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Transceiver Power Dissipation
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9/03
Application Note #112
INTRODUCTION
This application note will outline procedure find power dissipated MIL-STD- 1553A transceiver regardless type transceiver employed. There are, general, three types transceivers today differentiated type transmitter output circuitry utilized number power supplies required. three types Voltage Source, Current Source Clamped Current Source. Each type will require from power supplies operate. Most today's transceivers comprised single monolithic ASIC majority power dissipation will transmitter output stage chip when delivers current load. Therefore area chip will hotter than rest chip, producing thermal gradient across chip. Hopefully manufacturers will specify maximum Junction Case thermal resistance chip with respect hottest area. With this information power dissipated chip then determine maximum junction temperature rise.
TRANSCEIVER POWER DISSIPATION
manufacturer's specification sheet that necessary find power dissipation particular transceiver. Manufacturer's specification sheets vary widely format they generally list transceiver power supply currents various duty cycles, well Standby (not transmitting) condition power supplies. specification sheets usually list typical maximum currents. transceiver power dissipation will it's worst when transmitting 100% duty cycle word transmission with time) while supplying minimum load power. power dissipated transceiver will function input power transceiver minus power delivered load, PLOAD PTRANSCEIVER. power load refers average power load instantaneous power. Before calculations begin questions must answered with respect manufacturers specifications. question should which 100% power supply input current should transceiver PIn, typical maximum? What power supply voltage should since they usually have tolerance associated with their specification? strict worst case analysis sense should maximum power supply current maximum power supply voltage, each supply, along with minimum load power. these conditions usually co-exist, therefore some assumptions have made realistic maximum transceiver power dissipation. been experience that most manufacturer's transceiver's tend operate around their typical specifications. output voltage load most often midpoint 1553 specification. power supplies usually well regulated nominal voltages. maximum power dissipated transceiver will when load power minimum. obtain conditions minimum load power must know type transmitter output circuit used. transmitter output current source then minimum load power will occur minimum load resistance. other hand, transmitter output voltage source clamped current source then minimum load power will occur maximum load resistance. addition load power also function signal's frequency content, pattern. average power greater lower frequency components than higher frequency components rise fall times. Therefore there would more average power AAAA pattern (alternating "1"s "0"'s, 500KHz frequency) than FFFF pattern (all "1"s, 1MHz frequency). With following assumptions calculate transceiver power dissipation without regard transformer turns ratio: typical power supply input currents nominal power supply voltages. approximately Volts pk-pk, line line, transformer secondary voltage direct coupled stub mode, Voltage Source Clamped Current Source output drivers. maximum load resistance, Voltage Source Clamped Current Source output drivers, that seen transformer secondary direct coupled stub mode cable). Current Source output drivers, measure transformer secondary voltage with minimum load resistance cable). Since secondary load current independent load resistance, minimum load power minimum load resistance. worst case MIL-STD-1553 pattern, FFFF 0000, minimum load power. Figure reference.
Application Note #112
9/03
DATA
DATA
VSECONDARY Data Cable
DATA DATA
Note Center tapped ground connection dependent type transmitter output. Voltage Source connection; Current Source connected
FIGURE
calculation total power input straight forward. Total power into transceiver, PIN, power supply products. calculation average power load straight forward input power. average power load time integral instantaneous power (VSEc ISEC divided period, will affected shape signals pattern. Once this calculation, PLOAD, made power dissipated transceiver determined. sample calculations follow using Aeroflex ACT4487 ARX4404 hybrids. ACT4487 transceiver input supply current source type utilizes transformer with 1.414:1 turns ratio direct coupled stubs turns ratio transformer coupled stubs. ARX4404 transceiver voltage source type utilizes transformer with turns ratio direct coupled stubs 1.41:1 turns ratio transformer coupled stubs. sample calculations will made with previously stated assumptions.
Sample Calculation
Total Power Input
ACT4487
ACT4487 uses Volt supplies Volt supply. From specification sheet currents 100% duty cycles are; (+15V) (-15V) Input Power Calculation Volt supply input power: Watts Volt supply input power: 0.18 Watts Volt supply input power: 0.09 Watts Total Input Power 2.97 Watts
Load Power
Direct coupled stub mode current source output driver. VSECONDARY Vpk-pk, line line, measured with Ohms cable. LOAD Ohms (minimum cable impedance) ISECONDARY Ohms 103.45 mApk Instantaneous Power 103.45 1.55 Watts. Depending shape transmitter output signal average power load range from maximum value equal instantaneous power, zero risetime square wave, minimum value equal half instantaneous power, sine wave. Therefore ACT4487, whose transmitter output voltage shape single pole compensation, average power load will value between instantaneous power half instantaneous power. Figure scope plot ACT4487 hybrid Figure configuration. With Digital Storage Oscilloscope (DSO) VSEc, ISEC, VSEc ISEC product (instantaneous power) time integral VSEc ISEC product shown.
Application Note #112 9/03
FIGURE
Sample Calculation
ACT4487 (con't)
seen scope plot VSEC Vpk-pk, ISEC mApk-pk, VSEC ISEC (instantaneous power) 1.57 Watts, average power load 1.054 Watts. Therefore Power Dissipation Hybrid 2.97 Watts (total input power) 1.054 Watts (average power load) 1.92 Watts FFFF pattern. Since maximum junction case thermal resistance hybrid specified 4°C/ Watt, junction temperature rise will less than above temperature case.
Sample Calculation
Total Power Input
ARX4404
ARX4404 uses Volt supplies Volt supply. From spec sheet currents 100% duty cycles are; (+15V) (-15V) Input Power Volt supply input power: Watts Volt supply input power: Watts Volt supply input power: 0.125 Watts Total Input Power 4.025 Watts
Load Power
Direct coupled stub mode voltage source output driver. VSECONDARY 29.17 Vpk-pk, line line, measured with Ohms cable. LOAD Ohms ISECONDARY 14.59 Ohms 100.6 mApk Instantaneous Power 14.59 100.6 1.47 Watts
Application Note #112 9/03
FIGURE
Sample Calculation
ARX4404 (continued)
seen scope plot transmitter output signal nearly sinusoidal VSEC 29.17Vpk-pk, ISEC 199mApk-pk, VSEC ISEC (instantaneous power) 1.47 Watts, average power load 0.773 Watts. Therefore Power Dissipation Hybrid 4.025 Watts (total input power) 0.773 Watts (average power load) 3.25 Watts FFFF pattern. Since maximum junction case thermal resistance hybrid specified 5°C/Watt, junction temperature rise will less than 17°C above temperature case.
Conclusion
This only method finding power dissipated MIL-STD 1553 transceiver, does provide fairly accurate results since takes into account shape frequency content transmitter output signal. Another method would value transmitted signal. this only accurate output signals that approach sine wave shape. Approximations could made transmitter output signals that between square wave sine wave shape, since values these signals well known.
Prepared
Michael Consi Engineering Manager, Databus Aeroflex Circuit Technology
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9/03
Application Note #112
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always seeking improve products, information this document gives only general indication product capacity, performance suitability, none which shall form part contract. reserve right make design changes without notice. trademarks acknowledged. Parent company Aeroflex, Inc. ©Aeroflex 2003.
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Application Note #112
8/03

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