The WS28xx series of LED drivers are (were?) made by Worldsemi, but there does not appear to be a datasheet for the WS2813 available on the site (yet). It seems that another company, Shenzen Normand Electronic Co may be the manufacturer. Maybe it is a copy or a clone... The datasheet can be found here.
In any case, page 2 states that data at
DIN are compared.
BIN is used in the event
DIN does not receive valid data. It is not well-written; here is the relevant section:
The BIN receives the data signal, and then compare the data with the DIN side after phagocytosis of 24bit data, if DIN do NOT receive the signal, then switching to BIN for receiving the input signal, which ensure that any the IC's damage does not affect the signal cascade transmission and make the BIN in state of receiving signal until restart after power-off.
I'm amused by the inclusion of phagocytosis, a biological process whereby cells can "eat" large particles by engulfing them. I presume this is a bad translation that refers to the process of receiving and checking the 24-bit data packet common to the WS28xx family of LED drivers.
The main purpose of this is not to operate a second LED strip, but rather to allow a single contiguous strip to tolerate failed pixels.
Image from Elecrow.com
Essentially DIN is a primary data input and
BIN is a backup, just as you described. The datasheet does not specify how
BIN should be connected (or left disconnected) if the backup data function is not wanted.
Based on what I was able to find, it appears that you could easily connect data to both
BIN, and if one of the driver ICs fails, it appears that
DO will still pass whatever data was received at
If you prefer to not use this pin, you could connect it to ground as some suggest. You may want to test whether connecting
BIN to ground causes any additional current to flow, should that be a concern in your project. It could be that it is best left floating (not connected) instead. Measure to be sure.