LMR62014: Reverse polarity protection

Hi Tilen,

Does the "reverse current" mean the current flows from GND to SW when the SW voltage is negative during the low side FET is turning on?

Tilen Sluga said:

Are there any potential issues with the regulation feedback path?

Do you mean whether the feedback resistors and the feedforward capacitor are suitable?

Regards

Lei

Hi Lei,

Yes sorry I should have explained my question a little better.

In the application where the LMR62014 is used I need to provide protection against input reverse polarity. The LMR is only one part of the whole circuit and in some conditions there could be a reverse potential of up to 60V seen from GND to the SW pin. And I need to prevent any potential current flow that might flow from GND to the SW pin, so my idea was to use the bottom diode on the schematic (the diode to GND) to prevent this. Would the LMR work with this diode installed and connected like I have shown in the schematic?

Regards,

Tilen

Hi Tilen,

Thank you for your explanation. Sorry I'm still a little confused.

You said "in some conditions there could be a reverse potential of up to 60V seen from GND to the SW pin". As my understanding, two conditions may have this result:

1. The LMR62014 GND raises to 60V(may be coupled)
2. The SW decreases to -60V.

Understand that LMR62014 in only one part of the whole circuit, but it is a independent part. So I just wonder which of the above two conditions is, and how it comes?

I'll put this E2E thread in high priority to expedite the communication cycle.

Regards

Lei

Hi Lei,

60V is the max. voltage our circuit can operate at. But it must also survive being connected to the external power supply with the wrong polarity. So our circuit must also be able to handle a reverse polarity condition of up to 60V.

Not sure which case if more true. In the most simple terms, when we have reverse polarity condition on the input of our circuit (that just means that the user made the mistake and connected our circuit to the external power supply with the wrong polarity) the LMR62014 will then see the external power supply positive lead on its GND pin and the negative supply lead will be seen on the SW pin. So in this condition I'm guessing the internal FET of the LMR (being reverse biased with the full input voltage) can fail and current can flow from GND to the SW pin. And that is what I would like to prevent.

Regards,

Tilen

Hi Tilen,

Thank you for your detailed explanation.

The circuit you showed can survive when the input is reversely connected to the power, and it can also work normally when the input connection is correct.

Please pay attention that the voltage rating of the input capacitor should be high enough, and without polarity.

Regards

Lei

Hi Lei,

OK that's great. Thank you. Maybe just a side question in the schematic is better to leave the output capacitors (they are without polarity) connected directly to ground or have them connected trough the diode like I have done it in the schematic?

Thank you Lei.

Regards,

Tilen