Datasheet

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