add8754dacpz-reel7 Analog Devices, Inc., add8754dacpz-reel7 Datasheet - Page 18

• Manufacturer Part Number: add8754dacpz-reel7
• Description: Lcd Panel Power, Vcom, And Gate Modulation
• Manufacturer: Analog Devices, Inc.

POWER DISSIPATION
The ADD8754’s maximum power dissipation depends on the
thermal resistance from the IC die to the ambient environment
and the ambient temperature. The thermal resistance depends
on the IC package, PC board copper area, other thermal mass,
and airflow. The ADD8754, with the exposed backside pad
soldered to a 2-layer PC board with nine 12 mil-diameter
thermal vias, can dissipate about 1.5 W into 65°C still air before
the die exceeds 125°C. More PC board copper, cooler ambient
air, and more airflow increase the dissipation capability, whereas
less copper or warmer air decreases the IC’s dissipation capability.
The major contributors to the power dissipation are the LDO
regulator and the V
Step-Up Converter
The largest portions of power dissipation in the step-up
converter are the internal MOSFET, the inductor, and the output
diode. For a 90% efficiency step-up converter, about 3% to 5% of
the power is lost in the internal MOSFET, about 3% to 4% in the
inductor, and about 1% in the output diode. The rest of the 1%
to 3% is distributed among the input and output capacitors and
the PC board traces. For an input power of about 3 W, the
power lost in the internal MOSFET is about 90 mW to 150 mW.
LDO
The power dissipated in the LDO depends on the output
current, the output voltage, and the supply voltage:
PD
LDO
= (VIN_1 − LDO_OUT) × I
COM
amplifier.
LDO_OUT
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V
The power dissipated in the V
output current, the output voltage, and the supply voltage:
where:
I
amplifier.
I
AGND.
In a typical case where the supply voltage is 12 V and the output
voltage is 6 V with an output source current of 20 mA, the
power dissipated is 120 mW.
Thermal Overload Protection
Thermal overload protection prevents excessive power dissipation
from overheating the ADD8754. When the junction temperature
exceeds T
fault protection, which shuts down the device, allowing the IC
to cool. The device self-starts once the die temperature falls
below T
Thermal overload protection protects the controller in the event
of fault conditions. For continuous operation, do not exceed the
absolute maximum junction temperature rating of T
OUT
OUT
COM
(source) is the output current sourced by the V
(sink) is the output current that the V
PD
PD
Amplifier
SOURCE
SINK
J
= 105°C.
J
= 145°C, a thermal sensor immediately activates the
= I
= I
OUT
OUT
(sink) × V
(source) × (VDD_2 − V
OUT
COM
amplifier depends on the
COM
OUT
amplifier sinks to
)
ADD8754
COM
J
= 125°C.