Copyright © 2016, Texas Instruments Incorporated

±

+

ICHARGE

±

+

RSENSE

0.2

2 k

Ÿ

2 k

Ÿ

R2

R1

Load

10 k

Ÿ

R3

VOUT

Q1

2N3906

V

+

SENSE

3

OUT

Ch arg e

Ch arg e

1

R

R

V

I

1

I

R

x

x

: x

19

LMV712-N, LMV712-N-Q1

www.ti.com

SNOS534J – FEBRUARY 2001 – REVISED NOVEMBER 2016

Product Folder Links: LMV712-N LMV712-N-Q1

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Copyright © 2001–2016, Texas Instruments Incorporated

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LMV712-N devices are dual op amps derived from the LMV711 single op amp. Figure 34 contains a

simplified schematic of one channel of the LMV712-N.

8.2 Typical Applications

8.2.1 High-Side Current-Sensing

Figure 34. High-Side, Current-Sensing Schematic

8.2.1.1 Design Requirements

The high-side, current-sensing circuit (Figure 34) is commonly used in a battery charger to monitor charging

current to prevent over charging. A sense resistor RSENSE is connected to the battery directly. This system

requires an op amp with rail-to-rail input. The LMV712-N is ideal for this application because its common-mode

input range goes up to the rail.

8.2.1.2 Detailed Design Procedure

As seen in (Figure 34), the ICHARGE current flowing through sense resistor RSENSE develops a voltage drop equal

to VSENSE. The voltage at the negative sense point is now less than the positive sense point by an amount

proportional to the VSENSE voltage.

The low-bias currents of the LMV712-N causes little voltage drop through R2, so the negative input of the

LMV712-N amplifier is at essentially the same potential as the negative sense input.

The LMV712-N detects this voltage error between its inputs and servo the transistor base to conduct more

current through Q1, increasing the voltage drop across R1 until the LMV712-N inverting input matches the

noninverting input. At this point, the voltage drop across R1 now matches VSENSE.