LP3910 datasheet(36/72 Pages) TI1

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ISENSE

Rsense

VDD

Vbatt

ADC

1:4343

Charge

control Loop

LP3910

SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015

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The ADC multiplexes 4 different sources:

1. The battery voltage

2. The battery charge current

3. External source ADC1

4. External source ADC2

The voltage ranges for the first two sources are scaled to match the input voltage interval of the ADC: [VREFH,

2VREFH]. This is accomplished by using two internal scalars.

8.3.5.1 Battery Voltage Measurement

The battery voltage scalar transforms the battery voltage ranging from 2.6 V to 3.5 V to the reference voltage

interval: [VREFH, 2*VREFH]. A wider voltage range (2.6 V to 4.4 V) can be selected through I

2C by setting the

voltage range bit D7 in register 0xA to 0’b1.

8.3.5.2 Battery Charge Current Measurement

The battery charge current is indirectly measured by measuring the voltage across the ISENSE resistor, RSENSE.

A fixed portion of the battery charge current is mirrored over the RSENSE as in Equation 3:

VISENSE = K × ICHARGE × RSENSE

(3)

where K is a ratio between the ISENSE current and the charge current.

The battery charge current scalar transforms the voltage across the external ISENSE resistor to the [VREFH, 2 ×

VREFH] input voltage interval of the ADC.

Figure 58. Battery Charge Scalar

8.3.5.3 External General-Purpose Sources

Two additional ADC sources are available on the ADC1 and ADC2 pins of the LP3910. These two external ADC

sources are not internally scaled and have an input voltage range of [VREFH, 2 × VREFH]. The system designer can

use these two sources for general-purpose applications such as resistive keyboard matrix scanning, temperature

measurements, battery load current, battery ID resistor measurement, and others.

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LP3910 Datasheet(PDF) 36 Page - Texas Instruments