Troubleshooting AFE Resets in BQ76952 System
During an OCD test on a BQ76952 system, observations of cell voltage exceeding specified thresholds raised concerns of AFE resetting. The issue was suspected to be the underlying cause. Detailed analysis and modifications are discussed with schematics and digital images in this documentation.
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BQ76952: When the OCD1 threshold is reached, both the OTPB will reset and partial analog data will reset to default value. 2024/04/17 TI Forum
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.
20240417 Modified Schematics
AFE.pin15(VC1) AFE.pin16(VC0) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 5.13v Max. voltage Level = 5.25v VC1-VC0 VC1-VC0 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-
AFE.pin14(VC2) AFE.pin15(VC1) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 5.21v Max. voltage Level = 5.37v VC2-VC1 VC2-VC1 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-
AFE.pin13(VC3) AFE.pin14(VC2) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 4.97v Max. voltage Level = 5.33v VC3-VC2 VC3-VC2 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-
AFE.pin12(VC4) AFE.pin13(VC3) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 5.09v Max. voltage Level = 5.41v VC4-VC3 VC4-VC3 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-
AFE.pin11(VC5) AFE.pin12(VC4) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 4.97v Max. voltage Level = 5.37v VC5-VC4 VC5-VC4 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-
AFE.pin10(VC6) AFE.pin11(VC5) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 6.50v Max. voltage Level = 5.09v VC6-VC5 VC6-VC5 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-
AFE.pin9(VC7) AFE.pin10(VC6) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 6.58v Max. voltage Level = 5.13v VC7-VC6 VC7-VC6 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-
AFE.pin8(VC8) AFE.pin9(VC7) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 6.30v Max. voltage Level = 5.33v VC8-VC7 VC8-VC7 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-
AFE.pin7(VC9) AFE.pin8 (VC8) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 6.22v Max. voltage Level = 5.21v VC9-VC8 VC9-VC8 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-
AFE.pin6(VC10) AFE.pin7 (VC9) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 5.37v Max. voltage Level = 4.65v VC10-VC9 VC10-VC9 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-
AFE.pin48(VC11) AFE.pin6 (VC10) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 5.05v Max. voltage Level = 4.49v VC11-VC10 VC11-VC10 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-
20240417 Added VC11(TA1) VC0(TA12) Abnormal Pack [AFE.BAT CAP doubled](OTPB) Normal Pack (OCD-3) Max. voltage Level = 55.3v Max. voltage Level = 58.5v VC11-VC0 VC11-VC0 Green: Pink: Current(clamp meter) VC11(TA1) VC0(TA12) TP TP Green: Pink: Current(clamp meter) VC11(TA1) VC0(TA12) TP TP
20240417 Added AFE.Pin47(BAT) In the previous test, the BAT pin voltage stayed the same during the OCD test because the capacitors we added filter out voltage spikes. Yellow: Green: Blue: Pink: VPACK+ Current AFE.ALERT AFE.BAT BAT
20240417 Modified 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 VC11-VC0 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). Based on our previous test, the BAT pin voltage didn t change during the test .
