Datasheet

AD9557 Data Sheet
Rev. B | Page 52 of 92
THERMAL PERFORMANCE
Table 31. Thermal Parameters for the 40-Lead LFCSP Package
Symbol Thermal Characteristic Using a JEDEC51-7 Plus JEDEC51-5 2S2P Test Board
1
Value
2
Unit
θ
JA
Junction-to-ambient thermal resistance, 0.0 m/sec airflow per JEDEC JESD51-2 (still air) 30.2 °C/W
θ
JMA
Junction-to-ambient thermal resistance, 1.0 m/sec airflow per JEDEC JESD51-6 (moving air)
26.4
°C/W
θ
JMA
Junction-to-ambient thermal resistance, 2.5 m/sec airflow per JEDEC JESD51-6 (moving air) 23.6 °C/W
θ
JB
Junction-to-board thermal resistance, 0.0 m/sec airflow per JEDEC JESD51-8 (still air) 16.3 °C/W
θ
JC
Junction-to-case thermal resistance (die-to-heat sink) per MIL-Std 883, Method 1012.1 2.2 °C/W
Ψ
JT
Junction-to-top-of-package characterization parameter, 0 m/sec airflow per JEDEC JESD51-2 (still air) 0.2 °C/W
1
The exposed pad on the bottom of the package must be soldered to ground to achieve the specified thermal performance.
2
Results are from simulations. The PCB is a JEDEC multilayer type. Thermal performance for actual applications requires careful inspection of the conditions in the
application to determine if they are similar to those assumed in these calculations.
The AD9557 is specified for a case temperature (T
CASE
). To ensure
that T
CASE
is not exceeded, an airflow source can be used. Use the
following equation to determine the junction temperature on the
application PCB:
T
J
= T
CASE
+ (Ψ
JT
× PD)
where:
T
J
is the junction temperature (°C).
T
CASE
is the case temperature (°C) measured by the customer at the
top center of the package.
Ψ
JT
is the value as indicated in Table 31.
PD is the power dissipation (see the Table 3).
Values of θ
JA
are provided for package comparison and PCB
design considerations. θ
JA
can be used for a first order approxi-
mation of T
J
by the following equation:
T
J
= T
A
+ (θ
JA
× PD)
where T
A
is the ambient temperature (°C).
Values of θ
JC
are provided for package comparison and PCB
design considerations when an external heat sink is required.
Values of θ
JB
are provided for package comparison and PCB
design considerations.