【技術記事】簡略化された電源シーケンシング

Power Supply Sequencing Simplified Nathan Enger The challenges in designing a multiple power supply multiply with each additional supply rail. The designer must consider the dynamic environment of coordinated power supply sequencing and timing, generating power-on reset, monitoring for faults and responding appropriately to protect the system. An experienced designer recognizes that flexibility is key to successfully navigating the ebb and flow as a project moves from prototype to production. The ideal solution minimizes the number of hardware and software changes during development. The ideal multisupply design tool is a undervoltage conditions to within ±0.75%. sequence up to 300 supplies in a system, single IC that resides in a design from The comparator thresholds are individu- all using a single-wire communication bus. beginning to end, requiring no wiring ally programmable over a range of 0.2V V Power supply faults are controllable, changes through the life cycle of the to 6 with 8-bit resolution. The compara- visible and manageable through the product. It autonomously supervises and tors are fast, with deglitched propagation LTC2937’s autonomous fault response sequences multiple power rails, cooperat- delays of 10μs. Each sequencer channel behaviors, and through debug registers. ing with other ICs to seamlessly supervise has an enable output that can control an The LTC2937 automatically detects fault many power regulators in the system, external regulator, or the gate of a pass conditions and can power down the and provides fault and reset manage- FET. All aspects of supervisor voltage and system in a coordinated manner. It can ment. The designer can use powerful sequencer timing are individually configu- PC- remain off, or attempt to resequence the based software to configure, visual- rable, including up- and down-sequence supplies after the fault. In a system with ize and debug system behavior in real order, sequence timing parameters, and I C EEPROM a microcontroller and an I 2C/SMBus, time when connected to an 2 bus. fault response. The built-in the LTC2937 provides detailed informa- makes the part completely autonomous The LTC®2937 fits this bill. It is a 6-channel tion regarding the type and cause of and able to power-up in the correct state voltage sequencer and high accuracy the fault, and the state of the system. to control the system. In addition, multiple supervisor with EEPROM. Each of the six The microcontroller can make deci- LTC2937s can cooperate to autonomously channels has two dedicated comparators sions about how to respond, or allow to accurately monitor over- and the LTC2937 to respond on its own. Three Steps of Power Supply Control DC/DC CONVERTERS A power supply cycle has three operat- 12V VIN Figure 1. LTC2937 ing steps: sequence-up, monitoring and sequencing six supplies VPWRI2C/SMBus SDA EN1 RUN1 OUT1 5.0V sequence-down. Figure 2 shows these SCL EN2 RUN2 OUT2 3.3V INTERFACE ALERTB EN3 RUN3 OUT3 2.5V phases for a typical system. During LTC2937 EN4 RUN4 OUT4 1.8VON EN5 RUN5 OUT5 1.5V MARGB up-sequencing, each power supply must TO/FROM EN6 RUN6 OUT6 1.2V OTHER FAULTB GNDRSTB wait its turn, and then power up to the DEVICES SPCLK SHARE_CLK V1 correct voltage in a designated amount ASEL1 V2 R1 ASEL2 V3 of time. During the monitoring phase 3.3k ASEL3 V4 WP V5 each power supply must remain within VDD V6 C1 GND designated over- and undervoltage 2.2µF 10 | August 2016 : LT Journal of Analog Innovation

design features Each of the LTC2937’s six channels has two dedicated comparators to accurately monitor over- and undervoltage conditions to within ±0.75%. The comparator thresholds are individually programmable over a range of 0.2V to 6V with 8-bit resolution. limits. During down-sequencing, each comparators to continuously monitor the 5V supply must wait its turn (often in a voltage at each input against over- and different order from up-sequencing), 3.3V undervoltage thresholds. It ignores minor then power down within a configured 2.5VV1 glitches on the inputs, only triggering if the time limit. At any point, something V2 1.8V voltage crosses the threshold with suffi- V3 can go wrong, causing a fault in the V4 1.5V cient magnitude for sufficient time. When system. The design challenge is to V5 1.2V the LTC2937 detects a fault, it responds create a system in which all of these V6 immediately according to its configured steps, and all of the variables, are easily ON supervisor fault response. In a typical configurable, but carefully controlled. scenario, it shuts down all supplies simul- TIME taneously, asserting RESETB to the system, Sequence-up begins when the ON input Figure 2. Power supply sequencing waveforms then it attempts to resequence up accord- transitions to active. The LTC2937 advances ing to the normal start-up sequence. This through its up-sequence, enabling each two channels to sequence in a different prevents the supplies from powering parts supply in turn, and monitoring to ensure order, then the sequence positions can be of the system while others are unpowered, that the supply voltage rises above the swapped, powering the second channel or executing an uncoordinated recovery configured threshold before the configured in sequence position 1, and the first in after the fault. Multiple LTC2937s in a time. Any supply that fails to meet its position 2. Multiple LTC2937s can share system can share fault state, and respond assigned timing triggers a sequencing fault. sequence position information, so that to each other’s faults, maintaining A unique benefit of the LTC2937 is its sequence position N happens at the same complete coherence between cooperat- sequence position clock. Each channel is time for all LTC2937 chips, and channels ing channels during fault recovery. The assigned to a sequence position ( – 023), controlled by different chips can partici-1 1 LTC2937 offers numerous program- and receives its enable signal when the pate in the same sequence (see Figure 3). mable fault response behaviors to satisfy LTC2937 counts to the given number in the The monitoring phase begins when the many different system configurations. sequence. A channel with sequence posi- last channel sequences up and crosses its The sequence-down phase begins when tion 1 is always enabled before a channel undervoltage threshold. During monitor- the ON input transitions low. The with sequence position 2. If a system ing, the LTC2937 uses its high accuracy sequence position clock begins its count specification changes, requiring these Table 1. Programmable 6-channel sequencer and supervisors with EEPROM LTC2933 LTC2936 LTC2937 Sequencer No No Yes Comparator Outputs No Yes No Threshold Range 1V to 13.9V (1×) 0.2V to 5.8V (5×) 0.2V to 5.8V (6×) 0.2V to 6V (6×) Threshold Accuracy ±1% ±1% ±0.75% Power Supply 3.4V to 13.9V 3.13V to 13.9V 2.9V to 16.5V Package (mm × mm) 5×4 DFN-16, SSOP-16 4×5 QFN-24, SSOP-24 5×6 QFN-28 August 2016 : LT Journal of Analog Innovation | 11

The LTC2937’s extensive register set is powerful, yet mastering it is simple. The LTpowerPlay graphical user interface (GUI) displays all of the status and debug register information in one convenient interface. again to bring the supplies down, but LTC2937 can pull down on the supply Reconfigurable registers function in all of the sequence-down parameters with an optional current source to either time-based or event-based mode. are independent from the sequence-up actively discharge slow moving supplies. LTpowerPlay Makes it Simple parameters. Channels can sequence down The sequence position clock enforces in any order, and multiple LTC2937 chips The LTC2937’s extensive register set is event-based sequence order, with each coordinate sequencing of all controlled powerful, yet mastering it is simple. The event waiting for preceding events supplies. During the down-sequence, LTpowerPlay® graphical user interface before it can continue. The LTC2937 each supply must fall below its discharge (GUI) displays all of the status and debug also allows time-based sequencing, and threshold within its configured time register information in one convenient can participate in systems that enable limit, or trigger a sequencing fault. The interface. The GUI communicates with any supply rails at predetermined time points. Linear Technology power system manage- ment IC (including the LTC2937) on the I2C/ Figure 3. Typical connections between multiple LTC2937s SMBus. Configuring one or more LTC2937s TO HOST CONTROLLER is as simple as a few clicks of the mouse. SEQUENCE STATUS AND I2C UP/DOWN CONTROL I/0 INTERFACE CONTROL 12V DC/DC CONVERTERS LTpowerPlay saves settings on the PC, V and can write them into the LTC2937 IN C3 0.1µF EEPROM. The GUI also shows all of the SDA VPWR EN1 RUN1 OUT1 V1 debug information for system malfunc- SCL EN2 RUN2 OUT2 V2 ALERTB EN3 RUN3 OUT3 V3 tions. LTpowerPlay can show when LTC2937 EN4 RUN4 OUT4 V4ON EN5 RUN5 OUT5 V5 any supply is over- or undervoltage, or MARGB EN6 RUN6 OUT6 V6 FAULTB GND if a supply has failed sequence timing. RSTB SPCLK After a fault, the GUI allows complete SHARE_CLK V1 ASEL1 V2 control over restarting the system. In R1 ASEL2 V3 3.3k ASEL3 V4 every stage of the design—start-up, WP V5 VDD V6 C1 GND configuration, debug, and operation— 2.2µF LTpowerPlay is an indispensable DC/DC CONVERTERS window into system performance. VIN C4 Conclusion 0.1µF SDA VPWR EN1 RUN1 OUT1 V7 The LTC2937 simplifies power system SCL EN2 RUN2 OUT2 V8 ALERTB EN3 RUN3 OUT3 V9 sequencing and supervision. It requires ON LTC2937 EN4 RUN4 OUT4 V10 EN5 RUN5 OUT5 V11 very little board real estate for a complete MARGB EN6 RUN6 OUT6 V12 FAULTB GND system. It is flexible and reconfigurable, RSTB SPCLK yet autonomous through its EEPROM SHARE_CLK V1 ASEL1 V2 memory. It can operate on its own, or ASEL2 V3 ASEL3 V4 in concert with other chips in a large WP V5 VDD V6 C2 GND system, seamlessly orchestrating the 2.2µF operations of up to 300 power supplies. n DEVICE HANDSHAKING TO OTHER DEVICES 12 | August 2016 : LT Journal of Analog Innovation

design features The LTC2937 simplifies power system sequencing and supervision. It requires very little board real estate for a complete system. It is flexible and reconfigurable, yet autonomous through its EEPROM memory. It can operate on its own, or in concert with other chips in a large system, seamlessly orchestrating the operations of up to 300 power supplies. Figure 4. LTpowerPlay graphical user interface (GUI) displays all of the status and debug register information in one convenient interface. Configuring one or more LTC2937s is as simple as a few clicks of the mouse. LTpowerPlay saves settings on the PC, and can write them into the LTC2937 EEPROM. Two LTC2937s in system Easily review or change configuration Dashboard gives quick controlling 12 channels settings for each channel view of supply statuses August 2016 : LT Journal of Analog Innovation | 13