INA159 datasheet(31/51 Pages) TI2

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+Vs

-Vs

+Vs

-Vs

+Vs

Rg 5k

Vin

Temp

GND

Vout

Trim

U2 REF5025

Rset 2.5k

Rparasitic 5

V1 15

V2 15

Vout

RTD 100

Iset

Vset

VirtualGND

U1 OPA188

R2 1.5M

Ref

U4 INA826

Vref5025

+Vs

-Vs

INA826

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SBOS562G – AUGUST 2011 – REVISED JUNE 2020

Product Folder Links: INA826

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System Examples (continued)

Figure 71 shows an example of how the INA826 can be used for RTD signal conditioning. This circuit creates an

excitation current (ISET) by forcing 2.5 V from the REF5025 across RSET. The zero-drift, low-noise OPA188

creates the virtual ground that maintains a constant differential voltage across RSET with changing common-mode

voltage. This voltage is necessary because the voltage on the positive input of the INA826 fluctuates over

temperature as a result of the changing RTD resistance. Click the following link to download the TINA-TI file:

RTD Circuit.

Figure 71. RTD Signal Conditioning

The circuit in Figure 72 creates a precision current ISET by forcing the INA826 VDIFF across RSET. The input

voltage VIN is amplified to the output of the INA826 and then divided down by the gain of the INA826 to create

VDIFF. ISET can be controlled either by changing the value of the gain-set resistor RG, the set resistor RSET, or by

changing VOUT through the gain of the composite loop. Make sure that the changing load resistance RL does not

create a voltage on the negative input of the INA826 that violates the compliance of the common-mode input

range. Likewise, the voltage on the output of the OPA170 must remain compliant throughout the changing load

resistance for this circuit to function properly.

INA159 Datasheet(PDF) 31 Page - Texas Instruments

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