ADD8708 Analog Devices, Inc., ADD8708 Datasheet - Page 11

• Manufacturer Part Number: ADD8708
• Description: 18-channel Gamma Buffer With Regulator
• Manufacturer: Analog Devices, Inc.

VOLTAGE REGULATOR
The on-board voltage regulator provides a regulated voltage to
the resistor chain to provide stable gamma voltages.
The two mask-programmable internal resistors, R
and a reference voltage set the output of the regulator. The
typical values of these parts are shown in Figure 23. In addition,
see the Tap Point and Regulator Voltage Request Form in this
data sheet.
The internal resistors have a typical accuracy of 0.1%. External
resistors can be used to adjust the regulator voltage; however, it
is not recommended. Please contact your local sales office for
further details.
MAXIMUM POWER DISSIPATION
The maximum safe power dissipation in the ADD8708 package
is limited by the associated rise in junction temperature (T
the die. At approximately 150°C, the glass transition tempera-
ture, the properties of the plastic change. Even temporarily
exceeding this temperature limit may change the stresses that
the package exerts on the die, permanently shifting the para-
metric performance of the ADD8708. Exceeding a junction
temperature of 175°C for an extended period can result in
changes in the silicon devices, potentially causing failure.
V
1.2V
5kΩ
REF
Figure 23. Voltage Regulator
R
1
+
–
55kΩ
R
2
V
REG OUT
1
and R
2
,
J
) on
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LAND PATTERN
The LFCSP package comes with a thermal pad. Soldering down
this thermal pad dramatically improves the heat dissipation of
the package. It is necessary to attach vias that connect the
soldered thermal pad to another layer on the board. This
provides an avenue to dissipate the heat away from the part.
Without vias, the heat is isolated directly under the part.
Subdivide the solder paste, or stencil layer, for the thermal pad
to reduce solder balling and splatter. It is not critical how the
subdivisions are arranged, as long as the total coverage of the
solder paste for the thermal pad is greater than 50%. The land
pattern is critical to heat dissipation. A suggested land pattern is
shown in Figure 22.
The thermal pad is attached to the substrate. In the ADD8708,
the substrate is connected to V
thermal pad should be soldered to an area on the board that is
electrically isolated or connected to V
pad to ground adversely affects the performance of the part.
DD
. To be electrically safe, the
DD
. Attaching the thermal
ADD8708