BQ76952: AFE BQ76952

Hi Kish,

It sounds like the device is in SHUTDOWN mode and communications are disabled.

See this FAQ for the details on exiting SHUTDOWN mode: [FAQ] BQ76952: How does SHUTDOWN mode work? - Power management forum - Power management - TI E2E support forums.

Regards,

Max Verboncoeur

Thank you for the reply,

TS2 pulled low and and 100ms low-high-low pulse is given on Rst_shut pin to ensure IC reset still I am not able to see any response from the BQ76952.

Clock and SDA pullup register are 1.6K. 

Regards,

Kish

Hi Kish,

Is the device powered properly? You can check if the device is on and not in SHUTDOWN mode by measuring the voltage at REG18. It should be ~1.8V if the device is on.

You might also check the device comparison table in the datasheet (attached below) to see if the device version that you have is I2C by default and if it defaults to CRC as well.

Regards,

Max Verboncoeur

Thank you for reply,

I am using BQ76952 I2C without CRC and REG1 disable.

Any other method to check device is enabled or not? I expect quick answer so that I can try immediately.

One more question do you have any reference code for BQ76952  using NXP S32Kxx  MCU or method to port example code on NXP MCU. It will save my development time. our SOP date is Feb  2024 I can not effort time in any migration.

Regards,

Kishor

Hi Kish,

REG18 is enabled as long as the device is powered and not in SHUTDOWN mode. REG18 is an LDO meant exclusively for the internal circuitry and is not user configurable, so it is a good indication of whether the device is on or not.

We have example code for the MSP430 and STM32 microcontrollers found on the product page; unfortunately, we do not have examples for NXP MCUs, however you may be able to reference the existing examples for their logical structure.

Regards,

Max Verboncoeur

I am not able to establish stable communication with BQ79656.

observation 1:

    PINS_DRV_SetPins(PTD,1<<16);     //TS2 low to wake up AFE

    PINS_DRV_ClearPins(PTD,1<<16);   // AFE Reset pulse of 100ms

    OSIF_TimeDelay(100);

    PINS_DRV_SetPins(PTD,1<<17);

Sending wakeup pulse and resetting the device AFE by sending 100ms high pulse on Rst_Shutdown only once during initialization, the MCU pin output is verified for both pulses but  communication with AFE was never happened.

Q1: TS2 and Shut_Reset what is its sequence? timing and wait time after sending these commands? when it should be send to AFE? 

Q2: Why AFE is not responding to these commands? what should be the pulse duration of Rst_Shut to reset AFE?

Q3: What is proper wakeup sequence to follow to ensure wake up and initialization every time?

Q4: is it mandatory to provide all cell voltages? if only VBAT is provided with more than 20V does AFE works to check communication?

Observation 2: After removing TS2 (set to low) and sending 100ms high pulse on on Rst_Shut . Just by connecting power connection to AFE it start responding to read device version command.

Q5: what is the operation happening here how IC started communicating without any wakeup command? And the same code is not working in another board?

Q6: Communication is very unstable same build works some time but it fails on next flash what could be reason.

Q7: How to establish stable I2C communication?

I am expecting the response today.

Regards,

Kish

Hi Kish,

Based on your observations, the device may be in soft-shutdown state. If TS2 is held low while the device attempts to enter SHUTDOWN mode, then the device will be stuck in soft-shutdown. Depending on how you're controlling TS2 it may be staying low as the internal pullup is very weak, and even 1uA of leakage can pull the pin low. This also would explain why initiating a partial reset by pulsing RST_SHUT for <1s fixes the communications.

See this FAQ for more details: (+) [FAQ] BQ76952: What is the Soft SHUTDOWN state? - Power management forum - Power management - TI E2E support forums.

The proper wakeup sequence should just require pulling TS2 low, and then letting it float. That should transition the device to NORMAL mode.

Could you explain more about how the communication is unstable? Do you have logic analyzer outputs or scope waveforms to show any comms errors or signal integrity issues?

Regards,

Max Verboncoeur

Why device will try to enter in SHUTDOWN mode? RST_SHUT is low and only 100ms high pulse is given to this pin.
TS2 should be always low as I understand to keep the AFE in normal mode.
What are the possible trigger to push AFE in soft-shutdown state?

From MCU side both TS2 pin and RST_SHUT is configured as digital output. It can be either HIGH OR LOW how it can be left floating?

Please answer all sub questions.

1. does IC needs all cell connections? or just providing VBAT can test for communication?

In case there is no cell or power connections made to afe, after VBAT or CELL connection does it enters into normal mode directly?

Regards