NPM1100 Charge expected behaviour questions

[i_4556]

Hello, and thank you for your time. We have designed an NPM1100 into a product, and are unclear on if the behaviour of the charge pin is correct (nor indeed what exactly is the expected behaviour).

Our expectation is the following: when charging is actively occurring, thats to say current is flowing into the battery, the charge pin should be active (low). In all other cases, the charge pin should be inactive (high).

We have noticed the charge pin low when there is no Vusb and our device is operating off the battery. Is this correct, that the charge pin is active when charging could potentially occur (battery voltage within the charge range) even if it is not actually occurring?

Thank you!

[Susheel Nuguru]

The behavior of the CHG (charge) pin on the nPM1100 PMIC is as follows: When the nPM1100 PMIC is charging the battery, the CHG pin is pulled low. This pin is connected to General-Purpose Input/Output (GPIO) P1.00. The CHG pin and the ERR (error) pin sink 5 mA of current when active and are high impedance when disabled. This is suitable for driving LEDs or connecting to host GPIOs in a weak pull-up configuration. The charging indication pin, CHG, is active while the battery is charging which is mentioned here

However, the CHG pin should not be active (low) when there is no Vusb and the device is operating off the battery. If you are observing this behavior, it might be due to some other factors or conditions. It would be beneficial to check the charger error conditions as well as mentioned here.

[i_4556]

Thank you for your reply, however I would like further clarifications please.

Firstly, when you say "When the nPM1100 PMIC is charging the battery" does this mean when current is actively flowing, or just when current could potentially be flowing?

Secondly, the NRF5340 internal pullups are ~13K per the datasheet. Could I connect the LED pin directly to the MCU and use the internal pullup to pull the line high?

Thirdly, if the thermistor is missing, my understanding of the datasheet is that this will cause the NTP to think the battery is too cold to charge. When I test this, both the charge and error lines are high; should I expect the error pin low?

Lastly, if I have Vusb present but no battery, I would expect charge to be high; is this correct?

[i_4556]

Sorry to bump you but we really need an answer soon, thanks for your time and understanding

[ketiljo]

i_4556 said:

Firstly, when you say "When the nPM1100 PMIC is charging the battery" does this mean when current is actively flowing, or just when current could potentially be flowing?

Yes, only when the battery charger is effectively sourcing current in the battery

i_4556 said:

Secondly, the NRF5340 internal pullups are ~13K per the datasheet. Could I connect the LED pin directly to the MCU and use the internal pullup to pull the line high?

Yes, it would work

i_4556 said:

Thirdly, if the thermistor is missing, my understanding of the datasheet is that this will cause the NTP to think the battery is too cold to charge. When I test this, both the charge and error lines are high; should I expect the error pin low?

No, NTC does not trigger a Charger Error. Both lines will be high-impedance.

i_4556 said:

Lastly, if I have Vusb present but no battery, I would expect charge to be high; is this correct?

That is correct. Bear in mind, the pins are not actively pulled-high, they are only high-impedance. If they don't have external pull up, simply taking a measurement with a DMM will show 0V.

Our expectation is the following: when charging is actively occurring, thats to say current is flowing into the battery, the charge pin should be active (low). In all other cases, the charge pin should be inactive (high).

Inactive is not high unless pulled-up externally. It is high-impedance.

We have noticed the charge pin low when there is no Vusb and our device is operating off the battery. Is this correct, that the charge pin is active when charging could potentially occur (battery voltage within the charge range) even if it is not actually occurring?

No, the charge pin is not active if the battery is not being actively charged. How was the measurement performed? Is the pin pull-up externally by a resistor/LED/MCU?

[i_4556]

Thank you for all of your replies, this has greatly clarified our understanding, and the issues we have been having.

Upon further investigation, we noticed that we had connected the CRG pin to pin 0.18 on the NRF5340, and that this pin is, per the datasheet, optimized for QSPI. Although we had changed the pin in the .overlay file, we had not actually disabled the QSPI peripheral.

When we do that, the behavior becomes closer to the expected behaviors, although still incorrect and once again we would love your insight into what could potentially be happening. We have the pin configured as input-pullup, as before. When the charge pin is inactive, we get Vdd (1.8V) through the internal pullup, as expected. The problem seems to be when charging is active, and we would expect the pin to be low. When we measure the voltage, we get ~1.2V. The most obvious explanation here is that the pullup is too low a resistance, and is overwhelming the NPM. Per the datasheet, the NPM can sink 5mA when charging is active; when I measure with my DMM a dead short from 0.18 to ground, I can see ~30mA flowing.

Is it possible that the pullup on 0.18, because it is optimized for QSPI, is somehow stronger than the generic pullups on other pins? Or perhaps I am missing a step, it is not sufficient to disable QSPI, and actually the QSPI peripheral is still forcing 0.18 high?

I disable QSPI with:

&qspi {

status = "disabled";

}; in my .overlay file

Thanks for your help! I really appreciate it!