I2C over DC power: MAX20340 (and any others?) - Page 1
Forum section: electronics / projects

author: 741
author_rank: Frequent Contributor
timestamp: March 14, 2023, 09:13:27 pm
content: I'd like to power a chip that draws about 40mA at 3v3 and uses I2C. There should be just 2 wires, and the only chip I've found to support this is the MAX20340. This supports up to 1.2A.This part looks really good, but I'd rather not deal with the tiny BGA package.Are there any similar chips? Most hits I get still need a PSU at the remote side.BTW: I looked into 1-wire driver chips, but even with 'strong pull-up' there is still the all-zeroes packet to consider with about 50% duty and other issues. The 28E18 can deliver 10mA to sensors for example.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 14, 2023, 09:33:24 pm
content: His about using rs485? (SN65HVD96)

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2023, 11:12:08 pm
content: Quote from: 741 on March 14, 2023, 09:13:27 pmIf your goal is to basically have a transparent I2C bridge, I don’t think that part would do it — it looks to me like even on the slave side, you have to write data into its registers to send it, so that means having some kind of MCU on the remote side, too.

author: 741
author_rank: Frequent Contributor
timestamp: March 15, 2023, 09:14:47 pm
content: OK Thanks for the replies. It may be RS485 could be made to deliver power, but I'm not sure how easy that would be; my aim is to communicate to an I2C part which draws about 40mA.As for the MAX20340, as tooki points out it meeds a microcontroller at the slave side, and that is not viable in my application.For now I'm trying to make 1-wire work with "strong pull-up" (implemented as a current source) and a discrete parasitic power circuit.

author: tooki
author_rank: Super Contributor
timestamp: March 16, 2023, 08:03:13 am
content: I don’t see how RS-485 would help, if you can’t add an MCU on the sensor side. (Unless there’s a transparent I2C to RS-485 bridge I’m unaware of.)Just spitballing here: Is your 40mA sensor current the peak or average? If it’s just the peak, and the duty cycle is low enough, could you perhaps use parasitic power via a diode and current-limiting resistor to charge up a capacitor at <10mA, and then pull the 40mA peaks from the capacitor? That would theoretically allow you to use the 28E18 or similar.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 16, 2023, 12:46:31 pm
content: Have you considered 1-Wire with the second data wire repurposed to a power supply line?

author: Scrts
author_rank: Frequent Contributor
timestamp: March 16, 2023, 06:17:18 pm
content: Really odd solution to your problem, but one of the possible ones: you can use automotive serializer/deserializer chips without utilizing video interfaces, but using control interface, which is I2C.ROHMTIMaxim/ADI also has the same type of solution.In general, you could do your own power inject onto differential line, but need to convert I2C to some differential protocol and recalculate the filters.

author: dmendesf
author_rank: Frequent Contributor
timestamp: March 17, 2023, 03:03:19 am
content: Look for THVD8000 RS-485 Transceiver with OOK Modulation for Power Line Communication

author: tooki
author_rank: Super Contributor
timestamp: March 17, 2023, 07:55:24 am
content: Quote from: dmendesf on March 17, 2023, 03:03:19 amWhile that’s an interesting part, how does it solve any of the OP’s requirements? It doesn’t provide power to the sensor, and it can’t work without an MCU on the sensor end — both things the OP stated they want.

author: Nominal Animal
author_rank: Super Contributor
timestamp: March 17, 2023, 01:58:47 pm
content: Quote from: 741 on March 14, 2023, 09:13:27 pmI2C has two signal wires and ground: SCL, SDA, and GND. I2C does not work without a common ground reference.Quote from: 741 on March 14, 2023, 09:13:27 pmSo? 1-wire only needs one signal wire for bidirectional signaling, so that leaves you the "second" wire to supply current to the chip. Granted, the bandwidth is quite low, 16.3 kbit/s, compared to I2C (400 kbit/s typically). So, then you'd have VCC, 1WIRE, and GND. At the chip end, you have a MAXIM DS28E18, bridging the 1WIRE to I2C, so between the chip and the DS28E18, you have four wires (SCL, SDA, GND, VCC). But between your host microcontroller and the DS28E18, you only need VCC, 1WIRE, and GND.

author: 741
author_rank: Frequent Contributor
timestamp: March 17, 2023, 03:10:03 pm
content: QuoteYes - but the DS2480 converts 12C to 1-wire, and the DS28E18 converts it back. You can run I2C chips at the far side whilst only using "1-wire comms".QuoteQuoteI have only 2 wires for comms, including ground: There are just two wires in total.

author: dmendesf
author_rank: Frequent Contributor
timestamp: March 17, 2023, 04:07:46 pm
content: THVD8000 can be used for serial communication over 2 wires while also carrying power. You will need to translate between I2C and serial at both ends, but any 8 pin microcontroller can do that.

author: Nominal Animal
author_rank: Super Contributor
timestamp: March 17, 2023, 06:31:00 pm
content: Quote from: 741 on March 17, 2023, 03:10:03 pmSo, what you are asking for really is "1-wire over DC power", not "I2C over DC power", correct?Both 1-wire and I2C arebuses, and involve different numbers of signal lines. In particular, "I2C" always involves two signal lines, SDA and SCL.

author: Nominal Animal
author_rank: Super Contributor
timestamp: March 17, 2023, 07:30:50 pm
content: Quote from: dmendesf on March 17, 2023, 04:07:46 pmThat translation will have to be per message, and cannot be protocol-agnostic, because RS-485 over one pair is half-duplex, but I2C requires ACK/NAK acknowledgement after every byte (which is handled internally by the I2C peripheral, and cannot be forwarded to be confirmed by the remote end).MAX20340(which OP mentioned) is better suited for the task, and costs half as much as THVD8000, but OP is apprehensive of the 9-bump 0.4mm pitch WLP package. Also note that MAX20340 is limited to three-byte messages at most. While the center pad is /EN, and can be directly linked to the GND pin in the center of one of the edges, meaning only one layer is needed, the pitch is tiny. Placement by hand sounds ...tricky.Which is why I'd suggest designing a small 2-layer PCB with the MAX20340 and footprints for the associated resistors and capacitors, as a breakout board; and have it manufactured and assembled by e.g. PCBWay.