MSP430 datasheet(38/88 Pages) TI

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7.3.3.2 Alarm Voltage Generator

Figure 7-12 shows that the alarm voltage is generated independently from the DAC output voltage. The alarm

polarity control logic selects the output level of the alarm voltage generator. The alarm action control logic

selects between the DAC output and alarm voltage generator output voltages. The alarm action control logic also

controls the output buffer Hi-Z switch.

POL_SEL/

AIN1

VDD

GND

Alarm

Voltage

Generator

OUT = 0.15 V

OUT = 1.25 V

DAC_DATA

DAC

–

ALARM_ACT

VOUT

PVDD =1.8 V: G = 1

PVDD > 2.7 V: G = 2

Hi-Z

ALMV_POL

DAC_CLR_CODE

DAC_CODE

Figure 7-12. Alarm Voltage Generator Architecture

During normal operation, the expected VOUT voltage depends on the DAC_CODE. The ADC thresholds for the

SD4 (VOUT) diagnostic channel are set around the programmed DAC_CODE. During the alarm condition, if the

alarm action changes the VOUT voltage to the alarm voltage, or switches the VOUT buffer into Hi-Z mode, the

VOUT voltage no longer depends on the DAC_CODE. In this case, the SD4 (VOUT) diagnostic channel also

reports the alarm. To clear this alarm, as long as all other alarm conditions are cleared, set the alarm action

to either no action or to the DAC clear code. Applying either alarm action sets the VOUT voltage within the

expected ADC thresholds and clears the alarm after the next ADC measurement of the SD4 (VOUT) channel.

Give special consideration to the alarm logic during the transient events. When the new DAC_CODE goes

beyond the SD4 (VOUT) alarm thresholds with the ADC monitoring the SD4 (VOUT) input in auto mode, the

ADC conversion can occur while VOUT settles to a new value. This conversion can trigger a false alarm. There

are two ways to prevent this false alarm:

1. Use direct mode and allow VOUT to settle before triggering the next ADC conversion.

2. Set ADC_CFG.FLT_CNT > 0. With this configuration, a single error in SD4 or any other measurement does

not cause an alarm condition to be asserted.

7.3.3.3 Temperature Sensor Alarm Function

The AFEx8101 continuously monitor the internal die temperature. In addition to the ADC measurement, the

temperature sensor triggers a comparator to show a thermal warning and a thermal error. A thermal warning

alarm is set when the temperature exceeds 85°C. Additionally, a thermal error alarm is set when the die

temperature exceeds 130°C.

The thermal warning and thermal error alarms can be configured to set the ALARM pin and are indicated

in the ALARM_STATUS register. These alarms can be masked with the ALARM_MASK register and also be

configured to control the DAC output with the ALARM_ACT register.

7.3.3.4 Internal Reference Alarm Function

The devices provide out-of-range detection for the reference voltage. When the reference voltage exceeds ±5%

of the nominal value, the reference alarm flag (VREF_FLT bit) is set. Make sure that a reference alarm condition

has not been issued by the device before powering up the DAC output.

AFE78101, AFE88101

SLASF21 – DECEMBER 2022

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