Cirrus Logic CS5451A - Manual (Page 8)

CS5451A
8 DS635F4
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.
The decimating digital filters on all channels are Sinc
3
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