Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 5 of 30

-0 , 8

-0 , 6

-0 , 4

-0 , 2

0

0, 2

0, 4

0, 6

0, 8

F [ H z )

4 5

50

55

65

60

Graph 7: Error as a % of reading with mains frequency variation

Functional Description

The AS8118 is a CMOS mixed signal integrated circuit that measures electrical power over a dynamic range of 600:1, to an

accuracy of better than 0.1%.

The AS8118 comprises of standard functional blocks including two sigma/delta modulators, which convert the analog voltage

and current input signals into digital signals. The voltage and current signals are then digitally filtered, which eliminates

offsets thus enabling a single point calibration cycle. A power calculation block calculates the active energy value. An on-chip

voltage reference (

±30ppm/K typical), oscillator and non-volatile calibration registers and control block for programming the

AS8118 completes the core functional elements.

Programming of the AS8118 enables the device to be configured to suite the users specific input and output requirements

and allows for fast and efficient calibration. The AS8118 device provides the user with two complete opportunities to

programme the device. The following parameters may be programmed via the on-chip non-volatile memory:

-

Current channel input gain

-

Calibration pulse output frequency

-

Stepper motor output drive frequency

-

LED output frequency

-

Anti-creep threshold

-

Calibration constant

A detailed description of the versatility of the AS8118 is given below.

Current Inputs for Energy Calculation

The current channel input consisting of inputs IP and IN is differential and connected to a low resistance shunt or current

transformer, in series with the load. The current input signal level may be programmed by means of an on-chip

programmable gain amplifier (PGA). The gain is selected through the programming of 2 bits in the on-chip memory as

follows:

Parameter: Gain

Setting

Voltage

Gain

Input Voltage

Comments

1 1

20

Shunt mode

1 0

0 1

16

CT mode

0 0

4

CT mode