ETC DEM-ADS80XU

DEM-ADS80xU
®
EVALUATION FIXTURE
FEATURES
DESCRIPTION
● PROVIDES FAST AND EASY
PERFORMANCE TESTING FOR
ADS803/804/805
The DEM-ADS80xU evaluation fixture is designed
for ease of use when evaluating the high speed analogto-digital converter of the ADS80x family. It was
designed to be the common evaluation platform for
three of the models within the ADS80x family. The
board will accommodate the 12-bit converter ADS803
(5Msps version) the ADS804 (10Msps), as well as the
ADS805 the 20Msps model. Because of its flexible
design the user can evaluate the converter in many
different configurations: either with dc-coupled or
ac-coupled input, internal or external reference with
adjustable reference voltages.
● AC- OR DC-COUPLED INPUTS
● INVERTING /NON-INVERTING INPUT
CONFIGURATION
● ON-BOARD REFERENCE
● OUT OF RANGE INDICATOR
The data outputs from the ADS9xx converter are
decoupled from the connector via TTL-buffer.
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
© 1997 Burr-Brown Corporation
LI-494
Printed in U.S.A. September, 1997
INITIAL CONFIGURATION
By using solder switches and resistor placements, the demonstration board, DEM-ADS80xU, can be set up in a variety
of configurations to accommodate a specific model or function. Before starting an evaluation, the user should decide on
the configuration and make the appropriate connections or
changes. The demonstration board comes with the following
factory set configurations:
should feature a very low jitter. This is particularly important if the converter is to be evaluated in an undersampling
condition. The function of series resistor R17 is to dampen
any excessive over- and undershoot of the applied clock
pulse. It may be adjusted according to the amount of overshoot while maintaining a sufficiently fast rise and fall time.
EXTERNAL REFERENCE
The ADS80x converter can be operated with an external
reference. Doing so solder switch SS3 must be closed
applying 5V to the SEL-input (pin 18). This will disable the
internal reference of U4. It is important to remove R13 before
connecting the external reference voltage to the ADS80x,
which is done by closing solder switch SS1. The reference
voltage is generated using the on-board micro power reference IC, REF1004 (U1) and a general purpose single-supply
op amp, OPA237 (U2). The actual reference voltage can be
scaled by adjusting the values of resistors R8 and R9. The
REF1004 produces a stable +2.5V voltage. The selected
reference voltage determines the full-scale input signal range
of the converter. For example, with VREF = +1.25V, the
input range will be 2.5Vp-p.
• OPA642 set for a non-inverting configuration with a gain
of +2V/V. R3, R4, R6, C2 are not assembled.
• Using capacitors C5 and C8 the output of the driver op amp
OPA642 is AC-coupled to the converter input.
• The converter (U4) is set to operate with the internal
reference. R13 (0Ω) is installed, setting the full-scale input
range to 2Vp-p. The solder switch SS1 is open.
• The required common-mode voltage to bias the input of
the ADS80x is derived by R14 and R15 and applied to pin
25 (U4) via R10 (0Ω).
• The bias for the complementary input of the ADS80x is
developed in a similar fashion using R27, R28, R29.
The evaluation board typically requires a ±5V supply unit.
The negative supply is necessary to appropriately power the
OPA642 used in the interface circuit. Selecting a different
op amp like the OPA680, designed for simple supply applications, the evaluation board may be re-configured to operate with just a +5V supply.
DATA OUTPUT
The data output is provided at CMOS logic levels. All
ADS80x converters use straight offset binary coding. The
data output pins of the converter are buffered from the
connector, P2, by two CMOS octal buffers (HC or HCT541).
INPUTS
DC-Coupled
PC-BOARD LAYOUT
The standard configuration of the evaluation board uses the
high speed op amp OPA642, a voltage feedback type op amp
that features very low distortion. In order to implement level
shifting for the DC-coupled circuit configuration, op amp
U3 needs to be reconfigured for inverting mode, with the
level shifting voltage applied to the non-inverting input
through R6 and R5. It is then also necessary to take out
resistor R4. To bypass some of the noise capacitor C2
(0.1µF) should be inserted for this configuration. Note that
in this case the input impedance to the board is also determined by the input resistor, R3, and an appropriate termination resistor (R2) value should be selected.
The DEM-ADS80xU consists of a four-layer PC board. To
achieve the highest level of performance, surface-mount
components are used wherever possible. This reduces the
trace length and minimizes the effects of parasitic capacitance and inductance. The analog-to-digital converter is
treated like an analog component. Therefore, the demo
board has one consistent ground plane. Keep in mind that
this approach may not necessarily yield optimum performance results when designing the ADS80x into different
individual applications. In any case, thoroughly bypassing
the power supply and reference pins of the converter, as
demonstrated on the evaluation board, is strongly recommended.
CLOCK
For further application details please refer to the individual
data sheets.
The DEM-ADS80xU requires an external TTL clock applied at SMA connector J2. This input represents a 50Ω
input to the source. In order to preserve the specified
performance of the ADS80x converter, the clock source
®
DEM-ADS80xU
2
FIGURE 1. Circuit Schematic DEM-ADS80xU.
3
®
DEM-ADS80xU
Input
J1
R2
49.9Ω
R4
0Ω
C15
0.1µF
–5V
R3(1)
R5
(1)
C16
+ 2.2µF
–5V
C13
2.2µF
+5V
6
5
3
4
P1:1
P1:2
P1:3
–5
GND
+5
C9
10µF
U3
+5V
6
+5V
–5V
2
U2
6
+5V
2
3
1
GND
TP1
R8
4.75kΩ
R9
4.75kΩ
R7
10kΩ
R24
1kΩ
OPA237U
+5V
SS4
C3
0.1µF
1
R26
402Ω
–5V
OPA642U
R25
402Ω
2
3
+ C
10
10µF
+
7
2
POWER
8
1
C12
0.1µF
C14
0.1µF
R6(1)
+5V
U1
REF1004C-2.5
C2(1)
0.1µF
+
+5V
1
2
C1
0.1µF
R1
402Ω
0Ω
0Ω
0Ω
R13
C21
0.1µF
SS5
2
R16
24.9Ω
C17
0.1µF
1
R28
R12
R27
4.75kΩ
R14
4.75kΩ
R10
R29
4.75kΩ
R15
4.75kΩ
NOTE: (1) Part Not Assembled for Default Configuration.
SS1
R23
(1)
+
C8
2.2µF
R11(1)
C5
0.1µF
C4(1)
0.1µF
(1)
+5V
+5V
0.1µF
C20(1)
C26
100pF
C24
2.2µF
C23
0.1µF
+
1
1
SS2
SS3
C22
0.1µF
C25
0.1µF
2
2
+5V
+5V
15
16
17
18
19
20
21
22
23
24
25
26
27
28
C18
2.2µF
+
+5V
+VS
EXT CLK
OE
+VS
GND
SEL
VREF
REFB
CM
REFT
IN
GND
IN
GND
+5V
J2
OTR
C7
0.1µF
B11
B12
12
13
R17
49.9Ω
B10
11
14
B9
10
B2
B7
7
8
9
B10
B9
R19
402Ω
6
5
4
3
2
19
1
9
8
7
6
5
4
3
2
B11
C11
2.2µF
1
19
B12
B1
B3
B4
B6
B5
B5
B6
B4
B7
B3
B8
B2
B1
B8
C19
2.2µF
9
8
7
6
5
4
3
2
1
+5V
R21
49.9Ω
CLK
B12
B11
B10
B9
B8
B7
B6
B5
B4
B3
B2
(MSB) B1
U4
ADS80xU(1)
C6
0.1µF
VDRV
+
+5V
17
16
15
14
13
12
11
10
OE2
R18
1M
07
06
05
04
03
02
01
00
07
06
05
04
03
02
01
00
D1
U5
74HCT541
OE1
17
16
15
14
13
12
11
10
OE2
OE1
U6
74HCT541
+5
D2
R20
402Ω
11
12
13
14
15
16
17
18
11
12
13
14
15
16
17
18
+5
C27
0.1µF
C28
0.1µF
Out Of
Range
R22
4.75kΩ
P2:39
P2:37
P2:35
P2:33
P2:17
P2:19
P2:21
P2:23
P2:25
P2:27
P2:29
P2:31
P2:1
P2:3
P2:5
P2:7
P2:9
P2:11
P2:13
P2:15
OE
NC
NC
CLK
B9
B10
B11
B12
OTR
GND
GND
GND
B1
B2
B3
B4
B5
B6
B7
B6
Digital
Output
P2:40
P2:38
P2:36
P2:34
P2:18
P2:20
P2:22
P2:24
P2:26
P2:28
P2:30
P2:32
P2:2
P2:4
P2:6
P2:8
P2:10
P2:12
P2:14
P2:16
FIGURE 2. Top Layer (Component Side) with Silk-Screen.
FIGURE 3. Power Plane.
®
DEM-ADS80xU
4
FIGURE 4. Bottom Layer with Silk-Screen.
®
5
DEM-ADS80xU
COMPONENT LIST
REFERENCE
QTY
COMPONENT
DESCRIPTION
U1
1
REF1004C-2.5
2.5V Reference, SO-8
MANUFACTURER
Burr-Brown
U2
1
OPA237U
Single Op Amp, SO-8
Burr-Brown
U3
1
OPA642U
Low-Dist. Wideband Single Op Amp, SO-8
Burr-Brown
U4
1
ADS80xU
High-Speed ADC, 28-Pin SOIC
Burr-Brown
U5, U6
2
74HCT541
5V Octal Buffer, 20-Pin SOIC
D1
1
BAS16
Diode, SOT-23
Philips
D2
1
SSL-LX15IG-TR
LED-Diode, Red, SOT-23
Lumex (Digi-Key)
R4, 10, 13, 28
1
CRCW0805ZEROF
0Ω, MF 0805 Chip Resistor, 1%
Dale
R16
1
CRCW080524R9F
24.9Ω, MF 0805 Chip Resistor, 1%
Dale
R2, 17, 21
3
CRCW080549R9F
49.9Ω, MF 0805 Chip Resistor, 1%
Dale
R1, 19, 20, 25, 26
5
CRCW08054020F
402Ω, MF 0805 Chip Resistor, 1%
Dale
R8, 9, 14, 15, 22, 24, 27, 29
8
CRCW08054751F
4.75Ω, MF 0805 Chip Resistor, 1%
Dale
R7
1
CRCW08051002F
10Ω, MF 0805 Chip Resistor, 1%
Dale
R18
1
CRCW08051005F
1MΩ, MF 0805 Chip Resistor, 1%
Dale
R3, 5, 6, 11, 12, 23
6
Open, Use Depends on Configuration
—
C9, C10
2
ECE-V1CV100SR
10µF/16V, Surface Mount Polar. Alu Cap.
Panasonic (Digi-Key)
C8, 11, 13, 16, 18, 19, 24
7
TAJR225006
2.2µF/10V, 3216 Tantalum Capacitor
AVX
C1, 3, 5, 6, 7, 12, 14, 15
17, 21, 22, 23, 25, 27, 28
15
08055C104KAT
0.1µF/50V X7R 0805 Ceramic Capacitor
AVX
C26
1
08055C101KAT
100pF/50V NP0 0805 Ceramic Capacitor
AVX
C2, 4, 20
3
Open, Use Depends on Configuration
—
P1
1
ED555/3DS
3-Pin Term Block
On-Shore Technology
P2
1
IDH-40LP-S3-TG
20 x 2 Dual-Row Shrouded Header
Robinson-Nugent
EF Johnson
J1, J2
2
142-0701-201
Straight SMA PCB Connector
4
1-SJ5003-0-N
Rubber Feet, Black, 0.44 x 0.2
Digi-Key
1
PCBA 2266
PC Board A2266, Rev. B
Burr-Brown
®
DEM-ADS80xU
6