AS8218 datasheet(19/123 Pages) AMSCO

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Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 19 of 123

Independent calibration of the voltage (cal_v) and current signals (cal_i1 and cal_i2) is done after the voltage

and current signals are provided for power calculation. This ensures that calibration of the voltage (sos_v),

current channel 1 (sos_i1), current channel 2 (sos_i2) has no influence on the power (np) calibration.

The iMux (current multiplexer) allows the selection of the applicable current for power calculation (sel_i), while

the vMux (voltage multiplexer) allows the selection of either the mains voltage data, or a constant voltage

value, vconst (sel_v). The multiplication of the appropriately selected voltage and current signals is then

performed.

After multiplication, the next multiplexer (sel_p) enables the selection of either instantaneous power or real

power, which is filtered through a low pass filter, PLP. The direction indicator output (diro) is derived from the

output of the power low pass filter (PLP).

The following multiplexer (creep) allows the selection of the power signal, or blocks the power signal,

depending on the required anti-creep and starting current thresholds, which may be set in the microcontroller.

Only when constant voltage value (vconst) is selected by the vMux (voltage multiplexer) or when diro=1, it is

necessary to derive the absolute power value, for measurement (Abs).

The first pulse generator (Fast Pulse Gen) produces fast internal pulses, with the number of pulses being

proportional to the measured energy. The multiplexer enables the selection of the appropriate pulse level

(pulselev_i1 or pulselev_i2) depending on the current being used for energy measurement (sel_i). The output

of the Fast Pulse Gen is always directly proportional to the LED pulse output, generated in the LED Pulse Gen.

The LED output pulse rate is selectable (mconst). The polarity of the LED output pulses is also selectable

(ledpol).

To ensure that the power data transferred to the microcontroller (MCU) is identical to that of the LED pulses,

the power accumulator (P_ACCU) counts the pulses generated by the Fast Pulse Gen. After a defined number

of sampling periods (nsamp), an interrupt is sent to the MCU, for the MCU to collect the accumulated energy

data.

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