AMC7832 Datasheet, PDF (35/70 Pages) Texas Instruments – AMC7832 12-Bit Analog Monitor and Control Solution with Multi-Channel ADC, Bipolar DACs, Temperature Sensor and GPIO Ports

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AMC7832
SLAS836 – MARCH 2014
8.3.2.4.3 ALARMIN Alarm
The AMC7832 offers the option of using an external interrupt signal, such as the output of a comparator as an
alarm event. The GPIO0/ALARMIN terminal is used as the alarm input and must be configured accordingly in the
GPIO Configuration register (address 0x12). When the terminal is configured as an alarm input it is active low.
A typical application for ALARMIN is to use it as a hardware interrupt responsible for forcing one or more DACs
to a clear state: the DAC is loaded with a zero-code input and the output voltage is set accordingly to the
operating output range, however the DAC buffer or active registers do not change (refer to the DAC section for
more details). To enable this functionality ALARMIN must be enabled as a DAC clear alarm source in the DAC
Clear Source 1 register (address 0x1B). Additionally the DAC outputs to be cleared by the ALARMIN terminal
need to be specified in the DAC Clear Enable registers (address 0x18 – 0x19).
In this application when the ALARMIN terminal goes low, all the DACs set to clear in response to the ALARMIN
alarm in the DAC Clear Enable registers enter a clear state. When the ALARMIN terminal goes back high the
DACs get re-loaded with the contents of the DAC active registers thus allowing the DAC outputs to return to their
previous operating point without any additional commands.
8.3.2.4.4 Hysteresis
If a monitored signal is out of range and the alarm is enabled, the corresponding alarm bit is set ('1'). However,
the alarm condition is cleared only when the conversion result returns to a value of at least HYST below the
value of the high threshold register, or HYST above the value of the low threshold register. The ADC and LT
Hysteresis registers (address 0xA0 – 0xA4) store the hys value for the external unipolar inputs and internal
temperature sensor programmable alarms. HYST is the programmable value of hysteresis: 0 LSB to 127 LSB for
the unipolar inputs alarms, and 0°C to +31°C for the internal temperature sensor alarms. The die thermal alarm
hysteresis is fixed at 8°C.
High Threshold
Hysteresis
Low Threshold
Hysteresis
Over High Alarm
Below Low Alarm
Figure 50. AMC7832 Hysteresis
8.3.2.4.5 False-Alarm Protection
In order to prevent false alarms an alarm event is only registered when the monitored signal is out of range for
an N number of consecutive conversions. If the monitored signal returns to the normal range before N
consecutive conversions, an alarm event is not issued. The false alarm factor N for the unipolar input and local
temperature sensor out-of-range alarms can be configured in the False Alarm Configuration register (address
0x11).
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