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INA381-Q1

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SLYS041 – MARCH 2020

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7.4 Device Functional Modes

7.4.1 Alert Modes

The device has two output operating modes, transparent and latched, that are selected based on the RESET pin

setting. These modes change how the ALERT pin responds after an alert when the overcurrent condition is

removed.

7.4.1.1 Transparent Output Mode

The device is set to transparent mode when the RESET pin is pulled low, allowing the output alert state to

change and follow the input signal with respect to the programmed alert threshold. For example, when the

differential input signal exceeds the alert threshold, the alert output pin is pulled low. When the differential input

signal drops to less than the alert threshold, the output returns to the default high-output state. A common

implementation using the device in transparent mode is to connect the ALERT pin to a hardware interrupt input

on a microcontroller. When an overcurrent condition is detected and the ALERT pin is pulled low, the controller

interrupt pin detects the output state change and begins making changes to the system operation required to

address the overcurrent condition. Under this configuration, the ALERT pin high-to-low transition is captured by

the microcontroller, and the output returns to the default high state when the overcurrent event is removed.

7.4.1.2 Latch Output Mode

Some applications cannot continuously monitor the state of the output ALERT pin to detect an overcurrent

condition, as described in the Transparent Output Mode section. A typical example of this type of application is a

system that only periodically polls the ALERT pin state to determine if the system is functioning correctly. If the

device is set to transparent mode in this type of application, the state change of the ALERT pin can be missed

when ALERT is pulled low if the out-of-range condition does not appear during one of these periodic polling

events. Latch output mode is specifically intended to accommodate these applications.

As shown in Table 1, the device is placed into the corresponding output mode based on the signal connected to

RESET. The difference between latch mode and transparent mode is how the alert output responds when an

overcurrent event ends. In transparent mode (RESET = low), when the differential input signal drops below the

limit threshold level after the ALERT pin asserts because of an overcurrent event, the state of the ALERT pin

returns to the default high setting to indicate that the overcurrent event is complete.

Table 1. Output Mode Settings

OUTPUT MODE

RESET PIN SETTING

Transparent

RESET = low

Latch

RESET = high

In latch mode (RESET = high), when an overlimit condition is detected and the ALERT pin is pulled low, the

ALERT pin does not return to the default high state when the differential input signal drops to less than the alert

threshold level. To clear the alert, the RESET pin must be pulled low for at least 100 ns. If the differential input

signal is less than the alert threshold, pull the RESET pin low to return ALERT to the default high level. If the

input signal exceeds the threshold limit when the RESET pin is pulled low, the ALERT pin remains low. When the

alert condition is detected by the system controller, set the RESET pin back to high to place the device back in

latch mode.