+

±

Load

+

-

Q1

2N3906

VOUT

ICHARGE

V

+

0.2

Ÿ

RSENSE

R1

2

NŸ

2

NŸ

R2

10

NŸ

R3

Copyright © 2016, Texas Instruments Incorporated

3

SENSE R

OUT

CHARGE

CHARGE

1

R

V

I

1

I

R

u

u

: u

16

LPV511

SNOSAG7D – AUGUST 2005 – REVISED AUGUST 2016

www.ti.com

Product Folder Links: LPV511

Submit Documentation Feedback

Copyright © 2005–2016, 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 LPV511 is fabricated with Texas Instrument's state-of-the-art VIP50C process.

8.2 Typical Applications

8.2.1 Battery Current Sensing

The rail-to-rail common mode input range and the very low quiescent current make the LPV511 ideal to use in

high-side and low-side battery current sensing applications. The high-side current sensing circuit in Figure 28 is

commonly used in a battery charger to monitor the charging current to prevent over charging. A sense resistor

RSENSE is connected to the battery directly.

Figure 28. High Side Current Sensing

8.2.1.1 Design Requirements

The high-side current-sensing circuit (Figure 28) is commonly used in a battery charger to monitor charging

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

requires an op amp with rail-to-rail input. The LPV511 ideal for this application because its common-mode input

range extends up to the positive supply.

8.2.1.2 Detailed Design Procedure

As seen in Figure 28, the ICHARGE current flowing through sense resistor RSENSE develops a voltage drop equal to

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

proportional to the VSENSE voltage.

The low-bias currents of the LPV511 cause little voltage drop through R2, so the negative input of the LPV551

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

The LPV511 will detect 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 LPV511 inverting input matches the

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

IG, a current proportional to ICHARGE, will flow according to the following relation to:

IG = VRSENSE / R1 = ( RSENSE × ICHARGE ) / R1

(1)