"Thermal Design for AWM6432"
Application Note Thermal Design for AWM6432 Rev 0 RelevANt pRoducts were performed using a dc bias of 6V and a 3.2GHz • AWM6432 CW (no modulation) signal of various power levels, in • AWM6431 order to produce total currents between 350mA and 550mA in steps of 50mA. This procedure was used to oveRvIeW validate the consistency of the junction-case thermal ANADIGICS’ AWM6432 WiMAX Power Amplifier is resistance measured. a high performance device that delivers exceptional linearity and efficiency at high output power levels. In performing the thermal scans, the evaluation board The device operates over the voltage supply range temperature was raised until the case temperature of +5Vdc to +6Vdc, and its output power handling (Tc) of the device was 75°C, as measured at the capabilities increase as the supply voltage is raised bottom of the package. The peak thermal rise was towards the high end of this range. At higher output detected at the output amplification stage, and was powers, thermal considerations need to be taken into therefore used to derive the junction-case thermal account in order to maintain high levels of device resistance (θJ-C) for the device. reliability. Table 1 shows the thermal analysis for the AWM6432 This application note addresses thermal design device operating at 6V based on the thermal considerations for the AWM6432 by first measuring scan results. The data presents the derivations the junction-to-case thermal characteristics of the of the junction-case thermal resistance (θJ-C) and device, and performing a case-to-ambient thermal demonstrates the consistency of the θJ-C, which analysis. Thermal design examples and guidelines is typically 27°C/W under the application drive are then offered for specific applications and circuit conditions. boards used. Table 2 shows the derivation of the junction-case tHeRMAl cHARActeRIZAtIoN ANd ANAlYsIs temperatures (TJ-C) when Tc is at 25°C and 85°C. As Thermal characterizations for the AWM6432 were presented, the calculated typical value for TJ-C was performed on an open cavity device (no mold based on devices with a typical output stage gain compound) that was mounted to an evaluation of 9.5dB, θ J-C of 27°C/W, output power of +24dBm board. The AWM6432 is a class A/B amplifier, and (nominal) and output stage current of 255mA thus requires RF drive in order for the output stage operating at 6Vdc. to be fully operational. The thermal characterizations 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 dc Analysis Total current @ 6Vdc 350 400 450 500 550 mA Typical currents (1st and 2nd stage) 80 mA Icc1 + Icc2 (pin 1) Typical current at output stage 270 320 370 420 470 mA lcc3 (pin 12) Typical dc power dissipation at the output 1.62 1.92 2.22 2.52 2.82 W stage (P3) 10/2008 thermal design for AWM6432 table 1: thermal Analysis of an AWM6432 device operating at 6v under Multiple drive conditions (continued) Measured Tj at output stage 110.7 115.2 118.3 120.8 123.0 8C Tc 75 8C Temperature rise measured 35.7 40.2 43.3 45.8 48 8C RF Analysis 25.2 26.88 28.08 29.1 30.14 dBm RF output power (PRFOUT) 0.331 0.488 0.643 0.813 1.033 W Typical RF gain of the output stage 9.5 dB RF input power at the output stage 15.7 17.38 18.58 19.6 20.64 dBm (PRFIN3) 37.15 54.70 72.11 91.20 115.88 mW Total Power dissipation 1.326 1.487 1.649 1.798 1.903 W (Pdc + PRFIN3 - PRFOUT) Junction-case thermal resistance (J-c) 26.9 27.0 26.3 25.5 25.2 8c/W 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 Case Temperature 25 85 8C Total Current @ 6V (typical) 305 317 mA Output Stage Current @ 6V (typical) 225 237 mA Output Stage Power Dissipation (typical) 1.127 1.187 W Temperature Rise calculated using typ. J-C of 30.43 32.05 8C 278C/W Calculated Junction-Case Temperature TJ-C 55.43 117.1 8C 2 Application Note - Rev 0 10/2008 thermal design for AWM6432 pRINted cIRcuIt BoARd tHeRMAl desIGN Table 3 shows the derivation of the junction-ambient coNsIdeRAtIoNs temperature (TJ-A) based on the standard AWM6432 In general, it is essential to keep the junction EVB operating at 3.5GHz using supply voltages of 5V, temperature of the device as low as possible to 5.3V, and 6V with output powers of +20dBm, +22dBm, ensure long operating life. This can be accomplished and +24dBm, respectively. The junction-case data is by providing good thermal relief and adequate based on the device thermal characterizations as heat sinking. When mounted to a printed circuit previously calculated. board (PCB), the delta between the device case temperature and the ambient temperature will be The AWM6432 is packaged in a 4.5mm x 4.5mm determined by several factors; board thickness and laminate based module with a backside ground pad number of layers, copper plating thickness, size of an area of 2.05mm x 4.3mm (0.081” x 0.169”). This and number of via holes placed beneath the device ground pad provides RF, DC, and thermal ground for package ground area, the PCB layout, the method the package. Using vias that are fabricated with 0.012” of attachment of the PCB to the heat sink as well as (0.3mm) and 0.010” (0.25mm) diameter drilled and the design of the heat sink. For typical applications, finished-hole dimensions, respectively, it is possible it is recommended to maximize the number of vias to place approximately 28 vias of a 4 x 7 pattern placed below the package ground area. beneath the ground pad area of the package. ANADIGICS’ standard AWM6432 evaluation board The thermal resistance of a single copper via (not (EVB) is fabricated using double sided Rogers R3003 solder filled) can be calculated as: PCB material which has a dielectric constant of 3.38, dielectric thickness of 0.008” (0.2mm), and copper θVIA = L / (σ* p(Ro2 – (Ro – Rpl)) thickness of 0.0021” (0.054mm). table 3: AWM6432 evaluation Board derivation of Junction-Ambient temperatures under various drive and voltage conditions Vcc 5 5.3 6 V Total Current (typical) 212 238 280 mA Icc3 (pin 12) @ 258C 132 158 200 mA Icc3 (pin 12) @ 858C 144 170 212 mA 20 22 24 dBm RF output power (PRFOUT) 0.100 0.158 0.251 W Typical RF gain of the output stage 9.5 dB 10.5 12.5 14.5 dBm RF Input power at the output stage (PRFIN3) 11.22 17.78 28.18 mW J-C (typical) 27 27 27 8C/W Delta between the device case temperature and ambient temperature when device is mounted to an evaluation board 25.5 28 38.5 8C (Device powered up with 100% duty cycle) 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 Application Note - Rev 0 3 10/2008 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: Mktg@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. 4 Application Note - Rev 0 10/2008