Cirrus Logic CDB5451A - Manual (Page 3)

CDB5451A
DS458DB3 3
1. INTRODUCTION
The CDB5451A Evaluation Board demonstrates
the performance of the CS5451A 6-channel A/D
converter.
The CDB5451A evaluation board provides a quick
means of evaluating the CS5451A. Analysis soft-
ware supplied with the CDB5451A allows the user
to observe the CS5451A’s digital output data on
the user’s PC monitor. The PC software allows the
user to quantify the device’s performance in the
time-domain and frequency domain. The user can
save raw data from the CS5451A to a data file,
which allows to user to analyze performance with
other tools that may be preferable to the user.
1.1 CS5451A
The CS5451A is a highly integrated Six-Channel
Delta-Sigma Analog-to-Digital Converter (ADC)
developed for three-phase power/energy metering
applications. However the CS5451A has other po-
tential uses in other data acquisition applications,
particularly in motor/servo control applications that
require very high precision. The CS5451A com-
bines six delta-sigma modulators with decimation
filters, along with a master-mode serial interface on
a single-chip device. The CS5451A was designed
for the purpose of performing the A/D conversion
operations required at the front-end of a digital 3-
phase metering system. The six ADC channels
can be thought of as three pairs of voltage/current-
channel ADC’s in a digital 3-phase power metering
application.
The CS5451A contains one three-channel pro-
grammable gain amplifier (PGA) for the three cur-
rent input channels. The PGA sets the maximum
input levels of the all three current channels at
± 800 mV DC (for gain = 1x) or ± 40 mV DC (for gain
= 20x). The voltage channels have only the 1x gain
setting, and so the range of input levels on the volt-
age channels is
± 800 mV DC.
Additional features of CS5451A include a charge
pump driver, on-chip 1.2 V reference, and a digital
input that can select between two different output
word rates. (The two output word rates are equal to
XIN/2048 and XIN/1024.)
The CS5451A requires a 1.2 V reference input on
VREFIN. The
∆Σ modulators and high rate digital
filters allow the user to measure instantaneous
voltage and current at an output word rate of 4 kHz
(or 2000 kHz, depending on the state of the OWRS
pin) when a 4.096 MHz clock source is used.
1.2 Data Flow on Evaluation Board
The output serial bit-stream from the CS5451A is
shifted into an 8-bit latch circuit so that it can be
quickly ported to the DB25 connector. From this
connector, the data can be sent through the provid-
ed 25-pin printer cable to the parallel port of the us-
er’s IBM-compatible PC (the PC must run under
Windows ‘95/’98/2000 operating system).
Once the 8-bit segments of data are ported to the
user’s PC, the LabWindows software (included
with this kit) will re-segment the data into the ap-
propriate 16-bit word format for each of the
CS5451A’s six data channels. The data is sent
quickly to the user’s PC, which allows the software
to perform various data processing and graphical
illustrations on the digital output data. This in-
cludes real-time RMS, variance, and standard de-
viation calculations for all six channels. The output
data from each channel can be plotted on-screen
in the time domain or in the frequency domain. A
histogram function is also included to help the user
to evaluate the noise characteristics of each chan-
nel. The software can also calculate the mean and
standard deviation of the output codes for all six
channels. This feature allows the user to scrutinize
the variation of the A/D converters if the user ap-
plies constant DC voltage levels to the inputs.
RMS calculation is also provided to assist in the
quick analysis AC input signals.