CS5461A datasheet(19/44 Pages) CIRRUS

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CS5461A

DS661F2

EXAMPLE #2:

The required number of pulses per unit energy present

on E1 is specified to be 500 pulses per kWhr, given that

the line voltage is 250 Vrms and the line current is

20 Arms. In such a situation, the stated line voltage and

current do not determine the appropriate PulseRateE1,2

setting. To achieve full-scale readings in the instanta-

neous voltage and current registers, a 250 mV, DC-lev-

el signal is applied to the channel inputs.

As in example #1, the voltage and current channel gains

are 10x, and the voltage level at the channel inputs will

be 150 mV rms when the levels on the power lines are

250 V rms

and

20 A rms.

order

achieve

500 pulse-per-kW Hr

per

unit-energy,

the

PulseRateE1,2 Register setting is determined using the

following equation:

Therefor, the PulseRateE1,2 Register is approximately

1.929 Hz. The PulseRateE1,2 Register cannot be set to

a frequency of exactly 1.929 Hz. The closest setting is

0x00003E = 1.9375 Hz.

To improve the accuracy, either gain register can be

programmed to correct for the round-off error. This val-

ue would be calculated as

(MCLK/K)

not

equal

4.096 MHz,

the

PulseRateE1,2 Register must be scaled by a correction

factor of:

Therefore if (MCLK/K) = 3.05856 MHz the value of

PulseRateE1,2 Register is

5.5 Voltage Sag-detect Feature

Status bit VSAG in the Status Register, indicates a volt-

age sag occurred in the power line voltage. For a volt-

age sag condition to be identified, the absolute value of

the instantaneous voltage must be less than the voltage

sag level for more than half of the voltage sag duration

(see Figure 7).

To activate Voltage Sag detect, a voltage sag level must

be specified in the Voltage Sag Level Register

(VSAGLevel), and a voltage sag duration must be spec-

ified in the Voltage Sag Duration Register

(VSAGDuration). The voltage sag level is specified as the

average of the absolute instantaneous voltage. Voltage

sag duration is specified in terms of ADC cycles.

5.6 No Load Threshold

The CS5461A includes the LoadIntv (No Load Detec-

tion Interval) register and the LoadMin register to imple-

ment the no load threshold function. When the

accumulated energy measured within the time defined

by the LoadIntv register does not reach the value in the

LoadMin register, the pulse outputs will be disabled.

5.7 On-chip Temperature Sensor

The on-chip temperature sensor is designed to assist in

characterizing the measurement element over a desired

temperature range. Once a temperature characteriza-

tion is performed, the temperature sensor can then be

utilized to assist in compensating for temperature drift.

Temperature measurements are performed during con-

tinuous conversions and stored in the Temperature

sius scale (oC). The Temperature Gain Register (Tgain)

and Temperature Offset Register (Toff) are constant val-

ues allowing for temperature scale conversions.

The temperature update rate is a function of the number

of ADC samples. With MCLK = 4.096 MHz and K = 1

the update rate is:

PulseRateE

500pulses

kWHr

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

1Hr

3600s

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

1kW

1000W

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

250mV

150mV

250V

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

⎝⎠

⎛⎞

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

250mV

150mV

20A

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

⎝⎠

⎛⎞

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

Vgn or Ign

PulseRateE

1.929

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

1.00441

≅

0x404830

4.096MHz

(MCLK/K)

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

PulseRateE

4.096

3.05856

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

1.929Hz

2.583Hz

≅

Level

Duration

Figure 7. Voltage Sag Detect

2240 samples

(MCLK/K)/1024

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

0.56 sec

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