NPM1300 does not start with VBUS at very low VBAT (2.6V)

[mirhamza708]

Hi, 
I am seeing this weird behavior on my custom board. I have an npm1300 with nrf5340. The npm1300 stops working after the power fail comparator triggers at 2.8V, since the battery cutoff is 2.75V. So when the battery is completely depleted and cuttoff is activated the battery stays at 2.7-2.6V. At this point if I connect the VBUS (5V) the npm1300 does not start working the voltage at VSYS remains at 2.3-2.5V checked with multimeter. I have to remove the VBAT completely and then connect VBUS first after that I can connect VBAT and the npm1300 starts working again by charging the battery and powering the rest of the circuit.

Please comment on this, is this behaviour expected or there is something wrong with the circuit. The schematics of npm1300 are attached.



Thanks

[Kenneth]

Hello,

Comments on the schematic: 

• VBUS is missing bypass capacitor (1uF)
• VSET1 should be 68k for 2V output voltage
• VBUSOUT should be 1uF capacitor even if not used
• PVDD/VSYS should have 3x10uF capacitors 

Questions:

- Does the battery cutoff mean that that the battery protection circuit kicks in and effectively disconnects the battery? In any case, the behavior does not sound right and it could be related to the missing components on VBUS/PVDD etc. 

- Do you have nPM1300-EK to be used as a reference for testing this case?

Kenneth

[mirhamza708]

I am not sure about the battery cuttoff because the battery embeds the cuttoff circuit, all I know is I see a 2.5V on the battery output. The supplier mentioned that it has a 2.75V cuttoff. 

I do not have an EK board for reference. The VSYS fluctuates a lot on multimeter. so I think maybe it is the missings caps causing the problem. I will try to attach some capacitors to the pins. And see the results.

And the VSET1 is 68K already i think the picture quality is not showing the number correctly. 

thanks for the reply i will try to get back to you soon.