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[FAQ] What are the differences between the hardware and firmware protections?

Other Parts Discussed in Thread: BQ40Z50

Firmware Protections

The BQ40Z50 offers multiple protection functionalities which can be configured for the end application. The first level protection is firmware based, for example; the Cell Under Voltage (CUV), Over Current in Charge (OCC), Over Temperature Charge (OTC), etc. These protections operate on a 1 second timing interval. This means that it’s possible to have up to an additional 1 second to any of the protection delay times.

For example, if we set the OCC1 protection for 3 seconds to disable the CFET, it’s possible the gauge may take close to 4 seconds under worst case scenarios.

Hardware Protections

The BQ40Z50 also has faster hardware level protections to stop different short circuit conditions from causing damage to the batteries or system. Hardware protections are all current based, like Over Current in Discharge (OCD) and Short Circuit in Charge (SCC).

The hardware protections use preset comparator voltage thresholds on the current sense pins, SRN and SRP, to determine a fault. It should be noted that the value programmed according the AFE Threshold and Delay settings will have the tDETECT time added, which should be accounted for when setting the hardware thresholds, especially the Short Circuit in Discharge (SCD) delays.

For example, if a 1mOhm resistor is used in the application, to set the SCD1 threshold to 33.3A and delay time of 500us, and SCD2 to 55.5A with a delay time of 250us.

Settings:AFE:AFE Protection Control[RSNS] = 0

Settings:AFE:AFE Protection Control[SCDDx2] = 0

tDETECT = 160us

SCD1 delay setting = 0x05 = 305us + tDETECT = 465us +/-31us

SCD2 delay setting = 0x03 = 92us + tDETECT = 252us +/- 9us

SCD1 threshold = 0x01 = 33.3mV = 33.3A with 1mOhm resistor

SCD2 threshold = 0x03 = 55.5mV = 55.5A with 1mOhm resistor

SCD1,2 thresholds from R2 TRM:

Example settings for SCD1,2: