ADD8754ACPZ-REEL 查看數據表（PDF） - Analog Devices

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ADD8754ACPZ-REEL

LCD Panel Power, VCOM, and Gate Modulation

Analog Devices 

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 VCOM amplifier.

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:

PDLDO = (VIN_1 − LDO_OUT) × ILDO_OUT

ADD8754

VCOM Amplifier

The power dissipated in the VCOM amplifier depends on the

output current, the output voltage, and the supply voltage:

PDSOURCE = IOUT (source) × (VDD_2 − VOUT)

PDSINK = IOUT (sink) × VOUT

where:

IOUT (source) is the output current sourced by the VCOM

amplifier.

IOUT (sink) is the output current that the VCOM amplifier sinks to

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 TJ = 145°C, a thermal sensor immediately activates the

fault protection, which shuts down the device, allowing the IC

to cool. The device self-starts once the die temperature falls

below TJ = 105°C.

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 TJ = 125°C.

Rev. 0 | Page 18 of 28

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