse voltage current path on MAX16126

zari on May 13, 2026

Category: Hardware

Product Number: MAX16126

My MAX16126 circuit is short-circuited in the reverse polarity. My suspicion is it's because of the body diodes in my dual-FET package. I would have thought the protection diode would do the same if there is a path through the SRC pin, but since it's part of the recommended datasheet circuit, I didn't think it was an issue. Does anyone have any advice on how to fix this?

hardware MAX16126 reverse voltage MAX16126TCA+T Protection Switches & Controllers

pvid

on Jun 16, 2026 4:49 PM
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I've reviewed the schematic you shared and first off a note that if your MOSFET body diodes create any path that tries to drive the SRC node during reverse polarity, that internal clamp can turn into a short.

Before making any suggestions I just wanted to confirm a couple of things:
I can see the schematic symbol, but can you confirm the exact pin connections for each pin of the BUK7K12-60E on your board? Which pins are tied to SRC, which pins to the input side and which to output etc.
What exactly is connected to your J11 connector?
What's the full part number for D27?
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zari on Jun 16, 2026 5:32 PM
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Hi pvid

Yeah, I figured it's probably that body diode that's causing the issue. I wasn't sure of the internal connection of the SRC and GATE pins.

But, to your questions...

See snippets below.

J11 will be an off-board connection to a 24V Brick regulator

D27 is SMAJ24CA
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pvid

on Jun 22, 2026 4:58 PM
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Thank you for sharing the footprints, I have double checked your connections and this confirms the MOSFETs are wired correctly in a back-to-back configuration.

Could you please try the debug steps below:
Disconnect the output rail (remove the bulk caps/load)
Then re-test - apply reverse polarity with current limit

Then look at input current level, does the current drop significantly but still flows or short completely dissapears.

Let me know what you see whan you try this, or if you have any questions.
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zari on Jul 7, 2026 7:50 PM
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Hi pvid . Finally getting back to this project! I'm glad the FET I had speced is configured with protection diodes in the correct direction.
I removed the bulk capacitance on the load side and disconnected the load past that, as you suggested. No change to the current profile; still appears as a short. Any other ideas?
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pvid

on Jul 9, 2026 5:28 PM
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Thanks for trying that test. That rules out the output side as the primary cause.

Could you try applying reverse polarity with a current limited supply?
And provide the measurements below:
Reverse current being drawn
IN voltage
OUT voltage
SRC voltage
GATE voltage

In the next step to debug, this should help figure out if the current path is through the MAX16126, the MOSFETs, or another path on the board.

Let me know if you have any questions or if anything comes up in the meantime.
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zari on Jul 27, 2026 1:02 PM
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Thanks pvid ! OK, here are the measurements...

* Current limited to 1 A
* IN voltage = -3.83 V
* OUT voltage = -0.793 V
* SRC voltage = -3.73 V
* GATE voltage = -30 mV
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