sign applied. For example, assume a shunt voltage reading returns 1011 0100 0001 0000 0000. This is a

negative value due to the MSB having a value of one. Inverting the bits and adding one results in 0100 1011

1111 0000 0000 (311040d) which from the shunt voltage example in Table 8-4 correlates to a voltage of 97.2 mV.

Since the returned value was negative the measured shunt voltage value is -97.2 mV.

8.2.3 Application Curves

The figures below show the ALERT pin response to a bus overvoltage fault with a conversion time of 50 μs,

averaging set to 1, and the SLOWALERT bit set to 0 for bus only conversions. For these scope shots,

persistence was enabled on the ALERT channel to show the variation in the alert response for many sequential

fault events. If the magnitude of the fault is sufficient the ALERT response can be as fast as one quarter of the

ADC conversion time as shown in Figure 8-3. For fault conditions that are just exceeding the limit threshold, the

response time for the ALERT pin can vary from approximately 0.5 to 1.5 conversion cycles as shown in Figure

8-4. Variation in the alert response exists because the external fault event is not synchronized to the internal

ADC conversion start. Also the ADC is constantly sampling to get a result, so the response time for fault events

starting from zero will slower than fault events starting from values near the set fault threshold. Since the timing

of the alert can be difficult to predict, applications where the alert timing is critical should assume a alert

response equal to 1.5 times the ADC conversion time for bus voltage or shunt voltage only conversions.

TIME (10 µs / div)

Minimum Delay: 12.4 µs

Maximum Delay: 37.9 µs

Fault Threshold: 0.2 V

Figure 8-3. Alert Response Time (Sampled Values

Significantly Above Threshold)

TIME (10 µs / div)

Minimum Delay: 24 µs

Maximum Delay: 73.2 µs

Fault Threshold: 1.9 V

Figure 8-4. Alert Response Time (Sampled Values

Slightly Above Threshold)

INA229

SLYS023 – DECEMBER 2020

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