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