Revision 1.2, 11-Feb-05 Page 1 of 30
Features
- Extremely accurate, surpassing the accuracy
requirements of the IEC1036 Specification with less
than 0.1% error over a 1000 : 1 dynamic range
- On-chip programmable current input gain suitable for
use with low-resistance shunt resistor or current
transformer
- On-chip programming for output pulse rate selection.
- On-chip calibration eliminates the need for an external
resistor network or trim-potentiometer
- Programmable on-chip creep prevention under no-load
condition
- All on-chip programmable functions may be
reprogrammed a second time
- Outputs directly drive an electromechanical counter or
a two phase stepper motor counter and consumption
LED indicator
- Fast calibration pulse output for high speed manual or
automated calibration
- On-chip voltage reference and power supply
monitoring
- Bi-directional or unidirectional energy measurement,
with direction indication output available
Description
The AS8168 is a very accurate single-phase bi-directional
average energy measurement integrated circuit, which
surpasses all the accuracy requirements for IEC1036
alternating current static watt-hour meters. The measured
energy is converted into pulses with the number of output
pulses being proportional to the measured energy.
The AS8168 is ideal for use in ‘stand alone’ kWh meter
applications, where the IC directly drives an
electromechanical counter with a two-phase stepper
motor, or for more complex meter applications, the
AS8168 interfaces directly to a micro-controller.
The highly integrated AS8168 design includes all the
required functional blocks. The blocks comprise of analog
to digital converters (ADC) for the voltage and current
channels, digital filters, a digital signal processing block, a
control block and non-volatile calibration memory for the
on-chip programming. The on-chip programming enables
the setting of the current input gain, the anti-creep
threshold, the output pulse rates and the system
calibration. The high level of integration ensures a
minimum number of non-critical external components are
required.
The on-chip anti-creep circuit ensures that the AS8168
does not output pulses when the meter is in a no-load
condition and that the IEC1036 anti-creep test
requirements are fully complied with, for both direct or
transformer connection meters.
The AS8168 offers three different pulse outputs. A stepper
motor drive output for directly driving a stepper motor
display, a LED output for energy consumption indication
and a dedicated high frequency output for fast single point
system calibration.
The AS8168 is available in either surface mount SOIC-18
or dual-in-line DIP-18 packages.
Block Diagram
Σ∆-mod
VREF
Digital
Filter
Control
Power
Calculation
CAL
VS
SD
VDDD
IP
VP
Σ∆-mod
Crystal
Osc
Non-volatile
Calibration
PRO
G
VS
SA
V
DDA
TM
XIN
XOUT
DIRI
DI
RO
POR
AGND
Buffer
IN
LED
Digital
Filter
MON
MOP
VN
Figure 1 Block diagram of the AS8168
AS8168
Single Phase Average Energy Metering IC
with On-Chip Calibration, Stepper Motor Drive and LED Output DATA SHEET