Arria-10 FPGA Power PMIC vs Discrete Design

Hi Leonard,

The typical trade-offs between the discrete design and the PMIC are size and cost vs flexibility. The PMIC integrates multiple regulators into a single package, saving in total solution area as well as material cost. Of course, this is just a general trend and not always the case. The PMIC however has fixed requirements. For example, the converters (BUCK3, BUCK4, and BUCK5) of the TPS65086 have a max current of 3A. If a particular design needs 4A, you can't just swap it out for a bigger converter; you'd have to move to one of the controllers or add a discrete regulator.

The other item to consider is the default programming of the PMIC. For large volume business cases, an OTP (one time programmable) part like the TPS65086 can come pre-programmed to provide all the sequencing. Other PMICs, like the TPS65023, can utilize external enable pins like discretes or come pre-programmed with a few options. For smaller projects, the TPS65086 would require a small MSP430G2121 (or similar microcontroller) to set it up prior to booting up the SoC (Arria 10 in this case). This is typically still smaller than a full microcontroller to sequence all of the discretes in a power up (if sequencing is required), but not always.

The PMIC also has the advantage of being able to diagnose system issues in many cases and report by I2C or interrupt. For example, if BUCK2 of the TPS65086 has a short to GND, when booting it will trigger a power fault followed by an emergency reset. At that point, you can see by I2C that the PWR_FAULT_STATUS bit for BUCK2 will be set. This is helpful for debugging as well as informing the processor of any unexpected issues during normal operation.

Finally, PMICs typically focus on the lower currents (<5A) as higher currents can lead to heat dissipation issues. Parts like the TPS65086 can handle higher currents (25A or so with something like CSD87353Q5D) by utilizing controllers with external FETs. It also allows you to use light current (say 3A) effectively by utilizing smaller FETs (like the CSD85301Q2).

Regarding the Arria 10 specific use case, we are seeing huge variation design-to-design in the Arria 10. Some people are asking for 100A for VCC (like in the discrete design) while others are peaking at 10A. The TPS65086 is likely the best choice as far as PMICs are concerned, but customers need to evaluate how much current they realistically expect to use in their final design. In most cases it is looking like the PMIC + a discrete for VCC seem to be a good match.

If you want to find out about business case requirements for a specific OTP spin of this device, let me know (either by posting here or PM) and I can connect you with one of our marketing team to help evaluate business case.