Mil-COTS 270V Full Feature Recommendations Mil-COTS 270V Half Brick Full Feature Application Note Mil-COTS T -H xx TER 0 27 ER C- ONV S OT C C MC C/D Vin D 70 2 Designed and Manufactured in the USA This application note explains how to implement the features of Full Featured Mil-COTS 270 and 270N Half Brick Converters. Features include active current sharing, clock synchronization, and start-up synchronization. These items are explained in detail and layout suggestions and wiring schemes are presented. Product # MCOTS 270V Full Feature Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 1 Mil-COTS 270V Full Feature Recommendations Technical Specification Key Considerations When Using Full Feature Mil-COTS 270V Half Brick Converters 1. The current share pin of the 270V Mil-COTS half brick products is referenced to the primary, and its voltage varies from 0.5V to 3.5V as the converter’s output current ranges from zero to full rated load. 2. To force two or more modules to current share the Ishare pins need to be connected together. Care should be taken to minimize the circuit impedance between the IN RTN pins of the different modules. Any voltage mismatch on the IN RTN pins will result in discrepancies in the current share signal measured by the individual converters. This will cause a current miss-match between the converters. 3. When using the current share feature SynQor recommends that the START SYNC pins of all the modules be connected together. Connecting the START SYNC pins together allows all of the modules to start together. This is an important feature for systems that have a total system load that exceeds the load requirement of a single converter. Without this connection, any set of converters attempting to asynchronously start (or re-start) with a load greater than the current limit of a single unit will “hiccup”. This “hiccup” mode will continue until one converter attempts to start at the same time as the minimum number of additional units necessary to sustain the load condition. For example, three 43A 8.0V units starting into an 80A load would require two units to simultaneously attempt a start. The Start Sync pin connection synchronizes these starting attempts and provides a more consistent and reliable start-up sequence. 4. Synchronizing the clock frequencies of the different converters isn’t required for parallel operation. All SynQor DC/DC converters have input and output filters that minimize any interactions from mismatches in switching frequencies. 5. If external clock synchronization is required, a clock signal with a frequency in the range of 600 to 650 kHz must be supplied to each converter. The signal on the CLOCK SYNC pin should not exceed 5V amplitude (0 – 5V signal) and should have a 40% to 60% duty cycle. SynQor recommends that the CLOCK SYNC signal be applied prior to power-up of the different converters. Changing the system frequency once the converters are running is not recommended. 6. To avoid input instability a local damping network is recommended at the input power pins of each converter. An instability condition can occur because DC/DC converters appear at their inputs as an incrementally negative resistance load. A detailed application note titled “Input System Instability” is available on the SynQor web site (www.synqor.com) that provides guidelines for selecting the proper input damping network. (http://www.synqor.com/documents/appnotes/appnt_System_Instability.pdf) 7. Simple paralleling as described above does not provide full system redundancy. Achieving full redundancy requires OR’ing devices which can be Schottky diodes or MOSFETS driven by a suitable circuit. The OR’ing device disconnects the output of the specific converter from the system voltage in the event of a shorted converter output stage. A single converter failure should not result in a system failure. Additionally, a small MOSFET should be added in series with the +SNS line of each converter to disconnect the +SNS line in case of a module failure. An internal switch disconnects the converter from the Ishare line when a failure occurs, preserving load share functionality. Clock sync and frequency sync functions are not affected by a converter failure and don’t need protective external switches. Product # MCOTS 270V Full Feature Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 2 Mil-COTS 270V Full Feature Recommendations Technical Specification Key Considerations When Using Full Feature Mil-COTS 270V Half Brick Converters 8. If an EMI filter is used, care should be taken to avoid increasing the circuit impedance between the IN RTN pins of any converters connected for current sharing. SynQor recommends that a single EMI filter be used for each power board. SynQor further recommends if multiple power boards are used that a supplemental current share mechanism be used to force the power boards to share the system load . Due to the increased IN RTN imped ance between the power boards, the current share circuitry provided with each Mil-COTS module will not work well when trying to implement load share between physically separate power boards. 9. Load share controllers from TI (UCC39002, UCC3907) could be used to implement load share between mulitiple power boards. These two load controller chips sense the output current (load current) and adjust the output voltage of the module to force load sharing. In order to reduce the power dissipation on the sense resistor, the output current from a single Mil-COTS converter can be sensed using the UCC39002 load share controller and its output voltage adjusted by driving the TRIM pin voltage. SynQor’s recommends adjusting the TRIM pin voltage instead of pulling from the +SNS leads as described in the applications notes of the UCC39002. Since all of the modules in a single power board are forced to current share using the primary side current share feature in the 270V Mil-COTS product, adjusting the current in one of the modules in the power board will force all of the other converters in the power board to share. When using a load share controller like the UCC39002, good results are obtained when the load share controller responds very slowly to any changes in current (suggest having a current share cross over frequency of less than 50 Hz). 10. When using multiple EMI filters as suggested here (one EMI filter per power board), the ON/OFF signal between power boards is no longer referenced to a common voltage. In this case opto couplers should be used to transfer and control the ON/OFF signals to the converters in each power board. The ON/OFF pins between the differ ent converters on a given power board can be connected together as long as independent control of each module is not needed. SynQor recommends a small filter capacitor of 0.01 μF be placed locally between each ON/OFF pin and the IN RTN pin of the respective converter. 11. Similarly the START SYNC and Ishare pins between power boards are no longer referenced to a common refer ence and therefore these signals should not be connected together between power boards. Trying to implement the START SYNC function between different power boards becomes complex because the START SYNC signal has three states, high, low, and high impedance. The simplest solution would be to sequence the load so that the load is not enabled unless the system bus is present. Implementing a time delay between when the output voltage is enabled and the time the loads are enabled (~ 100 ms) is a good approach. Product # MCOTS 270V Full Feature Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 3 Mil-COTS 270V Full Feature Recommendations Technical Specification Figure A: Wiring diagram for multiple Mil-COTS half brick converters. Product # MCOTS 270V Full Feature Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 4 Mil-COTS 270V Full Feature Recommendations Technical Specification Figure B: Suggested layout for input and output power planes. Product # MCOTS 270V Full Feature Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 5 Mil-COTS 270V Full Feature Recommendations Technical Specification Figure C: Suggested functional interconnect for multiple Mil-COTS half brick converters and multiple boards. Note: Details of the load-share chip have been ommited for clarity. See UCC39002 datasheet for details. Product # MCOTS 270V Full Feature Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 6 Product # MCOTS 270V Full Feature Figure D: Example schematic for a functional interconnect for multiple Mil-COTS converters and multiple boards. Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A A B C D 270Vin- 270Vin+ On/Off Signal+ On/Off Signal+ 03/21/14 + SENSE(-) Vout(-) Vin(-) 1 2 TRIM Ishare Start Sync SENSE(+) Vout(+) Vin(-) Ishare Start Sync Vout(+) Vout(-) SENSE(-) TRIM SENSE(+) SENSE(-) Vout(-) Vin(-) TRIM Ishare Start Sync Vout(+) SENSE(+) 0.01uF SENSE(-) Vout(-) Vin(-) TRIM SENSE(+) Vout(+) Ishare Start Sync Clock Sync ON/OFF Vin(+) MCOTS-C-270N-08-HT (Converter 80) 0.01uF Clock Sync ON/OFF Vin(+) MCOTS-C-270N-08-HT (Converter 73) 0.01uF Clock Sync ON/OFF Vin(+) MCOTS-C-270N-08-HT (Converter 8) 0.01uF Clock Sync ON/OFF Vin(+) MCOTS-C-270N-08-HT (Converter 1) Note: the resistor Rtrim is used to trim up the output voltage from 8.0V to 8.5V 10uF/400V FUSE2 2 3 3 22uF 22uF 22uF 1uF Rtrim 22uF 8.5Vo/50A 1uF Rtrim 8.5Vo/50A 1uF Rtrim 8.5Vo/50A 1uF Rtrim 8.5Vo/50A Cvcc Cvcc Cvcc Cvcc 0.1uF/16V + 0.1uF/16V + 0.1uF/16V + 0.1uF/16V + 0.01uF/50V Cgate 0.01uF/50V Cgate 0.01uF/50V Cgate 0.01uF/50V Cgate Rt Q2 Rt Q2 Rt Q2 Rt Q2 4 4 Timer Vcc CS CS GND UVP FAULT CS OVP UVP FAULT OVP MAX8535 Gate GND UVP FAULT OVP MAX8535 Gate GND UVP FAULT OVP MAX8535 Rgate 10 Timer Vcc GND Gate Rgate 10 Timer Vcc CS MAX8535 Rgate 10 Timer Vcc Gate Rgate 10 Ccs Ccs Ccs Ccs Ceao Ceao Rcs2 Rcs1 Radj Rcs2 Rcs1 Radj 5 5 Date: File: B Size Title Rshunt Rcs3 EAO CSO Rshunt Rcs3 EAO CSO Ccs VDD VDD Rcs4 LS ADJ R? RES1 LS Revision 6 24-May-2010 Sheet of C:\Fred Fu\Synqor\Zichen\Institute 14\Design Drawn for 14th By:Institute.ddb Number CS- CS+ R? RES1 ADJ Q? PNP Rcs4 UCC29002 GND Ccs CS- CS+ UCC29002 GND Q? PNP (8.5V+) Vout+ Share Bus 6 (8.5V-) Vout- A B C D Text Technical Specification Board #10 On/Off Signal- U? F? FUSE2 + 10uF/400V + F? FUSE2 10uF/400V F? Filter Board #1 On/Off Signal- U? FUSE2 F? 10uF/400V + FUSE2 FUSE2 Filter F? F? 1 Mil-COTS 270V Full Feature Recommendations Page 7 Mil-COTS 270V Full Feature Recommendations Technical Specification HALF BRICK PIN LOCATIONS 8 5 6 7 4 TOP VIEW TOP 1 2 A VIEW B C 3 PIN DESIGNATIONS Pin 1 2 A B C 3 Name +VIN ON/OFF Function Pin Positive input voltage 4 TTL input to turn converter on 5 and off, referenced to Vin(-), with internal pull up CLOCK SYNC Clock synchronization 6 START SYNC Start-up synchronization 7 Ishare Active current sharing 8 IN RTN Negative input voltage Name OUT RTN -SNS Function Negative output voltage Negative remote sense TRIM +SNS +VOUT Output voltage trim Positive remote sense Positive output voltage Contact SynQor for further information: Phone: Toll Free: Fax: E-mail: Web: Address: Product # MCOTS 270V Full Feature 978-849-0600 888-567-9596 978-849-0602 [email protected] www.synqor.com 155 Swanson Road Boxborough, MA 01719 USA Phone 1-888-567-9596 www.synqor.com 065-0000016 Rev. A 03/21/14 Page 8