SA9103C
TYPICAL APPLICATIONS
IntheApplicationCircuits(Figures1and2), thecomponentsrequiredforpowermetering
applications, are shown.
In Figure 1 a shunt resistor is used for current sensing. In this application, the circuitry
requires a +2.5V, 0V, -2.5V DC supply.
In the case of Figure 2, when using a current transformer for current sensing, a +5V, 0V
DC supply is sufficient for the circuit.
The most important external components for the SA9103C integrated circuit are:
C1 and C2 are the outer loop capacitors for the two integrated oversampling A/D
converters. The value of these capacitors is 560pF. The actual values determine the
signal to noise and stability performance. The tolerances should be within ±10%.
C3 andC4aretheinnerloopcapacitorsoftheA/Dconverters. Theoptimumvalueis3.3nF.
The actual values are uncritical. Values smaller than 0.5nF and larger than 5nF should
be avoided.
R1, R2 and RSH are the resistors defining the current level into the current sense input.
The values should be selected for an input current of 16µA into the SA9103C at rated line
current.
Values for RSH of less than 200µΩ should be avoided.
R1 = R2 = (IL/16µA) * RSH/2
Where IL
= Line current
RSH = Shunt resistor/termination resistor
R3, R6 and R4 set the current for the voltage sense input. The values should be selected
so that the input current into the voltage sense input (virtual ground) is set to 14µA.
R7 defines all on-chip bias and reference currents. With R7 = 24kΩ, optimum conditions
are set.
XTAL is a colour burst TV crystal (f = 3.5795MHz) for the oscillator. The oscillator
frequency is divided down to 1.7897MHz on-chip to supply the A/D converters and digital
circuitry.
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