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힌트: 여러 단어는 쉼표로 구분
Date
예: 06/25/2022
Date
예: 06/25/2022
Global
China (简体中文)
Japan (日本語)
Korea (한국어)
Taiwan (繁體中文)
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Seven things to know about PMBus
デモ・ホール講義
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Seven things to know about PMBus
Hello, my name is George Lakkas, and I'm the Product Marketing Manager for TI's power management products. Today we will talk about seven things to know about PMBus. Here's the agenda. We're going to talk about the overall overview of the PMBus protocol, the basic requirements, the connections and the protocol itself, the value of PMBus in power supplies, implementing adaptive voltage scaling, telemetry through PMBus, how you would use a PMBus programming script in manufacturing, usage examples, and finally we will show you TI's PMBus power solutions ecosystem. So what is PMBus? PMBus is an I-squared-C based communication standard for power supplies. It's owned and regulated by the System Management Interface Forum. And the membership is open to all. Released specifications are widely available. Currently we are in PMBus specification 1.3. It works with all types of power management products-- AC to DC power supplies, isolated DC to DC converter and bus converter modules, non-isolated point of load converters and controllers, hot swap controllers and subsystem power monitors, supply sequencers and point of load voltage programmers, and monitors and fan controllers. So what are the PMBus basic requirements? Well, first of all, all PMBus devices must start up safely without any bus communication. Some devices may need to be programmed before startup. Others are pinstriped through small external components to program the initial power up or boot up. There's pinstriping components, for example, with program Soft Start, under voltage lockout, switching frequency, current limit, things like that. PMBus can be used with or without a power system manager or controller. However, PMBus does require a master in the system that tells the PMBus power supplies, which are the slaves, what to do and what command to use. PMBus supports set and forget mode. That means you can program a default value once at the time of manufacture, and then the PMBus power supply management IC should operate without any bus communication because it will be using the default value that's in the register. The PMBus devices can also load default settings from hard coded constants, pin programmed components, and the onboard nonvolatile memory. There are several on-off control options that give PMBus power supplies the very large degree of flexibility that they have. For example, if you want a power supply IC to be enabled as soon as input power is present in the IC or bias power, there's an always on option. A PMBus power supply IC can also respond to a control pin, which is the PMBus version of enable, while ignoring the operation command. The power supply IC can respond to the operation command while ignoring the control pin. And of course, PMBus can use both the control pin and the operation command to configure more complex modes of power up as needed. An off from either the control pin or the operation command turns the output off. And both must be on to enable the output. There are many configuration commands with PMBus. You can set the maximum output voltage. You can margin independently the output voltage high or low. This is typically done to essentially exercise the power supply and determine the corner points or the breaking points, especially when you are using a new ASIC or FPGA or processor. You can use the voltage scaling command to essentially take into account the external resistor divider network that you typically use to set the output voltage. This makes the programming of the output voltage a lot easier. You can set the maximum duty cycle, the switching frequency. You can set the undervoltage lockout to turn on or turned off, in other words, levels of the input supply. You can set the warning and fault input and output and temperature thresholds. So this would be input voltage, input undervoltage, or input overvoltage, output undervoltage, or output overvoltage, output current limit, and of course overtemperature. You can scale the current to take into account the current sensor systems. You can also use a command to offset the output voltage if you want. This is typically used to preposition the output voltage expecting a load transient, and this helps with meeting the tolerance requirements during that load transient. This is also known as a [INAUDIBLE]. And you can also calibrate the current measurement coming from the PMBus power supply IC. Once the IC is put on the board, obviously there's now additional inductance and resistance, and that may skew the gain and offset of the output current measurement that's coming back. So there are commands, like IOUT cal offset and IOUT cal gain to essentially eliminate the offset and the gain errors, and make sure that the output current reading that we get from the PMBus power IC is accurate. In PMBus there are also many other commands, like operational functions. Sequencing, for example. Sequencing can be time driven. In this particular case, you introduce a fixed, for example, soft start of soft stop time into individual devices without them depending on any other rail on the board. It can also be event driven. This requires a power system manager to close the loop or it also requires more complex power sequencing built in to the IC. In this particular case, a voltage rail would be dependent on another rail for its soft start and soft stop to make sure that certain power sequencing requirements are met, either up on power up or up on power down. There are also commands regarding tracking, another eternal rail, and interleaving in case of power supply ICs that can be stacked together and interleaved to displace their phase so that you get benefits for the [INAUDIBLE] operation to reduce input and output ripple currents. There are commands that can be used by the manufacturer to record the part number, PMBus revision, various ratings of the board, various specs of the board, project name into user defined registers on the IC. So this is more like a notepad that we give to the manufacturer to be able to record their own project information. Also, the manufacturer can use specific commands for certain loop coefficients or special features in the section. Finally, there are data security commands. So, for example, packet error checking, which we would command as the last command of any PMBus train of commands, can help to validate that data was written correctly into the part. So you would, for example, address the PMBus device, then write into it or send the command, then write the value of that command. And finally, you would want to use packet error checking to validate that the data that was written into the register is the correct one. There's also write protect command that prevents unwanted writes to the part. That's a software command, not a hardware command-- not a hardware feature. And finally, there's password protection to enable optional data security. These are some of the monitor parameters available via PMBus-- input voltage, input current, output voltage, output current, hold up capacitor voltage if you have any type of storage, you know, power supply or system, temperature-- where you can monitor up to three different temperatures-- fan speed-- you can monitor up to two fans-- duty cycle, and switching frequency. Now please remember, not all PMBus devices support all the commands. It depends on the PMBus power supply IC manufacturer on what commands their IC's options support. In terms of status reporting and fault management, the PMBus protocol supports two alarm levels. One is the warning level. It's a minor alarm. And basically, this notifies the host that attention is perhaps needed. There are customers where they said, for example, for the output current that's being monitored, they set a warning threshold close to the peak current of that power supply so that if the warning threshold is repeatedly tripped, that may indicate an issue or an upcoming issue with that power supply. Then there is the fault level. This is a major alarm. And it typically causes the device to take auction. Typically the power supply IC will issue an interrupt, an alert to the master, and it will interrupt the bus momentarily-- the PMBus. And so that would allow the master to take some type of action. There are also fault notification options. Now, keep in mind the parametrical information can be read from the PMBus device's real time. And-- which is a major benefit. And in terms of the fault notification options, the host can continuously poll the PMBus devices. The PMBus, upon a fault, can send an interrupted through the SMB alert pin, which is an output flag, that there's something wrong. And the master should take action. The PMBus device itself can become a master and transmit a notice to the system host. Fault response methods that are supported are again varied, and that indicates the tremendous flexibility you get with PMBus. For example, upon a fault, you can actually try to ride through the fault. You could assume that it's a momentary glitch and so there's no reason to notify the host to take action. So you continue the operation. You can delay shutting off. So you wait for a specific time, and then you shut down. You can shut down and retry. Basically, this is a hiccup mode operation where you-- if it's a [? back ?] regulator, it goes into a very low duty cycle operations or it doesn't really put a lot of current to the output, to the load. And it doesn't shut down. So it's a lot more easy to restart. And so in this hiccup mode, the converter will wait in this low duty cycle operation for a while. And after several periods, cycles it will try to soft start again. And so if that happens and the, for example again, for the output current, the overload condition is still there, then it will go back to the slow duty cycle operation. And it will continue to try to restart assuming that the overload has been removed at a later time. And of course, another option is to do immediately latch off. And in this case, again upon an overload condition, it will latch off and it will have to be re-enabled from an external device or signal again. So what are the PMBus connections and protocol? So here you see the PMBus connections. What you see in blue are the connections and pings that are part of the PMBus specification. What you see in green is the vendor specific ones that it's up to each vendor how to implement. And so we have, of course-- so what we see here is the system manager. This could be an ASIC, a CPU, an FPGA, or a port management controller. And on the right, you see the PMBus device. This would be the PMBus power supply ICs, whether it's a hot swap, a sequencer, or a voltage regulator. They're all slaves for PMBus. And so you see the data and clock connections right here that go to each IC from the master. And of course you see the clock lines as well. So the data in clock, they're the same as the I-squared-C, SDA, and SCL connections. The control pin, as we mentioned, is the PMBus version of enable. And it controls and it configures for PMBus to be active high or active low. Again, you know, indicating the flexibility you get for designing with PMBus. And the SMB Alert is the output flag which acts as an interrupt when there is a fault and essentially notifies the host to take action and activates the alert protocol. The address, it could be one or more pins to essentially make sure that you are addressing the correct voltage regulator, for example, on the board because-- for example, in an internet switch, it could be up to 30 or more voltage regulators. And if you want to program them through PMBus, you'll want to make sure you are addressing the correct one that you want to program a new command and value of that command into. And last but not least, the WP, write protect pin, if you want to make sure after you've stored your final value for the design to write that command in, the write protect command, to event [INAUDIBLE] after that. So why do you need PMBus? If you look at a cloud infrastructure, you know efficiency starts with the biggest loads. The biggest loads in cloud infrastructure systems, whether those are an enterprise internet switch that you see on the left or a server motherboard that we see on the right-- this is a quad processor, quad CPU server motherboard. So this is a high performance server motherboard design. So for the systems that you would find in cloud infrastructure, the biggest loads are, of course, the processors, the ASIC, and the FPGAs. And you can see the large heat sinks that go on top of the processors, the FPGAs, and the ASIC right here. And because in cloud infrastructure, especially for operators that own their own data farms and server buildings, the fixed power budget coming in-- the power budget coming in is fixed. For example, it could range from 15 to maybe 50 kilowatts. These operators, they want to make sure that they utilize all that input power coming in for throughput, to be able to transmit and process data. And so what is important is to maximize the efficiency, minimize the power losses, and that is done through what we call active power management on each board, whether that's a switch card or a server card. And essentially, what PMBus helps with is to be able to-- depending on the usage case and scenario-- to be able to, for example, reduce the power on each card, and that would mean reducing the power of the CPU or the FPGA dynamically. So that particular card, with a CPU being the biggest load, is not with working at 100%. You can perhaps reduce the voltage of that CPU, and that's what's known as adaptive voltage scaling or AVS. And by reducing the voltage, you obviously are reducing the power since power is equal to voltage times current. Also, PMBus can be used to enable, very easily, supply sequencing that you see here. And also be able to reconfigure and reprogram any type of sequencing built in-- into this power supply ICs with PMBus. You can see here where TI PMBus voltage regulators and we've programmed through PMBus the soft start of each. And you can see how they're actually dependent on each other. First comes this rail, then this rail, and then finally this rail. And in this particular case, we have a PMBus sequencer that is helping control these ICs so that their power up is dependent on the power up of the previous rail. Now this power supply [INAUDIBLE] also have their own built in self start that can be programmed through PMBus. But that soft start is basically a fixed soft start in, for example, milliseconds. PMBus can also enable very easy power supply monitoring. A lot of customers use these to essentially characterize their [INAUDIBLE] system test by monitoring voltage, current, temperature, and of course monitoring the warnings and faults. Last but not least, PMBus can use the temperature that's being monitored-- where that's external to the IC or internal-- for load balancing. So if there's a temperature being monitored that indicates that a particular power supply or voltage rail is getting warmer than it should be, then that can also help with balancing the load between that power supply that's on a specific card versus other cards that perhaps can share some of the load of the first card. And so this load balancing, again, helps with overall, you know, better performance of cloud infrastructure, data centers, and also of course high reliability. This shows you an example of delay-based sequencing that can be commanded through PMBus. In this particular case, you program the turn on and turn off delays as well as the rise and fall times via PMBus. So you can see in this particular case where the control signal-- this is the enable signal in PMBus-- that goes, in this particular case, it's active high. So now we wait. We actually had already introduced a turn on delay. So we basically said, OK, after you receive the enable signal, wait this particular amount of time until you actually begin to soft start, which is the TON-RISE command in PMBus. Similarly, after the enable signal goes low and the voltage regulator is supposed to be disabled or turning off-- in this particular case, actually turns off after a particular delay, perhaps in order to meet certain power supply sequencing requirements. And then after that delay, it's beginning to shut down. And this is the TOFF_Fall that's another command that you can program in PMBus. We have several devices here from TI that use this command, several of our TPS54k devices, 53k devices, our TPS40k controllers, and of course our UCD90k sequencers. And you can see how this helps because you can start the delays for multi-rail sequencing when you have the control signal coming in into, in this particular case, four voltage regulators and each one of them has a different TON delay, a different TON_RISE-- or maybe the same. This particular case looks like it's the same. And similarly, when the control signal will go off, you can also introduce a different TOFF_FALL and TOFF_DELAY so that each regulator can shut down after a particular time that is a good delay time that you've introduced. For more complex sequencing, we also can enable through PMBus dependency-based delays. So in this particular case, each rail actually starts while waiting for another rail to come up. So this is more intelligence power sequencing. So you have the control, the [? enable ?] thing, going high. And then we have the GPI pin going high. That would be coming from the sequencer, our UCD90k sequencers. And then after that pin going high, the first regulator turns on. So you can see here there's a particular TON_DELAY between VOUT1 and the GPI rail. And then it begins to soft start. So that would be the TON_RISE command. But now the second regulator actually is dependent on what the VOUT1, the first regulator, is doing and how it's soft starting before it soft starts itself. In this particular case, you can really have multiple dependencies. It's true flexibility of how you want to sequence various rails and this is really very beneficial when you have, again, multiple voltage regulators on the board. And where there used to be 90k sequencers, you can-- volt support a fixed delay as well dependent delay in your PMBus power supplies. So what is the value of being PMBus? And we talked a lot about flexibility and ease of use and customization. But the other major benefit, which can be obvious, is the cost savings and component savings. So what we are showing here is, if we compare an analog voltage regulator and a PMBus voltage regulator, and what function is supported by each regulator and how it's being implemented, we can see that all these analog components for each function-- for example, over current, limit, power good delay, undervoltage lockout, voltage margining, soft start, frequency, adaptive voltage scaling, turn on and off delay, overturn a warning, current sensing, how you configure the overcurrent's response, how you optimize the inductor and the filter, output filter, whether you want to use a temperature sensor for temperature monitoring, and of course device design revision-- you can see that with the analog voltage regulator, all these components are external. In the PMBus regulator, these are all integrated either in the controller or if we use a complementary smart power stage with our PMBus controllers they're integrated in the smart power stage in the case of current sensing. And so you can see that with PMBus you save all these components here in this column. These are not very expensive components but once they're all added together the amount is some type of BOM cost savings. And then if you multiply that with the volumes of the particular board, you know, if [INAUDIBLE] boards that have to be shipped then that begins to add up to some significant BOM cost savings. And of course, the other benefit is increased liability. The fewer external components you have on your board, the longer the mean time between failures, and therefore the higher the reliability. PMBus benefits in other applications also include data collection. So we have customers that collect data in the hopes that their analysis will help them to optimize the power supply design. After a board has been in the field for a while then they can collect data on the usage scenarios. For example, they may have designed a power supply to be able to support 50 amps of current, but then in the actual application after monitoring and collecting data, they realized that that particular CPU or ASIC, that card only consumed really 30 amps. So they can actually reduce the inductor size and cost and save money that way as well as increase power density. Other customers do live performance monitoring. These are, again, the big data farm customers we have and data farm owners, where they really want to be able to optimize the operation of the data center and the servers and switches and storage boxes in that building versus the fixed input power budget coming in. And these are the customers that monitor-- could be monitoring the overall input power and output power coming in because they are PMBus commands as well. And we have several ICs at TI that also enables you to monitor input power and output power. And once you know input and output power, you can calculate the efficiency of that supply and of that card. So these customers really care about real time monitoring and optimizing the power consumption through adaptive voltage scaling of the servers and switches in their buildings. With customers that use PMBus and telemetry to characterize their boards at in-circuit test to help refine unknown parameters so that, basically, they can finalize the power supply design and screen out the bad boards. These types of customers don't usually use PMBus in real time monitoring after they've ship those boards. Last but not least, with customers that want to use PMBus to perhaps enable some type of a diagnostic mode or predictive failure mode, and this is almost like the golden, you know, dream or the dream-- to be able to predict failure before it happens. And so we have customers that are asking for some type of black box or status saving feature to be able to log not only the type of fault that happened but also the time that it happened and perhaps log all the other rails the status of all the other rails to make sure that none of those other rails was the rail that actually somehow caused the fault on the rail that failed. So how do you implement adaptive voltage scaling in PMBus? One method is to do it through a couple of commands that are called VREF_TRIM, and set VREF_MARGIN_HIGH and set VREF_MARGIN_LOW. Now, and you see the TI parts on the right that use this type of AVS mode. So these are 40k controllers. These are dual output controllers. Here are 20 and 30 amp [INAUDIBLE] converters. And this is our 12 amps [INAUDIBLE] converter. And so with this command, essentially first you're looking at the equation of how to change the output voltage with an external resistor divider. So this is the top resistor right here. This is the bottom resistor. So in order to set the output voltage, the equation is the internalized [INAUDIBLE] reference voltage times 1 plus our top over our bottom. If you've done any margining at all, so you simply then in order to change the voltage, you do VREF equals 0.6 volts, which is the reference of [INAUDIBLE] plus VREF_TRIM. Now keep in mind for the VREF-TRIM and margins, the functions are relative to the reference voltage. So you need to scale the values by the resistor divider to reflect the multi-output. For example, let me give you an example. Here, for a 1 volt output at 0.051 margin high, this should result in 1 volt times 0.051 divided by 0.6 volts, which is the reference of the IC. So this basically results in a 0.085 volt change in the output voltage. If VREF_TRIM's set to 0.02 volts, then similarly the output should be 1.033 because that is 1 volt, which is a nominal voltage, plus 0.033 volts coming from the VREF_TRIM. If you want to extend the output voltage range for the adoptable voltage scaling further, then you use the MARGIN_HIGH or LOW commands. So then you would be adding 0.6 volts, which is the reference voltage of the IC plus VREF_TRIM plus STEP_VREF_MARGIN_HIGH if you want to change the voltage up. Or if you want to change the voltage down, VREF equals 0.6 volts plus VREF_TRIM plus STEP_VREF_MARGIN_LOW. So this is [INAUDIBLE] way to do it. Again, you do have to basically plug-in the values into the equation to be able to really-- to the resistor divider equation-- to be able to really come up with a new output voltage. So this type of adaptive voltage scaling method through VREF_TRIM and MARGIN_HIGH and LOW, is not an option you would change in the output voltage. You have to use the equation here to come up with the absolute output voltage value. Here, this is a scope charting. You can see the actual change of the output voltage, in this particular case, down. And what's interesting here is you can see that PMBus train of pulses. So you can see the SDA, so that's the data line in blue, and the SCL, this is the clock line in purple. So the first train of pulses is the address command. So here you are making sure you are addressing the correct power supply you see on the board. Then this is followed by the actual PMBus command. Then the third burst of pulses is the data for that PMBus command. And then last but not least, remember we talked about it, this is the packet error checking, the command that we recommend you use to check that the data that was written was valid. You can see here that there's actually a little bit of a latency between the very last command and the time at which the output voltage starts going down. That's because that this latency is based on, in this particular case, PMBus revision 1.2, 400 kilohertz clock which essentially yields a 2.5 microsecond period. And since you have four packets of data here, and each packet is 9 bits, essentially this gives you 4 packets time 9 bits times 2.5 microseconds of period. So it gives you 90 microseconds of latency-- again, being the time from the last train of pulses or bursts of pulses of the PMBus commands to the time that actually something's happening at the output. This scope shot shows you how you can expand the output voltage range by introducing not just of the VREF_TRIM command but also, in this particular case, the MARGIN_HIGH command because this shows that we are trying to change the voltage output high. So again, the same type of burst of PMBus pulses, address, PMBus command, the data, and the packet error checking. And so the nominal VOUT was here. We introduced, through the VREF_TRIM command alone first, a 9% change in the output voltage-- a plus 9% change in the output voltage, so that's this way from here. And then on top of that, we added STEP_MARGIN_HIGH command, and that introduced another plus 12% change in the output voltage as shown here. An easier way to implement adaptive voltage scaling is through the VOUT command. And now we have several parts with a VOUT command. The very first one was a TPS544C25 70 amp PMBus converter. And this command is the VOUT command, but essentially it's used in tandem with another command called VOUT_SCALE_LOOP. The VOUT SCALE LOOP essentially pre-calculates, pre-defines the voltage resistor divider. And so in a particular IC, you would see, for example, three values you could pick from for the VOUT_SCALE_LOOP. It could be a 1, 0.5, or 0.25. And each value, each number, that you pick in that VOSL register corresponds to a particular output voltage change you want to change output voltage between. And so, once you pick your number, which essentially again takes the resistor divider calculation into consideration. So this will be the equation right here. R bottom divided R bottom plus R top. Then when you use the VOUT command, this essentially is an absolute change in the output voltage to the value you want. And it's essentially this right here, the VREF divided by the VOUT_SCALE_LOOP, which is again the resistor divider ratio. So this VOUT command essentially has already taken into consideration the resistor divider. And you can change the output voltage in absolute numbers. So obviously PMBus is very useful in prototyping volt characterization, design of [INAUDIBLE], but can we implement PMBus in manufacturing? The answer is yes. We have two main tools at TI for PMBus. One is the Fusion Digital Power Designer Tool that enables you to customize your power supply, use the monitor on your screen to characterize it, you know, where you can be monitoring input/output voltage, current temperature, and input/output power. And then, after you've customized your power supply IC through writing the commands and their associated values into the non-volatile memory registers of the IC, you can finalize the script and then export the script into what we call a manufacturing GUI, where now this script becomes a file that you can load as a configuration file after you insert the test station. This is a PMBus programmer script example. It basically consists of two sections. One would be the address and write section, which is on the left. And then it should be followed by a reset and then a read section to make sure whatever values-- command and values you rolled into the IC were the correct ones. So you can see here the examples in this particular case. First we are verifying that the correct device is present. In this particular case, our TPS40422 dual output, dual phase PMBus controller. Then we are beginning to write. First we write into the user scratchpad, you know, for example it could be the project information, date, revision, things like that. And then we begin to write what we want into the IC. So here we have a command called write MFR_21. In this particular case, because this is a dual output controller, we have enabled it to this command to begin output voltage, output current, and temperature monitoring. And also, because again it's dual output, therefore two channels, we have increased the dead time for the [INAUDIBLE] drivers to ensure there's no [INAUDIBLE] in the device. This happens when both channels are on at the same time. And also-- this also increases the dead time obviously would increase depending on [INAUDIBLE] or decrease. And then we start to write how we would want the power supply to turn on or off. In this particular case, we think that we want the supply to be always converting. So as soon as, you know-- as soon as the control signal is enabled-- is present into the device and enabled, and as soon as power supply power-- IC power is present, then we basically are very telling the IC to turn on and start converting. And here the [INAUDIBLE] gain is the command I mentioned. In this particular case, we use it to calibrate out any gain errors coming back from the monitoring of the output current to ensure that then the next time we reset the device and we look at the output current, monitor the output current, it's as accurate as it can be. Finally-- I apologize. Finally, we store the configuration to the data [INAUDIBLE], the non-volatile memory by using this command, execute STORE_USER_ALL. And then we reset the power to the device and we start reading back those commands to make sure that the values that we used for those commands were the correct ones. And finally we end the script. So that what's known as the PMBus programming script. So what type of PMBus solutions does TI offer? TI has the largest PMBus power supply ecosystem. And you can see here our PMBus devices, which is what is shown in blue, can be used to down convert power from plus or minus 48 volts input typically found in communication systems and industrial systems as well. So we have plus minus 48 volt hot swap ICs that not only implement hot swap function, but also input current monitoring for PMBus. We have digital isolated PWM controllers. In this case, the UCD3138 that can be used to down convert 48 volts to an immediate bus, whether that's 3.3, 5, or 12 volts, in any type of an isolated DC to DC topology forward, half bridge, or full bridge. And then finally, take an intermediate bus voltage as the input power, with a very large selection of sequencers, hot swap ICs, and frontal load DC to DC controllers and converters that can be used with TI's power blocks and power stages to take that intermediate bus, let's say 12 volts, to down convert to the voltages needed for the CPU, ASIC, FPGA, CORE rail, I/O, DBR memory core, and any other auxiliary or standby voltages. And so our portfolio ranges from single face single output to dual face dual output, four and six phase driverless PMBus controllers as well as a large portfolio of integrated fets, where we integrate the high side low side MOSFETs in the [? back ?] converter that range from 12 amps all the way up to 30 amps that you see here. And that is the end of my presentation. Thank you for watching.
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2016년 8월 25일
This presentation will cover 7 things to know about the PMBus
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