The device can detect an open wire connection on the VS and AUX pins. A current sink is connected to each VS and AUX pin, except VS0 and AUX0 pins which are connected with a current source.

When the current sink (or current source) is enabled and if there is an open wire connection, the VS voltage measurement will drop to an abnormal level over time. Similar detection concept applies to the VS0 and AUX0 pins with a current source. If there is an open wire connection, the VS0 or AUX0 will be pulled up by the current source, resulting in a reduced voltage measurement over time.

When the diagnostic comparison is enabled, the device will compare the voltage measurement from Main ADC (for VS pins open wire detection) against a host-programmed threshold; or comparing the AUX measurement from the AUX ADC (for AUX pins open wire detection) against a host-programmed threshold.

If MCU lock to a single AUX channel though [AUX_IN_SEL] before starting the AUX open wire check. The device will report the AUX measurement used for the check comparison. The value is reported in DIAG_AUX_HI/LO registers. Since there is no single channel lock mechanism in Main ADC, VS channel measurement used for VS open wire will not be reported in DIAG_MAIN_HI/LO registers.

Figure 8-43 Open Wire Detection

Before starting the open wire comparison, host ensures:

• For VS open wire detection, Main ADC is running in continuous mode.
• For AUX open wire detection, AUX ADC is running in continuous mode
  • Configured in the ADC_CTRL2[AUX_IN_SEL4:0] to select the AUX channels
  • Select the desired settling time for the AUX channel through ADC_CONF1[AUX_SETTLE1:0].
• Configure the open wire detection threshold through DIAG_COMP_CTRL2[OW_THR3:0].

To start the open wire comparison:

1. Turn on the VS pins (or AUX pins) current sink or source through DIAG_COMP_CTRL3[OW_SNK1:0].
2. Wait for dV/dt time of the external capacitor to deplete to the detection threshold if there is an open wire fault.
3. For VS open wire detection, select DIAG_COMP_CTRL3[COMP_ADC_SEL2:0] = OW VS check (that is, 0b010) and set [COMP_ADC_GO] = 1. Or for AUX open wire detection, [COMP_ADC_SEL2:0] = OW AUX check (that is, 0b011).
4. The device compares all active VS measurement (for VS open wire) or AUX measurement (for AUX open wire) against the [OW_THR3:0] threshold setting.
5. When the comparison is completed, ADC_STAT2[DRDY_VSOW] = 1 for VS open wire (or [DRDY_AUXOW] = 1 for AUX open wire).
6. Host then turns off all current sinks and sources through DIAG_COMP_CTRL3[OW_SNK1:0].

Host checks the FAULT_COMP_VSOW1/2 or FAULT_COMP_AUXOW1/2 registers for the comparison result.