BQ27421EVM-G1A: Regarding to the sudden change in SOC

Netraja Kapdane

Prodigy 140 points

Part Number: BQ27421EVM-G1A
Other Parts Discussed in Thread: BQSTUDIO

Hi,

I have used BQ27421 in our system.

Whenever battery is low about say 15% and when it is in charging state the soc suddenly increases to 60%.

What is the reason of this sudden change in SOC ?

over 4 years ago

0 Wyatt Keller over 4 years ago

TI__Guru** 103375 points

Hello Netraja,

Have you followed the quick start guide to set the parameters needed like design capacity and taper current?

Here is the guide: https://www.ti.com/lit/ml/sluuah7b/sluuah7b.pdf?ts=1594735779414&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ27421-G1

Sincerely,

Wyatt Keller

0 Netraja Kapdane over 4 years ago in reply to Wyatt Keller

Prodigy 140 points

Hello Wyatt Keller

Yes. I have followed the quick start guide and according to it set the parameters design capacity and taper current.

0 Wyatt Keller over 4 years ago in reply to Netraja Kapdane

TI__Guru** 103375 points

Hello Netraja,

Can you log when this is occurring during your testing and export your .gg file to share it here?

Sincerely,

Wyatt Keller

0 Netraja Kapdane over 4 years ago in reply to Wyatt Keller

Prodigy 140 points

LogsFuelGauge.xlsx

0 Netraja Kapdane over 4 years ago in reply to Netraja Kapdane

Prodigy 140 points

Above file has logs of fuel gauge during operation of device.Please look into that.

Also implemented a state machine according to the quick start guide (Section 7). It is called after every 1sec. and SOC reading is done after every 2sec.

It is observed that for the very first time when system turned ON charging and discharging SOC gives reading per 1% change. But for the next time it given sudden changes in SOC value.

Is there in any time related issue??

Appreciate your support!!

0 Wyatt Keller over 4 years ago in reply to Netraja Kapdane

TI__Guru** 103375 points

Hello Netraja,

Could you share the full log from the EVM using bqStudio? If you could also include the Flags register so we can see how the gauge is setting those during the cycling. It would also be helpful if you could pull the .gg file from the gauge.

Are you performing all the cycles with a motor as the load? The ADC conversion time is 1 second, so reading every 2 seconds is okay.

Make sure the battery is detected in the flags register (BAT_DET) or the gauging could be compromised, this enables the impedance track algorithm.

Sincerely,

Wyatt Keller

0 Netraja Kapdane over 4 years ago in reply to Wyatt Keller

Prodigy 140 points

Hello Wyatt,

I will share the full log from the using bqstudio as soon as possible. But did you get chance to look into the excel sheet I have shared?

Its not the ADC value get read after 1S, its the state machine that implemented according to Section 7 as per quickstart guide without hibernate mode.

It is necessary to implement hibernate mode as well?

Whenever charger is connected the control status register value changes to 0x009A and Flag register value become 0x0108.

After what particular time the Qmax value get updated? Because everytime it set to default value of 16384??

Thank you.

0 Netraja Kapdane over 4 years ago in reply to Netraja Kapdane

Prodigy 140 points

SWConfig.gg.csv

0 Netraja Kapdane over 4 years ago in reply to Netraja Kapdane

Prodigy 140 points

6303.SWConfig.gg.csv

0 Netraja Kapdane over 4 years ago in reply to Netraja Kapdane

Prodigy 140 points

18TO5PECENT.xlsx

0 Wyatt Keller over 4 years ago in reply to Netraja Kapdane

TI__Guru** 103375 points

Hello Netraja,

Thank you for providing the log files, I will look at them and provide some feedback tomorrow.

Sincerely,

Wyatt Keller

0 Netraja Kapdane over 4 years ago

Prodigy 140 points

After what time duration(how many cycles) does Qmax get updated? or Qmax_UP bit will be set?

How do I test it?

It is recommended that the host save the Qmax and Ra profile in the system NVM once the [QMAX_UP] and [RES_UP] bits have set. After the initial Qmax update, updates to Qmax most likely occur upon:

• Entering discharge mode

• Exiting discharge mode

• Being in relaxation mode for a while after a certain amount of charge has been removed or added to the battery.

How to check fuel gauge entered into discharge mode?

0 Wyatt Keller over 4 years ago in reply to Netraja Kapdane

TI__Guru** 103375 points

Hello Netraja,

Qmax will update once there are 2 valid OCV measurements, usually one cycle of the battery where there is a rest long enough at each end to take an OCV measurement.

This gauge is a ROM based gauge, there are other gauges that have flash memory that can save the data so the host doesn't have to remember and update the Ra and Qmax tables.

I have been reviewing your logs, it looks like your gauge is in CFGUPMODE which suspends the gauging algorithm, it actually looks like it's switching between this mode and normal mode. Are you sending any commands while gauging? I wouldn't recommend setting the CFGUPMODE until you are not discharging/charging.

Sincerely,

Wyatt Keller

0 Netraja Kapdane over 4 years ago in reply to Wyatt Keller

Prodigy 140 points

Hello Wyatt,

You are absolutely right. Yesterday while debugging I got this observation and got to know from where it is setting and I have correct that in firmware and now it is in testing mode, everything seems to be working fine now.

Thank you for your support!!

But I am very much concern about Qmax value. Because it is not updated even we are using battery more than a month and multiple charging and discharging cycle,still getting the default value.

We need to store that Qmax and Ra table into FRAM for which need to check Qmax_UP bit and RES_UP bit then only store the value.

After reseting the gauge the Qmax_UP bit and RES_UP are 0 right?

0 Andy Liu (BMS) over 4 years ago in reply to Netraja Kapdane

TI__Guru 52115 points

Yes. Both the [QMAX_UP] and [RES_UP] bits remain set until the gauge is reset or a battery insertion event occurs.

Andy

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BQ27421EVM-G1A: Regarding to the sudden change in SOC