88 lines
3.9 KiB
Markdown
88 lines
3.9 KiB
Markdown
# Ethy
|
|
A project to learn how ethernet and the TCP/IP Stack works.
|
|
|
|
## Design
|
|
|
|
Ethy is designed to learn how ethernet and the entire OSI stack functions and
|
|
how it can be used on low-memory devices.
|
|
|
|
This project started in November, so the project is made in a christmassy
|
|
theme by making an LED display driver for a christmas tree over ethernet.
|
|
|
|
|
|
|
|
The block diagram above shows the main components of the system. First of
|
|
all we have the Ethernet chain, which is just a RJ45 connector together with
|
|
the magnetics and a chip to convert data from the microcontroller to the
|
|
differential signals. Another project that attempts something similar uses
|
|
the W5100 but is still a bit of an overkill for what I want to use. The
|
|
less of the process the chip automates the better.
|
|
|
|
The second chain is the USB and power. Although the main way to connect
|
|
to the device will be via ethernet, I still wanted some other way to talk to
|
|
it. Given that the RP2040 has an onboard USB PHY, this seemed the easiest
|
|
way. At the same time the USB PD standard (PD 2.0 and PD 3.0 have
|
|
a selection of easily attainable chips) allows for 100W of power.
|
|
How much of that will or can be used is still being figured out, but it makes
|
|
for an easy way to power multiple LEDS.
|
|
|
|
Lastly, from the USB PD and the RP2040 together power the LED strips. The
|
|
device should both support WS2812B and WS2815B LED strips. Since the user
|
|
may plug in either a WS2812B or WS2815B LED strip, the voltage needed for the
|
|
should be automatically detected. The easiest way of doing that would be to
|
|
use a voltage divider in the same way that the base power profile of the PD
|
|
standard uses it.
|
|
|
|
### USB Power Delivery
|
|
|
|
#### Possible PD chips
|
|
|
|
- STUSB4500
|
|
- STUSB4500L
|
|
- TPS25730
|
|
- TPS25751
|
|
|
|
#### Comparison
|
|
|
|
All of the PD chips can basically run in auto-run mode--also called
|
|
dead battey mode. Since Ethy does not have any battery, the PD devices
|
|
have to be able to auto-configure or atleast allow for the standard 5V
|
|
output of the USB. The STUSB4500 are specc'ed for USB type-C rev 1.2
|
|
(for STUSB4500) and type-c rev 1.4 (for STUSB4500L). Both seem to function
|
|
with the PD rev 2.0 standard. However, according to the STUSB4500 documentation
|
|
it is interoperable with USB PD rev 3.0
|
|
|
|
Both the TPS devices are built for USB PD rev 3.1.
|
|
|
|
The biggest difference, to me, seems to be the control of an external
|
|
power path. The STUSB devices can only function with an external power path
|
|
while the TPS devies also have an internal power path. The biggest difference
|
|
however, is the type of switch that can be used for each chip.
|
|
|
|
The STUSB4500 and STUSB4500L have active drain outputs, meaning that the
|
|
switches should be based on P-channel MOSFETS, as uses in their reference
|
|
design. The TPS devies have an internal charge pump which means they can
|
|
use N-channel MOSFETS. N-channel MOSFETS generally have a smaller footprint
|
|
and smaller R_ds(on) than the P-channel counterparts. This can be seen in
|
|
the reference designs of PD IC's. The TPS chips use the CSD87501L dual common
|
|
drain n-channel from Texas Instruments. This dual channel MOSFET has a
|
|
source-to-source R_ds(on) of 6.6 milliOhm at a Gate Source Voltage of 10 V.
|
|
For the maximum load of 12V @ 5A, the power loss would be around 165mW.
|
|
|
|
Comparing to the P-channel MOSFETS in the STUSB chips, the reference design
|
|
uses the STL6P3LLH6 MOSFET from STM. This MOSFET has a maximum R_ds(on) of
|
|
around 30milliOhm. at 5A this would result in 0.75 W of loss. Considering
|
|
that both designs need two MOSFETS, the loss in the MOSFETS for the STUSB chips
|
|
would be around 1.5W.
|
|
|
|
This difference in power loss can also be seen in the package size, since
|
|
the CSD87501L is half the size of a single STL6P3LLH6 MOSFET.
|
|
|
|
#### Possible DC/DC chips for controllers
|
|
|
|
- TPS56320x (except it only goes to 17V)
|
|
|
|
### Ehternet PHY
|
|
|
|
### LED Strip
|