OPA2277-EP_16 Datasheet, PDF (15/24 Pages) Texas Instruments – High-Precision, Low-Noise Operational Amplifier

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OPA2277-EP
SBOS700 – DECEMBER 2014
10 Power Supply Recommendations
The OPA2277 operational amplifier operates from ±2.5- to ±18-V supplies with excellent performance. Unlike
most operational amplifiers which are specified at only one supply voltage, the OPA2277 is specified for real-
world applications. A single set of specifications applies over the ±5- to ±15-V supply range. Specifications are
ensured for applications between ±5- and ±15-V power supplies. Some applications do not require equal positive
and negative output voltage swing. Power supply voltages do not need to be equal. The OPA2277 can operate
with as little as 5 V between the supplies and with up to 36 V between the supplies. For example, the positive
supply could be set to 25 V with the negative supply at –5 V, or vice-versa. In addition, key parameters are
ensured over the specified temperature range, –55°C to 125°C. The Typical Characteristics show parameters
which vary significantly with operating voltage or temperature.
11 Layout
11.1 Layout Guidelines
Solder the lead-frame die pad to a thermal pad on the PCB. Mechanical drawings in Mechanical, Packaging, and
Orderable Information show the physical dimensions for the package and pad.
Soldering the exposed pad significantly improves board-level reliability during temperature cycling, key push,
package shear, and similar board-level tests. Even with applications that have low-power dissipation, the
exposed pad must be soldered to the PCB to provide structural integrity and long-term reliability.
The OPA2277 has very-low offset voltage and drift. To achieve highest performance, optimize circuit layout and
mechanical conditions. Offset voltage and drift can be degraded by small thermoelectric potentials at the
operational amplifier inputs. Connections of dissimilar metals generate thermal potential which can degrade the
ultimate performance of the OPA2277. These thermal potentials can be made to cancel by assuring that they are
equal in both input terminals.
• Keep thermal mass of the connections made to the two input terminals similar.
• Locate heat sources as far as possible from the critical input circuitry.
• Shield operational amplifier and input circuitry from air currents such as cooling fans.
11.2 Layout Example
11.2.1 Board Layout
This demonstration fixture 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.
11.2.2 Measurement Tips
This demonstration fixture and the component values shown are designed to operate in a 50Ω environment.
Most data sheet plots are obtained in this manner. 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 the
amplifier 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.
Copyright © 2014, Texas Instruments Incorporated
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