ZHCSEX8A December 2015 – October 2016 INA300-Q1
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The INA300-Q1 is designed to enable configuration for detecting overcurrent conditions in an application. This device is individually targeted towards overcurrent detection of a single threshold. However, this device can be paired with additional devices and circuitry to create more complex monitoring functional blocks.
The INA300-Q1 device measures current through a resistive shunt with current flowing in one direction, enabling detection of an overcurrent event only when the differential input voltage exceeds the threshold limit.
Figure 33 shows the basic connections of the INA300-Q1 device. The input terminals, IN+ and IN–, must be connected as closely as possible to the current-sensing resistor to minimize any resistance in series with the shunt resistance. Additional resistance between the current-sensing resistor and input terminals can result in errors in the measurement. When input current flows through this external input resistance, the voltage developed across the shunt resistor can differ from the voltage reaching the input terminals.
Figure 34 shows the alert response transitioning from a high to a low state following the input signal exceeding the limit threshold voltage. The time required for the output to respond varies as a result of when the input signal crosses the threshold limit voltage relative to where in the continuous running internal 10-µs comparison window the overrange condition occurs. In Figure 34, the output response varies from roughly 2 µs to approximately
12 µs when the input exceeds the threshold level. This variance is a result of where in the 10-µs comparison window the overrange event occurs. If the overrange event occurs late in the 10-µs comparison window and is large enough to average the entire window measurement up above the threshold level, the alert appears to respond very quickly. If the alert occurs late in the 10-µs comparison window and is not large enough to average the entire window measurement up above the threshold level, the alert does not appear until the next 10-µs comparison window completes, assuming the input signal remains above the threshold for the entire duration.
Although the INA300-Q1 device is only able to measure current through a current-sensing resistor flowing in one direction, a second INA300-Q1 device can be used to create a bidirectional monitor.
With the input terminals of a second INA300-Q1 device reversed across the same current-sensing resistor, the second INA300-Q1 device is now able to detect current flowing in the other direction relative to the first device, as shown in Figure 35. The outputs of each INA300-Q1 device connect to an AND gate to detect if either of the limit threshold levels are exceeded. The output of the AND gate is high if neither overcurrent limit thresholds are exceeded. A low output state of the AND gate indicates that either the positive overcurrent limit or the negative overcurrent limit are surpassed.
Figure 36 illustrates two INA300-Q1 devices being used in a bidirectional configuration and an output control circuit to detect if one of the two alerts is exceeded.
The INA300-Q1 device can be used to create a window comparator function, detecting whether the current being monitored is within a programmed range or has fallen outside of the expected operating region.
Figure 37 shows how the window comparator function is setup using two INA300-Q1 devices. The input terminals of each INA300-Q1 device are connected to the same current-sensing resistor. The limit threshold for the top device is set to the upper limit of the window range. The bottom device limit threshold is set to the desired lower limit of the range. With a logic inverter placed at the output of the device monitoring the lower limit, the OCP– signal is high when the input signal is above the lower limit threshold. The OCP+ signal is high when the input signal is below the upper limit threshold. A high value at the output (output of the AND gate) indicates that the monitored current is operating within the desired window range.
|INPUT CONDITION||OUTPUT STATUS|
Figure 38 shows the output waveform from the device window comparator application. In Figure 38, the output signal is high when OCP– is low (the input signal is above the lower limit) and when OCP+ is high (the input signal is below the upper limit). If the signal rises above the upper limit or drops below the lower limit, the corresponding OCP output changes state, causing the state of the output (following the AND gate) to change to zero to indicate an out-of-range condition.