ATmega16HVB datasheet(109/273 Pages) ATMEL

109 / 273 page

109

8042A–AVR–07/09

ATmega16HVB/32HVB

In normal conversion mode two different output values are provided, Instantaneous Current and

Accumulate Current. The Instantaneous Current Output has a short conversion time at the cost

of lower resolution. The Accumulate Current Output provides a highly accurate current measure-

ment for Coulomb Counting.

The CC-ADC also provides a special Regular Current detection mode. This allows ultra-low

power operation in Power-save mode when small charge or discharge currents are flowing.

For offset cancellation the polarity of the input signal could be switched run time. Using this fea-

ture, the internal CC-ADC offset could be removed. See application note AVR352.

19.3

Normal Operation

When enabled the CC-ADC continuously measures the voltage over the external sense resistor

SENSE. Running in normal conversion mode, two data conversion outputs are provided.

• Instantaneous Conversion Result

• Accumulation Conversion Result

The Instantaneous Current conversion time is fixed to 3.9 ms (typical value) allowing the output

value to closely follow the input. After each Instantaneous Current conversion an interrupt is

generated if the interrupt is enabled. Data from conversion will be updated in the Instantaneous

Current registers CADICL and CADICH simultaneously as the interrupt is given. To avoid losing

conversion data, both the low and high byte must be read within a 3.9 ms timing window after

the corresponding interrupt is given. When the low byte register is read, updating of the Instanta-

neous Current registers and interrupts will be stopped until the high byte is read. Figure 19-2

shows an Instantaneous Current conversion diagram, where DATA4 will be lost because DATA3

reading is not completed within the limited period.

Figure 19-2. Instantaneous Current Conversions

The Accumulate Current output is a high-resolution, high accuracy output with programmable

conversion time selected by the CADAS bits in CADCSRA. The converted value is an accurate

measurement of the average current flow during one conversion period. The CC-ADC generates

an interrupt each time a new Accumulate Current conversion has finished if the interrupt is

enabled. Data from conversion will be updated in the Accumulation Current registers - CADAC0,

CADAC1, CADAC2 and CADAC3 simultaneously as the interrupt is given. To avoid losing con-

version data, all bytes must be read within the selected conversion period. When the lower byte

registers are read, updating of the Accumulation Current registers and interrupts will be stopped

until the highest byte is read. Figure 19-3 shows an Accumulation Current conversion example,

where DATA4 will be lost because DATA3 reading is not completed within the limited period.

Enable

Instantaneous

Interrupt

Instantaneous

Data

INVALID DATA

DATA 1

DATA 2

DATA 3

DATA 5

Read high byte

3.9 ms

~12 ms settling

7.8 ms

Read low byte

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