THS4509 Datasheet, PDF (30/42 Pages) Texas Instruments – WIDEBAND, LOW NOISE, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIER

THS4509
SLOS454H – JANUARY 2005 – REVISED NOVEMBER 2009
Layout Recommendations
It is recommended to follow the layout of the external
components near the amplifier, ground plane
construction, and power routing of the EVM as
closely as possible. General guidelines are:
1. Signal routing should be direct and as short as
possible into and out of the op amp circuit.
2. The feedback path should be short and direct;
avoid vias.
3. Ground or power planes should be removed from
directly under the amplifier input and output pins.
4. An output resistor is recommended on each
output, as near to the output pin as possible.
5. Two 10-μF and two 0.1-μF power-supply
decoupling capacitors should be placed as near
to the power-supply pins as possible.
6. Two 0.1-μF capacitors should be placed between
the CM input pins and ground. This configuration
limits noise coupled into the pins. One each
should be placed to ground near pin 4 and pin 9.
7. It is recommended to split the ground panel on
layer 2 (L2) as shown below and to use a solid
ground on layer 3 (L3). A single-point connection
should be used between each split section on L2
and L3.
8. A single-point connection to ground on L2 is
recommended for the input termination resistors
R1 and R2. This configuration should be applied
to the input gain resistors if termination is not
used.
9. The THS4509 recommended PCB footprint is
shown in Figure 93.
PowerPAD™ DESIGN CONSIDERATIONS
The THS4509 is available in a thermally-enhanced
PowerPAD family of packages. These packages are
constructed using a downset leadframe on which the
die is mounted (see Figure 92a and Figure 92b). This
arrangement results in the lead frame being exposed
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as a thermal pad on the underside of the package
(see Figure 92c). Because this thermal pad has direct
thermal contact with the die, excellent thermal
performance can be achieved by providing a good
thermal path away from the thermal pad.
Note that the THS4509 has no electrical connection
between the PowerPAD and circuitry on the die.
Connecting the PowerPAD to any potential voltage
between V_S+ and V_S– is acceptable. It is most
important that it be connected for maximum heat
dissipation.
The PowerPAD package allows both assembly and
thermal management in one manufacturing operation.
During the surface-mount solder operation (when the
leads are being soldered), the thermal pad can also
be soldered to a copper area underneath the
package. Through the use of thermal paths within this
copper area, heat can be conducted away from the
package into either a ground plane or other heat
dissipating device.
The PowerPAD package represents a breakthrough
in combining the small area and ease of assembly of
surface-mount with the previously awkward
mechanical methods of heatsinking.
DIE
Side View (a)
DIE
End View (b)
Bottom View (c)
Figure 92. Views of Thermally-Enhanced Package
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