Excessively high output error (4%) with NPM1100

[peterqu94305]

Hello,

We have designed a product with NPM1100.  With the NPM1100 set to output voltage of 3.0, we have measured the output across multiple devices to be in the 3.1 to 3.15V range.  This is an approximately 4% error on the output. 

Our questions are:

1. What is the expected output accuracy of NPM1100?
2. What is the expected accuracy of the charging termination voltage?  If the charging termination voltage has the same level of large error, then we have genuine concern about whether using NPM1100 can lead to potential safety hazard with lithium-ion battery.

Our configuration is as follows.

1. Micro USB input
2. Rechargeable lithium ion 80mAH
3. Output configured to 3.0V

Thank you,

Peter

[peterqu94305]

Now that we have this issue, and after we read the datasheet carefully.  Looks like the spec sheet states that the VOUTB accuracy is -2% to 8%. 

This is type of error budget is unbelievable.  A similar PMIC such as TI BQ24195 has +/-2% error. 

 

[Sigurd Hellesvik]

Hi Peter

I see you found the Output accuracy.

Under Electrical Characteristics, there is also a graph showing VOUTB accuracy for different temperatures.

I will check with our developers how this relates to the accuracy limits, and return with a better answer by Tuesday.

For the Charging termination voltage accuracy, see these parameters.

Regards,
Sigurd Hellesvik

[peterqu94305]

Hello Siguard,

Thank you for looking into it.  I have reviewed the graph showing the VOUTB accuracy across temperature range.  Since we are testing this in our office, which is around 25 degree Celsius, the graph indicates the error should be closer to 0%.  We have measured 4%.

Also for the termination voltage, the electrical parameters section in the datasheet only provided typical values, it did not provide min and max.  We usually don't concern about these parameters too much.  But in this case, we have measured 4% error across multiple NPM1100 and it made us to have real concern about all the parameters in the datasheet that do not have a min/max. 

Typically termination voltage and output voltage shares the same bandgap reference circuit. It is plausible that there is a high error in the charging termination voltage.  An incorrect charging termination voltage could leads to possibility of lithium ion cell explosion due to overcharging.  

Thank you,
Peter

[Sigurd Hellesvik]

Hi Peter

I am still waiting for some more information on the VOUTB accuracy from our developers.

For the Battery Charger accuracy, have a look at the V_TERMACC0 from the Charger Electrical parameters:

As you say, battery charging require good accuracy, so these are max +-1% in general and +-0.5% at 25 C.

For the VOUTB accuracy:

Do you measure this using the nPM1100-EK, or a custom board?

If you are going to use the Buck converter, will the 4% error here be an issue for your use-case?

Regards,
Sigurd Hellesvik

[Dom O]

Hi Peter - I'm getting the same result. 3.113V to 3.114V output, across GND and VOUTB, on my nPM1100-EK, with or without a 20mA load, with or without USB charging connected.

Checked with 2 different voltmeters, one calibrated and within 1mV agreement with each other.

Also the following values (typically about 3.5% high across all values):

Set Voltage	Measured Voltage
3.0V	3.113V
2.7V	2.801V
2.1V	2.176V
1.8V	1.863V