DEM-OPA68XU Datasheet, PDF (3/4 Pages) Burr-Brown (TI) – EVALUATION FIXTURE

OPA681U—Pin 8 disables the output when low. Table VIII
shows different ways to set up pin 8’s voltage using R₈, R₉
and C₇. Use Table III for the other components.
OPA682U—The OPA682U uses internal resistors to set the
gain at +1, +2, or –1. Pin 8 disables the output when low.
Table VIII shows different ways to set up pin 8’s voltage
using R₈, R₉ and C₇. Use Table III for the other components,
except for the changes shown in Table IX.
DUAL SUPPLY DUAL SUPPLY SINGLE SUPPLY
COMPONENT
(G = +2)
(G = –1)
(G = +1)
R₄
Open
0Ω
Open
R₅
0Ω
Open
Open
R₆
Open
Open
Open
TABLE IX. OPA682U Changes.
OPA686U—Use Table X for the higher gains needed by
this part, and Table IV for the other component values. Extra
care is needed to ensure pin 8 is not connected (see Table I).
COMPONENT
R₁
R₂
R₃
R₄
R₅
R₆
DUAL SUPPLY
(G = +10)
49.9Ω
20.0Ω
Open
Open
49.9Ω
453Ω
DUAL SUPPLY SINGLE SUPPLY
(G = –10)
(G = +20)
Open
Open
10.0Ω
49.9Ω
Open
499Ω
49.9Ω
10.0Ω
Open
Open
26.1Ω
499Ω
TABLE X. OPA686U Changes.
OPA688U—This VLA™ (Voltage Limiting Amplifier) has
two inputs (V_H and V_L in Table I), which limit the output
voltage swing. Table XI shows different ways to set up pin
5’s and pin 8’s voltages using R₈ - R₁₃ and C₅ - C₇. Use
Table IV for the other components.
Note that this board would require modification for the
single-supply circuit shown in the OPA688 data sheet. In
dual supply applications, using R₁₀ instead of R₈ makes V_H
negative, and using R₁₃ instead of R₁₁ makes V_L positive.
COMPONENT
R₈
R₉
R₁₁
R₁₂
R₁₃
C₅ - C₇
DUAL SUPPLY
(G = +2)
3.01kΩ
1.91kΩ
3.01kΩ
1.91kΩ
Open
0.1µF
DUAL SUPPLY SINGLE SUPPLY
(G = –1)
(G = +1)
3.01kΩ
1.91kΩ
3.01kΩ
1.91kΩ
Open
0.1µF
549Ω
1.58kΩ
Open
549Ω
1.58kΩ
0.1µF
TABLE XI. Limiting Pins—OPA68xU.
OPA689U—This VLA™ is the high gain-stable version of
the OPA688U. Set up this op amp the same as the OPA688U,
except for the changes shown in Table XII.
COMPONENT
R₁
R₂
R₃
R₄
R₅
R₆
DUAL SUPPLY
(G = +6)
49.9Ω
100Ω
Open
Open
150Ω
750Ω
DUAL SUPPLY SINGLE SUPPLY
(G = –6)
(G = +6)
82.5Ω
Open
130Ω
124Ω
Open
750Ω
49.9Ω
100Ω
Open
Open
150Ω
750Ω
TABLE XII. OPA689U Changes.
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.
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 7 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 selec-
tion.
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. Change the component
values for different input and output impedance levels.
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.
®
3
DEM-OPA68xU