Electronics > Beginners
Resistor on USB D+ and D-
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chancs:
I wish to use CP2102N as a USB to UART interface chip. And in the datasheet, they did not put any resistors in the USB data line. However, when I look at the Arduino UNO wifi ver2, they put 22Ohm resistors on the D+ and D- line. What is the purpose of these 2 resistors? To limit current in case of high voltage spike?


Arduino UNO wifi ver2



CP2102N Datasheet
chancs:
"The Universal Serial Bus function controller in the CP2102N is a USB 2.0 compliant full-speed device with integrated transceiver and
on-chip matching and pull-up resistors." Quote from the datasheet.

They didn't explicitly say impedance matching. But is that what you meant?
Berni:
These resistors also usually help save the chip from blowing up if 5V shorts to any of the data lines(Like a damaged connector or cable)
tszaboo:
FYI, any Arduino is NOT a good source to learn best design practices. Or OSHW for that matter. They copy stuff from each other, without really understanding what is going on. For example it is possible that you need the resistors for FTDI, say FT232D and they just copy it and use it for the FT232H, which doesnt need it, and then it is copied by a chinese engineer, who replaces it with a CP2102N, because it is 5 cent cheaper than the FT232H... And so on.
The difference is that everyone can tell apart a shoddy shed and a proper house, but it takes a bit of insight to spot bad electronics design.
chancs:

--- Quote from: NANDBlog on September 27, 2019, 09:12:15 am ---FYI, any Arduino is NOT a good source to learn best design practices. Or OSHW for that matter. They copy stuff from each other, without really understanding what is going on. For example it is possible that you need the resistors for FTDI, say FT232D and they just copy it and use it for the FT232H, which doesnt need it, and then it is copied by a chinese engineer, who replaces it with a CP2102N, because it is 5 cent cheaper than the FT232H... And so on.
The difference is that everyone can tell apart a shoddy shed and a proper house, but it takes a bit of insight to spot bad electronics design.

--- End quote ---

How about dev board schematic provided by the vendor, like this one (https://www.silabs.com/documents/public/schematic-files/CP2102N-MiniEK-schematic.pdf). I suppose vendor knows what they are doing.
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