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| USB Type C PD questions |
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| TmaxElectronics:
Hello, I'm working on an existing design for a portable LED studio light, that at the moment charges from a 20V Laptop adapter (but in theory could charge from anything between 5 and 24V). And since I want to include a usb connection (for data) in the next design anyway, i was wondering how easy it would be to use USB Type C PD. I haven't worked with it yet, and kind of failed to explain it to myself :-//. As far as I understood there are 'contracts' that the device can support and then communicates those to the charger, and i would probably need a controller IC for that. But looking at the websites of TI and cypress just confused me more with all the different chips available, and their features. The controller would need to support usb data (not sure if that even goes through the controller), be capable of the full 100W (so the light could be used with an external supply if desired) and have internal switches, if possible, as space is very limited. A Bonus would be if it supported source and sink contracts, as the charger has a 20V @ 6A capable OTG function, so i could in theory use it as a power bank (but only if it didn't need any extra components). Can anyone recommend a controller for such a situation? |
| Bratster:
This is for sink only, but can be completely stand alone and very simple integrate into your product. https://blog.st.com/stusb4500-usb-c-controller-charging/amp/ That's what I'm looking at for possibly using Type-C ports on stuff I tinker with. Sent from my Pixel 2 XL using Tapatalk |
| TmaxElectronics:
thanks. Do you know if i can leave out the VBus mosfet? The charger can be turned off by default and only start drawing current, once the controller got the contract. Or is that against the USB C spec? Also, what happens if the charger can't support the requested contracts (say the requested one is 20V @ 3A, but it can only do 20V @ 1A)? Can the controller read that and tell my device to charge at that 1A or would it fall back to the next lower power contract? |
| MaTkEOxjC:
If you stick to sink only it will become easier. You're already complaining about limited space ;) I build three of these: https://hackaday.io/project/20424-pd-buddy-sink --- Quote from: TmaxElectronics on May 20, 2019, 05:14:00 pm ---Do you know if i can leave out the VBus mosfet? Also, what happens if the charger can't support the requested contracts (say the requested one is 20V @ 3A, but it can only do 20V @ 1A)? Can the controller read that and tell my device to charge at that 1A or would it fall back to the next lower power contract? --- End quote --- The source will sent a "ready" signal after the sink requested a specific voltage and the source adjusted. So I guess you cannot omit the VBus mosfet. Why would you even? Don't make it more complicated. Isn't 20V 6A outside of the USB C PD spec? With the PD buddy sync you need to adjust the load appropriately (should be the same with any other system). So at first you (sink) request the capabilities from the source and source sends it to the sink, then you(sink) send back the capability you want from the source. Now you can adjust the load in the sink and after the source gives you a ready signal you can switch on the load. |
| TmaxElectronics:
--- Quote ---Isn't 20V 6A outside of the USB C PD spec? --- End quote --- I think so, I just wanted to say that it could at least meet the power requirements. I wanted to omit the VBus mosfet, because the charger circuit (buck-boost) can already disconnect all the high power circuitry and draw effectively no power. I thought that would make that mosfet kinda unnecessary ;) If I understood the datasheet correctly, the protocol is handled by the MCU, which then turns on the VBus mosfets right? And if the software already handles all of that it should be easy to start the charger in idle mode (input disconnected) and only switch it on once the the source is ready, if the spec allows for something like that. |
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