13892 datasheet(109/156 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

109

13892

FUNCTIONAL DEVICE OPERATION

ADC SUBSYSTEM

As follows from the previous description, using the CC requires a number of programming steps. A typical programming

example is given below.

1. SPI Access 1: Initialize

• Reg 9: Write STARTCC = 1, RSTCC = 1, CCCALA = 1, CCDITHER = 1, CCCALDB = 0

• RSTCC will be self clearing

• Register 10 is NOT to be programmed since by default the ONEC[14:0] scaler is set to 1

2. Wait for analog calibration period

3. SPI Access 2: Set scaler

• Reg 10: Write ONEC to desired value for CC use, for instance 2621DEC

4. SPI Access 3: Read analog offset and reset CC

• Reg 9: Write STARTCC = 1, RSTCC = 1, CCCALA = 0, CCDITHER = 1, CCCALDB = 0

• During the write access, on the MISO read line the most recent CCOUT[15:0] is available

• RSTCC will be self clearing

From this point on the ACC is running properly and CCOUT[15:0] reflects the accumulated charge. In order to be sure the

contents of the CCOUT[15:0] are valid, a CCFAULT bit is available. CCFAULT will be set '1' if the CCOUT content is no longer

valid, this means the bit gets set when a fault condition occurs and stays latched till cleared by software. There is no interrupt

associated to this bit. The following fault conditions are covered.

Counter roll over: CCOUT[15:0] = 8000HEX

This occurs when the contents of CCOUT[15:0] go from a negative to a positive value or vice versa. Software may interpret

incorrectly the battery charge by this change in polarity. When CCOUT[15:0] becomes equal to 8000HEX the CCFAULT is set.

The counter stays counting so its contents can still be exploited.

Battery removal: 'BP<UVDET'

When removing and replacing the battery, the contents of the counter are no longer valid. A battery removal is characterized

by the input supply to the IC dropping below the under voltage detect threshold, so BP<UVDET. To avoid false detection due to

short power cuts, the CCFAULT is set only after a long debounce of 1 second.

Battery removal when charging: BATTDETBS = 1

The battery removal detection as described previously, is not applicable when charging, since the charger will continue to

supply the application and the BP will not drop below UVDET. To still detect a battery removal, one can use the battery detect

function as described in the channel description earlier in this chapter. When the sense bit BATTDETBS becomes a 1, the

CCFAULT is set only after a long debounce of 1 second.

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