Application Note March 2010 Design Guidelines for Power Module Remote On/Off Circuits Introduction Isolated-Closure Remote On/Off The remote on/off feature on the board-mounted power modules (BMPMs) allows the user to switch the module on and off electronically. This feature provides greater flexibility in the start-up sequencing and provides fault control of the user's power system. this application note outlines the types of remote on/off circuits, explains the parameters defining their operation, and provides helpful design tips targeted at robust remote on/off control. An isolated closure is a closure with both high- and low-impedance states that sinks current, but does not source current. For on/off control, the closure is between the ON/OFF pin and VI(-), and can be provided by a device such as a mechanical switch, and open-collector transistor, or an optoisolator. Figure 1 shows an example of an optoisolator connected to a BMPM. Note the Von/off is defined as the voltage at the ON/OFF pin with respect to the VI(-) pin. Ion/off is the current flowing out of the ON/OFF pin. Types of Remote On/Off Control BMP modules are available in positive logic and/or negative logic versions for remote on/off. Table 1 shows a cross-reference for naming conventions of codes with the different logic types. VI(+) OPTOISOLATOR BMP Code Family Example Example Name with Name with Positive Negative Logic Logic MA/MH005 MA005A NA NA MC/MW/ ME005 MC005A NA NA MA/MH010 MA010A MA010A1 NA MC/MW/ ME010 MC010A MW010A1 NA + Von/off - Table 1. Remote On/Off Naming Conventions Example Name Without On/Off Ion/off ON/OFF POWER MODULE VI(-) 8-668 Figure 1. Isolated-Closure Remote On/Off JC/JW030 NA JC030A1* JC030A CC/CW/DC/ DW025XX NA CC025BK1* CC025BK CC/CW/DC/ DW025XXX NA CC025ABK1* CC025ABK FC/FW050/ 100/150 NA FC150A NA There are two types of isolated-closure on/off control circuits used in BMPMs. With negative logic, when Von/off is pulled low by the external closure, the unit operates. When Von/off is left isolated to float high, the unit is off. With positive logic, when Von/off is left isolated to float high, the unit operates, and when Von/off is pulled low or shorted to VI(-), the unit is off. Table 2 summarizes the logic levels and module states. FE200 NA FE200A NA Table 2. Isolated-Closure Logic Table JC050/100 NA JC100A1 JC100A* JW050/100150 NA JW150A1 JW150A* Logic State FW300 NA FW300A1 NA FC/FW 250 NA FW250A1 NA Logic Low- Switch Closed Logic High- Switch Open * Optional remote on/off logic. Note:NA--not available. Negative Logic Positive Logic Module on Module off Module off Module on Design Guidelines for Power Module Remote On/Off Circuits Application Note March 2010 Types of Remote On/Off Control (continued) Isolated-Closure Remote On/Off (continued) Isolated-closure negative-logic on/off control has been established as a Tyco standard being implemented in all new designs. this logic provides accurate control of the module during start-up since the module starts in a known state. Table 3 summarizes the electrical specifications for the ON/OFF pin and the switch for isolated-closure negative-logic on/off. Table 3. Isolated-Closure Negative-Logic Remote On/Off Parameter Remote On/Off; Negative Logic: Logic Low--Module On Logic High--Module Off Module Specifications: On/Off current--Logic Low (switch closed) On/Off Voltage: Logic Low (switch closed) Logic High (switch open) Open-collector Switch Specifications: Leakage Current--Logic High (Von/off = 18 V) Output Low Voltage During Logic Low (Ion/off = 1 mA) Symbol Min Max Unit Ion/off -- 1.0 mA Von/off Von/off 0 -- 1.2 18 V V Ion/off Von/off -- 0 50 1.2 A V Symbol Min Max Unit Ion/off -- 500 A Von/off Von/off 0 -- 0.4 11 V V Ion/off Von/off -- 0 10 0.4 A V Symbol Min Max Unit Von/off Ion/off 2 25 8 160 V A Von/off -Ion/off -- -- 1.25 10 V A Table 4. Isolated-closure Positive-Logic Remote On/Off Parameter Remote On/Off; Negative Logic: Logic Low--Module On Logic High--Module Off Module Specifications: On/Off current--Logic Low (switch closed) On/Off Voltage: Logic Low (switch closed) Logic High (switch open) Open-collector Switch Specifications: Leakage Current--Logic High (Von/off = 11 V) Output Low Voltage During Logic Low (Ion/off = 500 A) Table 5. Level-Controlled Remote On/Off Parameter Remote On/Off; Level Controlled: Unit Off: Voltage Level High Source Current Unit On: Voltage Level Low Sink Current 2 LINEAGE POWER Application Note March 2010 Design Guidelines for Power Module Remote On/Off Circuits Types of Remote On/Off Control (continued) Level-Controlled Remote On/Off Isolated-Closure Remote On/Off (continued) Some power modules employ a voltage-level-controlled remote on/off. Table 5 shows the specification for a level-controlled remote on/off. Isolated-closure positive-logic on/off is used in several BMPM families including the 674, Fx020, SK025, and ME025. Table 4 summarizes the electrical specifications for the ON/OFF pin and the switch for isolated closure positive-logic on/off. In order to satisfy the requirements for the low-impedance state, the closure must maintain a voltage less than the maximum logic-low on/off voltage while sinking the maximum logic-low on/off current. These specifications, therefore, define the maximum saturation or contact voltage of the switch and the current-sink requirement. The logic-high on/off voltage defines the maximum voltage to which the ON/OFF pin floats when the isolated closure is in the high-impedance state. The isolated closure must be rated to handle the logic-low on/off current during its low-impedance state and withstand the logic-high on/off voltage during its highimpedance state. The specified leakage current is the maximum allowable Ion/off while the switch is in the highimpedance state. The leakage current of the selected switch must be less than this value over the required application temperature range. For example, consider the negative -logic specification of Table 3. To activate the module, the user's switch must go to a low-impedance state and be capable of sinking up to 1 mA while providing less than 1.2 V with respect to VI(-). In particular, high-saturation voltage switches such as Darlington output optoisolators need to be checked carefully against this specification. To turn the module off, the switch must go to a highimpedance state and be able to withstand the 18 V on the output of the ON/OFF pin. The leakage current must be less than 50 A while the switch is blocking a Von/off of 18 V over the required temperature range. For negative-logic applications that do not require remote on/off, the ON/OFF pin can be shorted to VI(-). For positive-logic applications not requiring remote on/off, leave the ON/OFF pin open. control of the on/off with positive logic may require particular care because a falsely triggered switch can result in an undesired shutdown of the BMPM. If noisy traces are routed near the remote ON/OFF pin, it may be advisable to add filtering with a small capacitor (100 pF) between the ON/OFF pin and VI(-). the capacitor prevents highfrequency noise from triggering the on/off circuit. Von/off is defined as the voltage at the ON/OFF pin with respect to the VI(-) pin. Ion/off is the current flowing into the ON/OFF pin. For this type of module, the ON/OFF pin is an input, since control is achieved by applying a voltage and injecting a current. Voltage level high is the voltage range that must be maintained at the ON/OFF pin (Von/off) to turn the unit off. The source current must be provided in order to pull the ON/OFF pin high. From Table 5, between 2 V and 8 V must be provided at the ON/OFF pin to turn the module off. The module draws between 25 A and 160 A. Exceeding 8 V may damage the module. The minimum source current can be used as a guideline for the maximum amount of noise current that can be tolerated before shutdown of the module. Voltage level low is the voltage range that must be maintained at the ON/OFF pin (Von/off) to turn the unit on. Sink current is the amount of current that the supply must be able to sink to maintain a logic low. The polarity of this current is opposite the source current. Table 5 specifies a level control that maintains less than 1.25 V while sinking 10 A. Figure 2 shows a TTL output control. In order to meet the data sheet specification example in Table 5, the TTL gate must be capable of sourcing 160 A and sinking 10 A at an ouput-low voltage less than 1.25 V. The logic voltage, Vcc, must not exceed 8 V. An open-collector logic gate with a pull-up resistor could also be used here. A Vcc of 5 V with a 10 k pull-up would be appropriate for the Table 5 specifications. V I (+) TTL GATE SYSTEM ON/OFF CONTROL VCC(+) Ion/off + ON/OFF POWER MODULE Von/off - V I (-) 8-669 Figure 2. Level control Using TTL Output LINEAGE POWER 3 Design Guidelines for Power Module Remote On/Off Circuits Application Note March 2010 Types of Remote On/Off Control (continued) Level-Controlled Remote On/Off (continued) An example of a line-voltage driven circuit is shown in Figure 3. The Zener diode is sized to clamp Von/off below the maximum level high voltage, while the resistor limits the power dissipation in the Zener. If a Darlington optoisolator is used, the saturation voltage must be less than the maximum level low voltage (1.25 V in Table 5) to turn on the module. V I (+) ICBO SYSTEM ON/OFF CONTROL RB Ion/off + ON/OFF POWER MODULE Von/off - V I (-) 8-671 Figure 4. High-Leakage Open-Base Transistor (Not Recommended) V I (+) Ion/off + 6.2 V ON/OFF POWER MODULE Von/off - V I (-) 8-670 Here, the typically small collector cut-off current (LCBO) is amplified by the current gain of the transistor, resulting in substantial leakage currents. In addition, maximum leakage currents for the open-base arrangement at temperature extremes are generally not specified by device vendors, and can therefore be very unpredictable for the user. Consequently, use of a base-emitter resistor, as shown in Figure 5, is highly recommended to reduce leakage current and provide a more robust design. Figure 3. Level Control Using Line Voltage V I (+) Design Guidelines Power modules equipped with remote on/off respond very quickly when the appropriate signal is applied to the ON/OFF pin. this available speed gives users the most flexibility in their individual applications. However, the lack of filtering that makes this performance possible requires that users take certain precautions in their applications. The following design guidelines aid the user in developing robust, noise-insensitive circuits with which to control the remote on/off. Preventing High Leakage Current As stated earlier, a switch with a high-impedance state is required for control of the remote on/off. When in the high-impedance state, switch leakage currents greater than 50 A may be sufficient to trigger the on/off to the logic-low state. If a transistor is used as the switch, leakage currents of this magnitude can occur if the device is operated in an open-base configuration (see Figure 4). 4 SYSTEM ON/OFF CONTROL RB Ion/off + RBE ON/OFF POWER MODULE Von/off - V I (-) 8-672 Figure 5. Recommended Base-to-Emitter Resistor Configuration Filtering Capacitively Coupled Noise Designers should be cautions of circuits susceptible to high-frequency noise. Circuits using an open-base transistor as the switch can again be extremely sensitive. Noise coupling into the base of the transistor through parasitic capacitance is amplified by the transistor gain, possibly generating enough collector current to switch the on/off circuit to the logic-low state, as shown in Figure 6. LINEAGE POWER Design Guidelines for Power Module Remote On/Off Circuits Application Note March 2010 Design Guidelines (continued) Minimizing Inductively Coupled Noise Filtering Capacitively Coupled Noise Large loop areas are sensitive to inductively coupled noise. Keep loops in circuits used to control the remote on/off to a minimum area. For example, if a transistor is used, minimize the loop area between the base and emitter (use base-emitter resistors and/or capacitors placed in close proximity to the transistor). Otherwise, inductively coupled currents could be generated in the transistor base, turning the device partially on. Place the transistor close to the module to reduce the area of the loop between the collector and emitter and the power module pins (see Figure 8). (continued) V I (+) Ion/off Vnoise RB ON/OFF + POWER MODULE Von/off - V I (-) V I (+) ON/OFF 8-673 Figure 6. Susceptible to High-Frequency Noise (Not Recommended) CBE RBE B A POWER MODULE V I (-) To minimize switch noise susceptibility, route the path leading to the base as short as possible and away from any potentially noisy paths. Routing the base path close to VI(-) traces provides some beneficial capacitance. More importantly, use a base-emitter capacitor and/or resistor to filter coupled noise (see Figure 7). Circuits in noisy environments may benefit from a capacitor (100 pF) between the remote ON/OFF pin and VI(-) for high-frequency decoupling. ON/OFF POWER MODULE 8-675 Figure 8. Minimize Loop Areas A and B Using an Input Inductor If an external inductor is used for input filtering, place the switch that controls the module on/off on the module side of the inductor. Otherwise, the inductor appears in series with the switch, and the voltage developed across the inductor can interfere with the on/off control (see Figure 9). In addition, ensure that the inductor does not appear in series with the baseemitter resistor and/or the capacitor between the base and emitter. V I (-) V I (+) V I (+) 8-674 VI ON/OFF Figure 7. Recommended Remote On/Off Layout CBE LI POWER MODULE RBE V I (-) 8-676 Figure 9. Properly Placing the Input Inductor. LINEAGE POWER 5 Design Guidelines for Power Module Remote On/Off Circuits Application Note March 2010 Design Guidelines (continued) Summary Start-Up Sequencing Several types of fast, high-gain circuitry are used to provide the on/off feature. Be sure to follow simple noise-reduction techniques to prevent coupled noise from begin amplified and disrupting desired operation. The noise concerns discussed above are augmented once a circuit pack is operating in a system environment where thermal and noise stresses are at their worst. Some start-up sequences can provide a sneak inrushcurrent path through the remote on/off circuit of the module. In general, the remote ON/OFF pin is normally either open or tied to VI(-) (perhaps using a long finger on a circuit card) for the start-up sequence. If the pin is open, no sneak paths should be present. However, suppose an isolated-closure positive-logic module is being used (Type 2), and the remote ON/OFF pin is tied to the VI(-) voltage to keep the module off while the circuit card is inserted in the system. If the VI(+) voltage is applied to the module before the VI(-) is applied, the transistor internal to the BMPM's remote on/off circuit can become reverse biased with the input voltage. Overvoltage stress will break down the transistor and destroy the BMPM remote on/off circuit. In this case, ensuring VI(-) is applied before VI(+) helps avoid any problem. Most of the discussion above focused on problems that can result in the false turn-on of the user's switch. In modules with positive logic, this false trigger is usually much more troublesome, since the switch turn-on causes a power module shutdown. Negative logic, where the switch is closed during normal operation, eliminates many of the noise issues described here. A s ia -P a cific Hea dquarters Tel: +65 6593 7211 World Wide Headquarters L ineage P ower C orpora tion 601 Shiloh Road, Plano, TX 75074, USA +1-800-526-7819 (Outside U.S.A.: +1-972-244-9428) www.linea gepower.com e-ma il: techs upport1@ lineagepower.c om E urope, Middle-E a s t and Africa Hea dquarters Tel: +49 898 780 672 80 India Headquarters Tel: +91 80 28411633 Lineage Power reserves the right to make changes to the product(s) or information contained herein without notice. No liability is assumed as a result of their use or application. No rights under any patent accompany the sale of any such product(s) or information. Lineage Power DC-DC products are protected under various patents. Information on these patents is available at www.lineagepower.com/patents. (c) 2009 Lineage Power Corporation, (Plano, Texas) All International Rights Reserved. March 2010 AP97-038EPS (Replaces AP94-019EPS)