13892 datasheet(102/161 Pages) FREESCALE

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Analog Integrated Circuit Device Data

102

Freescale Semiconductor

13892

FUNCTIONAL DEVICE OPERATION

ADC SUBSYSTEM

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

Amplifier Offset

-2.0

2.0

Sense Resistor

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

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

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

1 111 111 111

-2.346

-0.586

5.865

To charger connection

1 000 000 000

-1200

-300.0

3000

To charger connection

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