SA2002P
sames
AUTOMATIC DEVICE CONFIGURATION (BOOT UP)
During power up, registers containing configuration and
calibration information are updated from an external
EEPROM. The device itself never writes to the EEPROM so
any write protect features offered by manufacturer of
EEPROM's may be used to protect the configuration and
calibration constants of the meter. The device reloads its
configuration every 1193 seconds from the external EEPROM
in order to ensure correct operation of the meter. Every data
byte stored in the EEPROM is protected with a checksum byte
to ensure data integrity.
FUNCTIONAL DESCRIPTION
The SA2002P is a CMOS mixed signal Analog/Digital
integrated circuit, which performs power/energy calculations
across a power range of 1000:1, to an overall accuracy of
better than Class 1.
The integrated circuit includes all the required functions for
single phase power and energy measurement such as
oversampling A/D converters for the voltage and current sense
inputs, power calculation and energy integration. Internal
offsets are eliminated through the use of cancellation
procedures.
Various pulse outputs (MOP, MON and LED) are available.
The pulse rate on these pins follows the active power
consumption measured.
A 5V stepper motor may be driven directly from the SA2002P
by connecting it between the MOP and MON pins, alternatively
an impulse counter may be driven directly by connecting it
between MOP and V
SS
.
The SA2002P configures itself from an external low cost
EEPROM that contains all meter configuration and calibration
data. No external trimming is required. Calibration of the
device may be fully automated.
POWER CALCULATION
In Figure 9, the voltage drop across the shunt r
esistor should
be more than 16mV at rated load current. The voltage is
converted to current by means of resistors R
10
and R
11
. The
current sense input saturates at an input current of ±25µA
peak.
ELECTROSTATIC DISCHARGE (ESD)
PROTECTION
The SA2002P integrated circuit's input's/outputs are protected
against ESD.
POWER CONSUMPTION
The power consumption rating of the SA2002P integrated
circuit is less than 30mW.
V DD
IIP
CURRENT
SENSOR
INPUTS
VSS
VDD
A
I
IIN
VSS
The mains voltage (230VAC) is divided down through a divider
to
14V
RMS
. The current into the A/D converter input is set at
14µA
RMS
at nominal mains voltage, via resistor R
7
(1M
W)
.
See Device Configuration for more details on the processing of
measured energy to frequency outputs.
ANALOG INPUT CONFIGURATION
The input circuitry of the current and voltage sensor inputs are
illustrated in figure 3. These inputs are protected against
electrostatic discharge through clamping diodes.
VDD
IVP
VOLTAGE
SENSOR
INPUT
V SS
A
V
GND
DR-01288
The feedback loops from the outputs of the amplifiers A
I
and A
V
generate virtual shorts on the signal inputs. Exact duplications
of the input currents are generated for the analog signal
processing circuitry.
Figure 3: Analog input internal configuration
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