SBOU024C august 2004 – july 2023 PGA309
To detect sensor burnout or a short-circuit, a set of four comparators are connected to the inputs of the Front-End PGA. If any of the inputs are taken to within 100mV of ground or VEXC, or violate the input CMR of the Front-End PGA, then the corresponding comparator sets a sensor fault flag that causes the PGA309 VOUT to be driven within 100mV of either VSA or ground, depending upon the alarm configuration setting (Register 5—PGA Configuration and Over/Under-Scale Limit). This will be well above the set over-scale limit level or well below the set under-scale limit level. The state of the fault condition can be read in digital form in Register 8—Alarm Status Register. If the Over/Under-Scale Limit is disabled, the PGA309 output voltage will still be driven within 100mV of either VSA or ground, depending upon the alarm configuration setting.
There are five other fault detect comparators that help detect subtle PGA309 front-end violations that could otherwise result in linear voltages at VOUT that would be interpreted as valid states. These are especially useful during factory calibration and setup and are configured through Register 5—PGA Configuration and Over/Under-Scale Limit. Their status can also be read back through Register 8—Alarm Status Register.