THVD1400V: Pull-up and pull-down resistors for logic lines

Hi Matteo,

So all the logic inputs have integrated bias resistors to set a default state - that means on DE, /RE, D, and SLR you only need to apply an external bias resistor (pull-up or pull-down) if the default state of the device is opposite of what you want.  10k is generally fine for bias resistors. 

DE is pulled down internally and by default will keep the driver off unless DE sees a high level signal on its pin. 

/RE is pulled up internally and by default will keep the receiver off unless /RE is pulled to ground - if you wish receiver to be on in a default state than a external pull-down is needed

D is pulled up internally and by default will output a high between A and B if driver is active (DE = Logic High) - so unless you can't have a default "high" on the bus when "D" is floating and DE is held high I wouldn't imagine you'd need an external bias resistor here. 

SLR - it is pulled down internally and will have slew rate limiting off by default - if you want to enable slew rate limiting you need to pull it up externally (which you are) - so if you want this device to be slew rate limited keep your pull-up on this pin. 

For the logic output R - the device itself does not need a pull-up or pull-down on "R" as "R" is a push-pull output. However, protocols like UART will require a pull-up on the "R" pin - as without it an interrupt is usually send causing communication failure - so in many applications this is pulled up. 

Currently you have the device set to the following default conditions:

Slew rate limit: on (pulled up)

Receiver: on (pulled down)

Driver: off (pulled down)

Driver input: Low (pulled down)

Receiver output bias: High (pulled up - this is needed for some protocols like UART)

This will take 4-5 resistors (if /RE and DE are shorted than only 4 resistors) - if this is the default setting you want. I'd honestly remove the pull-down from the driver input "D" as it does have a default state (high) and unless you need the default to be low it most likely isn't necessary to add a bias resistor here. 

Please let me know if you have any other questions - but essentially this device requires 0 to 1 bias resistors if the enables are separate where the only required one is on "R" to VCC if the protocol demands a default value of "HIGH"  on the "R" output. Other external resistors can be added if the default state doesn't match intended goals. This does change slightly when /RE and DE are shorted together as in that case an external resistor is needed to set a default state. 

Best,

Parker Dodson