VCA810_16 Datasheet, PDF (31/40 Pages) Texas Instruments – VCA810 High Gain Adjust Range, Wideband and Variable Gain Amplifier

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VCA810
SBOS275G – JUNE 2003 – REVISED DECEMBER 2015
10 Power Supply Recommendations
The VCA810 is designed for split supply operation with a nominal supply condition of 6 V. A power supply in the
range of 8 V to 12 V is acceptable, and balanced supplies (negative and positive voltages equal) are
recommended.
The power supply should be regulated to 10% or better accuracy and capable of sourcing 100 mA of current.
The device quiescent current is approximately 20 mA and the load current can be up to 60 mA.
Single supply applications are possible, however, the control voltage is referenced to the ground pin, so a single
supply application will require a mid supply reference voltage that can be applied to the ground pin. This
reference voltage should be set to 5% accuracy or better for accurate gain control.
11 Layout
11.1 Layout Guidelines
Achieving optimum performance with a high-frequency amplifier such as the VCA810 requires careful attention to
board layout parasitic and external component types. Recommendations that will optimize performance include:
• Minimize parasitic capacitance to any AC ground for all of the signal I/O pins. This includes the ground pin
(pin 2). Parasitic capacitance on the output can cause instability: on both the inverting input and the
noninverting input, it can react with the source impedance to cause unintentional band limiting. To reduce
unwanted capacitance, a window around the signal I/O pins should be opened in all of the ground and power
planes around those pins. Otherwise, ground and power planes should be unbroken elsewhere on the board.
Place a small series resistance (> 25 Ω) with the input pin connected to ground to help decouple package
parasitic.
• Minimize the distance (less than 0.25” or 6.35 mm) from the power-supply pins to high-frequency 0.1-μF
decoupling capacitors. At the device pins, the ground and power plane layout should not be in close proximity
to the signal I/O pins. Avoid narrow power and ground traces to minimize inductance between the pins and
the decoupling capacitors. The power-supply connections should always be decoupled with these capacitors.
Larger (2.2 μF to 6.8 μF) decoupling capacitors, effective at lower frequencies, should also be used on the
main supply pins. These capacitors may be placed somewhat farther from the device and may be shared
among several devices in the same area of the PCB.
• Careful selection and placement of external components will preserve the high-frequency performance of the
VCA810. Resistors should be a very low reactance type. Surface-mount resistors work best and allow a
tighter overall layout. Metal-film and carbon composition, axially-leaded resistors can also provide good high-
frequency performance. Again, keep the leads and PCB trace length as short as possible. Never use wire-
wound type resistors in a high-frequency application. Since the output pin is the most sensitive to parasitic
capacitance, always position the series output resistor, if any, as close as possible to the output pin. Other
network components, such as inverting or noninverting input termination resistors, should also be placed
close to the package.
• Careful selection and placement of external components will preserve the high-frequency performance of the
VCA810. Resistors should be a very low reactance type. Surface-mount resistors work best and allow a
tighter overall layout. Metal-film and carbon composition, axially-leaded resistors can also provide good high-
frequency performance. Again, keep the leads and PCB trace length as short as possible. Never use wire-
wound type resistors in a high-frequency application. Since the output pin is the most sensitive to parasitic
capacitance, always position the series output resistor, if any, as close as possible to the output pin. Other
network components, such as inverting or noninverting input termination resistors, should also be placed
close to the package.
• Socketing a high-speed part like the VCA810 is not recommended. The additional lead length and pin-to-pin
capacitance introduced by the socket can create an extremely troublesome parasitic network, which can
make it almost impossible to achieve a smooth, stable frequency response. Best results are obtained by
soldering the VCA810 onto the board.
Copyright © 2003–2015, Texas Instruments Incorporated
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