DC-DC Converter Applications Content ● Terminology ● Limiting Inrush Current Powerline – Definitions and Testing Calculation of heatsinks ● Line Impedance Stabilisation Network (LISN) ● Ambient Temperature ● Break-Down Voltage ● Line Spectra of DC-DC Converters ● Current Limiting ● Long Distance Supply Lines ● Efficiency ● Maximum Output Capacitance ● Fold Back Current Limiting ● ● No Load Over Voltage Lock-Out General Test Set-Up ● Input Voltage Range ● Output Filtering calculation ● Isolation ● Overload Protection ● Line Regulations ● Power Supply Considerations ● Load Regulation ● Recommended Values for Paralleled DC-DC Converters ● Operating Temperature Range ● Output Ripple and Noise ● Output Ripple and Noise (continued) ● Output Voltage Accuracy ● Output Voltage Trimming ● PI Filter ● Storage Temperature Range ● Switching Frequency ● Transient Recovery Time ● Temperature Coefficient ● Voltage Balance Efficiency at FulI Load Input and Output Ripple Input to Output Isolation Input Voltage Range Insulation Resistance Isolation Capacitance Line Voltage Regulation Load Voltage Regulation Mean Time between Failure (MTBF) Operating temperature range ● Settling Time No Load Power Consumption ● Shielding Noise ● Temperature Performance of DC-DC Converters Output Voltage Accuracy Switching Frequency Temperature above Ambient ● Temperature Drift Transfer Moulded Surface Mount DC-DC Converters Adhesive Placement Adhesive Requirements ● 3V/5V Logic Mixed Supply Rails ● Conducted and Radiated Emissions ● Connecting DC-DC Converters in Parallel Component Materials ● Connecting Component Placement Cleaning Component Alignment DC-DC Converters in Series ● EIA-232 Interface Production Guideline Application Note ● EMC Considerations Recommended Solder Reflow Profile ● Filtering Solder Pad Design ● Input Voltage Drop-Out (brown-outs) Solder Reflow Profile ● Interpretation of DC-DC Converter EMC Data ● Isolated Data Acquisition System ● Isolation ● Isolation Capacitance and Leakage Current ● LCD Display Bias 312 ● Custom DC-DC Converters March-2006 www.recom-international.com DC-DC Converter Applications Terminology The data sheet specification for DC-DC converters contains a large quantity of information. This terminology is aimed at ensuring that the user can interpret the data provided correctly and obtain the necessary information for their circuit application. Input Voltage Range The range of input voltage that the device can tolerate and maintain functional performance over the Operating Temperature Range at full load. Load Voltage Regulation The change in output voltage over the specified change in output load. Usually specified as a percentage of the nominal output voltage, for example, if a 1V change in output voltage is measured on a 12V output device, load voltage regulation is 8.3%. For unregulated devices the load voltage regulation is specified over the load range from 10% to 100% of full load. Line Voltage Regulation The change in output voltage for a given change in input voltage, expressed as percentages. For example, assume a 12V input, 5V output device exhibited a 0.5V change at the output for a 1.2V change at the input, line regulation would be 1 %/1%. Output Voltage Accuracy The proximity of the output voltage to the specified nominal value. This is given as a tolerance envelope for unregulated devices with the nominal input voltage applied. For example, a 5V specified output device at 100% load may exhibit a measured output voltage of 4.75V, i.e. a voltage accuracy of –5%). Input and Output Ripple and Noise The amount of voltage drop at the input, or output between switching cycles. The value of voltage ripple is a measure of the storage ability of the filter capacitors. The values given in the datasheets include the higher frequency Noise interference superimposed on the ripple due to switching spikes.The measurement is limited to 20MHz Bandwidth. Input to Output Isolation The dielectric breakdown strength test between input and output circuits. This is the isolation voltage the device is capable of withstanding for a specified time, usually 1 second (for more details see chapter “Isolation Voltage vs. Rated Working Voltage”). www.recom-international.com Insulation Resistance The resistance between input and output circuits. This is usually measured at 500V DC. Efficiency at FulI Load The ratio of power delivered from the device to power supplied to the device when the part is operating under 100% load conditions at 25°C. Temperature Drift The change in voltage, expressed as a percentage of the nominal, per degree change in ambient temperature. This parameter is related to several other temperature dependent parameters, mainly internal component drift. Switching Frequency The nominal frequency of operation of the switching circuit inside the DC-DC converter. The ripple observed on the input and output pins is usually twice the switching frequency, due to full wave rectification and the push-pull configuration of the driver circuit. No Load Power Consumption This is a measure of the switching circuits power cunsumption; it is determined with zero output load and is a limiting factor for the total efficiency of the device. Isolation Capacitance The input to output coupling capacitance. This is not actually a capacitor, but the parasitic capacitive coupling between the transformer primary and secondary windings. Isolation capacitance is typically measured at 1 MHz to reduce the possibility of the onboard filter capacitors affecting the results. Mean Time Between Failure (MTBF) RECOM uses MIL-HDBK-217F standard for calculation of MTBF values for +25°C as well as for max. operating temperature and 100% load. When comparing MTBF values with other vendor's products, please take into account the different conditions and standards i.e. MIL-HDBK-217E is not as severe and therefore values shown will be higher than those shown by RECOM. (1000 x 10³ hours =1000000 hours = 114 years!) These figures are calculated expected device lifetime figures using the hybrid circuit model of MIL-HDBK-217F. POWERLINE converters also can use BELLCORE TR-NWT000332 for calculation of MTBF. The hybrid model has various accelerating factors for operating environment (πE), maturity (πL), screening (πQ), hybrid function (πF) and a hybrid model is then given by: λ = ∑ (NC λC) (1 + 0.2πE) πL πF πQ (failures in 106 hours) The MTBF figure is the reciprocal of this value. In the data sheets, all figures for MTBF are given for the ground benign (GB) environment (πE = 0.5); this is considered the most appropriate for the majority of applications in which these devices are likely to be used. However, this is not the only operating environment possible, hence those users wishing to incorporate these devices into a more severe environment can calculate the predicted MTBF from the following data. The MIL-HDBK-217F has military environments specified, hence some interpretation of these is required to apply them to standard commercial environments. Table 1 gives approximate cross references from MILHDBK-217F descriptions to close commercial equivalents. Please note that these are not implied by MIL-HDBK-217F, but are our interpretation. Also we have reduced the number of environments from 14 to 6, which are most appropriate to commercial applications. For a more detailed understanding of the environments quoted and the hybrid model, it is recommended that a full copy of MIL-HDBK-217F is obtained. It is interesting to note that space flight and ground benign have the same environment factors. It could be suggested that the act of achieving space flight should be the determining environmental factor (i.e. missile launch). The hybrid model equation can therefore be rewritten for any given hybrid, at a fixed temperature, so that the environmental factor is the only variable: λ = k (1 + 0.2 πE) The MTBF values for other environment factors can therefore be calculated from the ground benign figure quoted at each temperature point in the data book. Hence predicted MTBF figures for other environments can be calculated very quickly. All the values will in general be lower and, since the majority of the mobile environments have the same factor, a quick divisor can be calculated for each condition. Therefore the only calculation necessary is to devide the quoted MTBF fig. by the divisor given in table 2. summation of each individual component characteristic (λC). The equation for the March-2006 313 DC-DC Converter Applications Environment Ground Benign πE Symbol GB Ground Mobile GM Naval Sheltered NS Aircraft Inhabited Cargo AIC Space Flight SF Missile Launch ML MIL-HDBK-271F Description Non-mobile, temperature and humidity controlled environments readily accessible to maintenance Equipment installed in wheeled or tracked vehicles and equipment manually transported Sheltered or below deck equipment on surface ships or submarines Typical conditions in cargo compartments which can be occupied by aircrew Earth orbital. Vehicle in neither powered flight nor in atmospheric re-entry Severe conditions relating to missile launch Commercial Interpretation or Examples Laboratory equipment, test instruments, desktop PC's, static telecomms In-vehicle instrumentation, mobile radio and telecomms, portable PC's Navigation, radio equipment and instrumentation below deck Pressurised cabin compartments and cock-pit, in flight entertainment and non-safety critical applications Orbital communications satellite, equipment only operated once in-situ Severe vibrational shock and very high accelerating forces, satellite launch conditions Table 1: Interpretation of Environmental Factors VO DC VIN DC GND 0V a) Single Output DC VIN +VO 0V -VO DC GND b) Dual Output VIN VO1 0V1 VO2 0V2 DC DC GND c) Twin Isolated Outputs Figure 1: Standard Isolated Configurations VCC +VO DC Environment Ground Benign Ground Mobile Naval Sheltered Aircraft Inhabited Cargo Space Flight Missile Launch πE Symbol GB GM GNS AIC SF ML πE Divisor Value 0.5 1.00 4.0 1.64 4.0 1.64 4.0 0.5 12.0 1.64 1.00 3.09 Table 2: Environmental Factors Noise Input conducted noise is given in the line conducted spectra for each DC-DC converter (see EMC issues for further details). Noise is affected significantly by PCB layout, measurement system configuration, terminating impedance etc., and is difficult to quote reliably and with any accuracy other than via a spectrum analysis type plot. There will be some switching noise present on top of the ripple, however, most of this is easily reduced by use of small capacitors or filter inductors, as shown in the application notes. Operating temperature range: Operating temperature range of the converter is limited due to specifications of the components used for the internal circuit of the converter. 314 The diagram for temperature derating shows the safe operating area (SOA) within which the device is allowed to operate. At very low temperatures, the specifications are only guaranteed for full load. Up to a certain temperature 100% power can be drawn from the device, above this temperature the output power has to be less to ensure function and guarantee specifications over the whole lifetime of the converter. These temperature values are valid for natural convection only. If the converter is used in a closed case or in a potted PCB board, higher temperatures will be present in the area around thermal converter because the convection may be blocked. If the same power is also needed at higher temperatures either the next higher wattage series should be chosen or if the converter has a metal case, a heatsink may be considererd. Calculation of heatsinks: All converters in metal-cases can have a heatsink mounted so the heat generated by the converters internal power dissipation Pd can be removed. The general specification of the whole thermal system incl. heatsink is it’s thermal resistance RTH case-ambient March-2006 DC -VO 0V GND a) Non-lsolated Dual Rails VCC DC DC +VO 0V -VO GND b) Non-lsolated Negative Rail VCC DC DC +VO (VO+VIN) 0V GND c) Dual Isolated Outputs (U/T) Figure 2: Alternative Supply Configurations Power dissipation Pd: Pd = Pin − Pout = RTHcase-ambient = Pout − Pout Efficiency Tcase − Tambient Pd www.recom-international.com DC-DC Converter Applications Example: RP30-2405SEW starts derating without heatsink at +65°C but the desired operation is 30W at +75°C so the size of the heatsink has to be calculated. Pout = 30 W Efficiency = 88% max. Pout 30 W – 30 W = 4,1 W Pd = − Pout = Efficiency 88 % Tcase = 100 °C (max. allowed case temperature) Tambient = 75 °C RTHcase-ambient T −T = case ambient Pd = 100 °C – 75 °C = 6,1°C/W 4,1 W So it has to be ensured that the thermal resistance between case and ambient is 6,1°C/W max. When mounting a heatsink on a case there is a thermal resistance RTH case-heatsink between case and heatsink which can be reduced by using thermal conductivity paste but cannot be eliminated totally. Heatsink mounted on case without thermal conductivity paste RTH case-heatsink = ca. 1…2 °C/W Heatsink mounted on case with thermal conductivity paste RTH case-heatsink = ca. 0,5…1 °C/W Heatsink mounted on case with thermal conductivity paste and electrical-isolation-film RTH case-heatsink = ca. 1…1,5 °C/W If a heatsink is mounted on the converter it’s thermal resistance has to be at least: RTHheat sink-ambient = RTHcase-ambient − RTHcase-heat sink = 6,1 °C/W – 1°C/W = 5,1 °C/W Using this value, a suitable heat sink can be selected. Adding a fan increases the efficiency of any additional heat sinking, but adds cost and power loading. In most cases choosing the next higher wattage-series and using power-decreasing via derating may be the more efficient solution. only, hence referencing the isolated ground will only work if all the current return is through the DC-DC and not via other external components (e.g. diode bias, resistor feed). Having an alternative return path can upset the regulation and the performance of the system may not equal that of the converter. Isolation Voltage vs. Rated Working Voltage The isolation voltage given in the datasheet is valid for 1 second flash tested only. If a isolation barrier is required for longer or infinite time the Rated Working Voltage has to be used. Conversion of Isolation Voltage to Rated Working Voltage can be done by using this table or graph. Isolation One of the main features of the majority of Recom International Power GmbH DC-DC converters is their high galvanic isolation capability. This allows several variations on circuit topography by using a single DC-DC converter. The basic input to output isolation can be used to provide either a simple isolated output power source, or to generate different voltage rails, and/or dual polarity rails (see figure 1). These configurations are most often found in instrumentation, data processing and other noise sensitive circuits, where it is necessary to isolate the load and noise presented to the local power supply rails from that of the entire system. Usually local supply noise appears as common mode noise at the converter and does not pollute the main system power supply rails. The isolated positive output can be connected to the input ground rail to generate a negative supply rail if required. Since the output is isolated from the input, the choice of reference voltage for the output side can be arbitrary, for example an additional single rail can be generated above the main supply rail, or offset by some other DC value (see figure 2). Regulated converters need more consideration than the unregulated types for mixing the reference level. Essentially the single supply rail has a regulator in its +VO rail www.recom-international.com Isolation Test Voltage (kV) RTHcase-ambient = RTHcase-heat sink + RTHheat sink-ambient 12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 Rated Working Voltage (kV) Figure 5: IEC950 Test Voltage for Electrical Strength Tests Isolation Test Voltage (V) Rated Working Voltage (V) 1000 130 1500 230 3000 1100 6000 3050 Table 2: Typical Breakdown Voltage Ratings According to IEC950 March-2006 315 DC-DC Converter Applications The graph and table above show the requirements from IEC950. According to our Isolation Test Voltage (1 second) 500 VDC 1000 VDC 1500 VDC 2000 VDC 2500 VDC 3000 VDC 4000 VDC 5000 VDC 6000 VDC experience and in-house-test, we can offer the following conversion tables: Isolation Test Voltage (1 minute) 400 VDC 800 VDC 1200 VDC 1600 VDC 2000 VDC 2400 VDC 3200 VDC 4000 VDC 4800 VDC Isolation Test Voltage (1 minute) 250 VAC 500 VAC 750 VAC 1000 VAC 1250 VAC 1500 VAC 2000 VAC 2500 VAC 3000 VAC Table 1 : D.C. Isolation Voltage test vs different conditions Isolation Test Voltage (1 second) 500 VAC 1000 VAC 1500 VAC 2000 VAC 2500 VAC 3000 VAC 4000 VAC 5000 VAC 6000 VAC Isolation Test Voltage (1 minute) 350 VAC 700 VAC 1050 VAC 1400 VAC 1750 VAC 2100 VAC 2800 VAC 3500 VAC 4200 VAC Isolation Test Voltage (1 minute) 565 VDC 1130 VDC 1695 VDC 2260 VDC 2825 VDC 3390 VDC 4520 VDC 5650 VDC 6780 VDC Table 2 : A.C. Isolation Voltage test vs different conditions 316 March-2006 www.recom-international.com DC-DC Converter Applications Connecting DC-DC Converters in Series Galvanic isolation of the output allows multiple converters to be connected in series, simply by connecting the positive output of one converter to the negative of another (see figure 3). In this way non-standard voltage rails can be generated, however, the current output of the highest output voltage converter should not be exceeded. When converters are connected in series, additional filtering is strongly recommended, as the converters switching circuits are not synchronised. As well as a summation of the ripple voltages, the output could also produce relatively large beat frequencies. A capacitor across the output will help, as will a series inductor (see filtering). Vcc DC DC DC DC +Vo 0V +Vo 2Vo 0V GND Figure 3: Connecting DC-DC Converters in Series Connecting DC-DC Converters in Parallel could occur, where there was only 1W being drawn from the RC/RD and 1.5W from the RA/RB. Even with parallel converters of the same type, loading will be uneven, however, there is only likely to be around a 10% difference in output load, when the output voltages are well matched. When connecting converter outputs together, it should be remembered that the switching will not be synchronous, hence some form of decoupling should be employed. One possible solution is to use a diode feed, this is suitable mainly for 12V and 15V output types only, where the diode voltage drop (typically 0.6V) will not significantly affect the output voltage (see figure 4). With 5V and 9V supplies the diode drop is generally too large to consider it as a suitable means of connecting paralleled converters. This method also generates a beat frequency that will superimpose itself over the ripple of the two converters. This can be reduced by using an external capacitor at the paralleled output. The preferred method of connecting converters in parallel is via series inductors on the output (see figure 5). This configuration not only has a lower loss of voltage than the diode method, but by suitable choice of inductor and an additional external capacitor, the beat frequency can be significantly reduced, as will the ripple from each converter. If the available power output from a single converter is inadequate for the application, then multiple converters can be paralleled to produce a higher output power. VCC +VO DC DC Recommended Values for Paralleled DC-DC Converters The capacitance value used (Cout) should be approximately 1μF per parallel channel (i.e. for 2 parallel single output converters, 2μF between the common positive output and OV). The same comments can be applied to the input circuit for converters whose inputs are paralleled, and similar values for inductance and input capacitance should be used as shown above. In general, paralleling of converters should only be done when essential, as a higher power single converter is always a preferable solution. There should always be a correction factor to the maximum power rating to allow for mismatch between converters, and a full load test with a selection of converters is recommended, to ensure the output voltage is matched to within 1% or 2%. In general a factor of 0.9 should be used to provide a power safety margin per converter (e.g. 2 RC/RD converters paralleled should only be used up to a power level of 3.6W, not their 4W maximum). At most three DCDC converters can be paralleled with a high level of confidence in the overall performance. If the circuit needs more power than three converters in parallel, then a single converter with a much higher power rating should be considered. Regulated output DC-DC converters should not be paralleled, since their output voltage would need to be very accurately matched to ensure even loading (to within the tolerance of the internal regulator). Pa-ralleling regulated converters could cause one of the parts to be overloaded. If a high power regulated supply is required, it would be better to parallel unregulated converters and add an external linear regulator. DC DC 0V GND VCC Figure 4: Diode Coupled Paralleled DC-DC Converters DC LIN LOUT +VO DC It should be noted that it is always preferable to parallel multiple converters of the same type. For example, if a 2.5W converter is required, then either 2 RC/RD should be used or 3 RA/RB, not one RC/RD and one RA/RB. The reason for this is that the output voltages are not sufficiently well matched to guarantee that a RC/RD would supply twice as much as an RA/RB and the situation www.recom-international.com CIN COUT DC LIN DC LOUT 0V GND Figure 5: Fully Filtered Paralleled DC-DC Converters March-2006 317 DC-DC Converter Applications Filtering When reducing the ripple from the converter, at either the input or the output, there are several aspects to be considered. Recom recommend filtering using simple passive LC networks at both input and output (see figure 6). A passive RC network could be used, however, the power loss through a resistor is often too high.The selfresonant frequency of the inductor needs to be significantly higher than the characteristic frequency of the device (typically 1OOkHz for Recom DC-DC converters). The DC current rating of the inductor also needs consideration, a rating of approximately twice the supply current is recommended. The DC resistance of the inductor is the final consideration that will give an indication of the DC power loss to be expected from the inductor. However, depending on your application design and loadsituation may interfer with the calculated filter so testing in the final application and re-adjustment of the component’s values may be necessary. When choosing a value for the filtering capacitor please take care that the maximum capacitive load is within the specifications of the converter. Limiting Inrush Current Using a series inductor at the input will limit the current that can be seen at switch on (see figure 7). If we consider the circuit without the series inductor, then the input current is given by; V i =_ R –t Voltage : V = Vin (1 – exp __ ) RC ( ) Output Filtering calculation: VIN Calculating of the filtering components can be done using fc = V Current : i = _ exp R 1 This frequency should be significant lower than the switching frequency of the converter. Example - RC series: Operating frequency = 85kHz max. fc =10 % of 85 kHz = 8,5 kHz A simple method of reducing the output ripple is simply to add a large external capacitor. This can be a low cost alternative to the LC filter approach, although not as effective. There is also the possibility of causing start up problems, if the output capacitance is too large. With a large output capacitance at switch on, there is no charge on the capacitors and the DC-DC converter immediately experiences a large current demand at its output. The inrush current can be so large as to exceed the ability of the DC-DC converter, and the device can go into current limit or an undefined mode of operation. In the worst case scenario the device continuously "hiccups" as it tries to start, goes into overload shutdown and then retries again. The DC-DC converter may not survive if this condition persists. Recom recommend a maximum safe operating value of 10μF for the lower power converters,unless otherwise specified. When used in conjunction with a series output inductor, this value can be raised to 47μF, should extremely low ripple be required. ( –t__ ) RC 2π L OUT C0 Maximum Output Capacitance time Figure 7: Input Current & Voltage at Switch On i = V exp R ( –RCt ) When the component is initially switched on (i.e. t=O) this simplifies to; 1 fc = 2π L OUT C0 i=V R 1 This would imply that for a 5V input, with fc = 8,5 kHz = 2π L OUT C0 say 50mOhm track and wire resistance, the for: inrush current could be as large as 1OOA. L OUT = 470 μH This could cause a problem for the DC-DC converter. ⎞ ⎛ ⎛ ⎞ 1 1 ⎟ =⎜ ⎟ = 745 nF A series input inductor therefore not only filters C0 = ⎜⎜ 2 ⎟ 2 ⎟ ⎜ the noise from the internal switching circuit, ⎝ (2 π fc) L OUT ⎠ ⎝(2 π 8,5 kHz) 470 uH ⎠ but also limits the inrush current at switch on. Settling Time The main reason for not fitting a series inductor internally, apart from size constraints, is that many applications require a fast switch on time. When the input voltage is a fast ramp, then the output can respond within 500μs of the input reaching its target voltage (measured on a range of RA/RB and RC/RD converters under full output load without external filters). The use of external filters and additional input or output capacitance will slow this reaction time. It is therefore left to the designer to decide on the predominant factors important for their circuit, settling time or noise performance. Isolation Capacitance and Leakage Current The isolation barrier within the DC-DC converter has a capacitance, which is a measure of the coupling between input and output circuits. Providing this is the largest coupling source, a calculation of the leakage current between input and output circuits can be calculated. Figure 6: Input and Output Filtering 318 March-2006 www.recom-international.com DC-DC Converter Applications Assuming we have a known isolation capacitance (Cis - refer to datasheet) and a known frequency for either the noise or test signal, then the expected leakage current (iL) between input and output circuits can be calculated from the impedance. The general isolation impedance equation for a given frequency (f) is given by: Zf = ___1___ j2 π C is For an RB-0505D, the isolation ca-pacitance is 18pF, hence the isolation im-pedance to a 50Hz test signal is: Z50 = ___1_______ = 177 M Ω j2 π 50 18 pf If using a test voltage of 1kVrms, the leakage current is: iL = Vtest = _1000V_ = 5.65 μA 177MΩ Z If there is an intelligent power management system at the input, using a series resistor (in place of the series inductor) and detecting the voltage drop across the device to signal the management system can be used. A similar scheme can be used at the output to determine the output voltage, however, if the management system is on the input side, the signal will need to be isolated from the controller to preserve the system isolation barrier (see figure 10). There are several other current limiting techniques that can be used to detect an overload situation, the suitability of these is left to the designer. The most important thing to consider is how this information will be used. If the system needs to signal to a controller the location or module causing the overload, some form of intelligence will be needed. If the device simply needs to switch off, a simple fuse type arrangement will be adequate. Unregulated RECOM DC/DC converters usually are short circuit protected only for a short time like 1 second. By option they can be continous short circuit protected (option /P), then their design is able to withstand high output current at overload situation without any protection extra circuits protection. All Recom DC-DC converters which include an internal linear regulator, have a thermal overload shut-down condition which protects these devices from excessive over-load. If this condition is to be used to inform a power management system, the most suitable arrangement is the output voltage detector (see figure 10a), since this will fall to near zero on shut-down. Wide input range regulated converters offer overload protection / short circuit protection via an internal circuit that interfers with the primary oscillator so the switching is regulated back in situations of overload or output short circuit. f It can be easily observed from these simple equations that the higher the test or noise voltage, the larger the leakage current, also the lower the isolation capacitance, the lower the leakage current. Hence for low leakage current, high noise immunity designs, high isolation DC-DC converters should be selected with an appropriate low isolation capacitance. VIN DC Fuse DC GND Figure 8: Simple Overload Protection Overload Protection Although the use of filtering will prevent excessive current at power-on under normal operating conditions, many of the lower cost converters have no protection against an output circuit taking excessive power or even going short-circuit. When this happens, the DC-DC converter will take a large input current to try to supply the output. Eventually the converter will overheat and destroy itself if this condition is not rectified (short circuit overload is only guaranteed for 1 s on an unregulated part). There are several ways to prevent overload at the outputs destroying the DC-DC converter. The simplest being a straight forward fuse. Sufficient tolerance for inrush current is required to ensure the fuse does not blow on power-on (see figure 8). Another simple scheme that can be applied is a circuit breaker. There is also the potential to add some intelligence to the overload scheme by either detecting the input current, or the output voltage (see figure 9). www.recom-international.com RIN VCC DC DC VOL GND a) Series Resistor for Input Current Measurement VCC ILIMIT DC R1 R2 GND b) Ground Current Monitor DC RGND Choose current limit (ILIMIT) and ground resistor (RGND) so that : 0.7V = RGND x ILIMIT. Figure 9: Input Monitored Overload Protection March-2006 319 DC-DC Converter Applications Input Voltage Drop-Out (brown-outs) VCC +VO DC DC OV GND RD RO Opto-Isolator VOL Opto-Isolated Overload Detector (On overload +VO falls and the LED switches off, the VOL. line is then pulled high.) Figure 10 : Ouput Monitored Overload Protection No Load Over Voltage Lock-Out LIN ZDX60 When the input voltage drops, or is momentarily removed, the output circuit would suffer similar voltage drops. For short period input voltage drops, such as when other connected circuits have an instantaneous current demand, or devices are plugged in or removed from the supply rail while 'hot', a simple diode-capacitor arrangement can prevent the output circuit from being effected. The circuit uses a diode feed to a large reservoir capacitor (typically 47μF electrolytic), which provides a short term reserve current source for the converter, the diode blocking other circuits from draining the capacitor over the supply rail. When combined with an in-line inductor this can also be used to give very good filtering. The diode volt drop needs to be considered in the power supply line under normal supply conditions. A low drop Schottky diode is recommended (see figure 11). DC 47μF Output Circuit DC Figure 11 : Input Voltage Drop-out R10% DC DC R10% Unregulated DC-DC converters are expected to be under a minimum of 10% load, hence below this load level the output voltage is undefined. In certain circuits this could be a potential problem. The easiest way to ensure the output voltage remains within a specified tolerance, is to add external resistors, so that there is always a minimum 10% loading on the device (see figure 12). This is rather inefficient in that 10% of the power is always being taken by this load, hence only 90% is available to the additional circuitry. Zener diodes on the output are another simple method. It is recommended that these be used with a series resistor or inductor, as when the Zener action occurs, a large current surge may induce signal noise into the system. R2 DC DC Figure 12: No Load over Voltage Lock-Out 320 March-2006 www.recom-international.com DC-DC Converter Applications Long Distance Supply Lines When the supply is transmitted via a cable, there are several reasons why using an isolated DC-DC converter is good design practice (see figure 13). The noise pick up and EMC susceptibility of a cable is high compared to a pcb track. By isolating the cable via a DC-DC converter at either end, any cable pick-up will appear as common mode noise and should be self-cancelling at the converters. Another reason is to reduce the cable loss by using a high voltage, low current power transfer through the cable and reconverting RB-0512D LCD Display Bias A LCD display typically requires a positive or negative 24V supply to bias the crystal. The RO-0524S converter was designed specifically for this application. Having an isolated OV output, this device can be configured as a +24V supply by connecting this to the GND input, or a –24V supply by connecting the +Vo output to GND (see figure 14). RO-2405 Cable DC Vin GND supply is required through the cable, a cable loss of 44mW. DC DC DC Target Circuit Figure 13: Long Distance Power Transfer RO-0524S DC DC Liquid Crystal Display -24V (up to 42mA) Figure 14: LCD Display Bias at the terminating circuit. This will also reduce noise and EMC susceptibility, since the noise voltage required to affect the rail is also raised. For example, compare a system having a 5V supply and requiring a 5V, 500mW output at a remote circuit. Assume the connecting cable has a 100 Ohm resistance. Using an RN-0505 to convert the power at either end of the cable, with a 100mA current, the cable will lose 1W (I2R) of power. The RO/RN would not be suitable, since this is its total power delivery; hence there is no power available for the terminating circuit. Using a RB-0512D to generate 24V and a RA-2405D to regenerate 5V, only a 21 mA www.recom-international.com EIA-232 Interface In a mains powered PC often several supply rails are available to power a RS232 interface. However, battery operated PC’s or remote equipment having a RS232 interface added later, or as an option, may not have the supply rails to power a RS232 interface. Using a RB-0512S is a simple single chip solution, allowing a fully EIA-232 compatible interface to be implemented from a single 5V supply rail, and only 2 additional components (see figure 15). March-2006 3V/5V Logic Mixed Supply Rails There has been a lot of attention given to new l.C.'s and logic functions operating at what is rapidly emerging as the standard supply level for notebook and palmtop computers. The 3.3V supply is also gaining rapid acceptance as the defacto standard for personal telecommunications, however, not all circuit functions required are currently available in a 3.3V powered IC. The system designer therefore has previously had only two options available; use standard 5V logic or wait until the required parts are available in a 3V form, neither being entirely satisfactory and the latter possibly resulting in lost market share. There is now another option, mixed logic functions running from separate supply rails. A single 3.3V line can be combined with a range of DC-DC converters from Recom, to generate voltage levels to run virtually any standard logic or interface IC. The Recom range includes dual output parts for powering analogue bipolar and amplifier functions (RA/RB series), as well a single output function for localised logic functions (RL/RM, RN/RO series). A typical example might be a RS232 interface circuit in a laptop PC using a 3.3V interface chip (such as the LT1330), which accepts 3.3V logic signals but requires a 5V supply (see figure 16). Recom has another variation on this theme and has developed two 5V to 3.3V step down DC-DC converters (RL-053.3 and R0-053.3). These have been designed to allow existing systems to start incorporating available 3.3V l.C.'s without having to redesign their power supply. This is particularly important when trying to reduce the overall power demand of a system, but not having available all of the functions at the 3.3V supply. The main application for this range of devices are system designers, who want to provide some functionality that requires a higher voltage than is available from the supply rail, or for a single localised function. Using a fully isolated supply is particularly useful in interface functions and systems maintaining separate analogue and digital ground lines. 321 DC-DC Converter Applications Isolated Data Acquisition System +12V EIA-232 Port VCC 5V VDD DCD RB-0512D DB9S Connector DSR +VO RX DC OV RTS TX -VO CTS DC DTR GND RI EMC Considerations When used for isolating a local power supply and incorporating the appropriate filter circuits as illustrated in Fig. 17), DC-DC converters can present simple elegant solutions to many EMC power supply problems. The range of fixed frequency DC-DC converters is particularly suitable for use in EMC problem situations, as the stable fixed switching frequency gives easily characterised and easily filtered output. The following notes give suggestions to avoid common EMC problems in power supply circuits. SN75C185 Figure 15: Optimised RS232 Interface 3.3VCC RL-3.305 3 1 Any active system requiring isolation will need a DC-DC converter to provide the power transfer for the isolated circuit. In a data acquisition circuit there is also the need for low noise on the supply line; hence good filtering is required. The circuit shown (see figure 17) provides a very high isolation barrier by using an RG/RH/RJ/RK converter; to provide the power isolation and SFH610 opto-isolators for the data isolation. An overall system isolation of 2.5kV is achieved. 8 DC DC +5V 7 OV GND GND VCC 1µF 1 3.3V 2 3 + 100nF -V +V 28 26 + 220nF 3.3V Logic 200nF 4 27 TX1 14 25 5 TX1 RX1 24 6 RX1 RS232 17 LT1330 GND Figure 16: RS232 Interface with 3V Logic 322 March-2006 www.recom-international.com DC-DC Converter Applications 5V Opto Isolators 4K7 Data RH-0505 1K2 5V 5V Logic Circuit Data CS 4K7 5V CS 1K2 4K7 Status VCC +5V 1K2 Status CLK +5V CLK Vref ZN509 47µH +5V AIN 1K2 +5V DC DC 1µF 470vF GND 4K7 1K2 SFH610 Power Supply Considerations Figure 17: Isolated Serial ADC System ● Eliminate loops in supply lines (see figure 18). ● Decouple supply lines at local boundaries (use RCL fitters with VCC PSU CCT1 8 CCT2 GND VCC PSU CCT1 3 CCT2 GND low Q, see figure 19). ● Place high speed sections close to the power line input, slowest section furthest away (reduces power plane transients, see figure 20). ● Isolate individual systems where possible (especially analogue and digital systems) on both power supply and signal lines (see figure 21). An isolated DC-DC converter can provide a significant benefit to help reduce susceptibility and conducted emission due to the isolation of both power rail and ground from the sys-tem supply. The range of DC-DC converters available from Recom all utilise toroidal power transformers and as such have negligible EMI. Isolated DC-DC converters are switching devices and as such have a characteristic switching frequency, which may need some additional filtering. Interpretation of DC-DC Converter EMC Data Figure 18: Eliminate Loops in Supply Line VCC CCT1 GND Figure 19: Decouple Supply Lines at Local Boundaries www.recom-international.com CCT2 Electromagnetic compatibility (EMC) of elec-trical and electronic products is a measure of electrical pollution. Throughout the world there are increasing statutory and regulatory requirements to demonstrate the EMC of end products. In Europe the EC directive 89/336/EEC requires that, any product sold after 1 January 1996 complies with a series of EMC limits, otherwise the product will be prohibited from sale within the EEC and the seller could be prosecuted and fined. Although DC-DC converters are generally exempt from EMC regulations on the grounds that these are component items, it is the belief of Recom that the information on the EMC of these components can help de- signers ensure their end product can meet the relevant statutory EMC requirements. It must be remembered however, that the DC-DC converter is unlikely to be the last component in the chain to the mains supply, hence the information quoted needs interpretation by the circuit designer to deter-mine its impact on the final EMC of their system. March-2006 323 DC-DC Converter Applications 150kHz to 1GHz, but as two separate and distinct modes of transmission. The Recom range of DC-DC converters feature toroidal transformers. These have been tested and proved to have negligible radiated noise. The low radiated noise is primarily due to toroidal shaped transformers maintaining the mag-netic flux within the core, hence no magnetic flux is radiated by design. Due to the exceptionally low value of radiated emis-sion, only conducted emissions are quoted. Conducted emissions are measured on the input DC supply line. Unfortunately no standards exist for DC supplies, as most standards cover mains connected equipment. This poses two problems for a DC supplied device, firstly no standard limit lines can be directly applied, since the DC supplied device does not directly connect to the mains, also all reference material uses the earthground plane as reference point. In a DC system often the OV is the reference, however, for EMC purposes, it is probably more effective to maintain the earth as the reference, since this is likely to be the reference that the shielding or casing is connected to. Consequently all measurements quoted are referenced to the mains borne earth. Local P S U Power Input High Speed Circuit Medium Speed Circuit Low Speed Circuit DC Circuit Filter Figure 20: Place High Spead Circuit Close to PSU VCC DC DC CCT1 DC DC CCT2 GND Figure 21 : Isolate Individual Systems Line Impedance Stabilisation Network (LISN) Power Supply 50Ω Termination – LISN DC Load DC + LISN To Spectrum Analyser Figure 22: Filtered Supply to DC-DC Converter The notes given here are aimed at helping the designer interpret the effect the DC-DC converter will have on the EMC of their end product, by describing the methods and rationale for the measurements made. Where possible CISPR and EN standards have been used to determine the noise spectra of the components, however, all of the standards reference to mains powered equipment and interpretation of these specifications is necessary to examine DC supplied devices. 324 Conducted and Radiated Emissions There are basically two types of emissions covered by the EC directive on EMC, radiated and conducted. Conducted emissions are those transmitted over wire connecting circuits together and covers the frequency spectrum 150kHz to 30MHz. Radiated are those emissions transmitted via electromagnetic waves in air and cover the frequency spectrum 30MHz to 1GHz. Hence the EC directive covers the frequency spectrum March-2006 It is necessary to ensure that any measurement of noise is from the device under test (DUT) and not from the supply to this device. In mains connected circuits this is important and the mains has to be filtered prior to supply to the DUT. The same approach has been used in the testing of DC-DC converters and the DC supply to the converter was filtered, to ensure that no noise from the PSU as present at the measuring instrument. A line impedance stabilisation network (LISN) conforming to CISPR 16 specification is connected to both positive and negative supply rails and referenced to mains earth (see figure 22). The measurements are all taken from the positive supply rail, with the negative rail measurement point terminated with 50 Ohm to impedance match the measurement channels. www.recom-international.com DC-DC Converter Applications 2 Conducted Emission (dBuV) 100 4 1 80 8 6 12 10 3 60 5 7 9 11 13 40 20 0 0 100 300 200 400 500 Frequency (kHz) Figure 23: Individual Line Spectra 50 40 Frequency (kHz) 30 20 10 0 0 2 4 6 8 10 12 14 Input Voltage (V) Figure 24: Frequency Voltage Dependency Conducted Emission (dBuV) 100 80 60 40 20 0 100kHz 1MHz 10MHz 100MHz Frequency Figure 25 : V Spectrum Shielding Line Spectra of DC-DC Converters At all times the DUT, LlSN's and all cables connecting any measurement equipment, loads and supply lines are shielded. The shielding is to prevent possible pick-up on cables and DUT from external EMC sources (e.g. other equipment close by). The shielding is referenced to mains earth (see figure 22). All DC-DC converters are switching devices, hence, will have a frequency spectra. Fixed input DC-DC converters have fixed switching frequency, for example the RC/RD range of converters has a typical switching frequency of 50kHz. This gives a stable and predictable noise spectrum regardless of load conditions. If we examine the noise spectrum closely (see figure 23) we can see several distinct peaks, these arise from the fundamental www.recom-international.com March-2006 switching frequency and its harmonics (odd line spectra) and the full rectified spectra, at twice the fundamental switching frequency (even line spectra). Quasi-resonant converters, such as the Recom range, have square wave switching waveforms, this produces lower ripple and a higher efficiency than soft switching devices, but has the drawback of having a relatively large spectrum of harmonics. The EC regulations for conducted interference covers the bandwidth 150kHz to 30MHz. Considering a converter with a 100kHz nominal switching frequency, this would exhibit 299 individual line spectra. There will also be a variation of absolute switching frequency with production variation, hence a part with a 90kHz nominal frequency would have an additional 33 lines over the entire 30MHz bandwidth. Absolute input voltage also produces slight variation of switching frequency (see figure 24). Hence, to give a general level of conducted noise, we have used a 100kHz resolution bandwidth (RBW) to examine the spectra in the data sheets. This wide RBW gives a maximum level over all the peaks, rather than the individual line spectra. This is easier to read as well as automatically compensating for variances in switching frequency due to production variation or differences in absolute input voltage (see figure 25). The conducted emissions are measured under full load conditions in all cases. Under lower loads the emission levels do fall, hence full load is the worst case condition for conducted line noise. Temperature Performance of DC-DC Converters The temperature performance of the DC-DC converters detailed in this book is always better than the quoted operating temperature range. The main reason for being conservative on the operating temperature range is the difficulty of accurately specifying parametric performance outside this temperature range. There are some limiting factors which provide physical barriers to performance, such as the Curie temperature of the core material used in the DC-DC converter (the lowest Curie temperature material in use at Recom is 125°C). Ceramic capacitors are used almost exclusively in the DC-DC converters because of their high reliability and extended life properties, however, the absolute 325 DC-DC Converter Applications Switching Frequency (kHz) 160 handle the components only by the central body area where there are no component pins. O/N 140 Under Full Load Conditions A/B 120 C/D 100 80 60 –20 0 20 40 60 80 100 Temperature (°C) Figure 26: Typical Switching Frequency vs. Temperature capacity of these can fall when the temperature rises above 85°C (ripple will increase). Other considerations are the power dissipation within the active switching components, although these have a very high temperature rating. Their current carrying capacity derates as temperature exceeds 100°C. Therefore this allows the DC-DC converters to be used above their specified operating temperature, providing the derating of power delivery given in the specification is adhered to. Components operating outside the quoted operating temperature range cannot be expected to exhibit the same parametric performance that is quoted in the specification. An indication of the stability of a device can be obtained from the change in its operating frequency, as the temperature is varied (see figure 26). A typical value for the frequency variation with temperature is 0.5% per °C, a very low value compared to other commercial parts. This illustrates the ease of filtering of Recom DC-DC converters, since the frequency is so stable across load and temperature ranges. Transfer Moulded Mount DC-DC Converters Production Guideline Application Note The introduction by Recom of a new and innovative method of encapsulating hybrid DC-DC converters in a transfer moulded (TM) epoxy molding compound plastic has enabled a new range of surface mount (SMD) DC-DC converters to be brought to market, which addresses the component placement with SOIC style handling. With any new component there are of course new lessons to be learned with the mounting technology. With the Recom SMD DCDC converters, the lessons are not new as such, but may require different production techniques in certain applications. 326 Component Materials Recom SMD converters are manufactured in a slightly different way than the throughhole converters. Instead of potting the PCB board inside a plastic case with conventional epoxy the whole package is molded around the PCB board with epoxy molding compound plastic. This ensures better thermal conductivity from the heat generating components like semiconductors, transformer, etc. inside to the surface from where it can dissipate via convection. This makes them ideal for reflow processes also under the stricter conditions of lead-free soldering temperatures that meet the requirements of the ROHS regulation. All materials used in RECOM lead-free products are ROHS compliant, thus the total amount of the restricted materials (lead, mercury, cadmium, hexavalent chromium, PBBs and PBDEs) are below the prescribed limits. Detailed chemical analysis reports are available. Component Placement Recom SMD DC-DC converters are designed to be handled by placement machines in a similar way to standard SOIC packages. The parts are available either in tubes (sticks) or in reels. The parts can therefore be placed using machines with either vibrational shuttle, gravity feeders, or reel feeders.The vacuum nozzle for picking and placing the components can be the same as used for a standard 14 pin or 18 pin SOIC (typically a 5mm diameter nozzle). An increase in vacuum pressure may be beneficial, due to the heavier weight of the hybrid compared to a standard SOIC part (a typical 14 pin SOIC weighs 0.1g, the Recom SMD DC-DC converter weighs 1.5 ~ 2,7g). It is advisable to consult your machine supplier on the best choice of vacuum nozzle if in doubt.If placing these components by hand, March-2006 Component Alignment The components can be aligned by either optical recognition or manual alignment. If using manual alignment it should be ensured that the tweezers press on the component body and not on the pins. The components themselves are symmetrical along their axis, hence relatively easy to align using either method. Solder Pad Design The Recom SMD DC-DC converters are designed on a pin pitch of 2,54mm (0.1") with 1,20mm pas widths and 1,80mm pad lengths. 12.00 8 5 1 2 4 1.20 Top View 1.80 This allows pads from one part to be used within a PCB CAD package for forming the pad layouts for other SMD converters. These pads are wider than many standard SOIC pad sizes (0.64mm) and CAD packages may not accommodate these pins with a standard SOIC pad pattern. It should be remembered that these components are power supply devices and as such need wider pads and thicker component leads to minimise resistive losses within the interconnects. Solder Reflow Profile RECOM's SMD converters are designed to withstand a maximum reflow temperature of 245°C (for max. 30seconds) in accordance with JEDEC STD-020C. If multiple reflow profiles are to be used (i.e. the part is to pass through several reflow ovens), it is recommended that lower ramp rates be used than the maximum specified in JEDEC STD020C. Continual thermal cycling to this profile could cause material fatigue, if more than 5 maximum ramp cycles are used. In general these parts will exceed the reflow capability of most IC and passive components on a PCB and should prove the most thermally insensitive component to the reflow conditions. www.recom-international.com DC-DC Converter Applications Lead-free Recommended Soldering Profile (SMD parts) 300 10-30s min. 300s Temperature (°C) 250 (245°C) 200 150 Pre - Heat 100 50 50 100 200 150 250 300 350 400 450 500 Time (seconds) Lead-free Recommended Soldering Profile (Through hole parts) Double Wave 340 320 300 3 - 5 seconds Temperature (°C) 280 260 240 220 Forced Cooling 60°C/s Min. 100°C ~ 150°C Max. 200 180 160 140 120 100 80 60 40 20 0 Natural Cooling Enter Wave Pre - Heat 0 10 20 30 40 50 60 70 80 Time (seconds) 90 100 110 120 Notes: 1. The wave solder profile is measured on lead temperature. 2. Need to keep the solder parts internal temperature less than about 210°C Recommended Solder Reflow Profile: The following 2 graphs show the typical recommended solder reflow profiles for SMD and through-hole ROHS compliant converters. The exact values of the profile’s peak and it’s maximum allowed duration is also given in the datasheet of each converter. Adhesive Requirements If SM surface mount components are going to be wave soldered (i.e. in a mixed through hole and SMD PCB) or are to be mounted on both sides of a PCB, then it is necessary to use an adhesive to fix them to the board www.recom-international.com prior to reflow. The adhesive prevents the SMD parts being 'washed off' in a wave solder, and being 'vibrated off' due to handling on a double sided SMD board. As mentioned previously, the Recom range of SMD DC-DC converters are heavier than standard SOIC devices. The heavier weight is a due to their size (volume) and internal hybrid construction. Consequently the parts place a larger than usual stress on their solder joints and leads if these are the only method of attachment. Using an adhesive between component body and PCB can reduce this stress considerably. If the final system is to be subjected to shock and vibration testing, then using adhesive attachment March-2006 is essential to ensure the parts pass these environmental tests. The Recom SMD DC-DC converters all have a stand-off beneath the component for the application of adhesive to be placed, without interfering with the siting of the component. The method of adhesive dispensing and curing, plus requirements for environmental test and in-service replacement will determine suitability of adhesives rather than the component itself. However, having a thermoset plastic body, thermoset epoxy adhesive bonding between board and component is the recommended adhesive chemistry. If the reflow stage is also to be used as a cure for a heat cure adhesive, then the component is likely to undergo high horizontal acceleration and deceleration during the pick and place operation. The adhesive must be sufficiently strong in its uncured (green) state, in order to keep the component accurately placed. Adhesive Placement The parts are fully compatible with the 3 main methods of adhesive dispensing; pin transfer, printing and dispensing. The method of placing adhesive will depend on the available processes in the production line and the reason for using adhesive attachment. For example, if the part is on a mixed though-hole and SMD board, adhesive will have to be placed and cured prior to reflow. If using a SMD only board and heat cure adhesive, the reflow may be used as the cure stage. If requiring adhesive for shock and vibration, but using a conformal coat, then it may be possible to avoid a separate adhesive alltogether, and the coating alone provides the mechanical restraint on the component body. Patterns for dispensing or printing adhesive are given for automatic lines. If dispensing manually after placement the patterns for UV cure are easily repeated using a manual syringe (even if using heat cure adhesive).If dispensing manually, dot height and size are not as important, and the ad-hesive should be applied after the components have been reflowed. When dispensing after reflow, a chip underfill formulation adhesive would be the preferred choice. These types 'wick' under the component body and offer a good all round adhesion from a single dispensed dot. The patterns allow for the process spread of the stand-off on the component, but do not account for the thickness of the PCB tracks. 327 DC-DC Converter Applications If thick PCB tracks are to be used, a grounded copper strip should be laid beneath the centre of the component (care should be exercised to maintain isolation barrier limits). The adhesive should not retard the pins reaching their solder pads during placement of the part, hence low viscosity adhesive is recommended. The height of the adhesive dot, its viscosity and slumping properties are critical. The dot must be high enough to bridge the gap between board surface and component, but low enough not to slump and spread, or be squeezed by the component, and so contaminate the solder pads. If wishing to use a greater number of dots of smaller diameter (common for pin transfer methods), the dot pattern can be changed, by following a few simple guidelines. As the number of dots is doubled their diameter should be halved and centres should be at least twice the printed diameter from each other, but the dot height should re-main at 0.4mm. The printed dot should always be positioned by at least its diameter from the nearest edge of the body to the edge of the dot. The number of dots is not important, provided good contact between adhesive and body can be guaranteed, but a minimum of 2 is recommended. 328 Cleaning The thermoset plastic encapsulating material used for the Recom range of surface mount DC-DC converters is not fully hermetically sealed. As with all plastic encapsulated active devices, strongly reactive agents in hostile environments can attack the material and the internal parts, hence cleaning is recommended in inert solutions (e.g. alcohol or water based solvents) and at room temperature in an inert atmospheres (e.g. air or nitrogen). A batch or linear aqueous cleaning process would be the preferred method of cleaning using a deionised water solution. standard series, the generic series specification can be used. All custom parts receive the same stringent testing, inspection and quality procedures, as standard products. However there is a minimum order quantity as this additional documentations and administrative tasks must be covered in terms of costs. A general figure for this MOQ can be around 3000pcs of low wattage converters (0,25pcs ~ 2W), 1000pcs medium sized wattage (2W~15W) and 500pcs for higher wattages (> 20W).Recom custom parts are used in many applications, which are very specific to the individual customer, however, some typical examples are: ● ECL Logic driver Custom DC-DC Converters In addition to the standard ranges shown in this data book, Recom have the capability to produce custom DC-DC converters designed to your specific requirements. In general, the parts can be rapidly designed using computer based CAD tools to meet any input or output voltage requirements within the ranges of Recom standard products (i.e. up to 48V at either input or output). Prototype samples can also be produced in short timescales. Custom parts can be designed to your specification, or where the part fits within a March-2006 ● Multiple cell battery configurations ● Telecommunications line equipment ● Marine apparatus ● Automotive electronics ● LCD display power circuitry ● Board level instrumentation systems To discuss your custom DC-DC converter requirements, please contact Recom technical support desk or your local distributor. www.recom-international.com Block diagrams Unregulated Single Output RM, RL, RQS, RO, RE, ROM, RSS, RB-xxxxS, RA-xxxxS, RBM-xxxxS, RK, RP-xxxxS, RxxPxxS, RxxP2xxS, RN,RTS, RI, REZ, RKZxxxxS, RV-xxxxS, RAA-xxxxS, RGZ +Vin +Vout Oscillator -Vout -Vin Unregulated Dual Output RQD, RSD, RB-xxxxD, RA-xxxxD, RBM-xxxxD, RH, RP-xxxxD, RxxPxxD, RxxP2xxD, RTD, RCxxxxD, RD-xxxxD, RKZ-xxxxD, RVxxxxD, RAA-xxxxD, RJZ +Vin +Vout Oscillator Com -Vout -Vin Unregulated Dual Isolated Output RU, RUZ +Vin +Vout1 -Vout1 Oscillator +Vout2 -Vout2 -Vin Post-Regulated Single Output RZ, RSZ (P), RY-xxxxS, RX-xxxxS, RY-SCP, REC1.5-xxxxSR/H1, REC1.8xxxxSR/H1, REC2.2-xxxxSR/H1, REC3-xxxxSR/H1 +Vin Reg +Vout Oscillator -Vout -Vin Post-Regulated Dual Output RY-xxxxS, RX-xxxxS, RY-DCP, REC2.2-xxxxDR/H1, REC3-xxxxDR/H1 +Vin Reg Oscillator Com Reg -Vin www.recom-international.com +Vout March-2006 -Vout 329 Block diagrams Regulated Single Output RSO, RS, REC2.2-xxxxSRW, RW-xxxxS, REC3-xxxxSRW(Z)/H1/H4/H6, REC5-xxxxSRW(Z)/H1/H4/H6, REC7.5-xxxxSRW/AM +Vin Noise Filter +Vout -Vout -Vin Oscillator & Controller Reference & Error AMP Isolation Regulated Dual Output RSO-xxxxD, RS-xxxxD, REC2.2-xxxxDRW, RW-xxxxD, REC3-xxxxDRW(Z)/H1/H4/H6, REC5-xxxxDRW(Z)/H1/H4/H6, REC7.5-xxxxDRW/AM +Vin Noise Filter +Vout Com -Vout -Vin Oscillator & Controller Reference & Error AMP Isolation Regulated Dual Isolated Output REC3-DRWI Reg +Vin +Vout2 Noise Filter -Vout2 +Vout1 -Vout1 -Vin Oscillator & Controller 330 Isolation March-2006 Reference & Error AMP www.recom-international.com TAPES RSS-xxxx & RQS-xxxx tape outline dimensions 13.2 Spocket hole Ø1.50+0.1/-0 Spocket hole tolerance over any 10 pitches ±0.2 0.40 ±0.05 16.00 2.00 4.00 11.4 1.75 7.6 11.5 24.0 ±0.2 RECOM RSS-0505 xxxx All dimensions in mm xx.xx ±0.1 1. 10 sprocket hole pitch cumulative tolerance ±0.20 2. All dimensions meet EIA-481-2 requirements 3. Component load per 13" reel : 500 pcs RECOM RSS-0505 xxxx 4. The diameter of disc center hole is 13.0mm www.recom-international.com RECOM RSS-0505 xxxx March-2006 331 TAPES RSD-xxxx, RQD-xxxx & RZ-xxxx tape outline dimensions 17.75 Spocket hole Ø1.50+0.1/-0 Spocket hole tolerance over any 10 pitches ±0.2 0.35 ±0.05 16.00 2.00 4.00 11.4 1.75 7.6 11.5 24.0 ±0.2 RECOM RSD-0505 xxxx All dimensions in mm xx.xx ±0.1 1. 10 sprocket hole pitch cumulative tolerance ±0.20 2. All dimensions meet EIA-481-2 requirements 3. Component load per 13" reel : 500 pcs RECOM RSD-0505 xxxx 4. The diameter of disc center hole is 13.0mm 332 RECOM RSD-0505 xxxx March-2006 www.recom-international.com Powerline – Definitions and Testing The following pages offer a rough explanation of basic specifications or details which are unique to the POWERLINE and cannot befound in the application notes for our other product-series. General Test Set-Up The need for EMC Most power converter tests are carried out with the general test set-up shown in Figure 1. Some general conditions which apply (except where noted) to test methods are outlined in these notes: ● Adequate DC power source, and normal DC input voltage ● +25°C ambient temperature ● Full rated output load 9L-TF002 L1 +Vin C1 Z 47μF 100V DC/DC Converter 47μF 100V C2 –Vin Figure 1-1: EMC application test for: RP10-, RP12-, RP15-, RP20-, RP30-, RP40- and RP60-Serie L1 = 1102.5 μH DCR = 0.1 C1, C2 = 47μF Ø 0.5mm Aluminum Electrolytic Capacitor Ripple: 180mA at 105°C, 120Hz 100V 9L-TF009 L1 +Vin C1 Z 47μF 100V DC/DC Converter 47μF 100V C2 –Vin Figure 1-2: EMC application test for: RP03-A Serie, RP05-A Serie and RP08-A Serie, L1 = 497 μH DCR = 55.1m C1, C2 = 47μF Ø 0.3mm Aluminum Electrolytic Capacitor Ripple: 180mA at 105°C, 120Hz 100V A DC Power Source A +V DC/DC Converter under Test V V (VDC or VRMS) Adjustable load -V Figure 1-3: General DC/DC converter test set-up Note: If the converter is under test with remote sense pins, connect these pins www.recom-international.com March-2006 to their respective output pins. All tests are made in "Local sensing" mode. 333 Powerline – Definitions and Testing Input Voltage Range PI Filter The minimum and maximum input voltage limits within which a converter An input filter, consisting of two capacitors, is connected in paralell with a series inductor to reduce input reflected ripple current. will operate to specifications. L Input C1 C2 Output Figure 2: Pš Filter Output Voltage Accuracy Voltage Balance Line Regulations 334 With nominal input voltage and rated output load from the test set-up, the DC output voltage is measured with an accurate, calibrated DC voltmeter. Output voltage accuracy is the difference between the measured output voltage and specified nominal value as a percentage. Output accuracy (as a%) is then derived by the formula: Vnom ist the nominal, output specified in the converter data sheet. For a multiple output power converter, the percentage difference in the volta- ge level of two outputs with opposite polarrities and equal nominal values. Make and record the following measurements with rated output load at +25°C: ● Output voltage at nominal line (input) voltage. Vout N ● Output voltage at high line (input) voltage. Vout H ● Output voltage at low line (input) voltage. Vout L The line regulation is Vout M (the maximum of the two deviations of output) for the value at nominal input in percentage. March-2006 Vout – Vnom Vnom N Vout M – Vout N Vout N X100 X100 www.recom-international.com Powerline – Definitions and Testing Load Regulation Efficiency Switching Frequency Output Ripple and Noise Make and record the following measurements with rated output load at +25°C: ● Output voltage with rated load connected to the output. (Vout FL) ● Output voltage with no load or the minimum specified load for the DC-DC converter. (Vout ML) Load regulation is the difference between the two measured output voltages as a percentage of output voltage at rated load. The ratio of output load power consumption to input power consumption expressed as a percentage. Normally measured at full rated output power and nominal line conditions. Vout ML – Vout FL Vout FL X100 The rate at which the DC voltage is switched in a DC-DC converter or switching power supply. Because of the high frequency content of the ripple, special measurement techniques must be employed so that correct measurements are obtained. A 20MHz bandwidth oscilloscope is used, so that all significant harmonics of the ripple spike are included. This noise pickup is eliminated as shown in Figure 3, by using a scope probe with an external connection ground or ring and pressing this directly against the output common terminal of the power converter, while the tip contacts the voltage output terminal. This provides the shortest possible connection across the output terminals. Output + - Ground Ring to Scope Figure 3: www.recom-international.com March-2006 335 Powerline – Definitions and Testing Output Ripple and Noise (continued) Figure 4 shows a complex ripple voltage waveform that may be present on the output of a switching power supply. There are three components in the waveform, first is a 120Hz component that originates at the input rectifier and filter, then there is the component at the switching frequency of the power supply, and finally there are small high frequency spikes imposed on the high frequency ripple. Peak-Peak Amplitude Time Figure 4: Amplitude The time required for the power supply output voltage to return to within a specified percentage of rated value, following a step change in load current. Transient Recovery Time Transient Recovery Time Overshoot Output Voltage 5V + U 5V Undershoot 5V - L V out U: upper limit L: lower limit I out Load Time Figure: 5 Transient Recovery Time Current Limiting Fold Back Current Limiting output current is limited to prevent damage of the converter at overload situations. A method of protecting a power supply from damage in an overload condition, reducing the output current as the load approaches short circuit. at short circuited outputs the output voltage is regulated down so the current on outputs cannot be excessive. V out Rated Io I out Figure 6: Fold Back Current LimitingTime 336 March-2006 www.recom-international.com Powerline – Definitions and Testing Isolation Break-Down Voltage The electrical separation between the input and output of a converter, (consisting of resistive and capacitive isola- The maximum DC voltage, which may be applied between the input and output terminal of a power supply without causing damage. Typical break-down voltage for DC-DC converters is 500VDC minimum. tion) normally determined by transformer characteristics and circuit spacing. R Resistive and Capacitive Isolation C Input Rectifier and Regulator Output Breakdown Voltage Figure 7: Temperature Coefficient Ambient Temperature Operating Temperature Range Storage Temperature Range www.recom-international.com With the power converter in a temperature test chamber with rated output load, make the following measurements: ● Output voltage at +25°C ambient temperature. ● Set the chamber for maximum operating ambient temperature and allow the power converter to stabilize for 15 to 30 minutes. Measure the output voltage. ● Set the chamber to minimum operating ambient temperature and allow the power converter to stabilize for 15 to 30 minutes. ● Divide each percentage voltage deviation from the +25°C ambient value by the corresponding temperature change from +25°C ambient. The temperature coefficient is the higher one of the two values calculated above, expressed as percent per change centigrade. The temperature of the still-air immediately surrouding an operating power supply. The range of ambient or case temperature within a power supply at which it operates safely and meets its specifications. The range of ambient temperatures within a power supply at non-ope- rating condition, with no degradation in its subsequent operation. March-2006 337 Powerline – Definitions and Testing Some converters from our Powerline offer the feature of trimming the output voltage in a certain range around the nominal value by using external trim resistors. Because different series use different circuits for trimming no general equation can be given for calculating the Output Voltage Trimming: trim-resistors. Following trim-tables give values for chosing these trimresistors. If voltages between the given trim-points are required a linear approximation of the next points is possible or using trimmable resitors may be considered. RP20-, RP30- XX1.8S Trim up Vout = RU = 1 1,818 11,88 2 1,836 5,26 3 1,854 3,09 4 1,872 2,00 5 1,89 1,35 6 1,908 0,92 7 1,926 0,61 8 1,944 0,38 9 1,962 0,20 10 1,98 0,06 % Volts KOhms Trim down Vout = RD = 1 1,782 14,38 2 1,764 6,50 3 1,746 3,84 4 1,728 2,51 5 1,71 1,71 6 1,692 1,17 7 1,674 0,79 8 1,656 0,50 9 1,638 0,27 10 1,62 0,10 % Volts KOhms RP20-, RP30- XX2.5S Trim up Vout = RU = 1 2,525 36,65 2 2,55 16,57 3 2,575 9,83 4 2,6 6,45 5 2,625 4,42 6 2,65 3,06 7 2,675 2,09 8 2,7 1,37 9 2,725 0,80 10 2,75 0,35 % Volts KOhms Trim down Vout = RD = 1 2,475 50,20 2 2,45 22,62 3 2,425 13,49 4 2,4 8,94 5 2,375 6,21 6 2,35 4,39 7 2,325 3,09 8 2,3 2,12 9 2,275 1,36 10 2,25 0,76 % Volts KOhms RP15-, RP20-, RP30-, RP40- xx3.3S RP40-, xx3.305T (Trim for +3.3V) Trim up Vout = RU = 1 3,333 57,96 2 3,366 26,17 3 3,399 15,58 4 3,432 10,28 5 3,465 7,11 6 3,498 4,99 7 3,531 3,48 8 3,564 2,34 9 3,597 1,46 10 3,63 0,75 % Volts KOhms Trim down Vout = RD = 1 3,267 69,43 2 3,234 31,23 3 3,201 18,49 4 3,168 12,12 5 3,135 8,29 6 3,102 5,74 7 3,069 3,92 8 3,036 2,56 9 3,003 1,50 10 2,97 0,65 % Volts KOhms RP15-, RP20-, RP30-, RP40(Trim for +5V) Trim up Vout = RU = 1 5,05 43,22 2 5,1 18,13 3 5,15 10,60 4 5,2 6,97 5 5,25 4,83 6 5,3 3,42 7 5,35 2,43 8 5,4 1,68 9 5,45 1,11 10 5,5 0,65 % Volts KOhms Trim down Vout = RD = 1 4,95 39,42 2 4,9 19,00 3 4,85 11,58 4 4,8 7,74 5 4,75 5,40 6 4,7 3,82 7 4,65 2,68 8 4,6 1,82 9 4,55 1,15 10 4,5 0,61 % Volts KOhms 338 March-2006 www.recom-international.com Powerline – Definitions and Testing RP15-, RP20- xx05D Trim up Vout = RU = 1 10,1 90,50 2 10,2 40,65 3 10,3 24,06 4 10,4 15,76 5 10,5 10,79 6 10,6 7,47 7 10,7 5,10 8 10,8 3,33 9 10,9 1,95 10 11 0,84 % Volts KOhms Trim down Vout = RD = 1 9,9 109,06 2 9,8 48,94 3 9,7 28,87 4 9,6 18,83 5 9,5 12,81 6 9,4 8,79 7 9,3 5,92 8 9,2 3,77 9 9,1 2,10 10 9 0,76 % Volts KOhms RP15-, RP20-, RP30-, RP40Trim up Vout = RU = 1 2 12,12 12,24 1019,45 257,41 3 12,36 134,39 4 12,48 84,06 5 12,6 56,68 6 12,72 39,47 7 12,84 27,65 8 12,96 19,03 9 13,08 12,47 10 13,2 7,30 % Volts KOhms Trim down Vout = RD = 1 11,88 270,20 2 11,76 149,63 3 11,64 95,76 4 11,52 65,24 5 11,4 45,59 6 11,28 31,88 7 11,16 21,77 8 11,04 14,01 9 10,92 7,86 10 10,8 2,87 % Volts KOhms RP15-, RP20, RP30Trim up Vout = RU = 1 24,24 210,51 2 24,48 96,13 3 24,72 57,18 4 24,96 37,54 5 25,2 25,71 6 25,44 17,80 7 25,68 12,14 8 25,92 7,89 9 26,16 4,58 10 26,4 1,93 % Volts KOhms Trim down Vout = RD = 1 23,76 283,54 2 23,52 125,47 3 23,28 73,95 4 23,04 48,40 5 22,8 33,14 6 22,56 22,99 7 22,32 15,76 8 22,08 10,34 9 21,84 6,13 10 21,6 2,76 % Volts KOhms RP15-, RP20-, RP30-, RP40Trim up Vout = RU = 1 15,15 455,67 2 15,3 192,89 3 15,45 111,48 4 15,6 71,85 5 15,75 48,40 6 15,9 32,90 7 16,05 21,90 8 16,2 13,68 9 16,35 7,31 10 16,5 2,23 % Volts K_ Trim down Vout = RD = 1 14,85 449,01 2 14,7 210,22 3 14,55 125,38 4 14,4 81,89 5 14,25 55,46 6 14,1 37,68 7 13,95 24,92 8 13,8 15,30 9 13,65 7,80 10 13,5 1,78 % Volts K_ RP15-, RP20-, RP30Trim up Vout = RU = 1 30,3 306,24 2 30,6 129,65 3 30,9 75,39 4 31,2 49,05 5 31,5 33,49 6 31,8 23,21 7 32,1 15,92 8 32,4 10,48 9 32,7 6,26 10 33 2,90 % Volts KOhms Trim down Vout = RD = 1 29,7 300,42 2 29,4 142,30 3 29,1 85,77 4 28,8 56,73 5 28,5 39,05 6 28,2 27,16 7 27,9 18,60 8 27,6 12,16 9 27,3 7,13 10 27 3,10 % Volts KOhms www.recom-international.com March-2006 339 Powerline Heat-Sinks 7G-0020A (9.5°C/W) A : A ( 5 : 1mm) 3.2 ±0.1 49.80 ±0.2 1.30 R 0.65 24.20±0.2 12.00 ±0.2 A :A R2 1.30 1.40 1.2 ±0.1 1.30 1.40 2.00 12.00 ±0.2 5.60 ±0.1 1.70 ±0.1 7G-0026A (7.8°C/W) 3.2 ±0.1 49.80 ±0.2 A : A ( 5 : 1mm) 1.30 49.80 ±0.2 12.00 ±0.2 1.30 1.40 A :A 1.30 1.2 ±0.1 12.00 ±0.2 1.40 1.30 R 0.65 5.60 ±0.1 1.70 ±0.1 340 March-2006 www.recom-international.com Powerline Heat-Sinks 7G-0011A (8.24°C/W) A : A ( 5 : 1mm) 50.00 ±0.2 R 0.65 37.40±0.2 15.00 ±0.2 1.30 A :A 1.40 1.30 3.00 ±0.1 1.00 2.00 27.00 ±0.2 5.60 ±0.1 1.70 ±0.1 7G-0022 57.91 ±0.25 8.41 60.96±0.25 1.42 R 0.58 50.80±0.25 R 1.07 3.56 4 -Æ 3.50 6.10 ±0.25 48.26 ±0.25 www.recom-international.com March-2006 2.29 ±0.25 341 Tubes 2. 1. 10.0 ± 0.5 9.0 ± 0.5 0.5 ± 0.2 12.0 ± 0.5 15.5 ± 0.5 13.5 ± 0.5 12.5 ± 0.5 17.8 ± 0.5 0.50 ± 0.2 4.9 ± 0.5 7.9 ± 0.5 TUBE LENGTH = 520mm ± 1.0 TUBE LENGTH = 520mm ± 2.0 3. 4. 0.5 ± 0.2 0.55 ± 0.2 14.5 ± 0.5 7.3 ± 0.4 10.5 ± 0.5 13.5 ± 0.4 15.5 ± 0.5 8.3 ± 0.4 4.3 ± 0.4 3.3 ± 0.5 17.0 ± 0.4 TUBE LENGTH = 520mm ± 1.0 TUBE LENGTH = 530mm ± 2.0 6. 5. 0.6 ± 0.15 12.0 ± 0.4 11.0 ± 0.4 9.4 ± 0.4 0.55 ± 0.2 16.15 ± 0.35 12.35 ± 0.35 12.6 ± 0.4 9.12 ± 0.4 19.2 ± 0.35 11.6 ± 0.35 5.3 ± 0.4 17.0 ± 0.4 7.1 ± 0.35 21.0 ± 0.35 TUBE LENGTH = 530mm ± 2.0 TUBE LENGTH = 520mm ± 2.0 342 March-2006 www.recom-international.com Tubes 8. 7. 0.55 ± 0.2 22.7 ± 0.35 0.5 ± 0.2 11.3 ± 0.35 24.0 ± 0.35 12.3± 0.35 18.3 ± 0.35 21.3 ± 0.35 7.85 ± 0.35 9.0 ± 0.35 TUBE LENGTH = 520mm ± 2.0 TUBE LENGTH = 520mm ± 2.0 9. 10. 0.8 ± 0.2 22.7 ± 0.35 0.55 ± 0.2 13.8 ± 0.35 18.3 ± 0.35 22.0 ± 0.5 15.45 ± 0.5 3.5 ± 0.5 13.5 ± 0.5 31.50 ± 0.5 8.85 ± 0.35 TUBE LENGTH = 538mm ± 2.0 TUBE LENGTH = 252mm ± 2.0 www.recom-international.com March-2006 343 Tubes 11. 54.0 ± 0.5 50.0 ± 0.5 22.0 ± 0.5 20.0 ± 0.5 7.0 ± 0.5 1.2 ± 0.2 6.0 ± 0.5 10.0 ± 0.5 15.0 ± 0.5 TUBE LENGTH = 292mm ± 2.0 12. 54.0 ± 0.5 50.0 ± 0.5 22.0 ± 0.5 20.0 ± 0.5 7.0 ± 0.5 1.2 ± 0.2 6.0 ± 0.5 10.0 ± 0.5 15.0 ± 0.5 TUBE LENGTH = 254mm ± 2.0 13. 80.0 ± 0.5 1.2 ± 0.2 0.5 ± 0.5 22.0 ± 0.5 9.0 ± 0.5 21.0 ± 0.5 344 TUBE LENGTH = 256mm ± 5.0 March-2006 www.recom-international.com Tubes No. Types 1. RO, RM, RE, ROM, RB, RBM, RK, RH, RP, RU, RI, RD, REZ, RKZ, RUZ, RY, RxxTR, R-78xx RS, RSO, RL, RN, RF, RA, RC, RX RSS, RSD, RQS, RQD, RZ, R-78Axx SMD RTD, RTS, RSZ RV, RW, RxxPxx, RxxP2xx R5, R6, R7, REC1.5-, REC1.8-, REC3-, REC5-, REC7.5RAA RP08, RP12 RP08-SMD, REC2.2-SMD, REC3-SMD, REC5-SMD, REC7.5-SMD REC10, REC15, REC20, REC30, REC40 RP10, RP15, RP20, RP30, RP40 RP40-E 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. www.recom-international.com March-2006 345