Frederik Dostal from Analog Devices talks to PSD about how the company’s latest product can make sequencing easier for powering processors.
Getting power to processors has become much more difficult over time. Initially, as long as the voltage was supplied to the input within the correct parameters, all would be well. Now, due to the addition of peripherals and other capabilities, today’s processors can require many different supply voltages. The processor is the brain of the system and most system will be based around some type of processor. It could be an AI accelerator, FPGA, MCU, DSP, or GPU, and each one demands several different voltage levels, which normally have to be supplied in a set sequence. Often the slew rate of the voltage signal is also required to be within set limits. After that the other areas of the circuit also have to be brought up in a controlled manner. This is a headache for those that have to design the power supply for processor-based circuits, as it usually involves linking multiple DC/DC converters and often requires designing in another microcontroller, just to take care of the power up sequencing for the main controller, and that requires a working knowledge of embedded systems, as well as power design.
Frederik Dostal, Subject Matter Expert for Power Management at Analog Devices expands, “there is a quick way of sequencing, by taking the output voltage of one DC/DC converter and feeding it into the Enable pin of the next DC/DC converter, and that sort of works, but you cannot shut the circuit down by reversing the sequence. So, you usually need a separate device for sequencing. A microcontroller can sequence, but then you have to make sure that it has its own supply voltage, is up and running first, and it is programmed correctly. An intelligent sequencer can also be used, but that requires memory, which has to be programmed, and at first start-up, the EEPROM or other flash memory, has to be tested before you begin to start up the system. Memory can be programmed before it's soldered into the system, but that also costs additional time and money”.
Analog Devices have tried to simplify power design for all but the most complex processor circuits by launching a new sequencer product. The ADM6840 can act as a supervisor, as well as a sequencer, that can control eight voltages, six of them with monitoring. The device has a delay that is adjustable by a capacitor to control when each voltage level is turned on. It doesn’t require a microcontroller, memory or any software. As such, it is a relatively simple device that has been designed to be as small and simple to use as possible, low cost, and operate from a wide input voltage range, as Dostal adds, you don’t want to design in another DC/DC converter just to run the sequencer. It is specifically designed to feed through the voltages that are is supplied, which are set by resistors, in the desired sequence, to the DC/DC converters feeding the processor, with a set delay between each. That capability should be more than enough for a large proportion of embedded designs, especially those that don’t use the latest and greatest processors. The ADM6840 is intended to fill an existing gap in the market for the need to provide easy start up and shut down sequencing as simply as possible.
Dostal expands on the capabilities of the ADM6840 by saying, “it is not just for sequencing, but also monitors the voltages. Each processor needs multiple DC/DC converters, and those are sequenced by ADM6840. At the same time, every rail is also sensed. If all are good, then a signal is sent to the Power OK pin. If that’s not the case, then an output is sent to the fault pin. A third pin signals when sequencing has been completed fully. It's attractive for many different applications, such as telecoms, test, networking, healthcare, and aerospace and defense. The IC’s input voltage ranges between 2.7V and 15V, so in most systems it can run directly from the system rail. If the system has more than eight different voltage rails, you can easily daisy chain more ADM6840 devices. The output is +/- 0.8% accuracy, and for many applications that is more than good enough, and monitoring is unnecessary, so the ADM6840 can be set up as a pure sequencer, simplifying the design further and cutting the BoM. Finally the package measures only 2.46mm x 2.46mm and can operate in a wide temperature range of between -40oC and 125oC.”
