AD9528BCPZ datasheet(46/67 Pages) AD

46 / 67 page

AD9528

Data Sheet

Rev. D | Page 46 of 67

POWER DISSIPATION AND THERMAL CONSIDERATIONS

The AD9528 is a multifunctional, high speed device that targets

a wide variety of clock applications. The numerous innovative

features contained in the device each consume incremental

power. If all outputs are enabled in the maximum frequency and

mode that have the highest power, the safe thermal operating

conditions of the device may be exceeded. Careful analysis and

consideration of power dissipation and thermal management

are critical elements in the successful application of the

AD9528.

The AD9528 is specified to operate within the industrial

temperature range of –40°C to +85°C. This specification is

conditional, such that the absolute maximum junction

temperature is not exceeded (as specified in Table 19). At high

operating temperatures, extreme care must be taken when

operating the device to avoid exceeding the junction

temperature and potentially damaging the device.

Many variables contribute to the operating junction

temperature within the device, including

•

Selected driver mode of operation

•

Output clock speed

•

Supply voltage

•

Ambient temperature

The combination of these variables determines the junction

temperature within the AD9528 for a given set of operating

conditions.

The AD9528 is specified for an ambient temperature (TA). To

ensure that TA is not exceeded, use an airflow source.

Use the following equation to determine the junction

temperature on the application PCB:

TJ = TCASE + (ΨJT × PD)

where:

TJ is the junction temperature (°C).

TCASE is the case temperature (°C) measured at the top center of

the package.

ΨJT is the value from Table 20.

PD is the power dissipation of the AD9528.

Values of θJA are provided for package comparison and PCB

design considerations. θJA can be used for a first order

approximation of TJ by the equation

TJ = TA + (θJA × PD)

where TA is the ambient temperature (°C).

Values of θJC are provided for package comparison and PCB

design considerations when an external heat sink is required.

Values of ΨJB are provided for package comparison and PCB

design considerations.

CLOCK SPEED AND DRIVER MODE

Clock speed directly and linearly influences the total power

dissipation of the device and, therefore, the junction temperature.

Two operating frequencies are listed under the incremental power

dissipation parameter in Table 3. Using linear interpretation is a

sufficient approximation for frequency not listed in the table.

When calculating power dissipation for thermal consideration,

remove the amount of power dissipated in the 100 Ω resistor. If

using the data in Table 3, this power is already removed. If using

the current vs. frequency graphs provided in the Typical

Performance Characteristics section, the power into the load

must be subtracted, using the following equation:

PLOAD = Differential Output Voltage Swing2/100 Ω

EVALUATION OF OPERATING CONDITIONS

The first step in evaluating the operating conditions is to

determine the maximum power consumption (PD) internal to

the AD9528. The maximum PD excludes power dissipated in

the load resistors of the drivers because such power is external

to the device. Use the power dissipation specifications listed in

Table 3 to calculate the total power dissipated for the desired

configuration.

Table 34 and Table 35 summarize the incremental power

dissipation from the base power configuration for two different

examples.

Table 34. Temperature Gradient Examples, Example 1

Description

Mode

Frequency

(MHz)

Maximum

Power (mW)

Base Typical

Configuration

N/A1

590

Output Driver

6 × HSTL

122.88

480

Output Driver

3 × LVDS

122.88

210

Output Driver

1 × LVDS

409.6

Total Power

1358

1 N/A means not applicable.

Table 35. Temperature Gradient Examples, Example 2

Description

Mode

Frequency

(MHz)

Maximum

Power (mW)

Base Typical

Configuration

N/A1

590

Output Driver

13 × HSTL

122.88

1040

Total Power

1630

1 N/A means not applicable.

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