BQ76952: OTP Programming not working

Dear Mounish Patel,

1. When you were doing the OTP programming, did you follow the steps outlined in section 3.1 of the BQ769x2 Calibration and OTP Programming Guide (shown below)? At the end of OTP, you should try to read from register 0x40 and see the value 0x80. Are you seeing this at the end? A common error is to not supply 10-12V across the BAT pin while programming.

2. Yes, the device is capable of operating fully autonomously without any MCU while using OTP programming for a personalized configuration.

I have a few quick questions.

1. In your configuration, are you using any of the following pins: TS2, CFETOFF, or DFETOFF?

2. Do you have an available schematic? It might help in figuring out why the FETs get disabled

3. What are you trying to OTP onto the device? 

Best,

Asher Nederveld

1. Yes I followed all the OTP programming guide, Previously I used REG1 and REG2 ( worked well), Now I am not using them, I have updated design over the course of time but never checked whether device is functional without MCU.

2.1 Yes I am using TS2,CFETOFF,DFETOFF as Cell Temperature sensors ( I even wrote these registers also while OTP)

2.2. Yes Please find the schematic

2.3. I want to use device functions autonomously and I use only MCU for reading data, So even in case of MCU failure, system will be functional

Dear Mounish Patel,

1. Is there anyway I could see the full schematic (maybe a PDF) you are using for the BQ76952?

2. To clarify, what changes are you making in the OTP? Are you enabling/disabling LDOs or something else?

3. What are you using to power the MCU if you have switched away from REG1 and REG2?

4. What voltage are you seeing on the CP1?

Best,

Asher Nederveld

Hi Asher Nederveld,

1. Please accept my friend request, ill share you completeschematic personally

2. Currently , I am using TS1, Ts2, HDQ, CFETOFF as temperature sensors (Iwrote registers also) other pins like TS3,DFET_OFF,DCHG,DDSG,Alert foot print is given but i left them open.

3. I am using external source to power MCU now, I am no longer using REG,REG2. Today i checked the OTP is successful i.e, if i read registers after OTP even after the power is reset device is holding register values, but not sure why device is not working without MCU

4. I think it will around 10, FETs are turning on properly there is no issue there, With MCU everything is perfect.

Do you think Alert pin or any other pin causing the issue?

Thanks&Regards

Mounish

Hello Mounish Patel,

Asher is currently out of office.

I am glad to hear OTP is working as expected. 

MounishPatel Seetha said:

but not sure why device is not working without MCU

What do you mean by this? Can please you elaborate more? In order for the device to run autonomously, the FET_EN bit should be OTP programmed so that when it powers up, it turns ON the FETs by default. 

Please share the schematic to me privately to review it.

Regards,
Jose Couso

I shared my schematic Please check

Also following are my registers Values, 

Hello Mounish Patel,

Please see my comments on the schematic below:

1- We do not recommend to use the TS2 pin as a thermistor. This will prevent the device from entering completely shutdown mode. The TS2 pin is mainly used to wake up the device by pulling it low.

2- We recommend to separate the high-path (BAT-) from the low-path (IC Ground) current by using net-ties or 0-Ω resistors. This is detailly explained in this E2E-thread. 

3- I see you are using multiple FETs in parallel. You might want to consider a turn OFF circuit to prevent FET failures during a Short-Circuit event. Switching too slow as well as switching too quickly can cause FET failures. You can reference to the multiple FET app note and also to this FAQ (this FAQ discusses what could go wrong in the parallel FET configuration).

3.1- I see some FETs are not connected in the schematic, carefully look at the connections. The multiple FET app note goes into more details.

Note: Leakage current at the CHG and DSG pins can prevent the Charge pump from turning ON the FETs. Make sure there's no current flowing into this pins.

I am still unclear on what the specific issue is. At the beginning of this thread you mentioned OTP was not working, but now it works. Please elaborate with more details what is the current issue to further help you.

Regards,
Jose Couso

OTP programming overwrites default register mappings, so that even when device is reset it will store the changed register values right?

 I wrote register values in config update mode by maintaining 11v at Bat Pin ( as mentioned in OTP programming guide ), and when I restart the device I can see that the change is done, but if I remove the MCU i.e break i2c connection , FETs are turning off, I want to use the device even in case of MCU failure, What all registers should I write? any hardware changes should I do?

Hello Mounish Patel,

In  regards to your first question. Yes, once you OTP program a register, it will power up with the changes made. It is good to remark that device has limited OTP signatures. More details in this thread. 

Which registers did you OTP programmed? For the FETs to remain ON or to operate the device in stand-alone mode, the following registers should be configured properly.

Settings:Manufacturing:Mfg Status Init[FET_EN] should be set

The Settings:FET:FET Options[FET_CTRL_EN] must be set for the device to enable the FETs at all

Note: The device also can transition to sleep mode autonomously if the current falls below the Power:Sleep:Sleep Current threshold. You can also disable sleep mode if not rquired for your applications and FETs should remain ON all the time.

Please share your settings if the above does not resolve your issue. 

Regards,
Jose Couso

Hi I have already shared my settings, any how the register value  is below

What else should I try?

Note : I am not using BREG,REG1,REG2 , Alert Pins