SBOS644C February 2013 – March 2018 INA231
The INA231 has a single Alert Limit register (07h) that allows the ALERT pin to be programmed to respond to a single user-defined event or to a conversion ready notification if desired. The Mask/Enable register allows for selection from one of the five available functions to monitor and set the conversion ready bit (CNVR, Mask/Enable register) to control the response of the ALERT pin. Based on the function being monitored, a value would then be entered into the Alert Limit register to set the corresponding threshold value that asserts the ALERT pin.
The ALERT pin allows for one of several available alert functions to be monitored to determine if a user-defined threshold has been exceeded. The five alert functions that can be monitored are:
The ALERT pin is an open-drain output. This pin is asserted when the alert function selected in the Mask/Enable register exceeds the value programmed into the Alert Limit register. Only one of these alert functions can be enabled and monitored at a time. If multiple alert functions are enabled, the selected function in the highest significant bit position takes priority and responds to the Alert Limit register value. For example, if the SOL and the SUL are both selected, the ALERT pin asserts when the Shunt Voltage Over Limit register exceeds the value in the Alert Limit register.
The conversion-ready state of the device can also be monitored at the ALERT pin to inform the user when the device has completed the previous conversion and is ready to begin a new conversion. The conversion ready flag (CVRF) bit can be monitored at the ALERT pin along with one of the alert functions. If an alert function and the CNVR bit are both enabled for monitoring at the ALERT pin, then after the ALERT pin is asserted, the CVRF bit (D3) and the AFF bit (D4) in the Mask/Enable register must be read following the alert to determine the source of the alert. If the conversion ready feature is not desired, and the CNVR bit is not set, the ALERT pin only responds to an exceeded alert limit based on the alert function enabled.
If the alert function is not used, the ALERT pin can be left floating without impacting the operation of the device.
Refer to Figure 21 to see the relative timing of when the value in the Alert Limit register is compared to the corresponding converted value. For example, if the alert function that is enabled is Shunt Voltage Over Limit (SOL), following every shunt voltage conversion the value in the Alert Limit register is compared to the measured shunt voltage to determine if the measurements have exceeded the programmed limit. The AFF bit (D4, Mask/Enable register) asserts high any time the measured voltage exceeds the value programmed into the Alert Limit register. In addition to the AFF bit being asserted, the ALERT pin is asserted based on the Alert Polarity bit (APOL, D1, Mask/Enable register). If the Alert Latch is enabled, the AFF bit and ALERT pin remain asserted until either the Configuration register is written to or the Mask/Enable register is read.
The bus voltage alert functions (BOL and BUL, Mask/Enable register) compare the measured bus voltage to the Alert Limit register following every bus voltage conversion and assert the AFF bit and ALERT pin if the limit threshold is exceeded.
The power overlimit alert function (POL, Mask/Enable register) is also compared to the calculated power value following every bus voltage measurement conversion and asserts the AFF bit and ALERT pin if the limit threshold is exceeded.
The alert function compares the programmed alert limit value to the result of each corresponding conversion. Therefore, an alert can be issued during a conversion cycle where the averaged value of the signal does not exceed the alert limit. Triggering an alert based on this intermediate conversion allows for out-of-range events to be detected faster than the averaged output data registers are updated. This fast detection can be used to create alert limits for quickly changing conditions through the use of the alert function, as well as to create limits to longer-duration conditions through software monitoring of the averaged output values.