100µA

REF200

+5V

100µA

3 Wire

RTD

+5V

R3 78.7

INA326

Vout

R1

R2

+

±

REF200

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SBVS020B – SEPTEMBER 2000 – REVISED JULY 2015

8 Application and Implementation

NOTE

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.

8.1 Application Information

Applications for the REF200 are limitless. Application Bulletin AB-165 (SBOA046) shows additional REF200

circuits as well as other related current source techniques. In this section, a collection of circuits are shown to

illustrate some techniques.

If the current sources are subjected to reverse voltage, a protection diode may be required. A reverse voltage

circuit model of the REF200 is shown in Figure 6. If reverse voltage is limited to less than 6 V or reverse current

is limited to less than 350 µA, then no protection circuitry is required. A parallel diode (see (a) in Figure 17)

protects the device by limiting the reverse voltage across the current source to approximately 0.7 V. In some

applications, a series diode may be preferable (see (b) in Figure 17), because it allows no reverse current. This

configuration, however, reduces the compliance voltage range by one diode drop.

8.2 Typical Application

Figure 11 shows the schematic of a circuit that translates RTD resistance to a voltage level convenient for an

ADC input. The REF200 precision current reference provides excitation and an instrumentation amplifier scales

the signal. The design also uses a 3-wire RTD configuration to minimize errors due to wiring resistance.

Figure 11. RTD Resistance to Voltage Converter Schematic

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