TRIP

SENSE

REF

LIMIT

LIMIT

I

R

GAIN

V

R

I

u

u

19

INA302, INA303

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SBOS775C – SEPTEMBER 2016 – REVISED MARCH 2019

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Feature Description (continued)

7.3.3.1 Setting Alert Thresholds

The INA30x family of devices determines if an out-of-range event is present by comparing the amplifier output

voltage to the voltage at the corresponding LIMITx pin. The threshold voltage for the LIMITx pins can be set

using a single external resistor or by connecting an external voltage source to each pin. The INA302 allows

setting limits for two overcurrent conditions. Generally, the lower overcurrent threshold is referred to as a warning

limit and the higher overcurrent threshold is referred to as the critical or fault limit. The INA303 allows setting

thresholds to detect both undercurrent and overcurrent limit conditions.

7.3.3.1.1

Resistor-Controlled Current Limit

The typical approach to set the limit threshold voltage is to connect resistors from the two LIMITx pins to ground.

The voltage developed across the RLIMIT1, RLIMIT2 resistors represents the desired fault current value at which the

corresponding ALERTx pin becomes active. The values for the RLIMIT1, RLIMIT2 resistors are calculated using

Equation 3:

where

•

ITRIP is the desired out-of-range current threshold.

•

RSENSE is the current-sensing resistor.

•

GAIN is the gain option of the device selected.

•

VREF is the voltage applied to the REF pin.

•

ILIMIT is the limit threshold output current for the selected comparator, typically 80 µA.

(3)

NOTE

When solving for the value of RLIMIT, the voltage at the corresponding LIMITx pin as

determined by the product of RLIMIT and ILIMIT must not exceed the compliance voltage of

VS – 0.6 V.

7.3.3.1.1.1

Resistor-Controlled Current Limit: Example

For example, if the current level indicating an out-of-range condition (ITRIP) is 20 A and the current-sense resistor

value (RSENSE) is 10 mΩ, then the input threshold signal is 200 mV. The INA302A1 has a gain of 20, so the

resulting output voltage at the 20-A input condition is 4 V at the output of the current-sense amplifier when the

REF pin is grounded. The value for RLIMIT is selected to allow the device to detect this 20-A threshold, indicating

that an overcurrent event has occurred. When the INA302 detects this out-of-range condition, the ALERTx pin

asserts and pulls low. For this example, the value of RLIMIT to detect a 4-V level is calculated to be 50 kΩ.