I want to measure the Coulomb count of the MC3371 during its sleep period. Before going to sleep, I cleared the relevant registers of the coulometer and configured CYCLIC_TIMER = 2S at the same time. After sleeping for 16 seconds, I woke up the MC33771 using CSB and then read the three registers -cc_nb_samples, COULOMB_CNT1, and COULOMB_CNT2. CC_NB_SAMPLES is always 65535, and COULOMB_CNT1 and COULOMB_CNT2 are normal values. Shouldn't the count of CC_NB_SAMPLES during hibernation be based on the CYCLIC_TIMER?
The relevant screenshots are as follows
This waveform is the voltage waveform of VANA:
Dear Ye Xiaoer,
if coulomb counting during the entire hour is not critical, you can disable coulomb counting in sleep mode by setting the I_MEAS_EN=0 and enable it only during short active windows. This avoids overflow but sacrifices continuous integration.
With Best Regards,
Jozef
Thank you very much for your answer. I confirmed that the SAMP_OVF flag bit was set. But now our project has a requirement: the BMS wakes up once every hour, and it is necessary to read the average current and sleep time during the sleep period after waking up? If CC_NB_SAMPLES reaches 0XFFFF within a very short actual cycle now(CycLic_Timer = 1s), then I cannot obtain the correct number of samples and cannot calculate the average current correctly? Is it also impossible to convert the duration of the sleep period based on the number of samplings? How to solve this problem? Looking forward to your reply.
Dear Ye Xiaoer,
CC_NB_SAMPLES is not tied to CYCLIC_TIMER ticks.
It is the raw number of ADC2 samples that contributed to the coulomb integration. In low‑power/sleep operation the coulomb counter can continue integrating independent of your cyclic timer, so CC_NB_SAMPLES can quickly saturate to 0xFFFF unless you read/reset it often enough or force a fresh conversion after wake. Check the CC_OVR_FLT flag to confirm an overflow.
Please refer to the MC33771C datasheet and to the AN12633.
- The coulomb counter accumulates the discrete integral of ADC2 samples.
- COULOMB_CNT1/2 hold the integral.
- CC_NB_SAMPLES holds the number of accumulated samples.
With Best Regards,
Jozef