CS5451A
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.
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.
3
The decimating digital filters on all channels are Sinc
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 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.
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.
Simultaneously, the current-sensing element introduces
a voltage waveform on the current channel input
+3 V
VD+
VA+
REFIN
Optional
External
REFOUT
1.2 V
Reference
VIN1+, VIN2+, or VIN3+
+
V
PHASE
VIN1-, VIN2-, or VIN3-
IIN1+, IIN2+, or IIN3+
I
PHASE
NOTE: Current input channels
actually measure voltage.
IIN1-, IIN2-, or IIN3-
AGND
DGND
VA-
-2 V
Figure 2. Typical Connection Diagram
8
DS635F2
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