SDAA159 October   2025 XTR200

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Detailed Description
    1. 2.1 Current Measurement
    2. 2.2 Current Transmission
    3. 2.3 Additional Output Circuitry
    4. 2.4 Simulations
  6. 3Summary
  7. 4References

2.2 Current Transmission

In the current transmission portion, illustrated in Figure 2-3, the XTR200 converts the 0V to 2V output signal from the INA241A5 into a current output with a transfer function defined by the resistance between the SET pin and ground, called RSET. The XTR200 is an extremely convenient building block for this function because the device integrates two op amps, precision resistors, an output transistor, and diagnostic and protection features in an extremely small 2mm x 3mm WSON package [3].

An XTR200 Converts the Output Voltage of the INA241A5 into the Monitor Current Figure 2-3 An XTR200 Converts the Output Voltage of the INA241A5 into the Monitor Current

The M-CRPS standard requires the current monitor to have a user-selectable transfer function of either 10µA per Amp of output current or 0mA to 2mA representing 0% to 200% of rated output current. Therefore, at 100A of output current, the XTR200 delivers either 1mA (10µA/A) or 2mA indicating 200% of rated output current for a 2V input signal from the INA241A5. The RSET values for both cases can be calculated using Equation 1 and Equation 2.

Equation 1. R S E T = 10 * V I N I O U T = 10 * 2 V 1 m A = 20 k Ω
Equation 2. R S E T = 10 * V I N I O U T = 10 * 2 V 2 m A = 10 k Ω

Because two RSET values are required, an NMOS transistor is shown to switch in a second resistor in parallel with the first. Two, 20kΩ resistors can be used to produce either a 20kΩ or 10kΩ RSET value.

The output disable (OD) pin of the XTR200 can be used to place the output into a high-impedance state. The error flag (EF) pin exerts low in the event of a fault condition such as a short or open at the SET pin, or an over-temperature condition. It's important to note that while the XTR200 error flag normally indicates an open circuit load fault, the clamping circuitry placed after the XTR200 in this example schematic prevents detection of an open circuit fault. The IS and VG pins of the XTR200 are shorted together in Figure 3. These pins are for the use of an external transistor which is not necessary in this application. Shorting the pins together allows the internal output transistor of the XTR200 to deliver the current monitor signal.

Although the input offset voltage of the XTR200 (800µV, max) is larger than the INA241A5, this does not meaningfully degrade the precision of the circuit. The total input offset voltage of the signal path can be calculated by referring the XTR200 offset to the input of the INA241 and combining the two uncorrelated offsets as a root-sum-of-squares as shown in Equation 3:

Equation 3. V O S ( T o t a l ) = V o s ( I N A 241 ) 2 + V O S ( X T R 200 ) A V ( I N A 241 ) 2 = 8 μ V 2 + 800 μ V 200 V / V 2 = 8.94 μ V

This brings the total error in the current measurement to 89.4mA, or 1.8% at 10% rated output. This does not include the tolerance of the 100µΩ shunt resistor or the drift of the circuit over temperature.