cs5506 Cirrus Logic, Inc., cs5506 Datasheet - Page 34

• Manufacturer Part Number: cs5506
• Description: Low-power, 16/20-bit A/d Converters
• Manufacturer: Cirrus Logic, Inc.

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Introduction
The CDB5505/6/7/8 evaluation board provides a
quick means of testing the CS5505/6/7/8 series
A/D converters. The CS5505/6/7/8 converters
require a minimal amount of external circuitry.
The evaluation board comes configured with the
A/D converter chip operating from a 32.768 kHz
crystal and with an off-chip precision 2.5 volt
reference. The board provides access to all of
the digital interface pins of the CS5505/6/7/8
chip.
The board is configured for operation from +5
and -5 volt power supplies, but can be operated
from a single +5 volt supply if the -5V binding
post is shorted to the GND binding post.
Evaluation Board Overview
The board provides a complete means of making
the CS5505/6/7/8 A/D converter chip function.
The user must provide a means of taking the
output data from the board in serial format and
using it in his system.
Figure 1 illustrates the schematic for the board.
The board comes configured for the A/D con-
verter chip to operate from the 32.768 kHz
watch crystal. A BNC connector for an external
clock is provided on the board. To connect the
external BNC source to the converter chip, a cir-
cuit trace must be cut. Then a jumper must be
inserted in the proper holes to connect the XIN
pin of the converter to the input line from the
BNC. The BNC input is terminated with a 50Ω
resistor. Remove this resistor if driving from a
logic gate. See the schematic in Figure 1.
The board comes with the A/D converter
VREF+ and VREF- pins hard-wired to the
2.5 volt bandgap voltage reference IC on the
board. The VREF+ and VREF- pins can be con-
nected to either the on chip reference or an
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off-board reference if the connections (2A and
2B) to the bandgap IC are cut.
Note that the pin-out of the CS5505/6/7/8 series
chips allows the 20-pin single channel devices to
be plugged into the 24-pin, four channel foot-
print. See Figure 2 which illustrates the footprint
compatibility.
Prior to powering up the board, select the serial
port operating mode with the appropriate jumper
on the M/SLP header. The device can be oper-
ated in either the SSC (Synchronous
Self-Clocking) or the SEC (Synchronous Exter-
nal Clocking) mode. See the device data sheet
for an explanation of these modes.
All of the control pins of the CS5505/6/7/8 are
available at the J1 header connector. Buffer ICs
U2 and U3 are used to buffer the converter for
interface to off-board circuits. The buffers are
used on the evaluation board only because the
exact loading and off-board circuitry is un-
known. Most applications will not require the
buffer ICs for proper operation.
To put the board in operation, select either bipo-
lar or unipolar mode with DIP switch S2. Then
press the CAL pushbutton after the board is
powered up. This initiates calibration of the con-
verter which is required before measurements
can be taken.
To select an input channel on the four channel
devices, use DIP switch S2 to select the inputs
A1
0
0
1
1
Table 1. Multiplexer Truth Table
A0
0
1
0
1
CDB5505/6/7/8
Channel addressed
AIN1
AIN2
AIN3
AIN4
CS5505/6/7/8
DS59DB2
DS59DB3