ETC DEM-OPA268XU

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