DEM-OPA268xU ® EVALUATION FIXTURE DESCRIPTION The DEM-OPA268xU demonstration board is an unpopulated printed circuit board (PCB) for the high speed dual op amps in SO-8 packages. Figure 1 shows the package pinout for this PCB. For more information on these op amps, and good PCB layout techniques, see the individual op amp data sheets. The ordering number for this board is MKT-352. Limit of 5 per customer. Top View 1 8 +VS –In A 2 7 Out B +In A 3 6 –In B –VS 4 5 +In B R1 and R7 set the I/O impedance, R2 - R6 set the gain, and C1 - C5 are supply bypass capacitors. C3 is optional; it adds a bypass between the supplies, which improves distortion performance for some models. L1 and L2 are ferrite chips that can reduce interactions with the power supply at high frequencies; if not desired, they can be replaced with 0Ω resistors. For single supply operation, do not connect L2; otherwise, the –VS input to P1 would be at ground potential. SO-8 Out A COMPONENTS Components that have RF performance similar to the ones in Table I may be substituted. Standard Current-Feedback Op Amps—Table II shows typical values for these parts. To select component values for your op amp (especially R6), consult its data sheet. FIGURE 1. Pin Configuration. CIRCUIT The circuit schematic in Figure 2 shows the connections for all possible components. Each model will only use some of the components. R7A 1 4 –VS + C2 C3 L1 + C1 C5 R3B R2B J1B IN B R4B R1B R5B EMI-Suppression Ferrite Chip, SMD 1206 (Steward LI 1206 B 900 R) Terminal Block, 3.5mm centers (On-Shore Technology ED555/3DS) Metal Film Chip Resistor, SMD 1206, 1/8W Out A C4 L2 +VS SMA or SMB Board Jack (Amphenol 901-144-8) J2A 2 R5A GND Multi-Layer Ceramic Chip Cap., SMD 1206, 50V J1A - J2B P1 R6A P1 Tantalum Chip Capacitor, SMD EIA size 3528, 20V TABLE I. Component Descriptions. 3 R4A R1A C1, C2 C3 - C5 R1A - R7B R2A IN A DESCRIPTION L1, L2 R3A J1A PART 5 8 7 6 R7B J2B Out B R6B COMPONENT DUAL SUPPLY (G = +2) R1 R2 R3 R4 R5 R6 R7 C1, C2 C3 C4, C5 49.9Ω 10.0Ω Open Open 402Ω 402Ω 49.9Ω 2.2µF 0.1µF 0.1µF DUAL SUPPLY SINGLE SUPPLY (G = –1) (G = +1) 57.6Ω Open 10.0Ω 402Ω Open 402Ω 49.9Ω 2.2µF 0.01µF 0.1µF 49.9Ω 10.0Ω Open Open Open 402Ω 49.9Ω 2.2µF Open 0.1µF NOTE: The values and gains shown will not work for all op amps. See the individual op amp data sheet to select proper values. The I/O impedances are 50Ω. TABLE II. Standard Current-Feedback Op Amps. FIGURE 2. Circuit Schematic for DEM-OPA268xU. 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/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 © 1998 Burr-Brown Corporation LI-514A Printed in U.S.A. October, 1999 BOARD LAYOUT This demonstration board is a two-layer PCB. It uses a ground plane on the bottom and signal and power traces on the top. The ground plane has been opened up around op amp pins sensitive to capacitive loading. Power supply traces are laid out to keep current loop areas to a minimum. The SMA (or SMB) connectors may be mounted either vertically or horizontally. Standard Voltage-Feedback Op Amps—Table III shows typical values for these parts. To select component values for your op amp, consult its data sheet. COMPONENT DUAL SUPPLY (G = +2) DUAL SUPPLY (G = –1) SINGLE SUPPLY (G = +1) R1 R2 R3 R4 R5 R6 R7 C1, C2 C3 C4, C5 49.9Ω 178Ω Open Open 402Ω 402Ω 49.9Ω 2.2µF 0.01µF 0.1µF 57.6Ω Open 210Ω 402Ω Open 402Ω 49.9Ω 2.2µF 0.01µF 0.1µF 49.9Ω 0Ω Open Open Open 24.9Ω 49.9Ω 2.2µF Open 0.1µF The location and type of capacitors used for power-supply bypassing are crucial to high frequency amplifiers. The tantalum capacitors, C1 and C2, do not need to be as close to pins 8 and 4 on your PCB and may be shared with other amplifiers. See the individual op amp data sheet for more information on proper board layout techniques, and component selection. NOTE: The values and gains shown will not work for all op amps. See the individual op amp data sheet to select proper values. The I/O impedances are 50Ω. MEASUREMENT TIPS This demonstration board, and the component values shown, are designed to operate in a 50Ω environment. Most data sheet plots are obtained this way. It is easy to change the component values for different input and output impedance levels. TABLE III. Standard Voltage-Feedback Op Amps. OPA2682U—The OPA2682U uses internal resistors to set the gain at +1, +2 or –1. Use Table II, except for the changes shown in Table IV. COMPONENT DUAL SUPPLY (G = +2) DUAL SUPPLY (G = –1) SINGLE SUPPLY (G = +1) R4 R5 R6 Open 0Ω Open 0Ω Open Open Open Open Open Do not use high impedance probes; they represent a heavy capacitive load to the op amps, and will alter their response. Instead, use low impedance (≤ 500Ω) probes with adequate bandwidth. The probe input capacitance and resistance set an upper limit on the measurement bandwidth. If a high impedance probe must be used, place a 100Ω resistor on the probe tip to isolate its capacitance from the circuit. TABLE V. OPA2682U Changes. (a) (b) FIGURE 3. DEM-OPA268xU Demonstration Board Layout; (a) Component Side Silkscreen and Metal, (b) Ground Plane Side Silkscreen and Metal (bottom view). ® DEM-OPA268xU 2