BQ40Z50: Shutdown Issue

Jerry%20Leung

Part Number: BQ40Z50

Hi Team,

Our customer is seeing some anomaly when sending the BQ40Z50 battery gauge into shutdown mode and having a charge voltage present during the DELAY time. Could you help provide some guidance from the observations below?

We observed that a charging voltage applied at the battery between the time after the command SHUTDOWN Mode (0x0010) was sent and the battery chip enters shutdown mode causes

an unexpected behaviour. According to the technical reference manual (bq40z50-r1 - July 2015 - page 81) it is stated that after the command is sent to the battery chip an internal counter is started.

When the counter reaches Ship FET off Time, it turns off the CHG and DSG FETs and if it reaches Ship Delay the battery chip will enter Shutdown mode.

In our case, the timings are as follows:

Ship FET off Time : 10s

Ship Delay : 20s

We tried following test sequence:

- send command to enter shutdown mode

- disconnect charger

- wait 10s- 13s - after 10s the voltage at the battery is turned off as expected

- connect charger

- wait e.g. 200ms - 1s

- disconnect charger

- wait additional 20s - expect that after wait time the battery chip is in shutdown mode.

- connect charger

- wait 5s - wake up battery chip

- disconnect charger

- check if battery is woken up

We observed the following behaviour after we ran the test sequence above:

1) wakes up automatically ~2 minutes after the command was sent to the battery chip

2) wake up works if charger is applied after ~1 minute. Before it does not wake up the battery chip

Additionally, if 1) or 2) happens, there is a chance that the battery chip does not enter shutdown mode via command for up to ~3 minutes.

We read out status registers 0x50 - 0x55 when the wake up did not work as expected.

In 0x54 OperationStatus we could see, that the flags

CHG = 0 - Charge FET inactive

DSG = 0 - Discharge FET inactive

SDM = 1 - Shutdown triggered via command active

Can you please give advice on how to avoid this state we’re ending up and how the set the chip back to normal operating mode?

Thanks for the help and best regards,

Jerry

over 6 years ago

0 Swaminathan Ramanathan75031 over 6 years ago

TI__Expert 6575 points

Hi Jerry,
This will take some time to duplicate and see what is going on.
WE should be able to get back to you in 2-3 working days.
Regards,
Swami

0 Jerry%20Leung over 6 years ago in reply to Swaminathan Ramanathan75031

TI__Intellectual 905 points

Hi Swami,

Thanks for the update and looking forward to the result and suggestions.

Best regards,
Jerry

0 Swaminathan Ramanathan75031 over 6 years ago in reply to Jerry%20Leung

TI__Expert 6575 points

Hi Jerry,
I am trying to duplicate the issue, and it might help if I use the same settings.
Can you please post the gg file from this pack?
Thanks,
Swami

0 Jerry%20Leung over 6 years ago in reply to Swaminathan Ramanathan75031

TI__Intellectual 905 points

Hi Swami,

Thanks for the help. Please see the attached gg file.

5482.gg.xlsx

Best,

Jerr

0 Swaminathan Ramanathan75031 over 6 years ago in reply to Jerry%20Leung

TI__Expert 6575 points

Hi Jerry,
I think I am able to duplicate your issue.
I will have to check with our firmware team after the holidays to find out why this will happen.
Regards,
Swami

0 Swaminathan Ramanathan75031 over 6 years ago in reply to Jerry%20Leung

TI__Expert 6575 points

Hi Jerry,
I discussed this with the firmware team and here is what happens when you send the shutdown command:
When the shutdown command is sent, the gauge will check that the PACK Voltage < "Charger Present Threshold", then turn off the fets after "FET off time ", and then shutdown the device after the "Ship off Delay" time (~from when the command was sent).
As you can see, it only checks the Pack Voltage at the start of the sequence, and also the shutdown is controlled by the firmware.
The exit from shutdown on the other hand is controlled by hardware, and once shutdown has completed the hardware will re-start when PACK voltage > Vstartup. But, it will not be check this unless the device has completed shutdown.
In this case it looks like the device is stuck in a state where the shutdown has not completed before the voltage is applied to PACK+, and that is the reason you are seeing this strange behavior.
Shutdown is typically intended to be used when the pack is going to be in storage i.e. there is a long time between the pack being put in shutdown and then reconnected tot he charger, so the only workaround would be to make sure that the shutdown is only initiated when the pack will not be used for some time.
Regards,
Swami

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BQ40Z50: Shutdown Issue