SA2002H
Bias Resistor
DIR. Note that the DIR output is not available in the PDIP8
package type.
R12 defines all on-chip and reference currents. Optimum
conditions are set by using R12=24k. Device calibration is
done on the voltage input of the device.
Shunt Resistor
…
VMAINS
t
The voltage drop across the shunt resistor at rated current
should be at least 20mV. A shunt resistor with a value of
625μis chosen. The voltage drop across the shunt resistor
is therefore 25mV at rated conditions (IMAX). The maximum
power dissipation in the current sensor is:
…
ILINE
t
푃 = 40퐴 ꢂ × 625휇Ω = 1푊
(
)
…
Current Sense Resistors
DIR
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 16μARMS on the current inputs
of the SA2002H at rated conditions. According to equation
described in the Current Sense Inputs section:
Figure 8: Behaviour of direction output DIR
Mains Zero Crossing Indication (FMO)
The square wave signal of FMO indicates the polarity of the
mains voltage. Due to comparator offsets, the FMO low to
high transition can occur within a range as shown in Figure 9.
The time between successive low to high transitions will be
equal to the mains voltage period. Note that the FMO output
is not available in the PDIP8 package type.
퐼퐿
푅푆퐻
2
40퐴 625휇Ω
푅6 = 푅7 =
×
=
×
= 781.25Ω
16휇퐴
16휇퐴
2
A resistor with value of 820 is chosen, the 5% deviation from
the calculated value will be compensated for when calculating
resistor values for the voltage path.
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:
VMAINS
t
푅퐴 = 푅1 + 푅2 + 푅3
(
)
푅퐵 = 푅11 || 푅10 + 푃1
Combining the two equations gives:
FMO
(
)
푅퐴 + 푅퐵
푅퐵
=
220ꢃ
14.7
tMAINS
Figure 9: Mains zero crossings on FMO
A 5k trimpot will be used in the voltage channel for meter
calibration. The center position on the pot is used in the
calculations. Therefore P1=2.5k and values for resistors
R10=22kand R11=1M are chosen.
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 IMAX operation. The most important
external components for the SA2002H integrated circuit are
the current sense resistors, the voltage sense resistors as
well as the bias setting resistor.
Substituting the values will result in RB=23.91k and
RA=334k. Therefore R1, R2 and R3 are chosen to be
110k.
SPEC-3116 (REV. 9)
29-09-2017
7/11
SAMES [ SAMES ]
