Teeny-Tiny GPAK4 mixed-signal FPGAs for embedded systems

March 26, 2015

Max the Magnificent-March 26, 2015

The vast majority of the embedded designers I know typically create MCU-based systems -- they rarely even consider using a Field-Programmable Gate Array (FPGA).

Now, I think just about every embedded designer has at least heard of FPGAs. They understand that these devices can be configured to perform different tasks, and they may also know that FPGA designers typically use languages like Verilog and VHDL to capture their designs, but that's about it -- they don’t actually know how these devices perform their magic, and they don’t really understand how the design in Verilog or VHDL is "compiled" into the FPGA.

One important thing to note here is that not all FPGAs are created equal. At one end of the spectrum we have humongous devices from Xilinx and Altera that can contain multiple processor cores and the equivalent of multiple millions of ASIC gates. Then we have some very tasty and affordable mid-range devices from companies like Lattice Semiconductor. And we also have some very interesting PSoC (Programmable SoC) devices from Cypress Semiconductor that contain a 32-bit processor core along with programmable analog fabric and programmable digital fabric.

All of these devices are capable of extraordinary things, yet embedded designers still tend to steer clear of them. Perhaps what is required is some way of "dipping one's toes into the water," as it were -- some way to experiment with programmable device technology without making one's brains leak out of one's ears. If so, Silego's teeny-tiny mixed-signal GPAK devices might be just what you are looking for.

I think of these GPAK chips as super-small mixed-signal FPGAs that you can literally design and program in just a few minutes, and that cost only a few cents each. GPAK mixed-signal FPGAs allow you to replace a number of off-the-shelf "glue" chips and gather their functionality into a single low-cost device. In addition to minimizing the component count and reducing costs, this shrinks board size and reduces power consumption.

The most recent addition to the GPAK family is the GPAK4, and the first member of this fourth generation is the SLG46620V. Presented in a 20-pin STQFN package (2.0 x 3.0 x 0.55mm with an 0.4mm pitch) and supporting a supply voltage of 1.8V to 5.0V, this little rascal boasts 18 general-purpose input/outputs (GPIOs), 6 analog comparators ACMPs, 3 digital comparators/pulse-width modulators DCMPs/PWMs, 2 digital-to-analog converters (DACs), 25 lookup tables (LUTs), and a variety of counter, delay, and flip-flop macrocells.

These tiny devices can be used to implement a wide variety of system functions, including comparators, logic, delays, counters, resets, power sequencing, voltage sensing, and interface circuits -- all while minimizing component count, board space, and power consumption.

One of the things the folks at Silego have done really well is to create an intuitive, easy-to-use, drag-and-drop graphical user interface (GUI) interface called GreenPAK Designer that allows you to play "what-if" games with different configuration scenarios, including defining input stimulus and simulating the way in which the GPAK will behave.

The image above shows relatively simple stimulus waveforms, but you can use the custom wizard to literally draw any waveforms you wish, thereby allowing you to verify how your design will respond to "interesting" input signals (e.g., signals with noise spikes). The GreenPAK Designer software is available free for Windows, Mac, and Linux platforms -- in fact I just downloaded the latest version to play with myself.

Once you've evaluated your design in the virtual world, you might decide to invest in a GreenPAK4 Development Kit as shown below.

This kit -- which costs only $59 -- includes a Universal Development Board, a GreenPAK4 TQFN-20 Socket Adapter, some SLG46620V samples, a USB Cable (A to Mini B), and a Quick Start Guide. Using this kit, you can verify your stimulus against a real device and monitor its real-world responses. When you're ready to rock-and-roll, you can program your design into the GPK4's non-volatile memory, pop it out of the socket adapter, and solder it onto your board. (When you are ready to go into production, Silego can make your life easy by delivering pre-programmed GPK4s to you.)

Now, Silego's target markets typically involve large-volume production runs. Having said this, for only $59 for the development kit with SLG46620V sample devices, I personally can see myself using these little beauties in my hobby projects and prototypes. If you have a few moments spare, why not download a free copy of the GreenPAK Designer software, have a play, see what you think, and then post a comment here sharing your findings with the rest of us. You never know; if you like working with GPAK4 devices, you might start thinking about experimenting with larger FPGAs in the future.


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