FAQ

Table of Contents

Layout

• What type of thermal relief should I use?

  In general, to provide improved solderability, customers will want to add thermal reliefs to the output pins of the converter. The design of these thermal reliefs should be carefully considered to prevent heating due to resistive power losses. SynQor has written an application note on this subject entitled "Thermal Relief Study." In general the aspect ratio of the conductive paths of the thermal relief spokes should be wider than they are long, to reduce their resistance. A significant fraction of the resistance between the converter and the load is the first few centimeters of copper from the output pins and the power / ground plane. Reductions in output resistance can be made by placing a copper pad on every layer of the PCB around each of the output pins. Place 8 to 12 vias surrounding the output pins, tying all the additional copper pads to the power and ground planes. These suggestions will limit the resistance (and power dissipation) in the board and increase the reliability of the plated through holes.

• What can you tell me about sockets for PCB-mounted SynQor products?

  SynQor generally recommends that our board-mounted products be soldered into the system application board, as this makes the most reliable and highest performing electrical and thermal connection for deployed products.
  
  For system prototypes and temporary testing, sockets are a convenient way of connecting converters to test boards and fixtures, and SynQor does provide evaluation boards with socketed connections. 
  
  It is important to keep in mind that sockets are a poor thermal connection between a converter or similar product and the host printed circuit board (PCB), which can compromise the thermal performance of converters, particularly open-frame converters. This problem is further exacerbated by the fact that the socket connection has significant electrical resistance that causes additional heat to be dissipated. For accurate thermal evaluation, it is important to solder the pins to the host PCB, particularly when evaluating open-frame converters.
  
  If the shippable system design requires the use of sockets for assembly or maintenance, then we recommend that the socket be of a type that uses tin-plated contacts having sufficient contact normal force to make and maintain a gas-tight electrical connection. The system design should also limit movement of the pin-socket interface during thermal cycling or vibration conditions in the product service environment to prevent tin-fretting corrosion.

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Conducted EMI

• What is the best strategy to minimize EMI?

  There is no one perfect EMI strategy for all applications, but some basic thought before-hand can make the task much easier. The first step is to make sure that the location of components minimizes noise. For example, de-coupling capacitors should be located as close as possible to the converter, especially X-caps and Y-caps. Use ground planes to minimize radiated coupling, minimize the cross sectional area of sensitive nodes, minimize the cross sectional area of high current nodes that may radiate such as those from common mode capacitors. The location of the EMI components is critical; avoid placing the converter in close proximity to your filter to avoid noise coupling back into the filter. Keep in mind that you are not just filtering the power supply, but all the circuitry that the converter is powering as well. Most of today's communication cabinets employ as much local filtering as possible at the card level, and then another filter at the power entry module, where the power feeds will enter your cabinet. SynQor has an EMI application note that further details these principles and includes recommendations for 1 and 2 stage filters that are designed around SynQor's converters. Please contact SynQor directly for design assistance, or email support@synqor.com .

• What type of conducted line filter should I use?

  While a pre-designed EMI filter may be adequate for a particular converter, there is no guarantee that it will suppress other sources of conducted EMI that are present on your board, such as the noise from high-speed processors and other digital logic devices. Better value and performance will be obtained with a discrete filter design. The key to a smooth EMI compliance process is to design as much filtering as possible onto your circuit pack. This will allow the flexibility to tweak and modify components when the initial testing is performed. It is best to over-design up front than be caught off guard; components can easily be deleted once the initial testing is completed. Adding components to an existing PCB design is much more difficult and can yield unpredictable results. SynQor has suggested one and two stage filters that are simple and reliable to implement, and for much less cost than an off-the-shelf filter. These suggested filter circuits are in SynQor's EMI application note. In general most modern communications equipment uses a local EMI filter on each of the circuit cards, and a final shielded filter located in or near the power entry module.

• How do I choose Y-Caps?

  Y-caps are the EMI capacitors that are connected from the input power feeds to chassis ground. Sometimes they are connected from each converter's power output terminal to chassis ground as well. SynQor filter designs use 2700pF Y-Caps. The voltage rating depends on the insulation and isolation safety rating of the -48VDC supply. If you are unsure of these attributes, use capacitors rated to 2000V. If the -48V is a reinforced insulation scheme, then 100V rated capacitors will suffice.

• What does the input filter of your converter look like?

  All SynQor bricks use a C-L-C input filter. All SynQor bricks have an L-C filter. The value of these components can be found in SynQor's EMI application note, or in the appropriate product datasheets.

• What if I don't have a chassis ground?

  While it is preferable to have and to use a chassis ground, it is not mandatory. Under some circumstances a chassis ground will not be available for the input conducted EMI filter. If this is the case, you will want to use a different filter topology. Contact SynQor Support for this circuit.

• What type of filter should I use for multiple converters?

  For multiple converters, you can still use SynQor's recommended filter design, just be sure to size the individual components to handle the maximum current at the lowest input voltage.

• I currently have my input and output filtering arranged for a different manufacturer's converter. Will your module work with this filtering or must it be changed?

  In general, a filter that has been previously designed around a 200 to 500KHz fixed frequency converter will be adequate for an equivalent SynQor converter. SynQor's converters have lower common mode noise due to their lack of a baseplate. Baseplated units have higher common mode noise as the switching noise of the power semiconductor's couples through the parasitic capacitance of the baseplate.

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Radiated EMI

• Are there any special concerns with an open frame converter?

  SynQor open frame converters are no worse, and often better, than baseplated converters. In general, most baseplated units have a plastic cover, and in 3 Meter and 10 Meter far field measurements offer no advantage compared to the SynQor open frame design. SynQor's unique topology and reduced common mode noise have a significant advantage over other manufacturers' converters in regards to reducing radiated emissions.

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Near-field EMI

• How will an open frame converter perform versus a baseplated converter?

  With few exceptions, most customers have found the near-field characteristics of SynQor's open frame converters to be no worse, and often better than the typical baseplated converter. SynQor has several suggestions for reducing near-field radiation- the first of which is to place a ground shield beneath the converter. SynQor suggests placing a primary referenced ground shield beneath the converter's primary circuitry, and a secondary referenced ground shield beneath the converter's secondary side circuitry. The isolation barrier on all SynQor converters is easily found by looking for the 1.4mm clearance gap located on both the top and bottom of the PCB, or by locating the optoisolators, which also identify the barrier. (Note: All of SynQor's magnetic assemblies are considered primary referenced.) With regard to the near-field EMI above the typical baseplated converter, a baseplate is not a perfect "shield" as commonly thought. Unfortunately, the baseplate is tightly coupled to the converter's high frequency switching nodes (in particular, the drains of the primary-side MOSFETs). The shield is therefore "bouncing" and attempts to stop it from doing so by grounding it to the output are challenging. Typically, the circuit path to ground is hindered by the parasitic inductance of the PCB connection. As such, the baseplate is not well-grounded at high frequencies, and radiates significant noise. There are also still the sides of the module to contend with, as these are not generally shielded. If there is sensitive circuitry, it is best not to place it directly over a converter or close to the edges of the converter unless it has a ground shield directly over or under the conduction path, as this will reduce any coupling. It is also helpful to note that the amount of noise that can be coupled is proportional to the cross sectional area of the conduction path; the smaller the loop, the less noise that will couple.

• What about other Parasitic Baseplate Effects?

  If you could hold the baseplate quiet by grounding through a low inductance path, the result would be a great deal of common-mode current that would flow from the primary side switching nodes to the baseplate (through parasitic capacitors) and to the output ground. This then creates other problems that need to be addressed, mainly conducted common mode noise. Common mode noise tends to be a challenging problem to control. SynQor's converter design eliminates this problem as it has very little parasitic capacitance to the output ground. What noise it does have is effectively controlled with a common mode capacitor that we place on our converter. Compared to the industry standard Class B conducted noise filter, you will find that the SynQor converter needs half as many filter stages due to the reduced common mode noise. Also see SynQor's EMI application note.

• What about magnetic fields?

  Baseplated converters will offer improved protection from near B-field radiation. At most frequencies, a baseplated converter will be approximately 10dB/uM more quiet than the open frame design. If B-field noise is a critical design consideration, any SynQor converter can be ordered with an optional baseplate, which will offer the same reduction in B-field noise.
  
   

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Enable Circuits/Inrush Control

• Why do I need an inrush controller?

  All converters act as negative resistors, and all power distribution paths have some inductance. These two elements require that some electrolytic capacitance be placed across a converter's input terminals to compensate for the negative resistance, preventing a possible oscillation. If a circuit card containing a converter is hot swapped into a back plane, the charging of the electrolytic capacitor can cause a low voltage transient or glitch on the 48V supply, which could upset other circuits sharing the common 48V feed. To prevent this glitch on the input rail, an inrush control circuit should be placed in series with the 48V feed. An inrush control circuit limits the charging of the 48V rail. A good example of a controller for an inrush circuit is Linear Technology's LT1640 and LT1641, Summit Micro's SMH4804, or Supertex's HV300 series.

• How do I select an inrush controller?

  You can drive the enable of a DC-DC converter with the inrush controller's power good or enable signal provided there is no EMI filter between the controller's ground reference and the converter's ground reference. If there is an EMI filter located between the inrush controller and the enable circuit, the noise which the EMI filter rejects will appear on the enable lines, and could cause the modules to turn on and off randomly depending upon the size of the injected noise. The inrush controller and the converter must have the same reference. This can be avoided by leaving the modules permanently enabled, not using the Power Good signal, moving the common mode filter to come before the hot swap circuit, or adding some isolation between the Power Good output and the input to the modules (such as an optocoupler).

• Why is there a 200ms delay at turn on for your new family of converters?

  Most all of SynQor's converters have a 200ms startup delay at initial turn on, and after a fault condition such as OVP or Over Temperature Shutdown. After recovering from any fault condition, the converter will not turn on for 200ms. When the bus voltage is below the under voltage lockout, this is considered a fault condition. This behavior is detailed in our data sheets, and should be studied before implementing an inrush or sequencing strategy. The delay ensures that the start up behavior is always consistent and well controlled. If the input voltage were to glitch momentarily to zero volts, then return to the full bus voltage, the delay gives the control circuitry time to return to proper startup conditions. Since the control circuitry has no voltage when the input voltage is brought to zero, it is difficult to distinguish between power up after a glitch and initial power up. Therefore, the module treats all recoveries from undervoltage lockout identically. The delay on power up also guarantees that the input voltage is well within the operating range before powering up the output load. Note that after the delay time has passed, the module will turn on quickly when the ON/OFF pin is set to the enabled state.

• How do I sequence multiple converters?

  Sequencing requirements need to be considered in the preliminary stages of the power supply design. Usually these requirements are driven by ASICs or processors, which have separate Core and I/O voltages. Often these voltage rails must turn on in a specific order (sequence) or are required to have no more than some maximum voltage difference between these rails. If this maximum difference is violated, the chip can be damaged or even destroyed. In general, there are three (3) ways to sequence the turn on characteristics of multiple converters.
  
  The first method is to turn the converters on in a specific sequence with either a control chip such as Summit Micro's SMH4804, or with discrete circuitry. A simple solution is to have the output of one converter drive an optoisolator that enables the second converter, and so on. In general most sequencing requirements will want the lowest voltage to turn on first, and off last. It is important to use an optoisolator to enable the other converter as the enable is a primary referenced signal, while the output of a converter is a low voltage isolated SELV signal. 
  
  Another method often used is to tie diodes between the different voltage rails in a manner that while powering up the diodes will conduct, but when the converter outputs are fully on, the diodes are reversed biased. For example, a diode between the 5V rail and the 3.3V rail, with the cathode connected to the 5V rail, will force the 5V rail to follow the 3.3V rail while turning on, but once the 5V rail is at 5V, the diode will be reversed biased. This forces the difference in voltage between the two rails to be no more than one diode drop apart. Conversely, 3 diodes with a 0.7V drop in series from the 5V rail towards the 3.3V rail will ensure that the 3.3V rail is charged should it come up after the 5V rail.
  
  The last and most complex solution is to place FETs in series with each converter's output, and enabling the FETs once the converters are fully turned on. By carefully controlling the turn on of the FET gates, the voltage rails can be brought up in strict adherence to any sequencing specification. Such a solution can be built with discrete components or by using a specific controller such as Summit Micro's SMT4004. One note of caution when implementing these solutions: if the sense lines are connected on the output side of the MOSFETs, the converter will not be able to sense its output voltage at turn on until the MOSFETs are on. This will cause the converter to raise its output until it reaches over voltage protection. You must either connect the sense lines directly to the converters output and trim up to compensate for the FETs on resistance, or add additional FETs to connect the sense lines after the main FETs are enabled.

• Any suggestions on using Summit Micro's hot swap controllers?

  It is important when defining a system's sequencing requirement that SynQor's 200ms initialization period be considered. As an example, if you are using a programmable delay to enable multiple converters in a specific sequence, you must make sure the delay is approximately 200ms. When using the Summit Micro devices, make sure to use their 160ms delay setting, and use the second delay tap to enable the first converter. As an example for a three converter solution, you use the SMH4804 where PG#2 would enable the first converter, PG#3 for the second and so on.

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Component Selection

• How do I choose an input electrolytic capacitor (input E-cap)?

  SynQor has written an application note on how to select an input electrolytic capacitor and why this capacitor is needed. In general, you will find that each converter will require a capacitor that is approximately 47uF to 100uF with a minimum voltage rating of 100VDC, and an ESR in the range of 0.5 to 1 Ohm.

• How do I choose a CM Inductor?

  Select an inductor that is rated for the desired input current. Leakage inductance in the common mode inductor will provide reduction of differential mode input current ripple. SynQor's recommended conducted EMI filters specify a primary inductance of 360uH (0.36mH) and a leakage inductance of 3.5uH. A popular choice for these inductors are Pulse Engineering's Self-Leaded SMT Common Mode Chokes, such as P/N P0353.
  
   

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General Application

• Can I create negative voltages with SynQor converters?

  All of SynQor's converters are fully isolated which allows them to generate negative output voltages. Simply connect the Vout+ terminal to the system output ground, and a negative voltage will be generated on the Vout- terminal.

• I have a negative 48V bus. Can I use SynQor converters?

  Because the converter is isolated, the Vin+ terminal can be tied to the input ground of a -48V system. The Vin- terminal should then be connected to the -48V rail. Keep in mind that the primary side signal pins are referenced to the Vin- terminal in all cases.

• How do I read the codes on the product label?

  Each product has a label which reveals the product part number, revision letter code and serial number for that module. This information can be found on the label in the specific locations detailed in this photo.

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Safety Issues

• Where do I find the safety certifications?

  All of SynQor's safety certificates can be found in our Quality & Compliance page.

• Where are the conditions of acceptability?

  All safety certifications, including the conditions of acceptability can be downloaded in PDF form from our Quality & Compliance page

• How do I choose a fuse?

  The Conditions Of Acceptability (COA) section of the safety file details the type of fuse required for each converter. SynQor's product datasheets specify the recommended fast blow external fuse to be used.

• What is creepage and clearance?

  Safety certification requires that the primary 48V circuitry (Primary) and the low voltage output (Secondary) circuitry be separated from each other. SynQor's converters use a Basic level of insulation, with 2000V of isolation. As such, all SynQor converters have a minimum distance of 1.4mm between primary and secondary circuitry.

• What is "insulation rating" and "isolation rating"?

  Insulation refers to the design parameters used to isolate the 48V primary side signals from the low voltage secondary side signals. This covers the specifications for creepage and clearance between traces and components, as well as the type of insulation used in the transformers. The transformers transfer energy between the primary (Input) and secondary (Output) stages of the converter. All SynQor converters use Basic Insulation which meets the most stringent requirements for 48V based DC systems. Isolation refers to the breakdown rating of the isolation stage, either in the transformer or between isolated components such as optoisolators. SynQor tests and guarantees all converters capable of withstanding a 2000V breakdown.

• Are any dangerous voltages exposed on the surface of the converter?

  In the United States, UL defines an "Unsafe" voltage as 60V, this is called the SELV (Safety Extra Low Voltage) limit. At input voltages of 0 to 60V, the highest voltage will be across the midbuss capacitors, this is an AC signal, operating at the switching frequency, with a maximum peak to peak amplitude of about 58V. Above a DC input of 60V the maximum voltage is the input voltage across the primary switching FETS, which is approximately Vin plus a few volts.

• Are safety covers recommended for the converters or is a "danger high voltage" or similar label required on the surface of the converters?

  If the input voltage remains below 60VDC, then all voltages are SELV, and no special care is needed. If the input voltage rises above 60VDC, then there will be non SELV voltages on the top side of the converter. The exact need for warning labels or covers, depends on the safety agency approvals needed. For UL, if non-technicians are to be allowed to change system configurations, i.e add more memory cards, the machine should be powered off to prevent access to the non-SELV voltages.

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Performance Issues

• How do I reduce output noise and ripple?

  In general, SynQor's converters have significantly lower output noise and ripple when compared to traditional isolated converters. This is due to SynQor's patented power topology, and excellent design practices. All of SynQor's ripple and noise measurements defined in our data sheets are made with 10uF of Tantalum and 1uF of Ceramic capacitance across the converter's output. This is not required, but is used so that our converter's measurements conform to standard industry practices. Further reduction of output ripple and noise is accomplished through the addition of both Tantalum and Ceramic capacitance. Ceramic capacitance provides attenuation of output ripple, while the inherent ESR of tantalum capacitors provides damping. It is possible to provide additional filtering through the use of LC filters, but care should be taken when placing these filters within the sense lines, as this can effect the converter's stability. Consult the SynQor for further support on this topic.

• What is SynQor's crossover frequency and phase margin?

  All SynQor converters are designed to have adequate stability margin (at least 20dB of gain margin and 50 Degrees phase margin) over variations of input and output conditions, including input voltage range, output voltage range, output current range, and load impedance. Performance is verified by using Bode plots and examining gain and phase margin.

• How much output capacitance can I drive with your converter?

  All SynQor data sheets define the maximum allowable startup capacitance with a fully loaded output. If the output load current at startup is reduced, then a larger amount of capacitance than defined in the data sheet is possible. An interesting benefit of SynQor's topology is that a large amount of output capacitance has little effect on the converter's stability! All SynQor data sheets define the maximum allowable startup capacitance with a fully loaded output. If the output load current at startup is reduced, then a larger amount of capacitance than defined in the data sheet is possible. An interesting benefit of SynQor's topology is that a large amount of output capacitance has little effect on the converter's stability!

• How do you trim a converter?

  All SynQor converters have a trim pin, which allows trimming the nominal output voltage higher and lower. In general, to trim a converter low, a resistor is connected from the trim pin to the -Sense pin. To trim up, connect a resistor from the trim pin to the +Sense pin. The value for the resistor is calculated with the formulas provided in the converter's data sheets. You can also use our Trim Resistor Calculator. The trim formulas match accepted industry standards for half, quarter and eighth bricks.

• Can I trim a converter actively?

  Trimming or margining converters with an external active circuit is possible and SynQor has several sample circuits available depending on your requirements. Please contact your local SynQor representative, or email support@synqor.com for details.

• How does Over Voltage Protection (OVP) work; does it track the trim?

  SynQor's OVP  is fixed and does not track the output voltage when using the trim function. Customers should use care when trimming the converter to ensure the OVP is not activated during transient conditions, or when series diodes or FETs are used on the converter's output. On SynQor's first generation half brick converters containing HNA in the part number, the OVP protection is measured across the sense lines. Care should be taken to ensure that the output pins do not become disconnected from the sense lines. If the output pins become disconnected, and there is some capacitance across the sense lines, damage could occur to the converter's output stage. This could happen if the output pins are not properly soldered, or if MOSFET's are placed in series with the output. On SynQor's new Kilo, Mega, Giga, and Tera half bricks, as well as the QNA/QGA quarter bricks, the OVP sense point is located across the output pins which avoids this condition.

• Can I put converters in series?

  SynQor's converters can be placed in series, however should one converter turn off, a protection mechanism should be implemented to ensure that the other converter is disabled.

• What are sense lines? Do I need to connect them?

  Sense lines are used to compensate for resistive drops along the power distribution path. The sense lines should be connected at the point of load, or at a minimum connected to the output pins at the converter. If the sense lines are not connected, the regulation and set point specifications contained in the data sheet will not be met. No damage will occur if the sense lines are left unconnected. Sense lines are used to compensate for resistive drops along the power distribution path. The sense lines should be connected at the point of load, or at a minimum, connected to the output pins at the converter. If the sense lines are not connected, the regulation and set point specifications contained in the data sheet will not be met. No damage will occur if the sense lines are left unconnected.

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Full Feature Converters

• What is the OR-FET signal used for?

  The primary function of the full feature converters OR-FET signal is to supply a voltage source higher than the converter's output voltage which can provide current to turn on the gate of an N-Channel "ORing" MOSFET. The signal has no implied "intelligence". ORing FETs are used to isolate the output of a converter in the event that the converter's output experiences a short fault. This is preferable to "ORing" diodes that have significant power losses at high output currents. This signal is very low power, and is not capable of supplying more than 50mW of power. Any control circuitry drawing beyond 50mW of power should be driven off the converter's main output.
  
  The OR-FET pin can also be used as a Power Good signal: when the converter is operating properly the OR-FET voltage will be much higher than the converters output, providing a positive indicator of a converter's health even in a system where converters are directly connected in parallel. More details are available in our Full Feature Application Note.

• Can I use the Cshare pin as an output current monitor?

  The current share pin will give a voltage that is proportional to the output current, but only for a single module. If two converters are sharing a common load by using the current share connection, the voltage will represent the average current of the two converters. This signal is referenced to the primary side of the converter, so to interface with a controller the signal will have to be brought across the isolation barrier through an optoisolator (unless of course the controller is on the primary side, then a direct interface is possible.) Any load impedance added to the CSHARE signal should be above 100kOhms. Loading on this signal will affect the current sharing performance. More details are available in our Full Feature Application Note.

• How do I synchronize modules?

  SynQor Full Feature converters have a pin to provide synchronization with an external clock. The signal should be a 5V TTL level rectangular wave with a duty cycle between 25% and 75%. The CSYNC signal is referenced to the Vin- pin of the converter. When synchronizing different output voltage converters, you should select the highest frequency specified for any converter as the common frequency. Converters will not synchronize properly at frequencies below that specified in their datasheet. More details are available in our Full Feature Application Note.

• Should I synchronize modules?

  While synchronizing converters may make EMI characterization and filter design simpler, it can also cause converter harmonics to stack on top of each other, creating a more difficult EMI problem to solve. Generally, EMI specifications require measurements be quasi-peak, and it is more beneficial to leave the converters not synchronized. Certain systems require synchronization so that the output ripple is at a single frequency. Applications such as wireless communications equipment, systems with extremely fast clocks, or sensitive optical circuits may find that the benefits of synchronizing the converters output ripple outweigh the EMI benefits of having un-synchronized converters. More details are available in our Full Feature Application Note.

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Parallel Converters

• Can I parallel converters for more power?

   SynQor's family of Kilo, Mega, Giga, Tera and some Peta half bricks can be ordered with the full feature set which allows converters to be paralleled for more power, as well as to take advantage of additional control features.

• How do I connect SynQor's full feature converters in parallel?

  To connect full feature modules in parallel, you simply connect the current share pins and the start sync pins of the sharing converters together. In addition, make sure that the Vin+ and the Vin- pins are tied together, as the Vin- pins provide a common reference for the current share signal. Outputs should be connected together at a common point with the sense lines. SynQor has an application schematic detailing these connections. Please refer to the Full Feature Application Note for this schematic.

• How do I trim converters in parallel?

  A trim circuit should be supplied for each individual converter, therefore each converter should have a trim resistor. Make sure that all trim resistors are the same value.

• Where do I connect the sense lines for parallel converters?

  The sense lines of converters in parallel should be connected together at the exact same point for balanced transient responses and the best output voltage regulation.

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Handling

• How should I store and handle open frame converters?
  Open frame converters can be damaged from poor handling, excessive mechanical shock, or from a static electric discharge. The units should be:

  • Carefully handled and not subjected to mechanical stresses
  • Treated as an ESD sensitive component
  • Stored in a static protective container which physically protects the converter
  • The converters should not be stored in plastic bags, or stacked on top of one another in any way
• Are SynQor's converters water wash compatible?

  SynQor converters are compatible with a water wash process, provided that the converters are dry before powering them on. SynQor uses a no clean flux, and as such, the flux residue on our converter may react with other chemicals from the manufacturing or wash process. Generally, this manifests itself as a white powder residue on the converter. This is usually benign, but any such residue should be analyzed to confirm its reactivity. Customers using an active detergent in the water wash process may need to apply a piece of kapton tape over the SynQor label to prevent the label from fading.

• What type of flux do you use?

  SynQor uses flux systems that meet or exceed Telcordia GR-78 CORE SIR and Electromigration requirements.

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Reliability

• What is SynQor's MTBF?

  SynQor's standard reliability measure is Mean Time Between Failure (MTBF) calculated in hours of time. SynQor uses the Military Standard MIL217-F to calculate MTBF based on ambient temperature and load. SynQor's standard calculations are for 48V nominal input, 300LFM, and 80% load at 25C, 40C, and 55C. SynQor can also calculate MTBF using the Telcordia (Formerly Bellcore) Parts Count Method TR332. In addition, SynQor also measures the actual field reliability in MTBF or FIT by product family. To request any of this reliability information please contact your local SynQor sales representative, or email support@synqor.com. Some MTBF is also presented in the product datasheets.

• What are common failure modes?

  The most common failure mode for units returned by our customers is NFF, or "No Fault Found". To prevent the return of NFFs through SynQor's RMA process, SynQor has evaluation boards available so customers can test the operation of the converter before returning them. The evaluation boards allow for simple testing and debugging.

• What is SynQor's qualification process?

  SynQor has a three-step release process: POD, POM, and Qualification. POD, or Proof Of Design, is the process during which the converter's performance is evaluated and characterized over all rated operating conditions and beyond, in accordance with HALT principles. POD measures component stresses to ensure that design guidelines are met and that no components are over-stressed in both normal and abnormal conditions. POD ensures that long-term reliability and life targets are achieved. Other tests performed at the POD stage include phase and stability margins, thermal margin, capacitive load tests, destructive thermal cycling, DFM, and waveform analysis.
  
  POM, or Proof Of Manufacturing, ensures that SynQor has designed a part that can be manufactured, is reliable, and has proper margins to be run in a high volume factory. POM ensures that target yields are met, that our ATE systems are optimized, and any new manufacturing equipment or processes constructed are optimized. Statistical Process Control analysis at this stage is mandatory, and CpKs are scrutinized to ensure that SynQor has a repeatable and consistent process.
  
  Qualification is the final stage of product release. The purpose of the qualification process is to ensure that SynQor has designed and built a product that exceeds our customers' expectations. Testing at this stage includes aggressive thermal shock cycles, extended high temperature life and humidity tests, vibration and mechanical shock tests in accordance with military standards, terminal solderability, full mechanical and dimensional compliance, as well as a thorough examination of the solder and manufacturing quality.

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Troubleshooting

• How do I measure output ripple?

  Measuring output ripple and noise is extremely dependent on the test setup. A good starting point for this is to use SynQor's Evaluation Board which can be purchased from SynQor. Our evaluation board provides a BNC connector for measuring output ripple. The industry standard noise measurement requires 20MHz bandwidth limit which is detailed in our data sheets. There is also an application note titled, "Output Voltage Ripple Measurements," which provides proper methodology and test set-ups to achieve accurate output ripple readings whether you are using our evaluation board or an application board.
  
  This paper also describes how using a traditional probe with a ground clip will allow radiated noise to couple into the probe creating a false measurement, which manifests as large high frequency spikes. These are largely measurement artifacts which are most often caused by two effects: magnetic coupling through a large scope ground loop, and/or transmission line effects on unterminated cables. SynQor's application note on this topic will show you how to reduce the measurement circuit loop to a minimum, almost eliminating magnetic noise pickup and allowing a more accurate measurement of the converter's output voltage ripple.

• How do I measure Output Load Current?

  You can easily measure the output load current of any SynQor open frame converter. The application note "Output Load Current Calculations" outlines the equations and other information needed to make this measurement.

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Thermal

• How do I choose a heatsink?
  Choosing a heatsink requires knowing several things:

  • The output power required.
  • The power dissipated by the converter at the load current and input voltage.
  • The worst case ambient temperature.
  • The amount of airflow available.
  • The maximum baseplate temperature of the converter, which is 100C for all SynQor baseplated converters.

  Example:
  What size heatsink is required for 3.3V quarterbrick at 20A, 48V input, 70C ambient, and 200LFM of airflow?

  Using SynQor's PQ48033QGA25 data sheet figure 3, at 48V input, and with a 20A load, the power dissipated by the SynQor's 3.3V quarterbrick converter is about 8.5 Watts. The allowable temperature rise is simply the maximum baseplate temperature minus the worst case ambient temperature. So in this example, 100C - 70C = 30C allowable rise. The thermal impedance of the heatsink required is simply the allowable temperature rise, divided by the power dissipated. In our example this is 30C/8.5Watts, giving a maximum thermal impedance requirement for our heatsink of 3.53C/W at 200LFM. Using any standard heatsink catalog you can now select a heatsink. A good choice would be Intricast's (www.intricast.com) HS1361XM01 heatsink, which is 0.5" tall and has a thermal impedance of 2.60 C/W at 200LFM.

• How do I measure the temperature on your converters? Where do I place thermocouples?

  SynQor's derating curves are created based on a derating of 125C for switching MOSFETs. Using SynQor's data sheet, locate the thermal image, which shows the hottest components on the power supply. Generally you will want to measure the input MOSFETs, the isolation stage MOSFETs, and the output synchronous rectifiers. Care should be taken not to block too much of a device's surface area, as this could significantly reduce its ability to remove heat via convection.

• How does SynQor's thermal protection work, and where is the sensor?

  On SynQor half bricks, a thermistor located on the topside of the PCB drives a comparator circuit. On the quarter brick converters there is an integrated temperature sensor that will trip the converter off if an over-temperature condition exists. Both methods work by sensing the PCB temperature. Email support@synqor.com for location details.

• Do you have flotherm models?

  SynQor has basic thermal models that can be used for customers to develop flotherm models, but due to the use of multiple power handling devices to spread the heat generation across the board, it is very difficult to provide a detailed thermal model of the open frame converter.

• What is the optimal orientation of the converter?

  In general, half bricks are less sensitive to orientation than quarter bricks. For half brick converters 2.5V and below, it is best to have the air flowing towards the output terminals, for half bricks 3.3V and above, it is better to have the airflow towards the input side of the converter. On quarter bricks and eighth bricks, it is always best to make the airflow perpendicular to the long side of the converter as this exposes the maximum surface area to a cooling airflow. Although the differences are minor, it is best practice to review the derating curves and thermal images found in the data sheets to determine optimal orientation.

• What is the difference in air speed measurements of CFM vs. LFM?

  Designers often need air speed measurements to calculate thermal derating and power dissipation for their DC-DC converters and for their overall systems. There are two basic units of measure: CFM (cubic feet/minute) is a measurement of volume, LFM (linear feet/minute) is a measurement of velocity. Fan manufacturers use CFM because they rate their fans according to the quantity of air they can move. Velocity (speed) is more meaningful to heat removal at the board level. This is what most DC-DC converter manufacturers will specify when calculating thermal derating curves and other performance specifications.
  
  To convert CFM measurements to LFM, use the following equation:
  LFM = CFM/AREA
  LFM = Linear feet per minute of airflow
  CFM = Cubic feet per minute of air volume
  AREA = the area of the opening in square feet.
  
  For example, let's assume you are blowing air through a 6" x 6" opening across the top of a DC-DC converter with a 100CFM, unobstructed fan. 
  LFM = 100/ 0.25 sq feet or about 400LFM calculated.
  
  The most accurate way to measure actual air speed is with an anemometer.
  Some manufacturers specify airflow in Linear Meters/Second. Use the table below to convert feet/minute into meters/second:
  100 f/m = 0.5 m/s
  200 f/m = 1.0 m/s
  300 f/m = 1.5 m/s
  400 f/m = 2.0 m/s
  500 f/m = 2.5 m/s

• How do I attach heatsinks?

  Use M3 screws with a length no longer than 0.125". Tighten the screws to a torque of 6.0 in-lb. Minimum screw length is 0.10" for adequate hold. For more details, please refer to the appropriate data sheet addendum for baseplated modules, located in the products section.

• What type of potting material do you use?

  In the baseplated versions of its modules, SynQor uses a proprietary potting material. Contact your local SynQor representative, or email support@synqor.com for details.

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