10.1.1 Basic Connections

Figure 27 shows the basic connections of the INA200-Q1, INA201-Q1, and INA202-Q1. Connect the input pins, V_IN+ and V_IN–, as close as possible to the shunt resistor to minimize any resistance in series with the shunt resistance.

Stability requires the use of power-supply bypass capacitors. Applications with noisy or high-impedance power supplies may require additional decoupling capacitors to reject power-supply noise. Connect bypass capacitors close to the device pins.

Figure 27. INA200-Q1 Basic Connections

10.1.2 Selecting R_S

The value chosen for the shunt resistor, R_S, depends on the application and is a compromise between small-signal accuracy and maximum permissible voltage loss in the measurement line. High values of R_S provide better accuracy at lower currents by minimizing the effects of offset, whereas low values of R_S minimize voltage loss in the supply line. Most applications attain best performance with an R_S value that provides a full-scale shunt voltage range of 50 mV to 100 mV. Maximum input voltage for accurate measurements is 500 mV, but output voltage is limited by supply.

10.1.3 Input Filtering

An obvious and straightforward location for filtering is at the output of the INA20x-Q1 series; however, this location negates the advantage of the low output impedance of the internal buffer. The only other option for filtering is at the input pins of the INA20x-Q1, but the internal 5-kΩ + 30% input impedance complicates input filtering, as illustrated in Figure 28. Use the lowest possible resistor values to minimize both the initial shift in gain and effects of tolerance. Equation 1 gives the effect on initial gain:

Equation 1.

Figure 28. Input Filter

To calculate the total effect on gain error, replace the 5-kΩ term with 5 kΩ – 30%, (or 3.5 kΩ) or 5 kΩ + 30% (or 6.5 kΩ). One can also be insert the tolerance extremes of R_FILT into the equation. If using a pair of 100-Ω 1% resistors on the inputs, the initial gain error is 1.96%. Worst-case tolerance conditions always occur at the lower excursion of the internal 5-kΩ resistor (3.5-kΩ), and the higher excursion of R_FILT + 3% in this case.

Note that one must then combine the specified accuracy of the INA20x-Q1 in addition to these tolerances. Although this discussion treated worst-case accuracy conditions by combining the extremes of the resistor values, it is appropriate to use geometric-mean or root-sum-square calculations to total the effects of accuracy variations.

10.1.4 Accuracy Variations as a Result of V_SENSE and Common-Mode Voltage

The accuracy of the INA20x-Q1 current-shunt monitors is a function of two main variables: V_SENSE (V_IN+ – V_IN–) and common-mode voltage, V_CM, relative to the supply voltage, V_S. The expression for V_CM is (V_IN+ + V_IN–) / 2; however, in practice, V_CM is effectively the voltage at V_IN+ because the voltage drop across V_SENSE is usually small.

This section addresses the accuracy of these specific operating regions:

• Normal Case 1: V_SENSE ≥ 20 mV, V_CM ≥ V_S
• Normal Case 2: V_SENSE ≥ 20 mV, V_CM < V_S
• Low V_SENSE Case 1: V_SENSE < 20 mV, –16 V ≤ V_CM < 0
• Low V_SENSE Case 2: V_SENSE < 20 mV, 0V ≤ V_CM ≤ V_S
• Low V_SENSE Case 3: V_SENSE < 20 mV, V_S < V_CM ≤ 80 V

10.1.4.1 Normal Case 1: V_SENSE ≥ 20 mV, V_CM ≥ V_S

This region of operation provides the highest accuracy. Here, use of a two-step method characterizes and measures the input offset voltage. First, Equation 2 determines the gain.

Equation 2.

where:

V_OUT1 = output voltage with V_SENSE = 100 mV

V_OUT2 = output voltage with V_SENSE = 20 mV

Then the offset voltage is measured at V_SENSE = 100 mV and referred to the input (RTI) of the current shunt monitor, as shown in Equation 3.

Equation 3.

In the Typical Characteristics, Figure 6 (Output Error versus Common-Mode Voltage curve) shows the highest accuracy for the this region of operation. In this plot, V_S = 12 V; for V_CM ≥ 12 V, the output error is at its minimum. Using this case also creates the V_SENSE ≥ 20 mV output specifications in the Electrical Characteristics: Current-Shunt Monitor table.

10.1.4.3 Low V_SENSE Case 1: V_SENSE < 20 mV, –16 V ≤ V_CM < 0 V; and
Low V_SENSE Case 3: V_SENSE < 20 mV, V_S < V_CM ≤ 80 V

Although not designed for accurate operation in either of these regions, the INA20x-Q1 family of devices may have exposure to these conditions in some applications. For example, when monitoring power supplies being switched on and off with V_S still applied to the INA20x-Q1, it is important to know what the device behavior is in these regions.

As V_SENSE approaches 0 mV, in these V_CM regions, the device output accuracy degrades. A larger-than-normal offset can appear at the current shunt monitor output with a typical maximum value of V_OUT = 300 mV for V_SENSE = 0 mV. As V_SENSE approaches 20 mV, V_OUT returns to the expected output value with accuracy, as specified in the Electrical Characteristics: Current-Shunt Monitor. Figure 29 illustrates this effect using the INA202-Q1 (gain = 100).

Figure 29. Example for Low V_SENSE Cases 1 and 3 (INA202-Q1, Gain = 100)

10.1.4.4 Low V_SENSE Case 2: V_SENSE < 20 mV, 0 V ≤ V_CM ≤ V_S

This region of operation is the least accurate for the INA20x-Q1 family. To achieve the wide input common-mode voltage range, these devices use two op amp front ends in parallel. One op amp front end operates in the positive-input common-mode voltage range, and the other in the negative-input region. For this case, neither of these two internal amplifiers dominates, and overall loop gain is very low. Within this region, V_OUT approaches voltages close to linear operation levels for normal case 2. This deviation from linear operation becomes greatest the closer V_SENSE approaches 0 V. Within this region, as V_SENSE approaches 20 mV, device operation is closer to that described by normal case 2. Figure 30 illustrates this behavior for the INA202-Q1. To test the V_OUT maximum peak for this case, maintain a constant V_S, set V_SENSE = 0 mV, and sweep V_CM from 0 V to V_S. The exact V_CM at which V_OUT peaks during this test varies from part to part, but the tested V_OUT maximum peak for any part is less than the specified V_OUT test limit.

Figure 30. Example for Low V_SENSE Case 2 (INA202-Q1, Gain = 100)

10.1.5 Transient Protection

The –16-V to +80-V common-mode range of the INA20X-Q1 is ideal for withstanding automotive fault conditions, ranging from 12-V battery reversal up to 80-V transients, because there is need for additional protective components up to those levels. In the event that the INA20x-Q1 are exposed to transients on the inputs in excess of their ratings, then external transient absorption with semiconductor transient absorbers (such as Zeners) is necessary. Do not use metal-oxide varistors (MOVs) or voltage-dependent resistors (VDRs) except when they are used in addition to a semiconductor transient absorber. Select the transient absorber such that it never allows exposure of the INA20X-Q1 to transients greater than 80 V (that is, allow for transient absorber tolerance, as well as additional voltage due to transient absorber dynamic impedance). Despite the use of internal zener-type ESD protection, the INA20x-Q1 do not lend themselves to using external resistors in series with the inputs, because the internal gain resistors can vary up to ±30%. (If gain accuracy is not important, then one can add resistors in series with the INA20x-Q1 inputs with two equal resistors on each input.)

10.2.1 Low-Side Switch Overcurrent Shutdown

The INA20x-Q1 measures current through a resistive shunt with current flowing in one direction, thus enabling detection of an overcurrent event only when the differential input voltage exceeds the threshold limit. When the current reaches the set limit of the divider R₁ / R₂, the output of CMP_OUT transitions high and Q1 turns on and pull the gate of the Pass-FET low and turn off the flow off current.

NOTE: In this case, Q1 is used to invert the comparator output.

Figure 31. Low-Side Switch Overcurrent Shutdown

10.2.1.3 Application Curves

Figure 32. Low-Side Switch Overcurrent Shutdown Response

10.2.2 High-Side Switch Overcurrent Shutdown

Figure 33 shows the basic connection for a high-side, switch overcurrent shutdown application. The high-side PMOS switch disconnects when an overcurrent event occurs. The previous Detailed Design Procedure section describes how to apply this application example. The difference is that the current is sensed on the high side of the bus in this application, and the low side of the bus in the previous application example.

NOTE: Q cascodes the comparator output to drive a high-side FET (the 2N3904 shown is good up to 60 V). The shunt can be located in any one of the three locations shown. Use the latching capability in shutdown applications to prevent oscillation at the trip point.

Figure 33. High-Side Switch Overcurrent Shutdown

10.2.3 Bidirectional Overcurrent Comparator

Figure 34 shows the basic connection for a bidirectional overcurrent comparator using two INA20x-Q1 devices of the same gain.

NOTE: It is possible to set different limits for each direction.

Figure 34. Bidirectional Overcurrent Comparator