SLUSDT5B September 2019 – October 2023 BQ75614-Q1
PRODUCTION DATA
The CS ADC is a high accuracy Delta-Sigma ADC with a SINC3 filter, dedicated for current sensing. It is used as divided down precision reference. The same precision reference is also used by the Main and AUX ADCs. The CS ADC block measures current by directly sensing the differential voltage across a sense resistor connecting between SRP and SRN pins. The CS ADC supports only low side sense resistor. The full scale ADC input range is -125mV to +125mV. If current sense ADC input is larger than Full Scale input voltage/125mV, CURRENT_HI/MID/LOW would be clamped around 75mV output reading. To verify, user could read MAIN_CURRENT_HI/LO.
The decimation ratio (DR) directly correlates to how quickly a conversion result is available to be read from the ADC. Lower DR corresponds to faster conversion time and lower effective number of bits (ENOB). The DR setting is controlled by ADC_CTRL1[CS_DR1:0]. The CS ADC shares the same start and mode control bits as the Main ADC located in ADC_CTRL1 register. Both the Main and CS ADCs stop together. Such design is to allow better voltage and current measurement alignment.
The measurement is reported in 24-bit hexadecimal in 2s complement. Results are reported to the corresponding CURRENT_HI (high-byte), CURRENT_MID (mid-byte) and CURRENT_LO (low-byte) registers. It first converts the hexadecimal results to decimal values. Convert the result to µV, where Result in µV = VLSB_CSResult in decimal
After receiving the GO command, the CS ADC start its first conversion after tCS_SETTLE. Since the CS ADC is using a SINC3 filter, the first conversion takes tCS_CONV time to complete, but any subsequence conversion takes (tCS_CONV / 3) time to complete. If MCU needs to catch every current measurement conversion, GPIO1 has an option to toggle low every time a CS ADC conversion is completed, the pin returns high when MCU read CURRENT_HI register. This signal can be used as an interrupt to the MCU to avoid missing a conversion. This function is enabled by setting GPIO_CONF2[CS_RDY_EN] = 1.