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Disable OCD on BQ76940 for higher Rsns values

Armin
Intellectual 290 points
Other Parts Discussed in Thread: BQ76940

Hi everybody,

I am now choosing the current sense resistor for BQ76940. I saw in the datasheet that the maximum threshold for the overcurrent protection feature of BQ79640 is at 100mV but the maximum recommendet range for srn and srp pin is 200mv. In my opinion it would be the best for accuracy of current measurement to use a resistor value calculateted by R=200mv / max current. with that I use the full range. But if I want to use the OCD feature i just can use less than 100mv for this calculation. Is there somthing I dont understand? If not is it possible to disable the ocd feature?


Thanks a lot.


Armin

  • 0
    TI__Expert 6085 points
    The SRN/SRP path has two signal paths. One to the 16-bit integrating ADC (Delta-Sigma converter, Coulomb counter) and other to the OCD/SCD comparator. 16 bit ADC has 1 bit resolution of 8.44uV and dynamic range of 200mV. When RSNS =1 , SCD threshold 44-200mV; OCD threshold 17mV-100mV. Rsense = 200mV/ peak discharge current.; max continuous current = SQRT ( allowed power on PCB/ Rsense); voltage across shunt resistor/ sense resistor; @Max OCD current limit = 100mV/ Rsense . OCD detection is totally HW implemented inside of the AFE and there is no scheme to disable the HW OCD feature. OCD/SCD will always operate ( even without a host controller). OV/UV will operate, If ADC is ON.