LP3941A Datasheet, PDF (21/32 Pages) National Semiconductor (TI) – Cellular Phone Power Management Unit

ADC and Charger Programming
(Continued)
MUX-1
1
A/D Input Selection Code
MUX-0
Input
1
BATT-ID (200 µA Scale)
Charger Current Selection Code
Data Code
4h’01
I_SET (mA)
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
I_CHARGE (mA)
Output Code
0 4.97 … 1262 1267
h’00 h’01
h’fe
h’ff
Device Temperature +25˚C
I_CHARGE (mA)
Output Code
0 3.95 … 1003 1007
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
I_CHARGE (mA)
0 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 (kΩ) Scale 1 (200 µA) Scale 1 (20 µA)
Data Code Range 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
10
h’1e–h’31
15
h’32–h’49
22
h’4a–h’6d
33
h’6e–h’b0
55
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.
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