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The application of the power module with the hot plug function and the safety control in the hot plu

1 introduction

Also called hot-plugging function, it is very important in power supply design. In the application system with fault tolerance power architecture, thermal plug and pull function is required to meet the requirement of zero downtime. In modern analog and data communication systems, this requirement is usually required.

In fact, many large telecommunications and data communications systems are built with multiple circuit boards or blades that are inserted into the common backplane of the rack. Since modern blades have more advanced functions, more power needs to be consumed, for example, advanced telecommunications computing architecture (ATCA) blades consume about 200W or more. The back panel provides power to the blades and their communications (e.g., +48V, -48v, and 12V). Because the backboard power is always on, it is called "hot" or "running". The blade must be inserted into the frame without affecting the work of the rest of the blade on the back plate. The newly inserted blade will be powered by the power of the back panel. If a blade failure is detected, the blade must be removed from the slot and the new blade inserted into the same slot to restore service. The process of inserting a blade into a running back plate or removing it from a slot is called "hot plugging". Blades that can support this function are called "hot-pluggable" blades.

Therefore, this paper will introduce the following two aspects: design issues that should be considered when using the power module with hot-pluggable function to compose the 48V distributed power structure; The hot plug controller circuit is used to solve the safety problems in the hot plug operation of multiple circuit boards or blades.

The design rules of 48V distributed power supply structure are formed by the power module with thermal plug and pull function (such as IAM type)

The hot plug function is especially important to ensure the safety of the hot plug element. In addition, in the process of hot-plugging, the function of hot-plugging should avoid obvious fluctuation of the voltage of the input and output power lines. Any significant, even instantaneous, fluctuations in busbar voltage may cause the system to work improperly. In common connector, each connector is not connected at the same time or broken at the same time, but connected or broken regularly. Therefore, the power supply must be switched on or off in sequence.

In order to meet the above requirements, the design rules of the power module with hot-pluggable function (such as the IAM type) composed of 48V distributed power supply structure should be noted as follows:

When a charged plug is inserted, the parameters must not exceed the limit value or absolute maximum rating of each element.

The surge current must be limited to an acceptable value, so as to avoid the interruption or fall of the 48V input bus voltage and reduce the sparks generated between each contact point.

The load current of the converter must be limited to the specified value when it is plugged into the dc-dc converter with a charge to ensure that the output bus voltage Vout is stable and there is no mutation affecting the adjustment rate.

The dc-dc converter must not be allowed to transfer energy when the load is disconnected or not connected to the sampling line, i.e., power mutation occurs.

2.1 functions of modules with live insertion

In order to achieve the above design rules, can charged inserted in each module (IAM) shall join in the simple protection and sequencing circuits, which can guarantee the power supply module, as it is pulled in DC - DC converter load switch off or sampling line is shut off before. At the same time, when the power module (IAM) is charged, all its input and output terminals are connected, and the dc-dc converter is temporarily shut down. Otherwise, when a live plug is plugged in, the connection point of the connector will have irregular power and power failure, which may damage the dc-dc converter module or even the whole system.

2.2 some uniform current control circuits shall be added in the power module

As is known to all, the first and the fault tolerance is the most important requirement is that redundancy, that is to say, in the power supply system, should have at least one additional converters or there is a redundant converter. This system is usually called N+M configuration, where N converters can meet the load required power, M converter modules for standby. Application process, a converter module to shut off or failure occurs, although each module of the load current is increased suddenly, but other modules can guarantee the system output is not affected by any. Similarly, when an additional converter module is connected to the power system, the output power of the system is not affected by any sudden decrease in the load current of each power module. For this reason, each converter should have the capacity of uniform flow and should minimize the dynamic response time required for each module to resume normal power supply. Therefore, in order to load automatic uniform current, some uniform current control circuits should be added in the power module. The working temperature of power module has a great influence on the reliability of each lower working temperature 10 ℃, the average time between failures can be extended. It has been proved that when the output current of one module in the power system is twice that of the output current of the other module, the temperature rise of the power module will be doubled.

The 48V distributed power supply scheme constructed by the second generation dc-dc converter and the power module with hot-plugging function (IAM48)

3.1 features of the second generation dc-dc converter module

The second generation converter module of Vicor is used today. It has some excellent features, which greatly simplifies the application in parallel redundant system. Important features include: the second generation of converter module enabling and shutoff, unique master-slave flow control and command function independently, including a converter module in the master position of the whole system; It also has some common features, such as low pressure blocking, soft start, output current limiting and remote sampling. Especially the Vicor converter USES zero current resonant switch. That is, the required power supply adjustment rate and load adjustment rate can be achieved by controlling the switching frequency and the energy pulse rate transmitted from the isolation converter to the secondary level. The pulse width is constant at any given input voltage, so the energy of each pulse is constant. In the case of stable output voltage, in order to meet the requirements of the load current, can control the pulse repetition rate (that is, the switch frequency), as a result, each module of the switching frequency synchronism, same module can realize automatic flow.

It can be seen that the PR pin on the second generation dc-dc converter module is a two-way port, which can connect the parallel bus of uniform current. This port can receive or transmit synchronous pulse signal, and it can control the transmission and synchronous work of converter module. All other modules accept synchronous pulse and ensure all modules work at the same frequency. The PC(primary control) pin is also a two-way port. The port is used as the output module state, in the working process of the converter, the dc voltage is 6 VDC feet, under fault conditions, such as overheating or output overvoltage, PC foot becomes low level (foot - Vin for the negative input voltage is close to 0 v). In the event that the failure continues, the PC foot periodically changes to a high level and tries its best to restart the converter module. Only after the failure state is eliminated, the PC foot can maintain high level. The PC pin can also be used to enable/disable the input pin. If the PC pin is connected to a low level, the converter will be switched off. When the PC pin is kept low, the output current is close to 2mA. Open collector or drain transistor switch (see Q3 in figure 1) can be used to complete the enabling/switching function.

The sampling pin S is used to improve the stability precision of the bus voltage of the output terminal power supply. The load of the power system is usually connected to the bus of the output terminal power supply. The terminal sampling closes the adjusting control loop and adjusts the converter's output voltage Vout to compensate the voltage drop generated on the output bus Vout(on the left end of figure 1). Sampling pin terminal connection is necessary to maintain output voltage control. In a fault tolerance parallel redundant system, a diode must be connected from the output end of each converter module Vout to the power bus (on the left end of figure 1). The total output current of the diode on the output bus is the sum of DC-DC converters. In this way, any failure state of any module including output short circuit can ensure the bus and power system works reliably. When the output voltage of the module is reduced, the series diode is subjected to the reverse voltage, so the power bus can be isolated from the converter simply. Each module of the sample in the front of the line must be in a series diode, and preferably in front of the hot plug plug, plug process can ensure the power supply module, the converter control circuit will not appear any moment. The best value for Ω / 24 V, that is, the resistance of the resistance depends on the output voltage. For example, the output voltage of 5 v, it is best to choose 120 Ω resistance.

In a word, the power module with hot plug and pull function should have the following characteristics: the power module should be closed before pulling out; When inserted, the power module should be temporarily closed. The power module should be able to limit the surge current.

3.2 application of IAM48 module

The Vin of IAM48 input power adjustment module is 36v-76v and 10A, while Vout is +75V ~ -75v, and its efficiency is 97%.

The IAM48 module contains a series FET switch, which can realize the on-off control of the input of 48V bus to dc-dc converter. The on-off control pin (see the pin of the IAM48 module in figure 1) has an internal pull-up circuit, and the on-off controller must be pulled to a low level in order to connect the 48V bus to the dc-dc converter module. There is also a parallel switch between the two output terminals (+Vout and -vout) in the module. When the on-off control pin is negative to a very high level (off) of the 48V bus, the parallel switch is in a state of conduction. When the 48V bus is off, the holding capacitance on the bus can be discharged rapidly through the parallel switch. In addition to the on-off control function, the IAM48 module also has the function of limiting the current of the wave poke, and can complete transient overvoltage protection in cooperation with the FiltMod module or EMI filter module. IAM48 and FiltMod modules are commonly used in communication devices to meet EMC (electromagnetic compatibility) standards (see the connection between the FiltMod module and the IAM48 module in figure 1). In communication equipment, the power module is required to have hot plug and pull function. Therefore, lAM48 power module or other modules that can limit surge current should be selected. 
3.3 features of the FiltMod module

VI - IAM (namely FiltMod module) input attenuation module is a component level DC input front filter, its characteristic is to take up very little space, at the same time provides maximum protection efficiency, suitable for precision electronic systems. Vi-iam can be used in conjunction with Vicor's 24V, 48V or 300V input modules to form a high efficiency and high power density power supply system. The output voltage of the system ranges from 1V to 95V, and the power reaches 400W (which can be extended to 800W). VI-IAM can be used to form a small, efficient and reliable power supply system to meet the highest requirements of telecommunications and industrial applications.

3.4 starting order when the power module is inserted into the power bus

First of all, except for short pins, all the pins of the connector are connected in an irregular order. Besides, the converter cannot start. Because the short pin of the on-off control is not connected, the pin keeps the IAM48 module in the off state through the Ql transistor. At the same time, the transistor Q3 also pulls the PC pin of the dc-dc converter module to a low level, so the converter module is in a state of shutdown. When all other pins are connected, the short pins are connected. IAM48 module on and off the foot is pulled to the low level, therefore IAM48 module conduction, 48 v power capacitor on the bus began to control the rate of recharge, busbar voltage start along the slope, so it can surge current within safe limits. After the 1AM48 module is switched on, the dc-dc converter module gets the enabling signal, but the dc-dc converter module cannot start until the bus voltage reaches the threshold of the under-voltage blocking gate (about 34V). Bus voltage reaches under-voltage blockade, due to the DC - DC converter module, soft start characteristics so at least still need after 100 ms, began to inhale current converter module, and the output voltage begin to rise. Finally, the converter module outputs a balanced load current when the output voltage of the converter module rises to make the diode in series at the output side forward offset.

The power module IAM48 works in roughly the opposite order when it is pulled from the bus than when it is inserted. The short pin is disconnected before the lAM48 module shuts off the other pins of the 48V power supply, and the converter module is closed. The bus capacitance rapidly discharges through the parallel switch at the output end of IAM48 module, and the discharge time is less than 50ms. At this point, the capacitor C2 continues to provide the current needed to maintain the transistor Q3 homing. This ensures that the PC pin remains low level until the bus voltage of 48V drops to the under-voltage blocking value. In this way, it is guaranteed that the dc-dc converter module does not generate power conversion pulses during the irregular disconnection of all other contacts.

The hotplug technology has been successfully used in many products, and in the process of plug, input and output bus voltage fluctuation is small, in the process of the plug, shall ensure that all modules of pin voltage does not exceed the highest rated voltage. When the power module IAM is inserted, the short pin must be disconnected after the other pins are completely disconnected.

4. Solve the safety problem in the operation of multiple circuit boards or blades by using the hot plug controller circuit

Although the power module with hot-pluggable function (such as IAM type) can form a 48V distributed power supply structure, how to ensure the safety of hot-pluggable operation is an important control technology. Therefore, the circuit technology of -48v or +48V with hot-pluggable controller applied to high-power blades has been put on the agenda for discussion.

4.1 basic circuit architecture of hot-pluggable controller

When the blade is inserted into the back plate, all the capacitors connected to the back plate on the blade start to charge, drawing a large amount of current from the back plate. The surge current causes a sudden drop in the backplate voltage and generates an arc on the connector. Excessive surge current can overload the power supply of the back plate, which can completely shut off the power supply and affect the work of other blades on the frame.

In order to minimize the influence of hot plug on the rest of the blade on the frame, the surge current of the blade needs to be limited during hot plug. The circuit limiting surge current is called the "hot plug controller circuit". FIG. 2 is the basic architecture of the hot plug controller circuit implemented in the high-power blade-48v.