AD9852SLASHPCB datasheet(32/42 Pages) AD

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AD9852

–32–

REV. 0

FREQUENCY – MHz

1400

1200

1000

800

600

400

200

100

140

180

220

260

300

Figure 57a. Power Consumption vs. Clock Frequency

Showing Supply Current Consumption When All Optional

Circuitry Is Enabled

FREQUENCY – MHz

450

400

350

300

250

200

150

100

140

180

220

260

300

100

MULTIPLIERS

INVERSE SINC

AUX DAC

COMPARATOR

Figure 57b. Decrease in Current Consumption When Vari-

ous Circuitry Is Disabled

EVALUATION OF OPERATING CONDITIONS

The ﬁrst step in applying the AD9852 is to select the internal

clock frequency. Clock frequency selections above 200 MHz

will require the thermally-enhanced package (AD9852ASQ);

clock frequency selections of 200 MHz and below may allow the

user to use the standard plastic surface-mount package, but more

information will be needed to make that determination.

The second step is to determine the maximum required operating

temperature for the AD9852 in the given application. Subtract

this value from 150

°C, which is the maximum junction tem-

perature allowed for the AD9852. For the extended industrial

temperature range of 85

°C, the result will be 65°C. This is the

maximum rise in temperature that the junction may experience

due to power dissipation.

The third step is to divide this maximum rise number by the

thermal impedance, to arrive at the maximum power dissipation

allowed for the application. For the example, so far, 65

°C divided

by both versions of the AD9852 package’s thermal impedances

of 38

°C/W and 16°C/W, yields a total power dissipation limit

of 1.7 W and 4.1 W (respectively). This means that for a 3.3 V

nominal power supply voltage, the current consumed by the device

under full operating conditions must not exceed 515 mA in the

standard plastic package and 1242 mA in the thermally-enhanced

package. The total set of enabled functions and operating condi-

tions of the AD9852 application must support these current

consumption limits.

Figure 57a and 57b may be used to determine the suitability

of a given AD9852 application vs. power dissipation requirements.

These graphs assume that the AD9852 device will be soldered to

a multilayer PCB per the recommended best manufacturing

practices and procedures for the given package type. This ensures

that the speciﬁed thermal impedance speciﬁcations will be

achieved.

THERMALLY ENHANCED PACKAGE MOUNTING

GUIDELINES

The following are general recommendations for mounting the

thermally enhanced exposed heat sink package (AD9852ASQ)

to printed circuit boards. The exceptional thermal characteristics of

this package depend entirely upon proper mechanical attachment.

Figure 58 depicts the package from the bottom and shows the

dimensions of the exposed heat sink. A solid conduit of solder

needs to be established between this pad and the surface of

the PCB.

Figure 59 depicts a general PCB land pattern for such an exposed

heat sink device. Note that this pattern is for a 64-lead device not

an 80-lead, but the relative shapes and dimensions still apply.

In this land pattern, a solid copper plane exists inside of the

individual lands for device leads. Note also that the solder mask

opening is conservatively dimensioned to avoid any assembly

problems.

UNT

14mm

10mm

Figure 58.

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