AD9852ASQ Analog Devices Inc, AD9852ASQ Datasheet - Page 39

• Manufacturer Part Number: AD9852ASQ
• Manufacturer: Analog Devices Inc

Specifications of AD9852ASQ

• Lead Free Status / RoHS Status: Not Compliant

POWER DISSIPATION AND THERMAL CONSIDERATIONS
The AD9852 is a multifunctional, very high speed device that
targets a wide variety of synthesizer and agile clock applications.
The numerous innovative features contained in the device each
consume incremental power. If enabled in combination, the safe
thermal operating conditions of the device may be exceeded.
Careful analysis and consideration of power dissipation and
thermal management is a critical element in the successful
application of the AD9852 device.
The AD9852 device is specified to operate within the industrial
temperature range of –40°C to +85°C. This specification is con-
ditional, however, such that the absolute maximum junction
temperature of 150°C is not exceeded. At high operating tem-
peratures, extreme care must be taken when operating the device
to avoid exceeding the junction temperature, which could result
in a damaging thermal condition.
Many variables contribute to the operating junction
temperature within the device, including
1.
2.
3.
4.
5.
The combination of these variables determines the junction
temperature within the AD9852 device for a given set of
operating conditions.
The AD9852 device is available in two package styles: a
thermally enhanced surface-mount package with an exposed
heat sink, and a nonthermally enhanced surface-mount
package. The thermal impedance of these packages is 16°C/W
and 38°C/W, respectively, measured under still-air conditions.
THERMAL IMPEDANCE
The thermal impedance of a package can be thought of as a
thermal resistor that exists between the semiconductor surface
and the ambient air. The thermal impedance of a package is
determined by the package material and its physical dimensions.
The dissipation of the heat from the package is directly depen-
dent on the ambient air conditions and the physical connection
made between the IC package and the PCB. Adequate dissipation
of power from the AD9852 relies upon all power and ground pins
of the device being soldered directly to a copper plane on a PCB.
In addition, the thermally enhanced package of the AD9852ASQ
contains a heat sink on the bottom that must be soldered to a
ground pad on the PCB surface. This pad must be connected to
a large copper plane, which, for convenience, can be the ground
plane. Sockets for either package style of the AD9852 device are
not recommended.
Package style.
Selected mode of operation.
Internal system clock speed.
Supply voltage.
Ambient temperature.
Rev. D | Page 39 of 52
JUNCTION TEMPERATURE CONSIDERATIONS
The power dissipation (P
application is determined by many operating conditions. Some
of the conditions have a direct relationship with P
supply voltage and clock speed, but others are less deterministic.
The total power dissipation within the device and its effect on
the junction temperature must be considered when using the
device. The junction temperature of the device is given by
Given that the junction temperature should never exceed 150°C
for the AD9852 and that the ambient temperature can be 85°C,
the maximum power consumption is 1.7 W for the AD9852AST
and 4.1 W for the AD9852ASQ (thermally enhanced package).
Factors affecting the power dissipation are described is the
Supply Voltage section.
Supply Voltage
Because P
dissipation and junction temperature. Users should design for
3.3 V nominally; however, the device is guaranteed to meet
specifications over the full temperature range and the supply
voltage range of 3.135 V to 3.465 V.
Clock Speed
Clock speed directly and linearly influences the total power
dissipation of the device, and, therefore, the junction temperature.
As a rule, the user should select the lowest internal clock speed
possible to support a given application to minimize power
dissipation. Typically the usable frequency output bandwidth
from a DDS is limited to 40% of the clock rate to keep
reasonable requirements on the output low-pass filter. For the
typical DDS application, the system clock frequency should be
2.5 times the highest desired output frequency.
Mode of Operation
The selected mode of operation for the AD9852 has a great
influence on total power consumption. The AD9852 offers
many features and modes, each of which imposes an additional
power requirement. The collection of features contained in the
AD9852 targets a wide variety of applications, and the device
was designed under the assumption that only a few features
would be enabled for any given application. In fact, the user
must understand that enabling multiple features at higher clock
speeds can cause the maximum junction temperature of the die
to be exceeded. This can severely limit the long-term reliability
of the device. Figure 59 and Figure 60 show the power require-
ments associated with the individual features of the AD9852.
These charts should be used as a guide in determining how to
optimize the AD9852 for reliable operation in a specific
application.
Junction Temperature = (Thermal Impedance ×
Power Consumption) + Ambient Temperature
DISS
= V × I, the supply voltage obviously affects power
DISS
) of the AD9852 device in a given
DISS
AD9852
, such as