Application Note

Application Note
Thermal Design for AWM6432
Rev 0
Relevant products
•
•
AWM6432
AWM6431
OVERVIEW
ANADIGICS’ AWM6432 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 +5Vdc to +6Vdc, 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 levels of device
reliability.
This application note addresses thermal design
considerations for the AWM6432 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 for the AWM6432 were
performed on an open cavity device (no mold
compound) that was mounted to an evaluation
board. The AWM6432 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 6V and a 3.2GHz
CW (no modulation) signal of various power levels, in
order to produce total currents between 350mA and
550mA in steps of 50mA. This procedure was used to
validate the consistency of the junction-case thermal
resistance measured.
In performing the thermal scans, the evaluation board
temperature was raised until the case temperature
(Tc) of the device was 75°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.
Table 1 shows the thermal analysis for the AWM6432
device operating at 6V based on the thermal
scan results. The data presents the derivations
of the junction-case thermal resistance (θJ-C) and
demonstrates the consistency of the θJ-C, which
is typically 27°C/W under the application drive
conditions.
Table 2 shows the derivation of the junction-case
temperatures (TJ-C) when Tc is at 25°C and 85°C. As
presented, the calculated typical value for TJ-C was
based on devices with a typical output stage gain
of 9.5dB, θ J-C of 27°C/W, output power of +24dBm
(nominal) and output stage current of 255mA
operating at 6Vdc.
Table 1: Thermal Analysis of an AWM6432 Device Operating at 6V under Multiple Drive Conditions
thermal Analysis under drive conditions
#1
#2
#3
#4
#5
Unit
350
400
450
500
550
mA
dc Analysis
Totalcurrent@6Vdc
Typicalcurrents(1stand2ndstage)
Icc1+Icc2(pin1)
80
mA
Typicalcurrentatoutputstage
lcc3(pin12)
270
320
370
420
470
mA
Typicaldcpowerdissipationattheoutput
stage (P3)
1.62
1.92
2.22
2.52
2.82
W
10/2008
Thermal Design for AWM6432
Table 1: Thermal Analysis of an AWM6432 Device Operating at 6V under Multiple Drive Conditions
(continued)
MeasuredTjatoutputstage
110.7
115.2
Tc
118.3
120.8
123.0
8C
75
Temperaturerisemeasured
8C
35.7
40.2
43.3
45.8
48
8C
25.2
26.88
28.08
29.1
30.14
dBm
0.331
0.488
0.643
0.813
1.033
W
RF Analysis
RFoutputpower(PRFOUT)
TypicalRFgainoftheoutputstage
9.5
dB
15.7
17.38
18.58
19.6
20.64
dBm
37.15
54.70
72.11
91.20
115.88
mW
Total Power dissipation
(Pdc + PRFIN3-PRFOUT)
1.326
1.487
1.649
1.798
1.903
W
Junction-case thermal resistance (J-c)
26.9
27.0
26.3
25.5
25.2
8c/W
RFinputpowerattheoutputstage
(PRFIN3)
The example below is for the AWM6432 device at 25°C:
Output Stage Power Dissipation: Pdiss = P3 + PRFIN3 - PRFOUT = (6 * 0.225) + 28.18*10-3 - 0.251 = 1.127W
Thermal rise of junction for the packaged device = Pdiss * θJ-C = 1.127W * 278C/W = 30.43°C
Calculated Junction Temperature with case at 25°C: 258C + 30.43 8C = 55.43°C
Table 2: of AWM6432 Junction-Case Temperatures
2
CaseTemperature
25
85
8C
TotalCurrent@6V(typical)
305
317
mA
OutputStageCurrent@6V(typical)
225
237
mA
OutputStagePowerDissipation(typical)
1.127
1.187
W
TemperatureRisecalculatedusingtyp.J-C of
278C/W
30.43
32.05
8C
CalculatedJunction-CaseTemperatureTJ-C
55.43
117.1
8C
Application Note - Rev 0
10/2008
Thermal Design for AWM6432
PRINTED CIRCUIT BOARD THERMAL DESIGN
CONSIDERATIONS
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 AWM6432 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” (0.2mm), and copper
thickness of 0.0021” (0.054mm).
Table 3 shows the derivation of the junction-ambient
temperature (TJ-A) based on the standard AWM6432
EVB operating at 3.5GHz using supply voltages of 5V,
5.3V, and 6V with output powers of +20dBm, +22dBm,
and +24dBm, respectively. The junction-case data is
based on the device thermal characterizations as
previously calculated.
The AWM6432 is packaged in a 4.5mm x 4.5mm
laminate based module with a backside ground pad
of an area of 2.05mm x 4.3mm (0.081” x 0.169”). This
ground pad provides RF, DC, and thermal ground for
the package. Using vias that are fabricated with 0.012”
(0.3mm) and 0.010” (0.25mm) diameter drilled and
finished-hole dimensions, respectively, it is possible
to place approximately 28 vias of a 4 x 7 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* p(Ro2 – (Ro – Rpl))
Table 3: AWM6432 Evaluation Board
Derivation of Junction-Ambient Temperatures under Various Drive and Voltage Conditions
Vcc
5
5.3
6
V
TotalCurrent(typical)
212
238
280
mA
Icc3(pin12)@258C
132
158
200
mA
Icc3(pin12)@858C
144
170
212
mA
20
22
24
dBm
0.100
0.158
0.251
W
RFoutputpower(PRFOUT)
TypicalRFgainoftheoutputstage
9.5
dB
10.5
12.5
14.5
dBm
11.22
17.78
28.18
mW
J-C(typical)
27
27
27
8C/W
Deltabetweenthedevicecasetemperatureandambient
temperaturewhendeviceismountedtoanevaluationboard
(Devicepoweredupwith100%dutycycle)
25.5
28
38.5
8C
Pdiss@TA=25°C
0.571
0.697
0.977
W
tJ-A @ tA = 25°c
65.92
71.81
89.88
8c
Pdiss@TA=85°C
0.631
0.760
1.049
W
tJ-A @ tA = 85°c
127.54
133.53
151.82
8c
RFInputpowerattheoutputstage(PRFIN3)
Application Note - Rev 0
10/2008
3
Thermal Design for AWM6432
For a via path length L = 0.254mm, with drilled hole
radius Ro = 0.15mm, copper plating Rpl = 0.036mm,
and copper thermal conductivity σ = 0.39W/mm°C,
the thermal resistance of each via is 21.7°C/W. Therefore, the thermal resistance of the PCB ground
pattern (θPCB) beneath the device ground pad is
approximately 0.775°C/W for the 28 copper plated
vias. For solder-filled vias, the thermal resistance of
each via is 18.4°C/W. Thus, the θPCB will be 0.657°C/W
for 28 solder-filled vias.
ADDITIONAL MANUFACTURING SUGGESTIONS
Refer to ANADIGICS’ AN-0003 for additional
information on soldering and manufacturing.
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
E-mail: [email protected]
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.
4
Application Note - Rev 0
10/2008