LM74610-Q1: LM7461 conducts from anode to cathode in both polarities

Daniel Rueppel

Part Number: LM74610-Q1

Dear Sir or Madam,

we built the reference circuit for the LM7461 for polarity protection. We double checked the correct wiring multple times, our build is a double sided PCB with SMD components.

The output is 12V or -12V depending on the applied polarity. We can remove the MOSFET and the LM7461 still conducts both ways. There is no polarity protection that can be observed.

Our input is 12.6V and the intented purpose is to protect a buck converter that is connected to a microcontroller.

Attached is our Eagle schematic and board. At this stage, we have stuck experiencing the above situation.

Thank you,
Daniel

board.brd

board.sch

over 5 years ago

0 Karikalan Selvaraj over 5 years ago

TI__Genius 16305 points

Hello Daniel,

We are looking into your schematic and layout files and will get back, if possible by today or if not by tomorrow.

Regards,

Kari.

0 Daniel Rueppel over 5 years ago

Prodigy 40 points

Dear Sir or Madam,

The following PDF document contains the circuit with all parts. We have built circuit # 4

We look forward hearing from you,

Daniel Rueppel

Reverse-battery-protection-circuits.pdf

0 Daniel Rueppel over 5 years ago in reply to Daniel Rueppel

Prodigy 40 points

Hi Kari,

to ensure the correct chip was supplied to us, here are the markings:

Front: 93 TI ZDSK

Back: 93A POZX

Part # LM74610QDGKRQ1

Origin: China, supplied by Mouser

Best Regards,

Daniel

0 Daniel Rueppel over 5 years ago in reply to Daniel Rueppel

Prodigy 40 points

Hi Kari,

I would like to assist to solve this issue as it is most likely either ...

1. A misunderstanding on my side as I am convinced the LM74610 is working should it not be damaged
2. A wiring fault caused by me or a board layout issue of using a VIA for the capacitor

I have checked my wiring and concluded all lines conduct correctly.

As of now, the circuit WORKS but I am observing a reverse voltage of -11V without load, or -0.4V when a capacitor is connected which essentially has virtually no current.

Therefore blocking the flow of reverse current works.

Do you have any explanation why there is a reverse voltage althouth the MOSFET is turned off?

Thank you,

Daniel

0 Karikalan Selvaraj over 5 years ago in reply to Daniel Rueppel

TI__Genius 16305 points

Hi Daniel,

Thank you for sharing this information, allow some time to get back on this, early next week is okay?

Regards,
Kari.

0 Karikalan Selvaraj over 5 years ago in reply to Karikalan Selvaraj

TI__Genius 16305 points

Hello,

-11V is due to the reverse leakage current (60uA) than can flow, for example through a multimeter probe or osicilloscope probe.

Its impedance is 10 MOhm and the reverse leakage current, though small, can cause high voltages to be seen.

The moment a load is connected or a capacitor is connected this would vanish to few mV.

Regards,

Kari.

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LM74610-Q1: LM7461 conducts from anode to cathode in both polarities