AS8118
Single Phase Instantaneous Energy Metering IC
with On-Chip Calibration, Stepper Motor Drive and LED Output
DATA SHEET
Features
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Description
The AS8118 is a very accurate single-phase bi-directional
instantaneous
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 AS8118 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
AS8118 interfaces directly to a micro-controller.
The highly integrated AS8118 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
AGND
Buffer
VP
VN
Σ∆-mod
Digital
Filter
Power
Calculation
IP
IN
Σ∆-mod
Digital
Filter
VREF
XIN
XOUT
PROG
VDDD
VDDA
VSSD
VSSA
Extremely accurate, surpassing the accuracy
requirements of the IEC 1036 Specification less than
0.1% error over a 600 : 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
counters with a two phase stepper motor 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
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 AS8118
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 AS8118 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 AS8118 is available in either surface mount SOIC-18
or dual-in-line DIP-18 packages.
Block Diagram
Non-volatile
Calibration
Crystal
Osc
POR
CAL
Control
LED
MON
MOP
Figure 1
Block diagram of the AS8118
Revision 1.8, 15-Feb-05
DIRO
DIRI
TM
Page 1 of 30
Data Sheet AS8118
Typical Connection Circuit
Load
VDD (5V)
IP
VDDA VDDD
PROG
TM
IN
LED
Shunt
Calibration
Programming
LED Output
VN
CAL
VP
XIN
XOUT VSSA VSSD
DIRI
MOP
MON
DIRO
Calibration
Pulse Output
Stepper Motor
Outputs
VSS
Voltage
Regulator
VDD (5V)
VSS
N
L
Figure 2
Typical connection circuit for the AS8118
Pin Configuration
1
2
3
4
5
6
7
8
9
VP
VN
TM
VSSA
PROG
VSSD
DIRO
CAL
MOP
IN
IP
DIRI
VDDA
XIN
XOUT
VDDD
LED
MON
10
18
17
16
15
14
13
12
11
Figure 3
Pin configuration of the AS8118
Revision 1.8, 15-Feb-05
Page 2 of 30
Data Sheet AS8118
Pin Description
Pin No.
1
2
3
Pin Name
VP
VN
TM
Description
Positive input for the voltage channel. VP is a differential input with VN. The differential voltage
should be set at
±150mV
peak for rated voltage conditions. VP is an analog input pin.
Negative input for the voltage channel. VN is a differential input with VP. VN is usually tied to 0V
potential (VSSA). VN is an analog input pin.
On ‘power up’, the test mode input defines the operation mode of the device. Either ‘Normal
Operation’, or ‘Calibration’ modes may be selected. TM has an on-chip pull down resistor and
should be left unconnected during ‘Normal Operation’. TM must be set to logic ‘1’ at ‘power up’ to
set the device in ‘Calibration’ mode.
Negative analog supply. VSSA is the ground reference for the analog circuitry.
Programming pin for calibration procedure. PROG is an analog input pin which must be left
unconnected during normal operation. Note: PROG must not be connected to VSS.
Negative digital supply. VSSD is the ground reference for the digital circuitry.
Direction output provides indication of the direction of current flow through the current sensor.
This digital input/output has an on-chip pull down resistor and provides logic ‘0’ for positive
power and logic ‘1’ for negative power. DIRO is used as an input during the programming cycle.
This output may be directly connected to a LED and is capable of driving 4mA.
Fast energy pulse output for calibration. CAL pulse rate is programmable and dependent upon
the selected MON/MOP frequency.
Positive motor drive signal. MOP and MON are low frequency outputs for directly driving a two
phase stepper motor. The frequency of the MOP/MON outputs is programmable to suite all
industry standards and is capable of driving 10mA.
Negative motor drive signal. MON and MOP are low frequency outputs for directly driving a two
phase stepper motor. The frequency of the MOP/MON outputs is programmable to suite all
industry standards and is capable of driving 10mA.
This output may be connected to an LED to display energy consumption. LED is a digital output,
which is programmable to a desired pulse rate. All the industry standard pulse rates are
available. This output is capable of driving 10mA.
Positive digital supply. VDDD provides the supply voltage for the digital circuitry. The required
supply voltage is 5V
±10%.
See XIN below, for the connection of a crystal or ceramic resonator. When an external clock is
applied to XIN, XOUT is not connected.
A 3.579545 MHz crystal or ceramic resonator may be connected across XIN and XOUT without
the need for external load capacitors. Alternatively, an external clock signal may be applied to
XIN.
Positive analog supply. VDDA provides the supply voltage for the analog circuitry. The required
supply voltage is 5V
±10%.
Direction input pin for selecting unidirectional or bi-directional energy measurement mode. When
DIRI is at logic ‘0’, the IC is set in unidirectional mode. When DIRI is at logic ‘1’ the IC is in bi-
directional mode. In default mode, when DIRI is not connected, the IC is in bi-directional mode.
DIRI is a digital input with an on-chip pull-up resistor.
Positive input for the current channel. IP is a differential input with IN. The input gain is
programmable depending on the desired current sensor. The maximum differential voltage is
±150mV
peak (Gain = 4). IP is an analog input pin.
Negative input for the current channel. IN is a differential input with IP. The input gain is
programmable depending on the desired current sensor. IN is usually at 0V potential. IN is an
analog input pin.
4
5
6
7
VSSA
PROG
VSSD
DIRO
8
9
CAL
MOP
10
MON
11
LED
12
13
14
VDDD
XOUT
XIN
15
16
VDDA
DIRI
17
IP
18
IN
Revision 1.8, 15-Feb-05
Page 3 of 30
Data Sheet AS8118
AS8118 Performance Graphs
0,8
0,6
0,4
Error [%]
Error [%]
0,8
0,6
0,4
- 40°C
+ 85°C
+ 25°C
0,2
0
-0,2
-0,4
-0,6
-0,8
0,01
GAIN 16
0,2
0
-0,2
-0,4
-0,6
-0,8
0,01
GAIN 4
GAIN 20
0,1
1
I [A]
10
100
0,1
1
I [A]
10
100
Graph 1: Error as a % of reading for gain settings 4, 16 and 20 at 25°C
°
Graph 4: Error as a % of reading at temperature limits and PF = 0.5
0,8
0,6
0,4
Error [%]
0,2
0
-0,2
-0,4
-0,6
-0,8
0,01
- 40°C
+ 85°C
+ 25°C
0,8
0,6
0,4
VDD_5.0V
VDD_5.5V
Error [%]
0,2
0
-0,2
-0,4
-0,6
-0,8
0,01
VDD_4.5V
0,1
1
I [A]
10
100
0,1
1
10
100
I [A]
Graph 2: Error as a % of reading at temperature limits and PF = 1
Graph 5: Error as a % of reading with variation in VDD
0,8
0,6
0,4
Error [%]
0,2
0
-0,2
-0,4
-0,6
-0,8
0,01
0,1
1
I [A]
10
100
- 40°C
+ 85°C
+ 25°C
0,8
0,6
0,4
Error [%]
0,2
0
-0,2
-0,4
-0,6
-0,8
0,01
0,1
1
I [A
]
10
100
V_MAIN_184
V_MAIN_264.5
V_MAIN_230
Graph 3: Error as a % of reading at temperature limits and PF = 0.8
Graph 6: Error as a % of reading with mains voltage variation
Revision 1.8, 15-Feb-05
Page 4 of 30
Data Sheet AS8118
0 ,8
0 ,6
0 ,4
0 ,2
0
-0 ,2
-0 ,4
-0 ,6
-0 ,8
45
50
55
F [H z )
60
65
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:
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Current channel input gain
-
Calibration pulse output frequency
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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
11
10
01
00
Voltage
Gain
20
16
4
Input Voltage
-30mV
peak
≤V
IP
≤30mV
peak
-38mV
peak
≤V
IP
≤38mV
peak
-150mV
peak
≤V
IP
≤150mV
peak
Comments
Shunt mode
CT mode
CT mode
Revision 1.8, 15-Feb-05
Error [%]
Page 5 of 30
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