CS5460 datasheet(12/34 Pages) CIRRUS

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CS5460

DS279PP5

2.4 Pulse-Rate Output

As an alternative to reading the energy through the

serial port, the EOUT and EDIR pins provide a

simple interface with which signed energy can be

accumulated. Each EOUT pulse represents a prede-

termined magnitude of energy. The accompanying

EDIR level represents the sign of the energy. With

MCLK = 4.096 MHz, K = 1, and both ADC inputs

at their maximum DC values, the pulses will have

a frequency equal to that in the pulse rate register.

The following example illustrates how to calculate

the pulse-rate register contents for a given meter

design. Suppose that a single two-phase power

meter (Figure 3) is required to generate 500 impuls-

es/KWH at Ib = 20 ARMS and V = 230 VRMS. As-

sume that the maximum current is Imax = 100 ARMS

and the maximum voltage is Vmax= 300 VRMS. To

utilize the full dynamic range of the CS5460, the

sensor gains can be calculated as:

where kv and ki are the sensor gains for the voltage

and current, respectively. The CS5460 is assumed

to be in the 30 mVRMS range to allow for the use of

a shunt resistor.

The average Impulse Rate, IR, at the rated inputs is:

Since the pulse-rate register is defined in terms of

full-scale DC (0.25 V for the voltage channel and

0.05 V for the current channel in this case), IR will

need to be scaled before being placed in the

pulse-rate register. Define a voltage ratio, Rv, and

a current ratio, Ri, as:

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

Frequency (Hertz)

200

400

600

800

1000 1200 1400

1600 1800 2000

Figure 6. Voltage Input Filter Roll-off

-2.5

-2

-1.5

-1

-0.5

0.5

200

400

600

800

1000

1200

1400

1600

1800

2000

Frequency (Hertz)

Figure 7. Current Input Filter Roll-off

150mV

RM S

max

-----------------------------

2000

------------

30mV

RMS

ma x

--------------------------

300

µΩ

500 impulses

KWH

--------------------------------





()

1KW

1000W

------------------



 1H

3600s

--------------





0.639 impulses

------------------------------------

≅

0.25 Volt

vV Volt

-----------------------

0.05 Volt

iIb Amp

-----------------------

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