Lowering the trigger point results in the device issuing an overcurrent alert prior to reaching the corresponding

VTRIP threshold. The averaging effect included with the 50-µs and 100-µs delay settings inherently eliminates the

effect internal noise has on the threshold voltage.

7.3.2.2 Voltage Source-Controlled Current Limit

The second method for setting the limit voltage is to connect the LIMIT terminal to a programmable DAC

(digital-to-analog converter) or other external voltage source. The benefit of this method is the ability to adjust

the current limit to account for different threshold voltages that are used for different system operating conditions.

For example, this method can be used in a system that has one current-limit threshold level that must be

monitored during the power-up sequence but different thresholds must be monitored during other system

operating modes.

In Table 7-3, VTRIP represents the overcurrent threshold the device is programmed to monitor for and VSOURCE

is the programmed signal set to detect the VTRIP level. NAF is included in the VSOURCE equation for the 10-µs

delay setting. This value equals 500 µV and is adjusts the operating point for the noise in the delay setting. The

50-µs and 100-µs delay settings do not use the NAF term in calculating the VSOURCE threshold. For these delay

settings, the NAF term is omitted. See the Noise Adjustment Factor (NAF) section for more details on the noise

adjustment factor.

Table 7-3. Calculating the Limit Threshold Voltage Source, VSOURCE

PARAMETER

EQUATION

VTRIP

Desired current trip value

ILOAD × RSENSE

VSOURCE (1)

Programmed threshold limit voltage

VTRIP + NAF

VSOURCE (1)

Programmed signal set to detect the VTRIP level

VTRIP + 500 µV

(1)

NAF is used with the 10-µs delay setting. NAF can be omitted in the VSOURCE calculation for the 50-µs and 100-µs delay settings.

TI recommends using NAF in calculating the value for VSOURCE at the 10-µs delay setting. Removing NAF from

the VSOURCE calculation at the 10-µs delay setting lowers the trigger point of the alert output. Lowering the

trigger point results in the device issuing an overcurrent alert prior to reaching the corresponding VTRIP threshold.

The averaging effect included with the 50-µs and 100-µs delay settings inherently eliminates the effect internal

noise has on the threshold voltage.

7.3.3 Delay Setting

The device response time for overcurrent events is adjustable based on the DELAY terminal setting. Three

response time settings are available, ranging from 10 µs to 100 µs. The primary purpose for the three different

delay settings is to offer a trade-off between a faster alert response and a more precise overcurrent threshold

level detection.

The device has a 10-µs internal comparison window. This single comparison window is the fundamental time

unit used for all three delay settings. For the 10-µs delay setting, the device compares the average of the

input signal during the 10-µs comparison window to the threshold limit programmed at the LIMIT terminal. If the

averaged input signal exceeds the threshold at the end of the 10-µs comparison window, the output alert triggers

and pulls the ALERT terminal low. However, if the averaged input does not exceed the threshold at the end of

the 10-µs comparison window, there is no change in the output alert status, which remains high to indicate that

no overcurrent event is detected.

For the 50-µs delay setting, there must be five consecutive 10-µs comparison windows that result in an average

input signal exceeding the threshold limit in order for the output alert to trigger and pull the ALERT terminal low.

If any single 10-µs comparison window fails to detect an overcurrent condition before reaching five consecutive

overcurrent comparisons, the internal counter is reset and no output alert is issued. With the internal counter

reset, a new group of five consecutive 10-µs comparison windows of overcurrent conditions are required in order

to trigger the alert and pull the ALERT terminal low.

The 100-µs delay setting operates in the same manner as the 50-µs method, but instead requires ten

consecutive 10-µs comparison windows with an input signal exceeding the threshold limit to issue an output

alert and pull the ALERT terminal low.

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INA300

SBOS613C – FEBRUARY 2014 – REVISED JUNE 2021

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