CS5467 datasheet(41/46 Pages) CIRRUS

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CS5467

DS714A1

ADVANCE RELEASE

shows that a positive (or negative) DC-level signal can

be used even though an AC gain calibration is being ex-

ecuted.

However, an AC signal cannot be used for DC gain cal-

ibration.

7.1.3.2 DC Gain Calibration Sequence

Initiate a DC gain calibration. The corresponding gain

tion averages the channel’s instantaneous measure-

ments over one computation cycle (N samples). The

average is then divided into 1.0 and the quotient is

stored in the corresponding gain register

After the DC gain calibration, the instantaneous register

will read at full-scale whenever the DC level of the input

signal is equal to the level of the DC calibration signal

applied to the inputs during the DC gain calibration.The

HPF option should not be enabled if DC gain calibration

is utilized.

7.1.4 Order of Calibration Sequences

1. If the HPF option is enabled, any DC component that

may be present in the selected signal path will be re-

moved and a DC offset calibration is not required.

However, if the HPF option is disabled the DC offset

calibration sequence should be performed.

When using high-pass filters, it is recommended that

the DC Offset register for the corresponding channel

be set to zero. When performing DC offset calibra-

tion, the corresponding gain channel should be set to

one.

2. If there is an AC offset in the VRMS or IRMS calcula-

tion, the AC offset calibration sequence should be

performed.

3. Perform the gain calibration sequence.

4. Finally, if an AC offset calibration was performed

(step 2), the AC offset may need to be adjusted to

compensate for the change in gain (step 3). This can

be accomplished by restoring zero to the AC offset

quence. The adjustment could also be done by

multiplying the AC offset register value that was cal-

culated in step 2 by the gain calculated in step 3 and

updating the AC offset register with the product.

7.2 Phase Compensation

The CS5467 is equipped with phase compensation to

cancel out phase shifts introduced by the measurement

element. Phase Compensation is set by bits PC[7:0] (for

channel 1) in the Configuration Register and bits

PC2[7:0] (for channel 2) in the Control Register

The default value of PC[7:0] (PC2[7:0]) is zero. With

MCLK = 4.096 MHz and K = 1, the phase compensa-

tion has a range of

±5.4 degrees when the input signals

are 60 Hz. Under these conditions, each step of the

phase compensation register (value of one LSB) is ap-

proximately 0.04 degrees. For values of MCLK other

than 4.096 MHz, the range and step size should be

scaled by 4.096 MHz/(MCLK/K). For power line fre-

quencies other than 60Hz, the values of the range and

step size of the PC[7:0] (PC2[7:0]) bits can be deter-

mined by converting the above values from angular

measurement into the time domain (seconds), and then

computing the new range and step size (in degrees)

with respect to the new line frequency. To calculate the

phase shift induced between the voltage and the current

channel use the equation:

7.3 Active Power Offset

The Power Offset Register can be used to offset system

power sources that may be resident in the system, but

do not originate from the power line signal. These sourc-

es of extra energy in the system contribute undesirable

and false offsets to the power and energy measurement

results. After determining the amount of stray power, the

Power Offset Register can be set to cancel the effects

of this unwanted energy.

Freq = Line Frequency [Hz]

PC[7:0] = 2’s Compliment number in the range of -128 < PC[7:0} < 127

Phase

Freq

360

PC 7:0

[]

MCLK K

⁄

() 8

⁄

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