F

G

R

Gain

1

R

_

_

_

_

OUT MAX

OUT MIN

IN MAX

IN MIN

V

V

Gain

V

V

_

_

SHUNT MAX

SHUNT

LOAD MAX

V

100mV

R

100m

I

1A

:

OUT

LOAD

SHUNT

V

I

R

Gain

u

u

+

±

7.5k

100m

LOAD

360k

LM7705

5 V

OPA2156

11

OPA2156

www.ti.com

SBOS900 – SEPTEMBER 2018

Product Folder Links: OPA2156

Submit Documentation Feedback

Copyright © 2018, Texas Instruments Incorporated

8.2 Typical Application: Low-Side Current Measurement

Figure 4 shows a channel of the OPA2156 configured in a low-side current sensing application. For a full

analysis of the circuit shown in Figure 4 including theory, calculations, simulations, and measured data see the 0-

1A, single-supply, low-side, current sensing solution, see TIPD129.

Figure 4. OPA2156 in a Low-Side, Current-Sensing Application

8.2.1 Design Requirements

The design requirements for this design are:

•

Load current: 0 A to 1 A

•

Output voltage: 4.9 V

•

Maximum shunt voltage: 100 mV

8.2.2 Detailed Design Procedure

The transfer function of the circuit in Figure 4 is given in Equation 1:

(1)

0 A to 1 A. To keep the shunt voltage below 100 mV at maximum load current, the largest shunt resistor is

defined using Equation 2.

(2)

amplified by the OPA2156 to produce an output voltage of 0 V to 4.9 V. The gain needed by the OPA2156 to

produce the necessary output voltage is calculated using Equation 3:

(3)

(4)