13892 datasheet(108/161 Pages) FREESCALE

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Analog Integrated Circuit Device Data

108

Freescale Semiconductor

13892

FUNCTIONAL DEVICE OPERATION

ADC SUBSYSTEM

a first order filtering of the signal across R1. Due to the sampling of the A to D converter and the filtering applied, the longer the

software waits before retrieving the information from the CC, the higher the accuracy. The capacitor will be connected between

the pins CFP and CFM, see Figure 31.

Figure 31. Coulomb Counter Block Diagram

The CC results are available in the 2's complement CCOUT[15:0] counter. This counter is preferably reflecting 1 Coulomb per

LSB. As a reminder, 1 Coulomb is the equivalent of 1 Ampere during 1 second, so a current of 20 mA during 1 hour is equivalent

to 72C. However, since the resolution of the A to D converter is much finer than 1C, the internal counts are first to be rescaled.

This can be done by setting the ONEC[14:0] bits. The CCOUT[15:0] counter is then increased by 1 with every ONEC[14:0] counts

of the A to D converter. For example, ONEC[14:0] = 000 1010 0011 1101 BIN = 2621 DEC yields 1C count per LSB of

CCOUT[15:0] with R1 = 20 mOhm.

The CC can be reset by setting the RSTCC bit. This will reset the digital blocks of the CC and will clear the CCOUT[15:0]

counter. The RSTCC bit gets automatically cleared at the end of the reset period which may take up to 40

μs. The CC is started

by setting the STARTCC bit. The CC is disabled by setting this bit low again. This will not reset the CC settings nor its counters,

so when restarting the CC with STARTCC, the count will continue.

When the CC is running it can be calibrated. An analog and a digital offset calibration is available. The digital portion of the

CC is by default permanently corrected for offset and gain errors. This function can be disabled by setting the CCCALDB bit.

However, this is not advisable.

In order to calibrate the analog portion of the CC, the CCCALA bit is set. This will disconnect the inputs of the CC from the

sense resistor and will internally short them together. The CCOUT[15:0] counter will accumulate the analog error over time. The

calibration period can be freely chosen by the implementer and depends on the accuracy required. By setting the ONEC[14:0] = 1

DEC this process is sped up significantly. By reading out the contents of the CCOUT[15:0] and taking into account the calibration

period, software can now calculate the error and account for it. Once the calibration period has finished the CCCALA bit should

be cleared again.

One optional feature is to apply a dithering to the A to D converter to avoid any error in the measurement due to repetitive

events. To enable dithering the CCDITHER bit should be set. In order for this feature to be operational, the digital calibration

should remain enabled, so the CCCALDB bit should not be set.

Table 98. Coulomb Counter Characteristics

Parameter

Condition

Min

Typ

Max

Unit

Sense resistor R1

Placed in Battery path of

Charger system

Sensed current

Through R1

±1.0

±3000

On consumption

CC active

μA

Resolution

1LSB Increment

381.47

μC

13892 Datasheet(PDF) 108 Page - Freescale Semiconductor, Inc

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