THVD2410V: Internal circuit for hot plug-in and failsafe

Hi Nishie,

I can't give you the internal circuits of our devices - its our IP so we don't share that outside of TI. 

I can give you a high level description of how it works - which is really all you need to design with the part. 

1) The glitch free power-up and power-down for hot plug  applications means that if the driver and receiver are disabled during power up you won't have a glitch. By default DE is pulled low and /RE is pulled high internally to the device - which means by default the device is disabled so during power up / power down that you would see in power-up and power down. The caveat on this device is that it is assumed that VIO is active during the hotplug because there is a direct connection from logic inputs to VIO - if this is unwanted than the THVD2410 is the better option because essentially it removes the VIO supply - the VIO supply is what causes this caveat to be mentioned. 

2) The receiver fail-safe on this device is timer based. Meaning if the input differential voltage is between -40mV and 40mV for t(OFS) then the receiver will output a high -during idle/open/short VID = 0V - so that time period is how long it takes to enter a fail-safe state. The value of t(OFS) depends on the state of SLR pin in the application as it does impact the delay value - this is listed in the switching characteristics of the receiver in the datasheet.  How this works in practice is if for example you are transmitting a logic low when a fail event occurs - lets say a short - the VID will go from < -200mV to 0V at this time the "R" pin will be continue outputting a "low" signal - if the VID remains between -40mV and 40mV for t(OFS) the "R" pin will then output a logic high and will continue until it leaves the -40mV to 40mV range and if t(FSO) has passed the "R" pin will follow VID input - please note that t(FSO) is different than t(OFS) - both listed in the same section of datasheet. 

Best,

Parker Dodson

Hi Nishie,

So hot plug can refer to the module being placed into a live backplane or it could include plugging an active RS-485 bus to an unpowered device. 

I believe your question is focusing on the second side - when just data is sent to an unpowered RS-485 device - in that case the RS-485 bus by standard has to be able to handle -7V to 12V inputs - and that is regardless of VCC state. So the RS-485 bus as required by standard is hot pluggable by that definition. This device specifically can handle up to -70V to 70V regardless of VCC state. I apologize I didn't make that clearer - but teh RS-485 bus pins are already hot-pluggable due to how the bus facing pins need to be designed. You may see a slightly different loading from these pins when VCC = 0V because an internal bias network is turned off without VCC, but ultimately it is hot-pluggable in that sense. 

Best,

Parker Dodson

RS-232 uses point-to-point connections, so it does not need to care about any ongoing communication while (un)plugging.

RS-232 receivers must be able to tolerate ±25 V. You should already have ESD and surge protection, depending on your environment; this will be enough to allow hotplugging.

Hi Nishie,

Clemens is correct. 

Best,

Parker Dodson