ZHCSC46C February 2014 – June 2021 INA300
PRODUCTION DATA
The typical approach for setting the limit threshold voltage is to connect a resistor from the LIMIT terminal to ground. The value of this resistor, R_{LIMIT}, is chosen to create a corresponding voltage at the LIMIT terminal equivalent to the voltage, V_{TRIP}, developed by the load current flowing through the current-sensing resistor. An internal 20-µA current source is present at the LIMIT terminal that creates the corresponding voltage depending on the value of R_{LIMIT}. In the equations from Table 7-2, V_{TRIP} represents the overcurrent threshold the device is programmed to monitor for and V_{LIMIT} is the programmed signal set to detect the V_{TRIP} level. The term noise adjustment factor (NAF) is included in the V_{LIMIT} equation for the 10-µs delay setting. This value is equal to 500 µV and adjusts the operating point for the internal noise in this delay setting. The 50-µs and 100-µs delay settings do not use the NAF term in calculating the V_{LIMIT} threshold. See Section 7.3.7 for more details on the noise adjustment factor.
In Table 7-2, the process for calculating the required value for R_{LIMIT} to set the appropriate threshold voltage, V_{LIMIT}, is shown. This calculation is based on the 10-µs delay setting so the NAF term is included in the calculation. For a delay setting of 50 µs or 100 µs, the NAF term is omitted.
PARAMETER | EQUATION | |
---|---|---|
V_{TRIP} | Desired current trip value | I_{LOAD} × R_{SENSE} |
V_{LIMIT} | Programmed threshold limit voltage | V_{LIMIT} = V_{TRIP} |
V_{LIMIT} ^{(1)} | Threshold voltage | (I_{LIMIT} × R_{LIMIT}) – NAF |
R_{LIMIT} ^{(1)} | Threshold limit setting resistor | (V_{LIMIT} + NAF) / I_{LIMIT} |
R_{LIMIT} ^{(1)} | Limit setting resistor | (V_{LIMIT} + 500 µV) / 20 µA |
TI recommends using NAF in calculating the value for V_{LIMIT} and R_{LIMIT} at the 10-µs delay setting. Removing NAF from the V_{LIMIT} and R_{LIMIT} 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 V_{TRIP} 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.