AD8385ASVZ datasheet(8/24 Pages) AD

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AD8385

Rev. 0 | Page 8 of 24

OVERLOAD PROTECTION

The AD8385 employs a 2-stage overload protection circuit with

an enable/disable function that is programmable through the

3-wire serial interface. It consists of an output current limiter

and a thermal shut down.

When enabled, the maximum current at any one output of the

AD8385 is, on average, internally limited to 100 mA. In the

event of a momentary short circuit between a video output and

a power supply rail (VCC or AGND), the output current limit is

sufficiently low to provide temporary protection.

The thermal shutdown debiases the output amplifier when the

junction temperature reaches the internally set trip point. In the

event of an extended short circuit between a video output and a

power supply rail, the output amplifier current continues to

switch between 0 mA and 100 mA typ, with a period deter-

mined by the thermal time constant and the hysteresis of the

thermal trip point. Thermal shutdown provides long-term

protection by limiting the average junction temperature to a

safe level. When disabled, no overload protection is present.

EXPOSED PADDLE

To ensure optimal thermal performance, the exposed paddle

must be electrically connected to an external plane such as

AVCC or GND, as described in the Applications Circuit section.

MAXIMUM POWER DISSIPATION

The junction temperature limits the maximum power that can

be safely dissipated by the AD8385. The maximum safe junction

temperature for plastic encapsulated devices, determined by the

glass transition temperature of the plastic, is approximately

150°C. Exceeding this limit can cause a temporary shift in the

parametric performance due to a change in the stresses exerted

on the die by the package. Exceeding a junction temperature of

175°C for an extended period can result in device failure.

OPERATING TEMPERATURE RANGE

The maximum operating junction temperature is 150°C. The

junction temperature trip point of the overload protection is

165°C. Production test guarantees a minimum junction

temperature trip point of 125°C.

Consequently, the maximum guaranteed operating junction

temperature is 125°C with the overload protection enabled, and

150°C with the overload protection disabled.

To ensure operation within the specified operating temperature

range, the maximum power dissipation must be limited:

(

)

(

lfm

Airflow

JMAX

DMAX

−

≈

1.5

2.5

2.0

3.0

*65

100

105

110

105

100

**90

115

120

125

130

AMBIENT TEMPERATURE (°C)

STILL AIR

200 lfm

500 lfm

100MHz

60Hz XGA

QUIESCENT

*OVERLOAD PROTECTION ENABLED

**OVERLOAD PROTECTION DISABLED

AD8385 on a 4-layer JEDEC PCB with a thermally optimized landing pattern,

as described in the Applications Circuit section.

Figure 2. Maximum Power Dissipation vs. Temperature

Note that the quiescent power dissipation of the AD8385 is

1.84 W when operating under the conditions specified in this

data sheet. When driving a 12-channel XGA panel with an input

capacitance of 150 pF, the AD8385 dissipates a total of 2.3 W

when displaying 1 pixel wide alternating white and black

vertical lines generated by a standard 60 Hz XGA input video.

When the frequency of the pixel clock is raised to 100 MHz, the

total power dissipation increases to 2.54 W. These specific

power dissipations are shown in Figure 2 for reference.

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