When the input voltage of lpcom is higher than VDD

[David_Kim]

HI

I'm trying to use lpcom to detect when the battery voltage is dropping.

The configuration is as follows: 5V battery voltage output is reduced to 3.0V through LDO and supplied to nRF52832.

* Battery voltage = 5.0V  --- >  LDO output =  3.0V -----> nRF52832 

* The battery voltage is divided by a resistance of approximately 2M or more and input to the lpcom port.

There were no problems with the basic implementation in operation tests and continuous tests for about a month.

But when I looked again,

When the battery is fully charged... the VDD voltage of nRF52 is set high by about 0.9V.

Could this part be a problem?

There is no problem in operation, but will there be a problem in the long run if a voltage higher than the guaranteed voltage is applied?

[Simonr]

Hi

If LPCOMP or any input pin has a voltage higher than VDD+0.3V that will result in unspecified behavior, as we haven't tested for it, but after doing so there is no guarantee the device will run as expected afterwards. Are you sure that the pins are input with a voltage higher than 3.3V?

Also, what do you mean with the VDD voltage of nRF52 is set high by about 0.9V exactly? Does the nRF52832 stat running when the VDD is 0.9V, this sounds incorrect.

Best regards,

Simon

[David_Kim]

HI

Simonr said:

If LPCOMP or any input pin has a voltage higher than VDD+0.3V that will result in unspecified behavior, as we haven't tested for it, but after doing so there is no guarantee the device will run as expected afterwards. Are you sure that the pins are input with a voltage higher than 3.3V?

As shown in the block below, when the battery is fully charged, it is 4.5V, but the voltage divided by the resistor and input to lpcom is up to 4.0V.

Of course, as the battery is consumed, the corresponding voltage goes down.

The actual operating voltage of lpcomp was configured to operate well by setting the register to the VDD reference voltage.

What I would like to inquire about is

If a voltage higher than the above VDD is applied, can there be a problem with durability, etc.?

It operated continuously for more than a month and worked well without any problems even after making more than 50 PCBs.

And as said above

The actual operating voltage is normally set based on VDD.

[Simonr]

Hi

David_Kim said:

If a voltage higher than the above VDD is applied, can there be a problem with durability, etc.?

Yes, since the behavior is unspecified we haven't tested for what might happen, so this can be a problem and this should be avoided since what will happen is not specified. You should add some kind of logic or component that ensures the input voltage on LPCOMP doesn't exceed 3.3V.

Note that since what will happen is unspecified, we can't guarantee that something will happen either, but you're operating the device outside of the product specification, so we can't tell what will or will not happen if you keep running it like this. We can only recommend that you don't.

Best regards,

Simon