LP3910 Datasheet, PDF (36/72 Pages) Texas Instruments – Power Management IC for Hard-Drive-Based Portable Media Players

LP3910
SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015
www.ti.com
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: [V_REFH,
2V_REFH]. 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: [V_REFH, 2*V_REFH]. A wider voltage range (2.6 V to 4.4 V) can be selected through I²C 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, R_SENSE.
A fixed portion of the battery charge current is mirrored over the R_SENSE as in Equation 3:
V_ISENSE = K × I_CHARGE × R_SENSE
(3)
where K is a ratio between the I_SENSE current and the charge current.
The battery charge current scalar transforms the voltage across the external ISENSE resistor to the [V_REFH, 2 ×
V_REFH] input voltage interval of the ADC.
VDD
ADC
1:4343
ISENSE
Rsense
Vbatt
Charge
control Loop
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 [V_REFH, 2 × V_REFH]. 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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