BUF16821-Q1 Datasheet, PDF (27/38 Pages) Texas Instruments – Programmable Gamma-Voltage Generator

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10 Layout
BUF16821-Q1
SBOS712 – MAY 2014
10.1 Layout Guidelines
10.1.1 General PowerPAD Design Considerations
The device is available in a thermally-enhanced PowerPAD package. This package is constructed using a
downset leadframe upon which the die is mounted; see Figure 25(a) and Figure 25(b). This arrangement results
in the lead frame being exposed as a thermal pad on the underside of the package; see Figure 25(c). This
thermal pad has direct thermal contact with the die; thus, excellent thermal performance is achieved by providing
a good thermal path away from the thermal pad.
DIE
Side View (a)
DIE
End View (b)
Thermal
Pad
Bottom View (c)
Figure 25. Views of a Thermally-Enhanced PWP Package
The PowerPAD package allows for both assembly and thermal management in one manufacturing operation.
During the surface-mount solder operation (when the leads are being soldered), the thermal pad must 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.
Soldering the PowerPAD to the printed circuit board (PCB) is always required, even with applications that have
low power dissipation. This technique provides the necessary thermal and mechanical connection between the
lead frame die pad and the PCB.
The PowerPAD must be connected to the most negative supply voltage on the device, GNDA and GNDD.
1. Prepare the PCB with a top-side etch pattern. There should be etching for the leads as well as etch for the
thermal pad.
2. Place recommended holes in the area of the thermal pad. Ideal thermal land size and thermal via patterns for
the HTSSOP-28 PWP package can be seen in the technical brief, PowerPAD Thermally-Enhanced Package
(SLMA002), available for download at www.ti.com. These holes should be 13 mils (0.33 mm) in diameter.
Keep these holes small, so that solder wicking through the holes is not a problem during reflow. An example
thermal land pattern mechanical drawing is attached to the end of this data sheet.
3. Additional vias may be placed anywhere along the thermal plane outside of the thermal pad area to help
dissipate the heat generated by the device. These additional vias may be larger than the 13-mil diameter
vias directly under the thermal pad. These vias can be larger because they are not in the thermal pad area to
be soldered; thus, wicking is not a problem.
4. Connect all holes to the internal plane that is at the same voltage potential as the GND pins.
Copyright © 2014, Texas Instruments Incorporated
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