about RS485 hot swapping

Hello Ishibashi-san,

So the THVD1452 is hot-swappable. The D, /RE, and DE pins do not have a diode to VCC so max voltage is independent of VCC on the single ended inputs and A , B, Y, and Z are all protected up to +/-15V (recommended) and up to +/-18V (absolute max)  independent of VCC. 

/RE has a integrated weak pull-up resistor so the receiver stays high-impedance unless you drive the /RE pin low. 

DE has an integrated weak pull-down resistor so the driver outputs stay high-z unless you drive DE high. 

Y/Z will be high-z as long as DE is low (which it is by default) 

A/B is just a receiver pair and will always act as a load regardless - but  since /RE by default is high (unless driven low) the corresponding "R" pin output will also be high-z. 

So essentially the device when hot-swapped remains hi-z during power up until you actively drive the enables to communicate with the device. 

The only real concerns are as follows - and it won't cause damage but it could cause glitches during hot-swap if this isn't followed. 

1. Do not have an external pull-up on DE - it could cause the driver to turn on during power up which could cause a glitch - the DE pin has an integrated pull-down. 

2. Do not have an external pull-down on /RE - it could cause the receiver to turn on during power up and cause a glitch. 

3. Do not short /RE and DE as the default value during hot swap may be be < 2V and cause an indeterminate device state. 

Please let me know if you have any other questions and I will see what I can do!

Best,

Parker Dodson