INA821 datasheet(31/41 Pages) TI1

31 / 41 page

= V

G + V

OUT V

REF

R + R

= V

G + V

= (I

R )

G + V

OUT I

REF

RG = 10.4 NŸ

R3 =

R2 = 4.17 NŸ

R1 = 100 NŸ

INA821

VOUT

±10 V

±20 mA

2.5 V ± 2.3 V

+VS

-VS

REF

15 V

REF5025

1 F

VOUT

VIN

GND

1 F

15 V

-15 V

-IN

+IN

OUT

INA821

www.ti.com

SBOS893A – AUGUST 2018 – REVISED DECEMBER 2018

Product Folder Links: INA821

Submit Documentation Feedback

9.2 Typical Application

Figure 69 shows a three-pin programmable-logic controller (PLC) design for the INA821. This PLC reference

design accepts inputs of ±10 V or ±20 mA. The output is a single-ended voltage of 2.5 V ±2.3 V (or 200 mV to

4.8 V). Typically, PLCs have these input and output ranges.

Figure 69. PLC Input (±10 V, 4 mA to 20 mA)

9.2.1 Design Requirements

For this application, the design requirements are:

•

4-mA to 20-mA input with less than 20-

Ω burden

•

±20-mA input with less than 20-

Ω burden

•

±10-V input with impedance of approximately 100 k

Ω

•

Maximum 4-mA to 20-mA or ±20 mA burden voltage equal to ±0.4 V

•

Output range within 0 V to 5 V

9.2.2 Detailed Design Procedure

There are two modes of operation for the circuit shown in Figure 69: current input and voltage input. This design

requires R1 >> R2 >> R3. Given this relationship, Equation 3 calculates the current input mode transfer function.

where

•

G represents the gain of the instrumentation amplifier

•

VD represents the differential voltage at the INA821 inputs

•

VREF is the voltage at the INA821 REF pin

•

IIN is the input current

(3)

Equation 4 shows the transfer function for the voltage input mode.

where

•

VIN is the input voltage

(4)

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

value is 100 kΩ because increasing the R1 value increases noise. The value of R3 must be small compared to R1

and R2. The value of R3 is 20 Ω because that resistance value is smaller than R1 and yields an input voltage of

±400 mV when operating in current mode (±20 mA).

INA821 bảng dữ liệu(PDF) 31 Page - Texas Instruments

INA821 bảng dữ liệu(HTML) 31 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

bảng dữ liệu tải về

Link URL