LPV521 datasheet(24/34 Pages) TI1

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10:

VOUT

LOAD

2N2907

RSENSE

24.9 k:

10 M:

ICHARGE

VOUT =

X ICHARGE

RSENSE X R3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

VSENSOR (mV)

C001

LPV521

SNOSB14D – AUGUST 2009 – REVISED DECEMBER 2014

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Typical Applications (continued)

8.2.2.3 Application Curve

Figure 67. Calculated Oxygen Sensor Circuit Output (Single 5V Supply)

8.2.3 High-Side Battery Current Sensing

Figure 68. High-Side Current Sensing

8.2.3.1 Design Requirements

The rail-to-rail common mode input range and the very low quiescent current make the LPV521 ideal to use in

high-side and low-side battery current sensing applications. The high-side current sensing circuit in Figure 68 is

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

resistor RSENSE is connected in series with the battery.

8.2.3.2 Detailed Design Procedure

The theoretical output voltage of the circuit is VOUT = [ ®SENSE × R3) / R1 ] × ICHARGE. In reality, however, due to

the finite Current Gain,

β, of the transistor the current that travels through R3 will not be ICHARGE, but instead, will

α × ICHARGE or β/( β+1) × ICHARGE. A Darlington pair can be used to increase the β and performance of the

measuring circuit.

Using the components shown in Figure 68 will result in VOUT ≈ 4000 Ω × ICHARGE. This is ideal to amplify a 1 mA

ICHARGE to near full scale of an ADC with VREF at 4.1 V. A resistor, R2 is used at the noninverting input of the

amplifier, with the same value as R1 to minimize offset voltage.

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