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USBPD devices can either act as the source (charger) or sink (device) or DRP (both). For our purposes we probably want a sink-only chip since we'll be plugging a charger into this board and the output will be a 12V/GND line. We don't need this to act as a source from a wall outlet.
Compatibility with USBPD 2.0 and USBPD 3.0 would be nice to allow us to use a wider array of laptop chargers.
USBPD 2.0 allows for fixed voltage outputs of 5, 9, 12, 15, and 20V
USBPD 3.0 allows for incremental voltage outputs anywhere from 3.3V to 21V in increments of 20mV. This is called PPS (programmable power supply). We don't really need this since we only need to provide fixed 12V and 5V.
Perhaps considerations should be made for USBPD 3.1 as well, as that would allow for a higher power delivery of 240W and possibly support driving contactors.
3.1 is backwards compatible so designing a 3.1 sink should allow for interfacing with 3.1/3.0/2.0 source
Since we want to max out current I think 3.1 makes the most sense as USBPD 3.1 EPR (Extended Power Rating) cables have the capability of providing up to 240W @ 48V
This may have to wait as there are not many 3.1 sink chips available
According to this reddit post, USBPD3.1 @ 240W probably isn't possible since the sink functionality of it is not well supported. I took a look at a few chips such as ST-ONEHP and TPS25730USB.
USBPD Controller Chip Evaluations:
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Buck Converter Research:
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Input Voltage Range
Buck Converter Pipeline
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(Infineon CYPD3177-24LQXQT) Question: What does this even do? Answer:
Let's try to understand the configuration (this is a slightly more detailed version with specific part numbers as presented in the Evaluation Board Design):
A similar configuration is used for the main output of the board as well. The reason we use a PMOSFET controlled switch for VBUS_OUT instead of just directly outputting to the sink is shown below (see pg 10 of Evaluation Board Design) |
TPS56A37RPAR Buck Converter
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Notes
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See section 7.2.2 of the datasheet linked above.
We’ll be using the same buck for both 15/20 → 12 and 12 → 5 purposes. From https://github.com/lhr-solar/USBCPowerPCB/blob/v1.0/TPS56A37.xlsx, the appropriate component values are as follows. 15/20V → 12V
12V → 5V
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ORring Diodes:
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