nPM1100 is not charging the battery

[Ziyao Zhou]

Hi,

I have a custom nPM1100 borad and want to charge the battery. My schemetic shows here, I notice the battery cannot be charged. My shcemetic shows below:

I have confirmed some things are working:

1. I got 1.8V target at Vout.

2. My Vsys  is 5V.

something confused me is:

1. I cannot charge the battery, the Vbat is 0.

2. I set to Vbus limit to 100 mA mode, but my real current is

3. When the PMIC is not working, if I have an external 1.8V source, whether the chip will broken in reverse voltage?

Thank you for your time!                                                                                                                                                                                                                                                                                            

[Tomi Koskela]

Hello,

It seems NTC is floating in the schematic. There should be 10kohm resistor if there is no NTC resistor on the battery pack. Having this pin floating the device detects this as battery being in very cold temperature and it will not charge. 

[Ziyao Zhou]

Thank you for your information! I should connect one 10kOhm between NTC and GND right?

[Tomi Koskela]

Yes, that is correct!

[Ziyao Zhou]

Hi, If I connect an external 1.8V to the chip, whether the chip will be broken?

[Tomi Koskela]

Since the buck is configured to AUTO mode, you should be able to source the output with slightly higher voltage than the target (let's say 1.82V). But then again I'm not sure what you are trying to accomplish with this and what other rails are connected. 

[Ziyao Zhou]

I havc a debugger could be a 1.8V source, I am afraid when I connect to the debugger the 1.8V will break nPM1100 through VOUTB

[Tomi Koskela]

nPM1100 has overcurrent protection on the buck converter. But connecting two supplies together with close to the same voltage can cause problems on either side. You could potentially add a resistor in between to avoid high current being sourced/sinked on the nPM1100 buck. 

[Ziyao Zhou]

Thank you for your information