CS5460A datasheet(13/54 Pages) CIRRUS

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CS5460A

Figure 3) will be enabled on the other channel; in

order to preserve the relative phase relationship

between the voltage-sense and current-sense in-

put signals. For example, if the HPF is engaged for

the voltage channel, but not the current channel,

then the APF will be engaged in the current channel,

to nullify the additional phase delay introduced by

the high-pass filter in the current channel.

2.1.5 Overall Filter Response

When the CS5460A is driven with a 4.096 MHz

clock (K = 1), the composite magnitude response

(over frequency) of the voltage channel’s input fil-

ter network is shown in Figure 4, while the com-

posite

magnitude

response

the

current

channel’s input filter network is given in Figure 5.

Note that the composite filter response of both

channels scales with MCLK frequency and K.

2.1.6 Gain and DC Offset Adjustment

After filtering, the instantaneous voltage and cur-

rent digital codes are subjected to offset/gain ad-

justments, based on the values in the DC offset

registers (additive) and the gain registers (multipli-

cative). These registers are used for calibration of

the device (see

Section 3.8, Calibration). After off-

set and gain, the 24-bit instantaneous data sample

values are stored in the Instantaneous Voltage and

Current Registers.

2.1.7 Real Energy and RMS Computations

The digital instantaneous voltage and current data

is then processed further. Referring to Figure 3, the

instantaneous voltage/current data samples are

multiplied together (one multiplication for each pair

of voltage/current samples) to form instantaneous

(real) power samples. After each A/D conversion

cycle, the new instantaneous power sample is

stored in the Instantaneous Power Register.

The instantaneous power samples are then

grouped into sets of N samples (where N = value in

Cycle Count Register). The cumulative sum of

each successive set of N instantaneous power is

used to compute the result stored in the Energy

of real energy registered by the device during the

most recent N A/D conversion cycles. Note from

Figure 3 that the bits in this running energy sum

are right-shifted 12 times (divided by 4096) to

avoid overflow in the Energy Register. RMS calcu-

lations are also performed on the data using the

last N instantaneous voltage/current samples, and

these results can be read from the RMS Voltage

2.2 Performing Measurements

To summarize Section 2.1, the CS5460A performs

measurements of instantaneous current and in-

stantaneous voltage, and from this, performs com-

putations of the corresponding instantaneous

power, as well as periodic calculations of real en-

ergy, RMS current, and RMS voltage. These mea-

surement/calculation results are available in the

form of 24-bit signed and unsigned words. The

scaling of all output words is normalized to unity

VOLTAGE

∆Σ

SINC2

V *

CURRENT

SINC4

TBC *

DELAY

REG

DELAY

REG

FIR

HPF

APF

Configuration Register *

PC[6:0] Bits

RMS

÷ 4096

Eto F

out

dir

PULSE-RATE*

* DENOTES REGISTER NAME

∆Σ

HPF

APF

FIR

SINC2

I *

SINC2

ACoff*

DCoff*

ACoff*

DCoff*

off

÷ N

Figure 3. Data Flow.

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