npm1300 LDO VOUT off state

[Richard_P]

Hi there,

I am considering using one of the npm1300 LDOs to supply 3.6V to the battery backup pin of a uBlox MAX-M10 module using a 100uF capacitor as energy storage for backup power over a few seconds (to allow system power cycle and minimising GNSS fix time).

I understand I must set the LDO to 3.6V, ensure the discharge resistor is disabled and place an external current limiting resistor since the soft start time will not be long enough.

My question is: What is the VOUTldo pin behaviour when the voltage at VOUTldo is greater than VSYS (before, during and after system shutdown)? This will determine if I need to implement reverse current protection at the VOUTldo pin myself (or find a more suitable part).

Many thanks,

Rich

[Szabolcs]

Hi Rich,

When the LDO/LS is off and the discharge resistor is disabled, the VOUT pin is in High-Z mode. However, there is an ESD protection diode from the VOUT to the VSYS pin, so if the VSYS voltage is lower, the VOUT voltage can backfeed into the VSYS pin. 

So yes, if you want to keep voltage on the VOUT pin while the VSYS is down, then a reverse-current protection circuit is recommended.

[Richard_P]

Thank you!