Understanding BQ76952 Overcurrent Detection and Analog Data Reset

The BQ76952 device features a protective mechanism where reaching the OCD1 threshold triggers a reset of OTPB and analog data. This was observed during an OCD test, where cell voltages exceeded specified thresholds. While it's not explicitly stated in the specs, exceeding the voltage threshold may be the cause behind the AFE resets. Detailed information, test results, and schematics are available for further analysis and understanding.

• BQ76952
• Overcurrent Detection
• Analog Data Reset
• Cell Voltage Threshold
• AFE Reset

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1. BQ76952: When the OCD1 threshold is reached, both the OTPB will reset and partial analog data will reset to default value. 2024/04/12 TI Forum

2. Forewords During the OCD test, we observed that the cell voltage for each AFE pin exceeds the threshold specified in the spec. The test results and plots are presented in the following slides. While the spec does not explicitly mention that exceeding the cell voltage threshold will cause the AFE to reset, we suspect this might be the underlying reason for the issue.

3. Spec

4. Schematics

5. AFE.pin15(VC1) AFE.pin16(VC0) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin15(VC1) AFE.pin16(VC0) CA11+ Green: Pink: Current(clamp meter) AFE.pin15(VC1) AFE.pin16(VC0) CA11+ CA11- CA11-

6. AFE.pin14(VC2) AFE.pin15(VC1) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin14(VC2) AFE.pin15(VC1) CA10+ Green: Pink: Current(clamp meter) AFE.pin14(VC2) AFE.pin15(VC1) CA10+ CA10- CA10-

7. AFE.pin13(VC3) AFE.pin14(VC2) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin13(VC3) AFE.pin14(VC2) CA9+ Green: Pink: Current(clamp meter) AFE.pin13(VC3) AFE.pin14(VC2) CA9+ CA9- CA9-

8. AFE.pin12(VC4) AFE.pin13(VC3) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin12(VC4) AFE.pin13(VC3) CA8+ Green: Pink: Current(clamp meter) AFE.pin12(VC4) AFE.pin13(VC3) CA8+ CA8- CA8-

9. AFE.pin11(VC5) AFE.pin12(VC4) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin11(VC5) AFE.pin12(VC4) CA7+ Green: Pink: Current(clamp meter) AFE.pin11(VC5) AFE.pin12(VC4) CA7+ CA7- CA7-

10. AFE.pin10(VC6) AFE.pin11(VC5) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin10(VC6) AFE.pin11(VC5) CA6+ Green: Pink: Current(clamp meter) AFE.pin10(VC6) AFE.pin11(VC5) CA6+ CA6- CA6-

11. AFE.pin9(VC7) AFE.pin10(VC6) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin9(VC7) AFE.pin10(VC6) CA5+ Green: Pink: Current(clamp meter) AFE.pin9(VC7) AFE.pin10(VC6) CA5+ CA5- CA5-

12. AFE.pin8(VC8) AFE.pin9(VC7) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin8(VC8) AFE.pin9(VC7) CA4+ Green: Pink: Current(clamp meter) AFE.pin8(VC8) AFE.pin9(VC7) CA4+ CA4- CA4-

13. AFE.pin7(VC9) AFE.pin8 (VC8) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin7(VC9) AFE.pin8 (VC8) CA3+ Green: Pink: Current(clamp meter) AFE.pin7(VC9) AFE.pin8 (VC8) CA3+ CA3- CA3-

14. AFE.pin6(VC10) AFE.pin7 (VC9) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin6(VC10) AFE.pin7 (VC9) CA2+ Green: Pink: Current(clamp meter) AFE.pin6(VC10) AFE.pin7 (VC9) CA2+ CA2- CA2-

15. AFE.pin48(VC11) AFE.pin6 (VC10) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Green: Pink: Current(clamp meter) AFE.pin48(VC11) AFE.pin6 (VC10) CA1+ Green: Pink: Current(clamp meter) AFE.pin48(VC11) AFE.pin6 (VC10) CA1+ CA1- CA1-

16. Normal Pack : Trigger the OCD1 as expected. OTPB Pack : The DUT that trigger OTPB flag. Test Result VC1 VC2 VC3 VC4 VC5 VC6 VC7 VC8 VC9 VC10 VC11 VCsum BAT+ OTPB Pack 5.13 5.21 4.97 5.09 4.97 6.5 6.58 6.3 6.22 5.37 5.05 61.39 55.3 (CA13CA14 added 2uF) Normal Pack 5.25 5.37 5.33 5.41 5.37 5.09 5.13 5.33 5.21 4.65 4.49 56.63 58.5 We observed that the maximum voltage spike in the cell, occurring when DFET is turned off due to OCD protection, exceeds the 5.5V threshold at certain cell pins. This phenomenon is unique to the OTPB pack. In a normal pack, the OCD is induced as expected. However, in the OTPB pack, it results in a partial reset, resetting some analog data to default values (voltage: 0, temperature: -273.15 C).