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Type-C Non-Negotiated Power and 20V protection

Discussion in 'Programming/Internet' started by Ilya, Aug 2, 2020 at 2:35 PM.

  1. Ilya

    Ilya Guest

    I'm developing a 5V device and I use 5V for powering/charging the device. I googled the subject of course, and came to the conclusion that 5V device should have 20V protection in case there is some knock-off charger that will send 20V before finding out the target device didn't negotiate for such voltage. I have two questions:

    Point number 1:

    How much power do type-c power bricks provide if there is no CC negotiation and I just connect its 5V VBUS to my charging/PMIC*? How many amps do I get at 5V by default? I need to decide whether I need to include USB IC or not. Does it have to be some QC+PD combined IC to cover all range of chargers? The whole charging standard mess is killing me. Any ICs you could recommend? While I believe that some 500ma should be enough for my project, I wanna know the number I can look at and decide, besides, charging at higher currents wouldn't hurt. I have place on PCB and budget to put an IC or two, but if there's no need, I wouldn't overcomplicate.

    Point number 2:

    Do I need to protect from accidental 20V input? If yes, what are the options? I just put a 5.1V Zener on Type-C VBUS, so that it will clip 20V spike before the charger realizes 20V are not needed. Will it work? Do I need a separate protection IC or some negotiation IC with 20V+ tolerance? Or is it maybe all unnecessary?

    *PMIC: SY6926QYC on LCSC, looks capable, charges, provides power to system (it bucks USB 5V down to charge battery with CC/CV and provides straight USB's 5V to the system or it boosts battery to 5V and powers the system with 5V again if no charger), can limit charging/system etc currents with external resistors, all-in-one, looks really lovely, but handles 18V max, had to design custom footprint for it too (eagle lib), haven't tested it before, but I kinda like its functionality, so I would want to stay with it.

    I insist I wanna use USB Type-C port (no micro-B)

    Edit: I've added a regular diode to zener to shift overvoltage threshold, since Zener will start to conduct before it reaches zener voltage, and I don't want to waste power. After all, the PMIC can take up to 18V with recommended maximum of 16V, so if I clip it around 6V, it should still be fine and waste less power. So there's 5.1V and 0.6V from a diode now. I guess it should help, but there is still no detailed answer anywhere to be found. Or maybe I could go for two zeners or a zener with higher voltage, I guess.

    Edit 2 (01.08.2020): I've decided to try to implement power delivery and use a chip that can withstand 20v. I will cry when I write software for it (it's an I2C controlled PD controller), but it's useful experience, and I can afford it in terms of time and costs.

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