0 V

ALERT1

LATCH1

Latch Mode

Transparent Mode

Alert Does Not Clear

Alert Clears

10

INA381

SBOS848 – DECEMBER 2017

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Feature Description (continued)

7.3.5.2 Latch Output Mode

Some applications do not have the functionality available to 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 application is a system that is only able to poll the ALERT pin state periodically 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 to indicate an out-of-range event if the out-of-range

condition does not appear during one of these periodic polling events. Latch 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 mode

RESET = low

Latch mode

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 below the alert

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

low returns the ALERT to the default high level, if the differential input signal is below the alert threshold. If the

input signal is above 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, the RESET pin can be set back to high to place the

device back in latch mode.

the first time, the RESET pin is pulled high. With the RESET pin is pulled high, the device is set to latch mode so

the RESET pin is pulled low does the ALERT pin return to the default high level, thus indicating that the input

signal is below the limit threshold. When the input signal drops below the limit threshold for the second time, the

RESET pin is already pulled low. The device is set to transparent mode at this point and the ALERT pin is pulled

back high when the input signal drops below the alert threshold.

Figure 3. Transparent versus Latch Mode