AWT6264R Thermal App Note Rev 0

Application Note
Thermal Design for AWT6264R
Rev 0
RELEVANT PRODUCTS
•
AWT6264R
INTRODUCTION
ANADIGICS’ AWT6264 Mobile WiMAX Power
Amplifier is a high performance device that delivers
exceptional linearity and efficiency at high output
power levels. The device operates over the voltage
supply range of +3.0 VDC to +4.2 VDC and its output
power handling capabilities increase as the supply
voltage is raised towards the high end of this range.
At higher output powers, thermal considerations
need to be taken into account in order to maintain
high level of device reliability.
This application note addresses thermal design
considerations for the AWT6264 by first measuring
the junction-to-case thermal characteristics of the
device, and performing a case-to-ambient thermal
analysis. Thermal design examples and guidelines
are then offered for specific applications and circuit
boards used.
THERMAL CHARACTERIZATION AND ANALYSIS
Thermal characterizations of the AWT6264 were
performed on an open cavity device (no mold
compound) that was mounted to an evaluation board.
The AWT6264 is a class A/B amplifier, and thus
requires RF drive in order for the output stage to be
fully operational. The thermal characterizations were
performed using a DC bias of 3.3 V and 4.2 V and a
2.5 GHz CW (no modulation) signal of various power
levels, in order to produce total currents between 300
mA and 500 mA in steps of 50 mA. This procedure
was used to validate the consistency of the measured
junction-case thermal resistance.
In performing the thermal scans, the evaluation board
temperature was raised until the case temperature
(Tc) of the device was 85 °C, as measured at the
bottom of the package. The peak thermal rise was
detected at the output amplification stage, and was
therefore used to derive the junction-case thermal
resistance (θJ-C) for the device.
Tables 1a and 2a show the thermal analysis based on
infrared images of the device-under-test operating at
3.3 V and at 4.2 V. The data presents the derivations
of the junction-case thermal resistance (θJ-C) under
multiple drive conditions
Tables 1b and 2b show the derivation of the junction
temperatures (TJ) when Tc is at 30 °C and 85.4 °C.
The typical value for TJ as presented was calculated
based on devices with a typical output stage gain
of 10.5 dB, an average θ J-C of 14.6 °C/W for a 3.3
V supply and 16.8 °C/W for a 4.2 V supply, and an
output power of +25 dBm (nominal).
06/2010
Thermal Design for AWT6264R
Table 1a: Thermal Analysis of an AWT6264 Device Operating at 3.3 V under Multiple Drive Conditions
Thermal characterizations under drive conditions
#1
#2
#3
#4
#5
Unit
[email protected]
299.5
350.9
400.5
450.3
501.7
mA
Typicalcurrent(1stand2ndstage)
ICC1+ICC2(pin1)
66.6
71.6
77.2
83.5
91.9
mA
Typicalcurrentatoutputstage
ICC3(pin12)
232.9
279.3
323.3
366.8
409.8
mA
Typicaldcpowerdissipationat
theoutputstage(P3)
0.769
0.922
1.067
1.210
1.352
W
MeasuredTjatoutputstage
96.4
97.2
97.5
98.2
99.3
°C
DC Analysis
Tc
85.4
Temperaturerisemeasured
°C
11.0
11.8
12.1
12.8
13.9
°C
19.70
21.74
23.37
24.96
26.22
dBm
0.093
0.149
0.217
0.313
0.419
W
RF Analysis
RFoutputpower(PRF-OUT)
TypicalRFgainoftheoutputstage
10.5
RFinputpowerattheoutputstage(PRF-IN3)
dB
9.20
11.24
12.87
14.46
15.72
dBm
8.32
13.30
19.36
27.93
37.32
mW
0.683
0.786
0.869
0.925
0.971
W
16.1
15.0
13.9
13.8
14.3
°C/W
Junction-case Thermal Resistance Analysis
Powerdissipation
(P3+PRF-IN3-PRF-OUT)
Junction-casethermalresistance( J-C)
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Application Note - Rev 0
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Thermal Design for AWT6264R
The example calculation below is for the AWT6264 device at 30 °C at 3.3 VDC, POUT = +25 dBm:
Power Dissipated in the Output Stage: PDISS = PIN – POUT = (VCC*ICC3) + PRF-IN3 – PRF-OUT
= (3.3 * 0.373) + (27.93*10-3) - 0.313 = 0.946 W
Thermal rise of junction for the packaged device = PDISS * θJ-C = 0.946 * 14.64 = 13.85 °C
Calculated Junction Temperature with case at 30 °C = 30 °C + 13.9 °C = 43.9 °C
Table 1b: Derivation of AWT6264 Junction Temperatures with 3.3 V supply
CaseTemperature
30
85.4
°C
[email protected](typical)
453.6
450.3
mA
[email protected](typical)
373.0
366.8
mA
OutputStagePowerDissipation(typical)
0.946
0.925
W
TemperatureRisecalculatedusingavg.
J-Cof14.6°C/W
13.9
13.5
°C
calculated Junction Temperature TJ
43.9
98.9
°C
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3
Thermal Design for AWT6264R
Table 2a: Thermal Analysis of an AWT6264 Device Operating at 4.2 V under Multiple Drive Conditions
Thermal characterizations under drive conditions
#1
#2
#3
#4
#5
Unit
[email protected]
300.5
352.6
400.6
453.4
503.6
mA
Typicalcurrent(1stand2ndstage)
ICC1+ICC2(pin1)
68.4
72.8
77.8
83.7
89.7
mA
Typicalcurrentatoutputstage
ICC3(pin12)
232.1
279.8
322.8
369.7
413.9
mA
TypicalDCpowerdissipationat
theoutputstage(P3)
0.975
1.175
1.356
1.553
1.738
W
MeasuredTjatoutputstage
102.1
104.1
105.1
105.9
107.1
°C
DC Analysis
Tc
85.4
Temperaturerisemeasured
°C
16.7
18.7
19.7
20.5
21.7
°C
19.37
21.15
22.63
24.04
25.45
dBm
0.087
0.130
0.183
0.254
0.351
W
RF Analysis
RFoutputpower(PRF-OUT)
TypicalRFgainoftheoutputstage
10.5
dB
8.87
10.65
12.13
13.54
14.95
dBm
7.71
11.61
16.30
22.60
31.30
mW
Powerdissipation(P3+PRF-IN3-PRF-OUT)
0.895
1.057
1.193
1.313
1.418
W
Junction-casethermalresistance( J-C)
18.7
17.7
16.5
15.6
15.3
°C/W
RFinputpowerattheoutputstage(PRF-IN3)
Junction-case Thermal Resistance Analysis
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Application Note - Rev 0
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Thermal Design for AWT6264R
The example below is for the AWT6264 device operating at 30 °C at 4.2 VDC:, POUT = +24.7 dBm
Power Dissipated in the Output Stage: PDISS = PIN – POUT = (VCC*ICC3) + PRF-IN3 – PRF-OUT
= (4.2 * 0.4504) + (26.30*10-3) - 0.295 = 1.623 W
Thermal rise of junction for the packaged device = PDISS * θJ-C = 1.623 * 16.8 = 27.27 °C
Calculated Junction Temperature with case at 30°C = 30 + 27.3 °C = 57.3 °C
Table 2b: Derivation of AWT6264 Junction Temperatures with 4.2 V supply
CaseTemperature
30
85.4
°C
[email protected](typical)
450.4
453.4
mA
[email protected](typical)
373.1
369.7
mA
OutputStagePowerDissipation(typical)
1.623
1.396
W
TemperatureRisecalculatedusingavg.
J-Cof16.8°C/Wat4.2V
27.3
23.5
°C
calculated Junction Temperature TJ
57.3
108.9
°C
PRINTED CIRCUIT BOARD
DESIGN CONSIDERATIONS
THERMAL
In general, it is essential to keep the junction
temperature of the device as low as possible to
ensure long operating life. This can be accomplished
by providing good thermal relief and adequate
heat sinking. When mounted to a printed circuit
board (PCB), the delta between the device case
temperature and the ambient temperature will be
determined by several factors; board thickness and
number of layers, copper plating thickness, size
and number of via holes placed beneath the device
package ground area, the PCB layout, the method
of attachment of the PCB to the heat sink as well as
the design of the heat sink. For typical applications,
it is recommended to maximize the number of vias
placed below the package ground area.
ANADIGICS’ standard AWT6264 evaluation board
(EVB) is fabricated using double sided Rogers R3003
PCB material which has a dielectric constant of 3.38,
dielectric thickness of 0.008” (0.2 mm), and copper
thickness of 0.0021” (0.054 mm).
Table 3 shows the calculation of the junction
temperature (TJ) based on the standard AWT6264
EVB operating at 3.3 V and 4.2 V with output power
levels of +25 dBm and +27 dBm, respectively. The
data has been verified by using thermal imagery of
the die in the laboratory.
The AWT6264 is packaged in a 4.0 mm x 4.0 mm
laminate-based module with a backside ground
pad of an area of 2.36 mm x 3.80 mm (0.093” x
0.150”). This ground pad provides RF, DC, and
thermal ground for the package. Using vias that are
fabricated with 0.012” (0.3 mm) and 0.010” (0.25
mm) diameter drilled and finished-hole dimensions,
respectively, it is possible to place approximately 24
vias of a 4 x 6 pattern beneath the ground pad area
of the package.
The thermal resistance of a single copper via (not
solder filled) can be calculated as:
θVIA = L / (σ* π(Ro2 – (Ro – Rpl))
For a via path length L = 0.254 mm, with drilled hole
radius Ro = 0.15 mm, copper plating Rpl = 0.036
mm, and copper thermal conductivity σ = 0.39 W/mm
°C, the thermal resistance of each via is 21.7°C/W. Therefore, the thermal resistance of the PCB ground
Application Note - Rev 0
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Thermal Design for AWT6264R
pattern (θPCB) beneath the device ground pad is
approximately 0.904 °C/W for the 24 copper plated
vias. For solder-filled vias, the thermal resistance of
each via is 18.4 °C/W. Thus, the θPCB will be 0.767
°C/W for 24 solder-filled vias. Table 3: Calculation of Junction Temperatures at Different Drive and Signal Conditions
AWT6264 Evaluation Board
VCC = 3.3 V
POUT = 25 dBm
VCC = 4.2 V
POUT = 27 dBm
AmbientTemperature
30°C
85°C
30°C
85°C
Totalcurrent(typical)
454
484
566
601
mA
OutputStageCurrent(typical)
373
399
466
501
mA
Deltabetweenthedevicecase
temperatureandambient
temperaturewhendeviceis
mountedtoanevaluationboard.
(Devicepoweredupwith100%
dutycycle)
13.8
15.0
25.2
27.7
°C
 J-C(average)
14.6
14.6
16.8
16.8
°C/W
OutputStagePDISS
0.943
1.029
1.501
1.648
W
OutputStageTJ
43.8
100.0
55.2
112.7
°C
ADDITIONAL MANUFACTURING SUGGESTIONS
Refer to ANADIGICS’ AN-0003 for additional information on soldering and manufacturing.
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Unit
Application Note - Rev 0
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ANADIGICS, Inc.
141 Mount Bethel Road
Warren, New Jersey 07059, U.S.A.
Tel: +1 (908) 668-5000
Fax: +1 (908) 668-5132
URL: http://www.anadigics.com
IMPORTANT NOTICE
ANADIGICS, Inc. reserves the right to make changes to its products or to discontinue any product at any time without notice. The product specifications contained in Advanced Product Information sheets and Preliminary Data Sheets are subject to
change prior to a product’s formal introduction. Information in Data Sheets have been carefully checked and are assumed
to be reliable; however, ANADIGICS assumes no responsibilities for inaccuracies. ANADIGICS strongly urges customers
to verify that the information they are using is current before placing orders.
warning
ANADIGICS products are not intended for use in life support appliances, devices or systems. Use of an ANADIGICS product
in any such application without written consent is prohibited.
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