Feeding Independent Current-Measurements to Fuel-Gauge Algorithm

[Tyekuhn]

Hello,

In a system that incorporates an nPM1300 (PMIC), we draw large amounts of current from our battery for certain portions of our circuit, and we must bypass the PMIC for this portion of the circuit.  Specifically, we have a high-current DC/DC circuit which has its input directly connected to the battery (bypassing the PMIC, and the VSYS output), however, the rest of the system runs off of the PMIC output (VSYS).  Because of this bypass, we must measure/estimate the battery current draw of this DC/DC circuit independently of the PMIC battery-current measurements, and feed this independent measurement to the fuel-gauge algorithm.

The question is:  Is there any precedent for doing this?  Is it expected that this would succeed or fail, with regards to getting accurate fuel-gauge information?

Thank you,

Ted

[runsiv]

Hi

I have asked internally and will get back to you

Regards

Runar

[runsiv]

Hi

As this is an unite case we need a bit more information

What kind of battery you are planning to use (chemistry /capacity for ex.)?

Operating temperature range? 

How often such bypassing are made / For how long/ and what's the peak current during such bypass points?

Any estimate of the current consumption/ loading behavior in normal operating mode and device operating time?

Regards

Runar

[Tyekuhn]

Hello,

We are using a LiPo pouch-type battery, 1000mAh, 3.7V nominal...standard LiPo chemistry.

Operating temperature range is ~20C to 40C; this is a wearable application.

This bypassing occurs in the active-mode of our device, so nearly all of the time.  The peak current can get up to about 1200mA (1.2A); and this can last for several minutes as battery voltage gets lower.  Our device is roughly a constant power device, so as battery voltage gets lower, current increases, and vice-versa.  However, nominal current is closer to 800mA; this can last up to 30 minutes.  The normal operational mode of our device has the battery being completely discharged in approximately 60 minutes.  So a 1000mAh battery is nearly discharged in 60 minutes, and then fully charged again before used again.

When our device is not in active-mode, the current draw is far less, <10mA.

Our charge current is set to 500mA right now, if that's of any consequence.

Thanks!

Ted

[runsiv]

Thanks for the update, I have forwarded the information to our developers and will get back to you

Regards

Runar

[runsiv]

Hi

This is not something that we can support out of the box with our solution today, so we can't promise anything. You can still try with our fuel gauge solution and evaluate its performance for your application.

The nRF Fuel Gauge Fuel Gauge algorithm relies on instantaneous battery current and voltage measurements and uses a pre-profiled battery model to estimate the state of charge. Good thing is you don't really need to accurately count every coulombs going in and out of the battery for a stable fuel gauge prediction. 

For the initial evaluation, you could use nPM1300 EK and nPM-PowerUP PC application for the evaluation. I believe the evaluation would be straightforward and fast since the run time of the device application is 1 hour.

Here are some steps. 

• First they need to profile their battery at room temperature using nPM-FG Board for better accuracy. 
  ( There is also a pre-profiled LiPol (LP602760) 1000mAh battery model available for testing)
• Export that model to the host SoC to initialize the fuel gauge.
• In the nPM1300 EK, you have the access to VSYS pins where they could connect the rest of the system which runs off of the PMIC.
• There is also an extra VBAT Pin they could use to connect high-current DC/DC circuit independently out of the PMIC.
• Use the graph tab to evaluate fuel gauge predictions.

Regards

Runar