LAMBDA ADVANCED ANALOG INC. λ PRELIMINARY AFL2803.3S Series Single Output, Hybrid - High Reliability DC/DC Converter DESCRIPTION The AFL Series of DC/DC converters feature high power density with no derating over the full military temperature range. This series is offered as part of a complete family of converters providing single and dual output voltages and operating from nominal +28, +50, +120 or +270 volt inputs with output power ranging from 80 to 120 watts. For applications requiring higher output power, individual converters can be operated in parallel. The internal current sharing circuits assure accurate current distribution among the paralleled converters. This series incorporates Lambda Advanced Analog's proprietary magnetic pulse feedback technology providing optimum dynamic line and load regulation response. This feedback system samples the output voltage at the pulse width modulator fixed clock frequency, nominally 550 KHz. Multiple converters can be synchronized to a system clock in the 500 KHz to 700 KHz range or to the synchronization output of one converter. Undervoltage lockout, primary and secondary referenced inhibit, soft-start and load fault protection are provided on all models. These converters are hermetically packaged in two enclosure variations, utilizing copper core pins to minimize resistive DC losses. Three lead styles are available, each fabricated with Lambda Advanced Analog's rugged ceramic lead-to-package seal assuring long term hermeticity in the most harsh environments. Manufactured in a facility fully qualified to MIL-PRF38534, these converters are available in four screening grades to satisfy a wide range of requirements. The CH grade is fully compliant to the requirements of MIL-PRF-38534 for class H. The HB grade processed and screened to the class H requirement, may not necessarily meet all of the other MIL-PRF-38534 requirements, e.g., element evaluation and Periodic Inspections (P.I.) not required. Both grades are tested to meet the complete group "A" test specification over the full military temperature range without output power deration. Two grades with more limited screening are also available for use in less demanding applications. Variations in electrical, mechanical and screening can be accommodated. Contact Lambda Advanced Analog for special requirements. FEATURES n 16 To 40 Volt Input Range n 3.3 Volt Output n High Power Density - 50 W / in3 n 66 Watt Output Power n Parallel Operation with Stress and Current Sharing n Low Profile (0.380") Seam Welded Package n Ceramic Feedthru Copper Core Pins n High Efficiency - 72% n Full Military Temperature Range n Continuous Short Circuit and Overload Protection n Remote Sensing Terminals n Primary and Secondary Referenced Inhibit Functions n Line Rejection > 40 dB - DC to 50KHz n External Synchronization Port n Fault Tolerant Design n Dual Output Versions Available n Standard Military Drawings Available SPECIFICATIONS AFL2803.3S ABSOLUTE MAXIMUM RATINGS Input Voltage Soldering Temperature Case Temperature -0.5V to 180V 300°C for 10 seconds Operating-55°C to +125°C Storage -65°C to +135°C TABLE I. Electrical Performance Characteristics. Test Symbol Conditions -55°C ≤ TC ≤ +125°C VIN = 28 V dc ±5%, CL = 0 unless otherwise specified Group A Subgroups Device Type Limits Min 3.27 Output voltage VOUT IOUT = 0 1 Unit Max 3.33 01 V 3.23 2,3 3.37 20 Output current 6/ IOUT VIN = 16, 28, 40 v dc 1,2,3 01 A Output ripple voltage VRIP VIN = 16, 28, 40 v dc B.W.= 20 Hz to 10 MHz 1,2,3 01 30 Line regulation VRLINE VIN = 16, 28, 40 v dc 1,2,3 01 ± 20 mV 1,2,3 01 ± 35 mV 1 01 80 mA MV p-p IOUT = 0, 10 A, and 20 A Load regulation VRLOAD VIN = 16, 28, 40 v dc IOUT = 0, 10 A, and 20 A Input current Input ripple current IN IRIP IOUT = No load 2,3, 100 Inhibit 1, (pin 4) shorted to input return (pin 2) Inhibit 2, (pin 12) shorted to output return (pin 8) 1,2,3 5 1,2,3 50 IOUT = 20 A 1,2,3 01 1,2,3 01 72 60 mA p-p B.W.= 20 Hz to 10 MHz Efficiency EFF IOUT = 20 A Isolation ISO Input to output or any pin to case (except pin 3) at 500 V dc, TC = +25°C 1 01 100 Maximum Capacitive load 1/ CL No effect on dc performance, TC = +25°C 4 01 10,000 See footnotes at end of table. 2 % MΩ µF AFL2803.3S TABLE I. Electrical Performance Characteristics - Continued. Test Symbol Conditions -55°C ≤ TC ≤ +125°C VIN =28 V dc ±5%, C= 0 unless otherwise specified Group A subgroups Device type Limits Min Power dissipation load fault PD Overload 6/ Current Limit Point 5/ ICL VOUT = 90% VNOM VIN = 28 V 1,2,3 01 Unit Max 33 Short circuit 33 1 01 2 3 115 125 105 125 115 140 % FS IOUT = 20 A 1,2,3 01 500 600 KHz Sync frequency range Fsync IOUT = 20 A 4,5,6 01 500 700 KHz Output response to step transient load changes 2/ 8/ VOTLOAD 50% to/from 100% 4,5,6 01 -450 +450 -450 +450 Switching frequency 10% to/from 50% Recovery time, step transient load changes 2/ 8/ TTLOAD 50% to/from 100% 4,5,6 01 200 10% to/from 50% VOTLINE Input step 16 V to/from 40 V dc, IOUT = 20 A 4,5,6 01 Recovery time transient step line changes 1/ 2/ 3/ TTLINE Input step 16 V to/from 40 V dc, IOUT = 20 A 4,5,6 Turn on overshoot 4/ VTonOS IOUT = 0 and 20 A Turn on delay TonD IOUT = 0 and 20 A 4/ mV pk µs 400 Output response to transient step line changes 1/ 2/ 3/ Load fault recovery TrLF 500 mV pk 01 500 µs 4,5,6 01 250 mV pk 4,5,6 01 10 ms 4,5,6 01 10 ms -500 Notes: 1/ 2/ 3/ 4/ 5/ 6/ 7/ 8/ 9/ W Parameters not tested but are guaranteed to the limits specified in the table. Recovery time is measured from the initiation of the transient to where VOUT has returned to within ± 1 percent of VOUT at 50 percent load. Line transient transition time ≥10 microseconds. Turn on delay is measured with an input voltage rise time of between 100 and 500 volts per millisecond. Current limit point is that condition of excess load causing output voltage to drop to 90% of nominal. Parameter verified as part of another test. All electrical tests are performed with remote sense leads connected to the output lead at the load. Input step transition time ≥100 microseconds. Enable inputs internally pulled high. Nominal open circuit voltage = 4.0VDC. 3 AFL2803.3S Case Outlines Case X Case W Pin Variation of Case Y Case Y Case Z Pin Variation of Case Y Tolerances, unless otherwise specified: 4 .XX = ±0.010 .XXX = ±0.005 AFL2803.3S Pin Designation Pin No. Designation 1 Positive Input 2 Input Return 3 Case 4 Enable 1 5 Sync Output 6 Sync Input 7 Positive Output 8 Output Return 9 Negative Output 10 Output Voltage Trim 11 Share 12 Enable 2 Available Screening Levels and Process Variations for AFL 2803.3S Series. MIL-STD-883 Method Requirement Temperature Range No Suffix ES Suffix HB Suffix CH Suffix -20°C to +85°C -55°C to +125°C -55°C to +125°C -55°C to +125°C Element Evaluation MIL-PRF-38534 Internal Visual 2017 Temperature Cycle Yes Yes Yes 1010 Cond B Cond C Cond C Constant Acceleration 2001 500g Cond A Cond A Burn-in 1015 96hrs @ 125°C 160hrs @ 125°C 160hrs @ 125°C 25°C 25°C -55, +25, +125°C -55, +25, +125°C Final Electrical (Group A) MIL-PRF-38534 * & Specification Seal, Fine & Gross 1014 Cond A Cond A, C Cond A, C Cond A, C External Visual 2009 * Yes Yes Yes * per Commercial Standards Part Numbering AFL 28 03.3 S X / CH Model Input Voltage Screening Case Style 28 = 28V, 50 = 50V 120 = 120V, 270 = 270V W, X, Y, Z Output Voltage Outputs S = Single D = Dual 03.3 = 3.3V, 05 = 5V 08 = 8V, 09 = 9V, 12V = 12V 15 = 15V, 28 =28V 5 – , ES HB, CH AFL2800S Circuit Description Figure I. AFL Single Output Block Diagram DC Input 1 Enable 1 4 Input Filter Output Filter Primary Bias Supply 7 +Output 10 +Sense Current Sense Sync Output 5 Control Sync Input 6 FB Case Share Amplifier Error Amp & Ref 11 Share 12 Enable 2 Sense Amplifier 3 Input Return 2 Circuit Operation and Application Information The AFL series of converters employ a forward switched mode converter topology. (refer to Figure I.) Operation of the device is initiated when a DC voltage whose magnitude is within the specified input limits is applied between pins 1 and 2. If pin 4 is enabled (at a logical 1 or open) the primary bias supply will begin generating a regulated housekeeping voltage bringing the circuitry on the primary side of the converter to life. A power MOSFET is used to chop the DC input voltage into a high frequency square wave, applying this chopped voltage to the power transformer at the nominal converter switching frequency. Maintaining a DC voltage within the specified operating range at the input assures continuous generation of the primary bias voltage. The switched voltage impressed on the secondary output transformer winding is rectified and filtered to generate the converter DC output voltage. An error amplifier on the secondary side compares the output voltage to a precision reference and generates an error signal proportional to the difference. This error signal is magnetically coupled through the feedback transformer into the controller section of the converter varying the pulse width of the square wave signal driving the MOSFET, narrowing the width if the output voltage is too high and widening it if it is too low, thereby regulating the output voltage. 9 -Sense 8 Output Return point of application. When the remote sensing feature is not used, the sense leads should be connected to their respective output terminals at the converter. Figure III. illustrates a typical remotely sensed application. Inhibiting Converter Output As an alternative to application and removal of the DC voltage to the input, the user can control the converter output by providing TTL compatible, positive logic signals to either of two enable pins (pin 4 or 12). The distinction between these two signal ports is that enable 1 (pin 4) is referenced to the input return (pin 2) while enable 2 (pin 12) is referenced to the output return (pin 8). Thus, the user has access to an inhibit function on either side of the isolation barrier. Each port is internally pulled “high” so that when not used, an open connection on both enable pins permits normal converter operation. When their use is desired, a logical “low” on either port will shut the converter down. Figure II. Enable Input Equivalent Circuit +5.6V 100K Pin 4 or Pin 12 Remote Sensing 1N4148 Disable 290K Connection of the + and - sense leads at a remotely located load permits compensation for excessive resistance between the converter output and the load when their physical separation could cause undesirable voltage drop. This connection allows regulation to the placard voltage at the 6 2N3904 150K Pin 2 or Pin 8 (unconnected) thereby permitting the converter to operate at its’ own internally set frequency. Internally, these ports differ slightly in their function. In use, a low on Enable 1 completely shuts down all circuits in the converter while a low on Enable 2 shuts down the secondary side while altering the controller duty cycle to near zero. Externally, the use of either port is transparent save for minor differences in standby current. (See specification table). The sync output signal is a continuous pulse train set at 550 ±50 KHz, with a duty cycle of 15 ±5%. This signal is referenced to the input return and has been tailored to be compatible with the AFL sync input port. Transition times are less than 100 ns and the low level output impedance is less than 50 ohms. This signal is active when the DC input voltage is within the specified operating range and the converter is not inhibited. This output has adequate drive reserve to synchronize at least five additional converters. A typical connection is illustrated in Figure III. Synchronization of Multiple Converters When operating multiple converters, system requirements often dictate operation of the converters at a common frequency. To accommodate this requirement, the AFL series converters provide both a synchronization input and a synchronization output. Parallel Operation — Current and Stress Sharing Figure III. illustrates the preferred connection scheme for operation of a set of AFL converters with outputs operating in parallel. Use of this connection permits equal sharing among the members of a set where total load current exceeds the capacity of an individual AFL. An important feature of the AFL series operating in the The sync input port permits synchronization of an AFL converter to any compatible external frequency source operating between 500 and 700 KHz. This input signal should be referenced to the input return and have a 10% to 90% duty cycle. Compatibility requires transition times less than 100 ns, maximum low level of +0.8 volts and a Figure III. Preferred Connection for Parallel Operation Power Input 1 12 Vin Enable 2 Rtn Share Case Enable 1 Optional Synchronization Connection AFL + Sense - Sense Sync Out Return Sync In + Vout 6 7 1 12 Share Bus Enable 2 Vin Share Rtn Case Enable 1 AFL + Sense - Sense Sync Out Return Sync In + Vout to Load 7 6 1 12 Enable 2 Vin Rtn Share Case Enable 1 AFL + Sense - Sense Sync Out Return Sync In + Vout 7 6 (Other Converters) minimum high level of +2.0 volts. The sync output of another converter which has been designated as the master oscillator provides a convenient frequency source for this mode of operation. When external synchronization is not required, the sync in pin should be left open parallel mode is that in addition to sharing the current, the stress induced by temperature will also be shared. Thus if one member of a paralleled set is operating at a higher case temperature, the current it provides to the load will be reduced as compensation for the tempera7 by the following expression: ture induced stress on that device. When operating in the shared mode, it is important that symmetry of connection be maintained as an assurance of optimum load sharing performance. Thus, converter outputs should be connected to the load with equal lengths of wire of the same gauge and sense leads from each converter should be connected to a common physical point, preferably at the load along with the converter output and return leads. All converters in a paralleled set must have their share pins connected together. This arrangement is diagrammatically illustrated in Figure III. showing the outputs and sense pins connected at a star point which is located close as possible to the load. As a consequence of the topology utilized in the current sharing circuit, the share pin may be used for other functions. In applications requiring only a single converter, the voltage appearing on the share pin may be used as a “current monitor”. The share pin open circuit voltage is nominally +1.00v at no load and increases linearly with increasing output current to +2.20v at full load. Thermal Considerations Because of the incorporation of many innovative technological concepts, the AFL series of converters is capable of providing very high output power from a package of very small volume. These magnitudes of power density can only be obtained by combining high circuit efficiency with effective methods of heat removal from the die junctions. This requirement has been effectively addressed inside the device; but when operating at maximum loads, a significant amount of heat will be generated and this heat must be conducted away from the case. To maintain the case temperature at or below the specified maximum of 125°C, this heat must be transferred by conduction to an appropriate heat dissipater held in intimate contact with the converter base-plate. Because effectiveness of this heat transfer is dependent on the intimacy of the baseplate-heatsink interface, it is strongly recommended that a high thermal conductivity heat transferring medium is inserted between the baseplate and heatsink. The material most frequently utilized at the factory during all testing and burn-in processes is sold under the trade name of Sil-PadR 4001 . This particular product is an insulator but electrically conductive versions are also available. Use of these materials assures maximum surface contact with the heat dissipater thereby compensating for any minor surface variations. While other available types of heat conductive materials and thermal compounds provide similar effectiveness, these alternatives are often less convenient and are frequently messy to use. A conservative aid to estimating the total heat sink surface area (AHEAT SINK) required to set the maximum case temperature rise (∆T) above ambient temperature is given A HEAT SINK . ∆T −143 ≈ − 3.0 80P 0.85 where ∆T = Case temperature rise above ambient 1 − 1 P = Device dissipation in Watts = POUT Eff As an example, it is desired to maintain the case temperature of an AFL2815S at ≤ +85°C while operating in an open area whose ambient temperature is held at a constant +25°C; then ∆T = 85 - 25 = 60°C. From the Specification Table, the worst case full load efficiency for this device is 83%; therefore the power dissipation at full load is given by 1 − 1 = 120 • ( 0.205) = 24.6 W P = 120 • .83 and the required heat sink area is . −143 60 − 3.0 = 71 in 2 A HEAT SINK = 80 • 24.6 0.85 Thus, a total heat sink surface area (including 2 fins, if any) of 71 in in this example, would limit case rise to 60°C above ambient. A flat aluminum plate, 0.25" thick and of approximate 2 dimension 4" by 9" (36 in per side) would suffice for this application in a still air environment. Note that to meet the criteria in this example, both sides of the plate require unrestricted exposure to the ambient air. Input Filter The AFL2800S series converters incorporate a two stage LC input filter whose elements dominate the input load impedance characteristic at turn-on. The input circuit is as shown in Figure IV. 1Sil-Pad is a registered Trade Mark of Bergquist, Minneapolis, MN 8 Figure IV. Input Filter Circuit 900nH Figure V. Connection for Vout Adjustment. 130nH Pin 1 Enable 2 Share R ADJ 6 µfd 11.2 µfd AFL28xxS + Sense - Sense Pin 2 Return To Load + V out Attempts to adjust the output voltage to a value greater than 120% of nominal should be avoided because of the potential of exceeding internal component stress ratings and subsequent operation to failure. Under no circumstance should the external setting resistor be made less than 500W. By remaining within this specified range of values, completely safe operation fully within normal component derating limits is assured. Examination of the equation relating output voltage and resistor value reveals a special benefit of the circuit topology utilized for remote sensing of output voltage in the AFL2800S series of converters. It is apparent that as the resistance increases, the output voltage approaches the nominal set value of the device. In fact the calculated limiting value of output voltage as the adjusting resistor becomes very large is » 25mV above nominal device voltage. Undervoltage Lockout A minimum voltage is required at the input of the converter to initiate operation. This voltage is set to 14.0 ± 0.5 volts. To preclude the possibility of noise or other variations at the input falsely initiating and halting converter operation, a hysteresis of approximately 1.0 volts is incorporated in this circuit. Thus if the input voltage droops to 13.0 ± 0.5 volts, the converter will shut down and remain inoperative until the input voltage returns to »14.0 volts. Output Voltage Adjust In addition to permitting close voltage regulation of remotely located loads, it is possible to utilize the converter sense pins to incrementally increase the output voltage over a limited range. The adjustments made possible by this method are intended as a means to “trim” the output to a voltage setting for some particular application, but are not intended to create an adjustable output converter. These output voltage setting variations are obtained by connecting an appropriate resistor value between the +sense and -sense pins while connecting the -sense pin to the output return pin as shown in Figure V. below. The range of adjustment and corresponding range of resistance values can be determined by use of the following equation. The consequence is that if the +sense connection is unintentionally broken, an AFL28xxS has a fail-safe output voltage of Vout + 25mV, where the 25mV is independent of the nominal output voltage. It can be further demonstrated that in the event of both the + and - sense connections being broken, the output will be limited to Vout + 440mV. This 440 mV is also essentially constant independent of the nominal output voltage. General Application Information The AFL2800 series of converters are capable of providing large transient currents to user loads on demand. Because the nominal input voltage range in this series is relatively low, the resulting input current demands will be correspondingly large. It is important therefore, that the line impedance be kept very low to prevent steady state and transient input currents from degrading the supply voltage between the voltage source and the converter input. In applications requiring high static currents and large VNOM Radj = 100 • VOUT - VNOM -.025 Where VNOM = device nominal output voltage, and VOUT = desired output voltage Finding a resistor value for a particular output voltage, is simply a matter of substituting the desired output voltage and the nominal device voltage into the equation and solving for the corresponding resistor value. transients, it is recommended that the input leads be made of 9 adequate size to minimize resistive losses, and that a good quality capacitor of approximately 100µfd be connected directly across the input terminals to assure an adequately low impedance at the input terminals. Table I relates nominal resistance values and selected wire sizes. multiplied by the number of paralleled devices. By choosing 14 or 16 gauge wire in this example the parasitic resistance and resulting voltage drop will be reduced to 25% or 31% of that with 20 gauge wire. Another potential problem resulting from parasitically induced voltage drop on the input lines is with regard to operation of the enable 1 port. The minimum and maximum operating levels required to operate this port are specified with respect to the input common return line at the converter. If a logic signal is generated with respect to a ‘common’ that is distant from the converter, the effects of the voltage drop over the return line must be considered when establishing the worst case TTL switching levels. These drops will effectively impart a shift to the logic levels. In Figure VI, it can be seen that referred to system ground, the voltage on the input return pin is given by Table I. Nominal Resistance Of Cu Wire Wire Size, AWG 24 Ga 22 Ga 20 Ga 18 Ga 16 Ga 14 Ga 12 Ga Resistance per ft 25.7 mΩ 16.2 mΩ 10.1 mΩ 6.4 mΩ 4.0 mΩ 2.5 mΩ 1.6 mΩ eRtn = IRtn • Rp As an example of the effects of parasitic resistance, consider an AFL2815S operating at full power of 120 W. From the specification sheet, this device has a minimum efficiency of 83% representing an input power of nearly 145 W. If we consider the case where line voltage is at its’ minimum of 16 volts, the steady state input current necessary for this example will be slightly greater than 9 amperes. If this device were connected to a voltage source with 10 feet of 20 gauge wire, the round trip (input and return) would result in 0.2 Ω of resistance and 1.8 volts of drop from the source to the converter. To assure 16 volts at the input, a source closer to 18 volts would be required. In applications using the paralleling option, this drop will be Therefore, the logic signal level generated in the system must be capable of a TTL logic high plus sufficient additional amplitude to overcome eRtn. When the converter is inhibited, IRtn diminishes to near zero and eRtn will then be at system ground. Incorporation of a 100 µfd capacitor at the input terminals is recommended as compensation for the dynamic effects of the parasitic resistance of the input cable reacting with the complex impedance of the converter input, and to provide an energy reservoir for transient input current requirements. Figure VI. Effects of Parasitic Resistance in Input Leads Rp I in Vin 100 µfd e source Rp I Rtn e Rtn Rtn Case Enable 1 System Ground Sync Out Sync In 10 NOTES Lambda Advanced Analog The information in this data sheet has been carefully checked and is believed to be accurate; however no responsibility is assumed for possible errors. These specifications are subject to change without notice. LAMBDA ADVANCED ANALOG INC. λ MIL-PRF-38534 Certified ISO9001 Registered 9849 2270 Martin Avenue Santa Clara CA 95050-2781 (408) 988-4930 FAX (408) 988-2702