VCA8500_0803 Datasheet, PDF (33/40 Pages) Texas Instruments – 8-Channel, Ultralow-Power, Variable Gain Amplifier with Low-Noise Pre-Amp

VCA8500
www.ti.com
GROUNDING AND BYPASSING
The VCA8500 uses a thermally-enhanced QFN
package, with an exposed PowerPAD on the back
side of the package. This backside pad is the only
ground reference point of the VCA8500, and it should
be connected to a low-noise system ground plane. All
bypassing and power supplies for the VCA8500
should be referenced to this ground point.
All supply pins should be bypassed with 0.1µF
ceramic chip capacitors (size 0603 or smaller). In
order to minimize lead and trace inductance, the
capacitors should be located as close to the supply
pins as possible. Where double-sided component
mounting is allowed, these capacitors are best placed
directly under the package. In addition, larger bipolar
decoupling capacitors (2.2µF to 10µF), effective at
lower frequencies, may also be used on the main
supply pins. They can be placed on the PCB in
proximity to (less than 0.5in, or 12.7mm from) the
VCA8500.
The VCA8500 internally generates a number of
reference voltages, such as the bias voltages (VB1
through VB6). Note that in order to achieve the best
low-noise performance, VB1 (pin 13) must be
bypassed with a capacitor value of at least 1µF; the
recommended value is 2.2µF. All other designated
SBOS390A – JANUARY 2008 – REVISED MARCH 2008
reference pins can be bypassed with smaller
capacitor values, typically 0.1µF. For best results
choose low-inductance ceramic chip capacitors (size
402) and place them as close to the device pins as
possible.
BOARD LAYOUT
Proper grounding and bypassing, short lead length,
and the use of ground planes are particularly
important for high-frequency designs. Achieving
optimum performance with a high gain amplifier such
as the VCA8500 requires careful attention to the PCB
layout to minimize the effect of board parasitics and
optimize component placement. A multilayer PCB
usually ensures best results and allows convenient
component placement.
More details on the PowerPAD PCB layout and
assembly process can be found in the Texas
Instruments Application Reports, Power-Pad
Thermally-Enhanced Package (SLMA002), and
QFN/SON PCB Attachment (SLUA271A). These
documents can be downloaded from the TI web site
(www.ti.com).
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): VCA8500
Submit Documentation Feedback
33