AD9530 datasheet(26/41 Pages) AD

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AD9530

Data Sheet

Rev. 0 | Page 26 of 41

POWER DISSIPATION AND THERMAL CONSIDERATIONS

The AD9530 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 AD9530.

The AD9530 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 14). 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 AD9530 for a given set of operating

conditions.

The AD9530 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 14.

PD is the power dissipation of the AD9530.

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.

Table 3 lists the currents required by the driver for a single

output frequency. If using the current vs. frequency graphs

provided in the Typical Performance Characteristics section,

subtract the power into the load using the following equation:

PLOAD = (Differential Output Voltage Swing2/50 Ω)

EVALUATION OF OPERATING CONDITIONS

The first step in evaluating the operating conditions is to

determine the AD9530 maximum power consumption for the

user configuration by referring to the values in Table 2. The

maximum PD excludes power dissipated in the load resistors of

the drivers because such power is external to the device. Use the

current dissipation specifications listed in Table 2, as well as the

power dissipation numbers in Table 3 to calculate the total

power dissipated for the desired configuration.

The second step in evaluating the operating conditions is to

multiply the power dissipated by the thermal impedance to

determine the maximum power gradient. For this example, a

thermal impedance of θJA = 21.1°C/W is used.

Example 1

Example 1 is as follows:

(1358 mW × 21.1°C/W) = 29°C

With an ambient temperature of 85°C, the junction temperature is

TJ = 85°C + 29°C = 114°C

This junction temperature is below the maximum allowable

temperature.

Example 2

Example 2 is as follows:

(1630 mW × 21.1°C/W) = 34°C

With an ambient temperature of 85°C, the junction temperature is

TJ = 85°C + 34°C = 119°C

This junction temperature is greater than the maximum allowable

temperature. The ambient temperature must be lowered by 4°C

to operate in the condition of Example 2.

THERMALLY ENHANCED PACKAGE MOUNTING

GUIDELINES

See the AN-772 Application Note, A Design and Manufacturing

Guide for the Lead Frame Chip Scale Package (LFCSP), for more

information about mounting devices with an exposed pad.

AD9530 Datasheet(PDF) 26 Page - Analog Devices

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