Current flow from Battery while Vbus is present

[bearsh]

Hi

I measure a constant current flow from the battery of 103uA while the nPM is connected to USB and the battery is fully charged.

According to the datasheet 6.2.10:

The battery is isolated when VBUS is connected and the battery is fully charged

Is this a know problem?

[Asbjørn]

Hello,

The section 6.2.9 says that battery is isolated, but there's more.

" If more current is required, CHARGER enters supplement state to provide current from the battery, up to IBATLIM."

Q1: What sort of state is your board in and what kind of current consumption is it drawing overall? Is there going current from VBUS and battery at the same time through Charger to supply the overall system?

Q2: Are you getting end-of-charge state prior to this? Is the voltage of the battery at Vterm? Do you receive an interrupt on this event?

Best regards

Asbjørn

[bearsh]

Q1: Normally the application draws about 20uA. When connected to USB, the current goes to something below 5mA. So the application is supposed to be fed entirely from VBUS.

Q2: I didn't check the events in detail. But one GPIO is configured as charge indication and that IO shows it is not charging. Furthermore, why should current flow out of the battery while the system is charging considering the currents are far below any limits?

[bearsh]

It's reproducible with the pmic dk



here the battery is charging (charger enabled in PC software)

and then, charging disabled. we have a constant current of about 100uA out of the battery.

[Tharaka]

Hi 

This leakage current from the battery is intentional for safety reasons. It ensures that the battery is not charged to a higher termination voltage than configured by allowing a safe discharge current. ( compensates for the VBUS/USB leakage through the pass FET into the battery, thereby preventing overcharging). For the nPM1300, this safe leakage current of around 100µA is expected behavior. 

There is also an option to automatically restart charging when VBAT drops below VRECHARGE, as described in the nPM1300 product specification

If this safe leakage current is a concern due to the capacity of your battery (e.g., for very small cells where the drain matters), I would recommend considering the nPM1304 PMIC, which is designed for small-capacity batteries and offers a much lower safe leakage current, close to 5 µA.

Regards 

Tharaka