The term PMIC (Power Management IC) gets thrown around a lot when discussing power. In my experience it could mean anything from a dual output power regulator, to a full featured device with a dozen outputs, reset controllers, GPIO and more.
So how do I know what I’m looking for and where to go for information? Well, the answer to that question isn’t always easy. It varies by manufacturer based on how they categorize these devices on their websites which sometimes makes it difficult to locate a part that may be perfect for your needs. Let’s take a step back and talk about defining your power requirements first. Rarely if ever do modern designs consist of a single supply outside of perhaps some wearable or low power battery driven devices. That means when you are talking about your power needs, you aren’t talking about a simple Vin and Vout, you are talking about a system Vin, multiple outputs, possibly multiple power modes, sequencing requirements and more.
It’s not until you really dig into the system level requirements where you see that a PMIC that may have been conceptualized and designed as a companion to a specific processor family, for example, actually fits a tremendous number of applications when you look at the ins and outs in their simplest forms.
Take for example the DA9062 from Dialog Semiconductor. I’m not sure what this device was initially designed around, but after looking at the system requirements for one of Avnet’s upcoming designs I found that it was a near perfect fit for what we needed. I was able to combine multiple devices into a single part, in a smaller footprint and at a lower cost by approaching my power architecture selection from a system level rather than a point of load (POL) level.
Look at it the way you select a processor. You may not use EVERYTHING in the processor, but you have a list of things you need and you find a single device that does most, if not all of those things for you. Back to my DA9062 example. We needed 4 DC outputs, as well as a DDR3 termination regulator and a push button reset controller. The DA9062 provides 4 switching outputs, one that can be configured as a termination regulator, 4 LDOs, 5 GPIOs, an RTC and a backup battery charger. Honestly did I need all those features? No, but I was able to use 3 switching outputs, utilize the 4th as my termination regulator, operate 2 of the LDOs in parallel to get enough current for my 4th DC output, then configure the GPIO pins to handle my push button debounce input and reset control. I was also able to use footprint capability to add an RTC to the system if desired. I didn’t fully utilize the device, but I didn’t need to and I still got all the functions I needed at a much lower cost and smaller footprint than if I had used discrete devices.
That specific device is admittedly targeted at lower power applications. In contrast, let’s look at the higher power UltraZed SOM that was recently released by AVNET. This SOM (System on Module) basically contains a complete Xilinx Zynq UltraScale subsystem that customers can define custom carrier cards around to provide their application specific circuitry in a production ready package. For this SOM, I decided that I wanted to support all the power modes of the Zynq UltraScale device. I also wanted to include PMBus communication capability for real time monitoring and control. Having had a good experience on a previous design using Infineon’s IRPS38060 single channel PMBus regulator, I looked at their 5 output PMIC based on the same architecture of the single channel device. The IRPS5401 provides 4 switching outputs as well as an LDO, all accessible through the PMBus I2C hardware interface. The UltraZed requires 14(!) supplies to meet all of the various requirements to support power modes and our use cases. Four of these rails provide power to individual devices and/or weren’t required for power mode support so these are powered by lesser featured devices. The main ten rails though, are powered by two IRPS5401 PMICs that were then tied back to the Zynq UltraScale SoC. By doing so, the Zynq UltraScale can now send PMBus commands to turn off/on supplies, control slew rate, read real time voltage and current (meaning power too), temperature as well as read error flags such as overcurrent warnings, errors, etc.
Again the integration level of these devices allowed us to cram the very full featured UltraZed SOM with its 14 power supplies into the footprint about the size of a business card.
While not as full featured as the PMBus enabled Infineon device, the Dialog device also features an I2C interface (although not PMBus compatible) that can be used in circuit to enable/disable supplies, read fault registers and more. Point being, when you start looking at defining your power architecture be sure to consider it from the system level. You may find that there is a PMIC out there that does everything you need (and more) for less real estate and a lower cost than the solution you were considering piecing together.
-- written by Chris Ammann, AVNET