BQ76952: Delayed DDSG output and DCHG toggle issue

Manuj Agrawal1

Part Number: BQ76952

Dear TI Team,

I have set the DDSG and DCHG outputs to be Active High outputs driven by REG1. Here are the issues I have been facing:

Issue 1. Upon SCD Fault trigger I have noticed significant delay in DDSG signal to trigger and go high as in the image below. In the scope image, Red spike is the current going beyond SCD threshold and then falling back quickly, however there is a significant delay in the blue channel (DDSG) to go high (approx 500ms). This will cause significant issue in stacking two ICs since the lower IC sensing the current will provide a delayed SCD or OCD signal though DDSG pin to external MOSFET driver.

I have used the following Switching Circuit with a PMOS for the DFET off path as described in the TIDA

Issue 2. DCHG pin toggles once (goes low) for a small amount of time when the DFETOFF pin (configured active low input and BOTOFF) is toggled to high input to turn ON both mosfets.

Please help me out with both of these issues.

Thanks and Regards

Manuj Agrawal

over 4 years ago

0 Matt Sunna over 4 years ago

TI__Guru* 81035 points

Hi Manuj,

Can you tell me your settings for CHG FET Protections A and DSG FET Protections A?

Thanks,

Matt

0 Manuj Agrawal1 over 4 years ago in reply to Matt Sunna

Prodigy 175 points

Dear Matt,

I have set the following:

CHG FET Protections A (0x98): SCD:1 OCC:1 COV:1

DSG FET Protections A (0xA4): SCD:1 OCD2:0 OCD1:1 CUV:1

After realizing what you mentioned in the reply from the datasheet, I have set the DSG FET Protections-A to 0xE4 and have been able to solve the issue of delayed DDSG output. :D

However the DCHG output still toggles when the DFETOFF pin (configured active low input and BOTOFF) is toggled to high input to turn ON both mosfets.

Thanks and Regards

Manuj

0 Matt Sunna over 4 years ago in reply to Manuj Agrawal1

TI__Guru* 81035 points

Hi Manuj,

Do you have a waveform for the 2nd issue? When the FETs are disabled with the DFETOFF pin, they should both turn off quickly. However, when enabling the FETs again, the BQ76952 needs to make sure that conditions are safe for the FETs to turn on which takes some time.

Best regards,

Matt

0 Manuj Agrawal1 over 4 years ago in reply to Matt Sunna

Prodigy 175 points

Dear Matt,

I will provide the waveform for the second issue shortly. However, here is the link to one of my previous posts where it was clarified that DDSG/DCHG toggle is observed while turning ON/OFF mosfets through commands and should not happen when using DFETOFF and CFETOFF pins.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/963339/bq76952-need-clarification-on-ddsg-and-dchg-operation

Thanks and Regards

Manuj

0 Matt Sunna over 4 years ago in reply to Manuj Agrawal1

TI__Guru* 81035 points

Hi Manuj,

Yes, this is my understanding. That is why I would like to see waveforms to understand if there is some behavior I am not aware of.

Thanks,

Matt

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BQ76952: Delayed DDSG output and DCHG toggle issue