CS5451A

8

DS635F3

3. THEORY OF OPERATION

The CS5451A is a six-channel analog-to-digital convert-

er (ADC) followed by a serial interface that allows com-

munication with a target device. The analog inputs are

structured for 3-phase power meter applications, with

three dedicated voltage and current channels. Figure 2

illustrates the CS5451A typical inputs and power supply

connections.

The voltage-sensing element introduces a voltage

waveform on the voltage channel inputs VIN(1-3)

± and

is subject to a fixed 1x gain amplifier. A fourth-order del-

ta-sigma modulator samples the amplified signal for dig-

itization.

Simultaneously, the current-sensing element introduces

a voltage waveform on the current channel input

IIN(1-3)

± and is subject to two selectable gains of the

programmable gain amplifier (PGA). The amplified sig-

nal is sampled by a fourth-order delta-sigma modulator

for digitization. Both converters sample at a rate of

XIN/8, the over-sampling provides a wide dynamic

range and simplified anti-alias filter design.

filters. The single bit data is passed to the low-pass dec-

imation filter and output at a fixed word rate. The deci-

mation rate is selectable for two output word rates.

The 16-bit output word is then transmitted via a master

serial data port. The six-channel data is multiplexed on

the serial data output and is preceded by a frame sync

signal.

VA+

VD+

VIN1+, VIN2+, or VIN3+

VIN1-, VIN2-, or VIN3-

IIN1+, IIN2+, or IIN3+

IIN1-, IIN2-, or IIN3-

AGND

DGND

REFIN

REFOUT

Optional

External

Reference

V

PHASE

+

I

-2 V

PHASE

VA-

+3 V

1.2 V

NOTE: Current input channels

actually measure voltage.

Figure 2. Typical Connection Diagram