Datasheet

FUNCTIONAL DEVICE OPERATION
ADC SUBSYSTEM
Analog Integrated Circuit Device Data
Freescale Semiconductor 103
MC13892
The value of the sense resistor used, determines the accuracy of the result as well as the available conversion range. Note
that excessively high values can impact the operating life of the device due to extra voltage drop across the sense resistor.
CHANNEL 2 APPLICATION SUPPLY
The application supply voltage is read at the BP pin at channel 2. The battery voltage is first scaled as V(BP)/2 in order to fit
the input range of the ADC.
CHANNEL 3 CHARGER VOLTAGE
The charger voltage is measured at the CHRGRAW pin at channel 3. The charger voltage is first scaled in order to fit the input
range of the ADC. If the CHRGRAWDIV bit is set to a 1 (default), then the scaling factor is a divide by 5, when set to a 0 a divide
by 10.
CHANNEL 4 CHARGER CURRENT
The charge current is read by monitoring the voltage drop over the charge current sense resistor. This resistor is connected
between CHRGISNS and BPSNS. The voltage difference is first amplified to fit the ADC input range as V(CHRGISNS-BPSNS)*4.
The conversion is read out in a 2's complement format, see
Table 89. The positive reading corresponds to the current flow from
charger to battery, the negative reading to the current flowing into the charger terminal. Unlike the battery current and voltage
readings, the charger current readings are not interleaved with the charger voltage readings, so when RAND = 1 a total of 8
readings are executed. The conversion circuit is enabled by setting the CHRGICON bit to a one. If the CHRGICON bit is not set,
the ADC will return a 0 reading for channel 4.
The value of the sense resistor used determines not only the accuracy of the result as well as the available conversion range,
but also the charge current levels. It is therefore advised not to select another value than 100
mOhm.
Table 86. Battery Current Reading Specification
Parameter Condition Min Typ Max Units
Amplifier Gain
19 20 21
Amplifier Offset
-2.0 – 2.0 mV
Sense Resistor
– 20 – mOhm
Table 87. Application Supply Voltage Reading Coding
Conversion Code
ADDn[9:0]
Voltage at input
ADC in V
Voltage at BP
in V
1 111 111 111
2.400 4.800
1 000 010 101
1.250 2.500
0 000 000 000
0.000 0.000
Table 88. Charger Voltage Reading Coding
Conversion Code
ADDn[9:0]
Voltage at input
ADC in V
Voltage at CHGRAW in V,
CHRGRAWDIV = 0
Voltage at CHGRAW in V,
CHRGRAWDIV = 1
1 101 010 100 2.000 20.000 10.000
0 000 000 000 0.000 0.000 0.000
Table 89. Charge Current Reading Coding
Conversion Code
ADDn[9:0]
Voltage at input
ADC in mV
CHRGISNS – BPSNS in mV
Current through
100 mOhm in mA
Current Flow
0 111 111 111 1200 300.0 3000 To application/battery
0 000 000 001 2.4 0.586 5.865 To application/battery
0 000 000 000 0.0 0.0 0.0 -
1 111 111 111 -2.346 -0.586 5.865 To charger connection
1 000 000 000 -1200 -300.0 3000 To charger connection