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PM9102APE

SINGLE PHASE POWER/ENERGY METERING MODULE PULSE OUTPUT

South African Micro Electronic Systems 

PM9102AP

5. Circuit Description

The Application Circuit (Figure 2) details the components required for the power

metering module, using a shunt resistor for current sensing.

In this application the device requires +2,5V, 0V, -2,5V DC supply.

The most important external components 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

signal to noise and stability performance. The tolerance should be within ± 10%.

C3 and C4 are the inner loop capacitors of the A/D converters. The optimum value

is 3.3nF. The actual values are uncritical. Values smaller than 0.5nF and larger

than 5nF should be avoided.

R , R and RSH are the resistors defining the current level into the current sense

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input. The values should be selected for an input current of 16µARMS into the SA9102

/ SA9602 at maximum line current.

Values for RSH of less than 200µS should be avoided.

R1 = R2 = (IL/16µARMS) * 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 .

RMS

R7 and P7 defines all on-chip bias and reference currents. With R7 + P7 = 24kS,

optimum conditions are set. R7 + P7 may be varied by ±10% for calibration

purposes. Any change to R7 + P7 will affect the output quadratically.

XTAL is a colour burst TV crystal (f = 3.5795MHz) for the oscillator. The oscillator

frequency is divided down to 1.7897MHz on-chip and supplies the A/D converters

and the digital circuitry.

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