CS5462 datasheet(11/18 Pages) CIRRUS

11 / 18 page

CS5462

3.1

Theory of Operation

A computational flow diagram for the two data

paths is shown in Figure 1. The analog waveforms

at the voltage/current channel inputs are subject to

the gains of the input PGAs.

3.1.1

Digital Filters

The modulators convert the analog input voltages

on the I and V channels to a digital bitstream; which

is then filtered by the digital filter section. The digi-

tal filter is composed of low pass sinc 3 and IIR fil-

ters. The IIR filters are used to compensate for the

magnitude roll-off of the low pass filter section.

Both channels provide a high-pass filter option

which can be engaged into the signal path to re-

move the DC content from the current/voltage signal

before the energy calculations are made.

3.1.2

Gain Calibration

After being filtered, the instantaneous voltage and

current digital codes are used to calculate real av-

erage power. This power is then adjusted based on

the internal calibration setting defined at startup.

Calibrating the CS5462 is done by externally con-

necting the configuration input pins, CAL1 and

CAL0, to the program select output pins, P1 - P7,

in a particular sequence. These connections will in-

ternally compensate for small gain errors.

3.1.3

Energy-to-Frequency Conversion

The calibrated energy value is then converted into

a pulse output stream with a average frequency

proportional to the measured energy. Pulse output

pins E1 and E2 can be set to lower frequencies to

directly drive a stepper motor or a mechanical

counter or interface a microcontroller or infrared

LED. The FOUT pulse output pin is set to max fre-

quency of 10 kHz. With full scale inputs on both the

current and voltage channels FOUT will output

pulses with an average frequency of 10 kHz.

VIN±

IIN±

PGA Gain Select

HPF Select

Freq Select

Energy to

Pulse Rate

Converter

FOUT

Calibration

Digital

Filters

Digital

Filters

4th Order

∆Σ

Modulator

2nd Order

∆Σ

Modulator

PGA

10x

On-Chip

Configuration

Output Mode Select

HPF

Figure 1. Data Flow

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