nPM1100 doesnt start charging empty battery

[Jekin]

Hello,

We found a problem with a device in mass production: nPM1100 doesnt start charging a deeply discharged battery.

Here is detailed information. This device was kept discharged by a customer for long time. But this is not an isolated case, there are more such devices. Voltage on battery leads (VBAT) is 0 V, battery cell voltage is 1.09 V (battery's leads are switched off by the battery's protection module due to under voltage).

After attaching external power to the device (VBUS = 5.0 V) there is a short pulse on VBAT generated by nPM1100:

But charging not started. Pin CHG disabled, pin ERR enabled.

We've tried desoldering C24 and C25, it doesnt help:

Also tried soldering a single 1uF capacitor instead of C24 and C25 as suggested by 

https://docs.nordicsemi.com/bundle/errata_nPM1100_Rev2/page/ERR/nPM1100/Rev2/latest/anomaly_100_7.html

but charging not started.

After connecting the battery to a power supply, charging it for little time (the protection module enables voltage on battery's leads) and soldering it back to the device nPM1100 starts charging OK: there is increasing voltage on VBAT, CHG pin enabled, ERR pin disabled.

Here is related schematic:

The battery's characteristics:

And protection module circuit diagram from the battery's datasheet:

[Jekin]

Here is specification of the PCM module. Release voltage to restore circuit after triggered over discharge protection is 3.5V:

[Priyanka]

Hi Eugene,

The nPM1100 has automatic trickle charging which allows to bring the battery charge to a certain limit before fast charging. But there is a required minimum charge for the battery below which it can show an error:

This might be the reason that you have an error since 1.09V is below the required 2.1V. You could likely try pre-charging the battery maybe.

Regards,

Priyanka

[Jekin]

Hi Priyanka,

Thanks for your reply.

This case is quite common, any lithium-ion/polymer battery may have voltage below 2.1V when deeply discharged.

After learning the datasheet I can't find any information about pre-charging, also reference circuits haven't it.

Does Nordic has any reference circuit for the nPM1100 showing the required pre-charging module implementation? Adding extra components connected to VBAT and sinking current into this pin may break the nPM1100 battery detection algorithm and also the charging algorithm too.

Best regards,

Eugene

[Priyanka]

Hi Eugene,

I am not sure regarding whether we have any reference for the pre-charging circuit. I will check internally and get back to you.

Regards,

Priyanka

[Jekin]

Hi Priyanka,

Any news on this?

Best regards,

Eugene

[Priyanka]

Hi Eugene,

We do not have any schematics etc for the pre-charging circuit that we can share, but maybe you can overcome this issue by placing a diode and a serial resistor from VSYS to the VBAT pin in parallel with the nPM1100 to slightly and slowly charge the battery when it is too low. 

Hope this helps.

-Priyanka

[Jekin]

Thanks. I was thinking already about the exact same solution. I'll test that.