INA159 datasheet(27/51 Pages) TI2

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−10

−5

Input Voltage (V)

G071

−0.02

−0.01

0.01

0.02

Input Current (A)

G070

49.4 kW

49.4 k

INA826

= 1 +

INA826

= 10.4 kW

49.4 k

5.75

OUT

REF

G =

= 5.75

4.8 V

2.5 V

400 mV

R + R

V = V

= 4.167 kW

= V

G + V

OUT V

REF

R + R

= V

G + V

= (I

R )

G + V

OUT I

REF

INA826

www.ti.com

SBOS562G – AUGUST 2011 – REVISED JUNE 2020

Product Folder Links: INA826

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Typical Application (continued)

9.2.2 Detailed Design Procedure

There are two modes of operation for the circuit shown in Figure 63: current input and voltage input. This design

requires R1 >> R2 >> R3. Given this relationship, the current input mode transfer function is given by Equation 2.

where

•

G represents the gain of the instrumentation amplifier

(2)

The transfer function for the voltage input mode is shown by Equation 3.

(3)

R1 sets the input impedance of the voltage input mode. The minimum typical input impedance is 100 kΩ. This

value is selected for R1 because increasing the R1 value also increases noise. The value of R3 must be

extremely small compared to R1 and R2. 20 Ω for R3 is selected because that resistance value is much smaller

than R1 and yields an input voltage of ±400 mV when operated in current mode (±20 mA).

Equation 4 can be used to calculate R2 given VD = ±400 mV, VIN = ±10 V, and R1 = 100 kΩ.

(4)

The value obtained from Equation 4 is not a standard 0.1% value, so 4.12 kΩ is selected. R1 and R2 also use

0.1% tolerance resistors to minimize error.

The ideal gain of the instrumentation amplifier is calculated with Equation 5.

(5)

Using the INA826 gain equation, Equation 1, the gain-setting resistor value is calculated as shown by Equation 6.

(6)

10.4 kΩ is a standard 0.1% resistor value that can be used in this design. Finally, the output RC filter

components are selected to have a –3-dB cutoff frequency of 1 MHz.

9.2.3 Application Curves

Figure 64 and Figure 65 illustrate typical characteristic curves for Figure 63.

Figure 64. PLC Output Voltage vs Input Voltage

Figure 65. PLC Output Voltage vs Input Current

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