21
1
CAPACITOR TYPE CHIP SIZE THERMAL IMPEDANCE (°C/W)
Accu-P
®
0805 6.5
1210 5
Microwave MLC 0505 12
1210 7.5
ADVANTAGES OF ACCU-P
®
IN RF POWER CIRCUITS
The optimized design of Accu-P
®
offers the designer of RF
power circuits the following advantages:
• Reduced power losses due to the inherently low ESR of
Accu-P
®
.
• Increased power dissipation due to the high thermal
conductivity of Accu-P
®
.
PRACTICAL APPLICATION
IN RF POWER CIRCUITS
• There is a wide variety of different experimental methods
for measuring the power handling performance of a
capacitor in RF power circuits. Each method has its
own problems and few of them exactly reproduce the
conditions present in “real” circuit applications.
• Similarly, there is a very wide range of different circuit appli-
cations, all with their unique characteristics and operating
conditions which cannot possibly be covered by such
“theoretical” testing.
• THE ONLY TRUE TEST OF A CAPACITOR IN ANY PARTICULAR
APPLICATION IS ITS PERFORMANCE UNDER OPERATING
CONDITIONS IN THE ACTUAL CIRCUIT.
Accu-F
®
/ Accu-P
®
Performance Characteristics RF Power Applications
RF POWER APPLICATIONS
In RF power applications capacitor losses generate heat. Two
factors of particular importance to designers are:
• Minimizing the generation of heat.
• Dissipating heat as efficiently as possible.
CAPACITOR HEATING
• The major source of heat generation in a capacitor in RF
power applications is a function of RF current (I) and ESR,
from the relationship:
Power dissipation = I
2
RMS
x ESR
• Accu-P
®
capacitors are specially designed to minimize
ESR and therefore RF heating. Values of ESR for
Accu-P
®
capacitors are significantly less than those of
ceramic MLC components currently available.
HEAT DISSIPATION
• Heat is dissipated from a capacitor through a variety of
paths, but the key factor in the removal of heat is the
thermal conductivity of the capacitor material.
• The higher the thermal conductivity of the capacitor, the
more rapidly heat will be dissipated.
• The table below illustrates the importance of thermal
conductivity to the performance of Accu-P
®
in power
applications.
1210
0805
Amps
8
6
4
2
0
0 200 400 600 800 1000 1200 1400MHz
1210
0805
0603
0402
PRODUCT MATERIAL THERMAL CONDUCTIVITY W/mK
Accu-P
®
Alumina 18.9
Microwave MLC Magnesium Titanate 6.0
Power Handling
Accu-P
®
10pF
Data used in calculating the graph:
Thermal impedance of capacitors:
0402 17°C/W
0603 12°C/W
0805 6.5°C/W
1210 5°C/W
Thermal impedance measured using RF generator,
amplifier and strip-line transformer.
ESR of capacitors measured on Boonton 34A
THERMAL IMPEDANCE
Thermal impedance of Accu-P
®
chips is shown below com-
pared with the thermal impedance of Microwave MLC’s.
The thermal impedance expresses the temperature difference
in °C between chip center and termination caused by
a power dissipation of 1 watt in the chip. It is expressed in
°C/W.
