An intro into programmable mixed-signal ICs

tl;dr Needed a board to test what I can do with GreenPAKs, picked the SLG47011V because it offers the widest macrocell coverage. Added three ways to probe it (pads, loops, pin header) and ESD/TVS protection on every GPIO so I can connect anything I can think of (at 3V3). An MCU is present to work around the OTP limit, with optional NOR flash for PWM patterns and samples.

What is this?

The board centers around a SLG47011V—a member of the GreenPAK family by Renesas. Think of these chips as lite FPGAs on a diet, focused on analog.

After spending hours comparing them (see attached screenshot), this specific model stood out because it packs "everything" needed to build an analog front-end, which I need for the automation side of the platform. I mean an ADC, DAC, pattern-based PWM, multi-channel DCMP, PGA, current source... plenty of options packed into a 2x2 mm footprint. Sure, you only get a few or even just one of each, but they are cheap and tiny.

Key specs worth mentioning:

• Analog / Mixed-Signal: 4-channel 14-bit ADC, 12-bit DAC, Math Core, Current Source, Data Buffers, Voltage Reference, and a PGA.
• Logic & Timing: Up to 11x 12-bit counters (chainable), 2x 16-bit counters, up to 33 flip-flops, and 11x 3-bit LUTs (Look-Up Tables).
• I/O: 11 GPIOs and 1 GPI.

The bad (and the workaround)

The main downside of this chip is that you can only buy them with I2C disabled. The official way to enable it requires buying a €50 programmer, plus a socket adapter to put the chip into for programming (which runs another ~€67, but comes with 50 chips) or the DIP variant for 5€.

The SLG on the board has I2C enabled via said contraption, so the OTP is used. I wrote a Java app (wip but programming works) that can read the .aap files and send those over CDC to the board. It can also monitor a file you are working on in 'Greenpak Designer' and commit saved changes. This took some time reverse engineering and might not be 100% functional, still in the progress of testing each macro and so far PWM and DAC are verified.

Given that the I2C connection is brought out to a connector, you can program other SLG boards with it (that have I2C enabled).

Why did I make it?

So why did I make this board? I really like the idea of the Greenpak; small, easy to program configurable logic that I can alter in the field. The SLG47011V contains a bit of everything to get to know the platform and what it's capable off. The current plan I have for it is to be the controller for a discrete efuse (also planned to be in the shop) and the front end for a general automation board.

Another option (might be a different one) is to act as a 'companion' to an MCU to handle the recurring stuff like watchdog, put in bootloader, external nvm and other things to hand off. Then there are with programmable LDO's or rheostats or load switches...

What's on it?

STM32U073

Besides the CPLD there's a STM32U073. Yes, that's massive overkill for the application. But at the moment, my wip HAL is based on the STM32U0 family .

MCP2221A

The same chip the official programmer uses but sadly the official software doesn't play nice with other boards for now. So this currently provides:

• UART to the STM via CDC
• I2C via HID to both (for raw access with https://pypi.org/project/greenpak/)
• GPIO connected to toggle RST/Boot0 to put the STM32 in bootloader.

Inside the repo you'll find a small utility to program the SLG and toggle the GPIO on the MCU.

Optional

I wanted to keep the price low, so the chips most won't need aren't on it by default.

• AT25EU0081A 1MB Nor Flash: the stm32 has about 180KB flash available, code has routines to use this.
• ZXCT1086 50V/V current sense amp: for the few that want to have a onboard current measurement option.

Protection

• Each connection that has ESD/TVS protection and GPIO also get 22R
• The USB-C connection has ESD/TVS
• A PPTC with a 90mA trip point before the SLG to prevent it going over absolute max

Connections

SLG47011V

Lots of debug probing options:

• Each IO pin has:
  • An 0.8mm test point
  • A small ring to a hook probe on.
  • 2.54mm pinheader
  • A selection of them also have an LED. Via solder jumper so it's not connected if you don't want it to.
  • A header compatible to the Renesas programmer

STM32U073

• 4 GPIO get the same 0.8mm test point and small ring.
• A single led for heartbeat or other indications.
• A JST 1mm 5pin header that brings out all the pins to connect a STLink (or compatible).
• Solder jumpers if you need to short reset or Boot0 manually.
• 3 GPIO with solder jumper to SLG pins

Ground

• There are Large rings , one on each side.
• One pin on each pinheader.
• Two of the mounting holes.

Power

The board is powered via USB or via either of the 1mm JST headers (at own risk). There's an 150mA LDO present to go to 3V3. Just to be sure I've added a PPTC fuse before the SLG and STM32. In addition, a 3R9 resistor sit before the Vcc pins of the SLG so you can monitor the current draw (via the same rings as GPIO). Given the cost, an actual current sense amp is added as an option.

Because the internal reference is 1.62V I've added a second LDO that outputs 2V5 on the external ref pin of the SLG with a solder jumper incase you don't want it connected.

Pricing

Given the full bom is listed below, there's no point in hiding that this ends up being just shy of 18€ a piece of you want to make 10 of them. I'm assembling these on a afarco PnP, test them, package them and so on. All of that added puts me at 28€. Applying a standard maker multiplier and various fees brings it to 38€, which feels like a fair price.

For now, B2C restricted to Benelux pending PPWR resolve. For B2B, send a message to add shipping.

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