LM74610-Q1: Reverse Potential on Unpowered Source Terminal of ORing Circuit

Hi Praveen,

1.6V buildup can be because of leakage from cathode to anode.

Regards,

Shiven Dhir

Hi Shiven Dhir,

Thanks for your response!

From the datasheet, we understand that the Anode and Cathode pins of the LM74610 are used to measure the potential across the body diode of the NMOS. Given this function, we’re trying to understand how leakage might occur across these pins. Could you please clarify the possible sources of such leakage, and if this is a known behavior, do you have any recommendations to minimize or avoid it?

Hi,

We were aware of the leakage issue, but it was previously understood to be a very small current. When we force the gate of the NMOSFET to GND, the voltage drops to 0V, confirming that the leakage is occurring through the MOSFET.

According to the specification, if VDS exceeds -20mV, the pin pull-down (PD) should activate and pull the gate node down. However, we are observing VGS around 300mV in this condition, which is inconsistent with the expected behavior.

Could you please help us understand why we’re seeing this elevated voltage?

Hi Praveen,

The GATE gets pulled low actively when the device is turned on.

When in off-state, the GATE is pulled low passively. That can be a reason for 300mV buildup.

Regards,

Shiven Dhir

Hi Shiven Dhir,

We checked the power, and it looks like the device is powered properly. If there’s a specific way to confirm this, please let us know.

Also, can we add a pulldown resistor to the gate of the MOSFET to fix this issue? Will adding a pulldown have any negative impact?

Hi Praveen,

I remember you mentioned that the rail was "unpowered"

"However, we are observing an unexpected voltage of approximately 1.6V on the terminal of the unpowered supply. Additionally, we are measuring a VGS of around 300 mV on the MOSFET Gate terminal."

Adding a pulldown to MOSFET gate is not recommended.

Regards,

Shiven Dhir

Hi Shivendhir,

Just to clarify my earlier point: in our current project, we're using the power supplies in a redundant configuration. To confirm proper redundancy, we tested one power supply at a time—24V_1 is powered ON while 24V_2 is turned OFF.

Under this condition, we observed a return potential of 1.6V on the 24V_2 rail and a VGS of 300 mV. We observed the same behavior vice versa—when 24V_2 is powered ON and 24V_1 is turned OFF.