The CS ADC is a high accuracy delta-sigma ADC with a SINC3 filter, dedicated for current sensing. It is used a 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. Bi-directional current can be measured. The CS ADC supports only low side sense resistor. The full-scale ADC input range is V_{CS_RANGE}. See the Electrical Characteristics table for the recommended range. If current sense ADC input is larger than Full Scale input voltage/V_{CS_RANGE}, CURRENT_HI/MID/LOW would be clamped around 75-mV output reading. To verify, user could read CSAUX_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 = V_{LSB_CS} result in decimal.

After receiving the GO command, the CS ADC starts its first conversion after t_{CS_SETTLE}. Since the CS ADC is using a SINC3 filter, the first conversion takes t_{CS_CONV} time to complete, but any subsequent conversion takes t_{CS_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. The CSADC is measuring the input throughout its conversion time.

Auxiliary measurement of the voltage across the shunt resistor can be done by the SAR ADC in the MAIN ADC path. The CSADC and the Auxiliary measurement path are shown in Figure 8-10 and Figure 8-11. Details pertaining to the Auxiliary measurement are available in the Main ADC measurement section.

Over current detection scheme can be implemented using the OVUV comparators in this device. Refer to Section 9.2.1.2.5 for the implementation details.

Figure 8-10 CS ADC

Figure 8-11 CS ADC Measurement