SA4101A South African Micro-Electronic Systems, SA4101A Datasheet - Page 11

• Manufacturer Part Number: SA4101A
• Description: Single Phase KWH Metering ic With Pulse Output
• Manufacturer: South African Micro-Electronic Systems

TYPICAL APPLICATION
In figure 10, the components required for a stand alone power
metering application, are shown. The application uses a shunt
resistor for the mains current sensing. The meter is designed
for 220V/40A operation.
The critical external components for the SA4101A integrated
circuit are the current sense resistors, the voltage sense
resistors as well as the bias setting resistor.
BIAS RESISTOR
R13 defines all on-chip and reference currents. With
R13=47kW, optimum conditions are set. Device calibration is
done on the voltage input of the device.
SHUNT RESISTOR
The voltage drop across the shunt resistor at rated current
should be at least 20mV. If a shunt resistor of 625µW is chosen
and a voltage of 25mV across the shunt is required at I
then the power dissipation in the current sensor is:
P = I R
CURRENT SENSE RESISTORS
The resistors R6 and R7 define the current level into the
current sense inputs of the device. The resistor values are
selected for an input current of 16µA on the current inputs of
the SA4101A at I
According to equation described in the Current Sense inputs
section:
R6 = R7 = (I
A resistor with value of 820W is chosen, the 5% deviation from
the calculated value will be compensated for when calculating
resistor values for the voltage path.
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SA4101A
=(40A)² x 625µW
= 1W.
2
= 40A / 16µA x 625µ/2
= 781.25W
L
/ 16µA) x R
MAX
.
SH
/2
MAX
11/16
VOLTAGE DIVIDER
The voltage divider is calculated for a voltage drop of 14V +
5%(14.7V). Equations for the voltage divider in figure 10 are:
R1 + R2 + R3 = RA and R12 || (R11+P1) = RB. Combining the
two equations gives:
(RA + RB) / 220V = RB / 14.7V
A 5k trimpot will be used in the voltage channel for meter
calibration. The center position on the pot is used in the
calculations. P1 = 2.5kW and values for resistors R11 = 22kW
and R12 =1MW are chosen.
Substituting the values will result in:
RB=23.91kW and RA=RB x (220V/14.7V - 1) resulting in
RA=333kW so the resistor values of R1, R2 and R3 are chosen
to be 110kW.
PROGRAMMING
The resistor values are calculated for a 40A rated meter. The
LED pulse rate must be set accordingly by programming pins
R0, R1 and R2. Using the Rated Conditions Select section,
pins R0 and R2 is set to VSS and R1 set to VDD. These
settings will configure the SA4101A for 220V/40A operation
with a LED pulse rate of 1600 pulses/kWh. The FAST pin is set
to VSS for STANDARD operation.
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