Summer of FPGAs: MAX77714 Multichannel PMIC EVM - Review

Table of contents

RoadTest: Summer of FPGAs: MAX77714 Multichannel PMIC EVM

Author: navadeepganeshu

Creation date:

Evaluation Type: Power Supplies

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: MPM54304 by Monolithic Power Systems, MAX20303 and MAX8660 by Analog Devices

What were the biggest problems encountered?: No specific problems were seen.

Detailed Review:

Power supplies, converters, switchers are what fuels the world around us. Something like this(if you still know biology). An era has come up now where we can imagine the locomotion without conventional fossil fuel, but while thinking of the one without power, it really stalls my brain. They're just inevitable and maybe one of the areas which weren't growing very rapidly or has hardly seen a revolution. This powerelectronicsnews article is super insightful forecasting a bit on these and what tech giants are up to!

 

What's PMIC? What's special about MAX77714?

Power Management ICs perform operations on power delivery and manage power requirements as a whole integrated system. One step below, Buck Converters, Low-Drop-Out(LDO) Regulators are by far the most common blocks existing in low power devices and applications. Mobile phones, microcontroller power supplies, chargers, smart devices and all of this house one of these power blocks as a building unit. With this MAX77714 evaluation kit, the multichannel feature with many of these power blocks with software configurability is what looked interesting to me. GUIs really brings down the job to a noob level and allows super seamless operation of the device. One another tweaking factor that also interested me is its onboard sections with RTC, battery operation capability, test MOSFET loads and I thought of using it as a precise low voltage bench supply. I know we can never have enough power supply channels while testing stuff and devices now require small voltage levels but at a higher current demand like the 1.8V standard for processors and 3.7V for communication modems.

 

First Look!

The box came well packed the board was sealed inside an antistatic ESD shielded cover. The board looks nice with utmost space management, easily accessible test points for probing/testing and sufficient silkscreen texts. The core, PMIC with buck convertor and LDO passives (capacitors, inductors) is 20mm x 15mm which is far smaller than it looks. The backside of the board is also quite densely populated mainly having 4 power MOSFETs for electrical loading, their drivers, a microcontroller and USB/UART bridge.

 

{gallery} First Look!

 

Parts and Specs

The board has a lot of components including the PMIC, supercap, IO expanders, MOSFET switches, resistive loads, DACs, MOSFET loads, onboard dedicated MCU, LDOs for logic supplies to the PMIC etc. I created a higher level block diagram just to keep everything in view and keep track of parts.

Over the left side here is the main MAX77714 PMIC which directly takes in the 3.6V external power input. There is also a provision for SuperCap or a Coin Cell to keep the PMIC's RTC and systems running. Out of it goes the 9 channels of LDOs and 4 channels of buck converters. The PMIC also has 8 GPIOs for taking in/out the signals or interrupts. Communication for PMIC is through I2C interface and so for many other parts onboard like the IO expander and DAC with the MAXQ2000 MCU being the I2C master.

There are dedicated LDOs of 1.8V, 2.5V and 3.3V for the MCU and its peripherals which is directly powered from 3.6V external input. Connected to the I2C master is the SX1502 IO expander putting out 9 channels to optionally load the 9 LDOs with resistors. This is driven by the same number of MOSFET switches. Next to it is the MAX5815 DAC for optionally loading 4 of the buck converters. This is a clever trick to use digital input from the GUI via I2C and convert it to ranges of analog values to drive the load MOSFET's gate-source voltage.

 

Getting Started

The MAX77714 EVM has a bunch of systems and all are powered by the main MBATT/GND inputs(was tricky to find where to power this unit from? until there was no VIN pin found as in the manual). The EVM manual recommends to use a 3.6V/3A external supply to power up the EVM with USB attached to PC for the communication interface with GUI. Once powered up, the PMIC channels(LDOs and Bucks) come up with their default set voltages in each channel. Then the MAX7714 EVM GUI can be opened and it provides option to configure and reconfigure the output of all channels, load them, customize and manually tweak internal registers etc.

 

{gallery} The GUI

 

The left side window gives options to configure the system LDO, Buck, Loads, GPIOs etc. The GUI provides a nice scroller for configuring output voltages of convertor and upon hitting 'write' it gets fed into the PMIC via USB to the onboard MCU and then through the I2C interface. The load adjustment also has a similar scroll tab option and is updated in real-time.

More on this with a demo in the below video:

 

Working and Testing

 

 

I noted down the output voltage value against the load current for testing the load regulation of the PMIC channel SD3(so for other 2 channels too).

* X is where my bench supply jumped to OCP mode

 

Plotting the load profile:

With the 0.8V and 1.8V tests, the output drop for an increase in load current from 0mA to 1260mA  is quite near. It's ~28mV. Around the edge of SD3's operation voltage limit 3.3V, the drop is quite significant having it down from 3.3V to 2.5V with the variation of load current from 0mA to 1080mA.

 

Load Test

For this, I found some SMD5630 LEDs ripped off of a 10W 220V general-purpose household lamp(the capacitor inside them used to get burst and then the board comes to me) and had cut the PCB in hexa blade and sanded the edges the expose traces to solder. Desoldering them as such is complicated and sometimes they break down. I had made a floral LED out of it a few years ago and used the same in pieces for this test.

 

 

Adjusted the LDO2 to 3.0V, LDO3 to 3.3V, SD3 to 3.4V and it's LIT! (these were the only channels that could supply above 2.8V Vf of SMD5630 LED). The brightness of these can be seamlessly tuned by adjusting forward voltage(Vf) i.e., the output of power converters using the GUI.

 

 

Summary

This turns out to be a pretty versatile PMIC and the availability of configurable power channels makes it more interesting. Support of multiple standard logic levels is a cool feature of it which is quite hard to do by discretely choosing multiple power converters for low voltage(0.8V, 1V), standard levels(3.3V, 3.7V), high current(3.7V, 3A) applications. I have plans to use this PMIC in my upcoming project on DSP with FPGA where a Spartan-7 chip will be used and this PMIC having multiple voltage level support would serve for the FPGA powerup and also a communication MODEM which has to be put on board, having a high current requirement. Above all, thanks to E14, Maxim(now ADI) for sponsoring this kit and choosing me as one of the RoadTester!

 

Links and References

Evaluation Kit Manual: https://datasheets.maximintegrated.com/en/ds/MAX77714EVKIT.pdf

MAX77714 Datasheet: ttps://datasheets.maximintegrated.com/en/ds/MAX77714.pdf

Serial Interfacing Guide: https://pdfserv.maximintegrated.com/en/an/AN6564.pdf
Maxim PMIC: https://www.maximintegrated.com/en/products/power/power-management-ics.html
PMIC FAQ- Power Electronics Tips: Power Management ICs, part 1: PMIC functions (powerelectronictips.com)
NPTEL Course on PMIC: https://nptel.ac.in/courses/108/106/108106159/
Anonymous