Differential Input Voltage to INA213-Q1 (V)

-0.02

-0.01

0

0.01

0.02

0

500

1000

1500

2000

2500

3000

3500

4000

4500

D001

fs

sup ply

V

VREF

V

2

<

-

fs

V

VREF

2

>

fs

V

1.5V

= ±

fs

V

15mV

100

= ±

´

fs

diff

INA 214

V

VIN

G

=

´

ADS7828-Q1

SBAS456B – DECEMBER 2008 – REVISED JANUARY 2016

www.ti.com

Typical Applications (continued)

8.2.1.1 Design Requirements

For this design example, the ADS7828-Q1 device is paired with a current shunt monitor. Bi-directional current

monitoring is required when there is both charging and discharging. The requirements for this example are as

follows:

•

Voltage across current shunt varies –15 mV to 15 mV

•

5-V supply

•

3.3-V rail available as reference

8.2.1.2 Detailed Design Procedure

8.2.1.2.1

Part Selection

The INA214-Q1 device was selected because of the low offset and zero drift of the device. The ADS7828-Q1

device has a low noise floor, so it can support more of the gain. For this reason, the lowest gain option was

selected from the INA21x-Q1 family. The INA214-Q1 device has a gain of 50.

8.2.1.2.2

Full-Scale Differential Range

First, determine the full-scale differential range into the ADS7828-Q1 device.

(1)

(2)

(3)

8.2.1.2.3

Circuit Implementation

Because the ADS7828-Q1 device has a differential input, connect the reference voltage of the INA214-Q1 device

to the negative input terminal of the ADS7828-Q1 device. Because bi-directional current sensing is required in

this application, VREF must be chosen so that:

(4)

where

•

Vfs = 3 V

(5)

A 3.3-V reference is used for this example. Because the ADS7828-Q1 device is a differential input ADC, a

resistive divider can be used to generate the reference voltage because impedance effects on the INA214-Q1

device is canceled out by the ADS7828-Q1 device.

8.2.1.3 Application Curve

Figure 26. ADC Code vs Voltage Across Current-Shunt Resistor in Bi-Directional Current Sensing

Application

26

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