nPM1100 low VOUTB voltage

[Joao Colombari]

Hi guys, 

I have been working with a custom PCB based around the nRF5340 that uses the nPM1100 as the PMIC. 

I have configured it for 1V8 VOUTB output, fixed VBUS, VTERM high and 75mA current limit (find attached the schematic) 

We have a couple of PCBs and one of them suddenly dropped the 1V8 output to (about) 0V9 suddenly. I was not flashing or even touching the PCB, it was just running a test application on idle. 

In this setup, nothing was connected to VBUS and a 4V voltage supply (linear regulator) was connected to VBAT. 

I did not find any specific overcurrent voltage info in the datasheet, and passive components look good, but now VOUTB is shorted to GND (around 3.5R of resistance).  

Is there any problem in the schematic/setup? What is the IC supposed to do when an overcurrent event happens? Can I guess if I have a dead PM or a dead cap by any chance? 

Thanks a lot!!

João Colombari. 

[JONATHAN LL]

Hi João,

How many devices have you tested?

Only one short found between VBOUT and GND?

We do have a check list available here https://docs.nordicsemi.com/bundle/npm1100-design-checklist/resource/nPM1100_design_checklist_1.0.0.xlsx 

Why is D- connected to GND?


Does the rest of the schematic follow our example setup here for application example? https://docs.nordicsemi.com/bundle/ps_npm1100/page/chapters/application/doc/frontpage.html#ariaid-title2 


Regards,
Jonathan

[Joao Colombari]

Hi Jonathan, 

We have five PCBs of which we were working with two. One of them had the short on VDD as I described. Now I'll start working on another now. 

Yes, the only short I found is between VBOUT and GND.

I took a look at the checklist and aparently everything looks good. 

I tied ISET and D- to GND for fixed 100mA VBUS current limit. 

As far as the specific operating options goes, yes, everything is in accordance with the example. 

What should be the output voltage in case of a short/overcurrent in the output?

Best,

João.

[JONATHAN LL]

Hi João, 

In this setup, nothing was connected to VBUS and a 4V voltage supply (linear regulator) was connected to VBAT. 

Why not supply from VBUS? or use a battery?

The VBOUT is defective\broken here in you setup as it should not be short to GND. 
Why the VBOUT is defective is difficult to say from just this info, so if you can measure the VSYS and VBAT when testing a functional circuit to see if there are any high spikes or abnormality happening in the voltage waveform. 

Regards,
Jonathan 

[Joao Colombari]

Hi Jonathan,

No particular reason. We had uncharged batteries and wanted to test the other ICs before testing the charging and used the power supply in VBAT.

We will try to capture the voltage waveforms in a working PCB.

Is there any additional protection in the VBUS that is not present in VBAT? Should it be more reasonable to use the supply in it from a safety perspective?

João.

[JONATHAN LL]

The VBUS does have protection built inn, the VBAT does not, we state that batteries connected to the VBAT should have protection built inn.

https://docs.nordicsemi.com/bundle/ps_npm1100/page/chapters/core_components/sysreg/doc/frontpage.html#ariaid-title4 
and
https://docs.nordicsemi.com/bundle/ps_npm1100/page/product_overview.html#ariaid-title9 

Regards,
Jonathan