10.2.1.2.1 Shunt Resistor

As illustrated in Figure 10-2, the value of VSHUNT is the ground potential for the system load. If the value of

VSHUNT is too large, issues may arise when interfacing with systems whose ground potential is actually 0 V. Also,

a value of VSHUNT that is too negative may violate the input common-mode voltage of the differential amplifier

in addition to potential interfacing issues. Therefore, limiting the voltage across the shunt resistor is important.

Equation 6 can be used to calculate the maximum value of RSHUNT.

(max)

LOAD

(max)

SHUNT

(max)

SHUNT

I

V

R

(6)

Given that the maximum shunt voltage is ±25 mV and the load current range is ±2.5 A, the maximum shunt

resistance is calculated as shown in Equation 7.

:

m

10

A

5

.

2

mV

25

I

V

R

(max)

LOAD

(max)

SHUNT

(max)

SHUNT

(7)

To minimize errors over temperature, select a low-drift shunt resistor. To minimize offset error, select a shunt

resistor with the lowest tolerance. For this design, the Y14870R01000B9W resistor is used.

10.2.1.2.2 Differential Amplifier

The differential amplifier used for this design should have the following features:

1. Single-supply (3 V),

2. Reference voltage input,

3. Low initial input offset voltage (VOS),

4. Low-drift,

5. Fixed gain, and

6. Low-side sensing (input common-mode range below ground).

For this design, a current-shunt monitor (INA213) is used. The INA21x family topology is shown in Figure 10-3.

The INA213B specifications can be found in the INA213 product data sheet.

-

+

IN-

IN+

REF

GND

V+

OUT

Copyright © 2017, Texas Instruments Incorporated

Figure 10-3. INA21x Current-Shunt Monitor Topology

The INA213B is an excellent choice for this application because all the required features are included. In

general, instrumentation amplifiers (INAs) do not have the input common-mode swing to ground that is essential

for this application. In addition, INAs require external resistors to set their gain, which is not desirable for low-drift

applications. Difference amplifiers typically have larger input bias currents, which reduce solution accuracy at

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SBOS600E – JULY 2018 – REVISED FEBRUARY 2022

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