SN65HVD1781-Q1: SN65HVD1781-Q1 VS SN65HVD1781A-Q1

Alex L said:

What is(are) the difference(s) between SN65HVD1781-Q1 and SN65HVD1781A-Q1 ?

Regarding SN65HVD1781-Q1 ("A" version DS is the same):

I don't see any major differences between these two devices. 

Alex L said:

What is the max. |Vod| for 4.75V <= Vcc <= 5.25V, Rl= 60 Ohm ? (DS, page 5, ch. 5.6)

I'm not able to find the repository where the validation data is kept since the device is so old.

Technically the max datasheet value could be capped at Vcc. In actual practice there are diodes infront of both the PFET and NFET which would cause a voltage drop and reduce the VoD as more current is drawn. The best approximation you could probably draw is by looking at the differential voltage vs. differential load current graph (Figure 6-3 in the A version). Looking at the Vcc=5.5V at 60 ohm load the VoD is 2.4V. Which means the voltage drop across the diodes+driver  FETs are 3.1V. You could probably carry this approximation across the 4.75 to 5.25V range. 

Alex L said:

What is the ohmic value of the pulldown on DE pin ? (DS, page 14, ch. 7.4) 
What is the ohmic value of the pullup on D pin ? (DS, page 14, ch. 7.4)
What is the ohmic value of the pullup on ~RE pin ? (DS, page 15, ~RE left open)

From what I was told by design, they want to aim for a very low leakage current on the pin and these resistors are not trimmed. So I'm told the approximation could be 2M ohms with +/-35% tolerance. 

Alex L said:

Are R1 and R2 resistors in Fig. 8-4 recommended or optional only ?

They are optional. They provide some additional protection to the driver during large transient events but the downside to using them is they will lower the max data rate and the max cable distance the device can achieve without them.

Alex L said:

Regarding TVS, is it recommended or optional only ?

Optional as well. Same reason as above, adds more protection but adds some additional capacitive loading to the bus. Typically external TVS diodes can handle more power than what is on the die of the device so adding it can be helpful.

Alex L said:

And what is the min. Voh (on R pin) for 4.75V <= Vcc <= 5.25V for 8mA ?

You're probably overthinking this, the R pin should swing to Vcc in most applications. The only time it wouldn't if you actually applied a load that caused it to be forced to drive a current (like directly tying it to an LED). In most situations the R pin is tied directly to the Rx of a processor. So the minimum wouldn't really matter.

If you wanted to calculated it could just assume that the value provided can get you the Ron of the PFET on the R pin. Then you could just do 2.4V/8mA to get the Ron. Then use that in whatever load you are assuming is on R.

Alex L said:

2.4V as stated on the datasheet? (DS, page 5, ch. 5.6)
i.e. for Rl = 2.4V / 8mA = 300 Ohm ?

Yes, this would assume a worst case condition for Ron when you use the VoH minimum. This is probably a worst case number since the datasheet recommended operating condition includes 3.3V in the spec for VoH.

Alex L said:

Then, what is the (approx.) loading to have Voh>= 3V ? 

What type of load are you anticipating is going to be on the R pin?

-Bobby

Hi Alex,

Bobby is out of office for the rest of this week. He will return next week.

In the meantime, I can answer some of your questions. The "A" version does come with the Functional safety documentation. The "A" version does share the same base design as the non-A version, but it has some additional silicon processing changes to further improve it's reliability. They are still functionally the same, and they are still made in the same fab/AT site. 

Best,

Ethan