LP3941A datasheet(21/32 Pages) NSC

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ADC and Charger Programming

(Continued)

A/D Input Selection Code

MUX-1

MUX-0

Input

BATT-ID (200 µA Scale)

Charger Current Selection Code

Data Code

SET (mA)

4h’01

530

4h’02

574

4h’03

617

4h’04

660

4h’05

703

4h’06

746

4h’07

789

4h’08

832

4h’09

874

The following table is the conversion table for main battery

charger current measurement using the on-chip ADC. Tem-

perature dependency is due to the temperature coefficient of

the aluminum sense resistor. The ADC itself is temperature

compensated as is the charging current in the main battery

charger.

A/D Converter’s Charge Current Output Code

ADC Control Register Code 2h’0X

Device Temperature −40˚C

CHARGE (mA)

4.97

…

1262

1267

Output Code

h’00

h’01

h’fe

h’ff

Device Temperature +25˚C

CHARGE (mA)

3.95

…

1003

1007

Output Code

h’00

h’01

h’fe

h’ff

A/D Converter’s Charge Current Output Code

ADC Control Register Code 2h’0X

Device Temperature +85˚C

CHARGE (mA)

3.27

…

831

834

Output Code

h’00

h’01

h’fe

h’ff

The next table shows the relationship between ADC output

code and main battery voltage in ADC Battery Voltage Mea-

surement Mode.

A/D Converter’s Battery Voltage Output Code

ADC Control Register Code 2h’0X

Battery Voltage (V)

3.000

3.006

…

4.494

4.500

Output Code

h’00

h’01

h’fe

h’ff

The battery ID resistor value can be determined using the

following table in the two ADC Battery ID Modes.

Battery ID Detection Code

ADC Control Register Code 2h’0X

ID Resistor (k

Ω) Scale 1 (200 µA)

Data Code Range

Scale 1 (20 µA)

Data Code Range

0.22

h’00–h’12

0.75

h’13–h’32

1.8

h’33–h’65

3.3

h’66–h’a7

5.1

h’a8–h’ff

h’1e–h’31

h’32–h’49

h’4a–h’6d

h’6e–h’b0

h’b1–h’ff

ADC Block Functional Diagram

The ADC block provides four different functions on the LP3941A:

•

Main battery voltage measurement

•

Main battery charger charging current measurement

•

Battery ID resistor resistance measurement with 200 µA sense current

•

Battery ID resistor resistance measurement with 20 µA sense current

The following picture shows the implementation of these measurements with the ADC.

LP3941A Datasheet(PDF) 21 Page - National Semiconductor (TI)

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