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SN65LVDS049: Datasheet question: Is Table 2 - Receiver Truth table correct?

Josefin Strahl
Prodigy 60 points

Part Number: SN65LVDS049

When I look at Table 2 "Receiver Truth table", I get confused.

In column one it says "Rin- - Rin+" 

I interpret the other pictures in the datasheet, for example Figure 6 and Figure 11 in such a way that Rout follows Rin+. So if Rin+ is "high", then Rout is high.

However, when I look at receiver truth table, it says that if Vid>=100mV, then ROUT is high.

If I take the following example:

Rin- = 350mV

Rin+ = -350mV

Then "Rin- - Rin+" = 350 - - 350 = 700mV. 700mV > 100mV, so ROUT should be high. But Rin+ was negative. This tells me that according to the truth table, the ROUT is inverted compared to Rin+??

When looking at the figures and reading the datasheet my assumption is that ROUT is following Rin+ so if Rin+ is high, then Rout is high.

Could you please clarify if ROUT follows Rin+ or Rin- ?

Is the truth table in Table 2 incorrect or am I just misunderstanding something?

BR

Josefin 

  • 0
    TI__Prodigy 60 points

    Hello Josefin,

    When looking at the truth tables, Table 1 – Driver Truth Table lends itself to logic, in which: Dout+ follows Din, and Dout- inverts Din if the enable is on in both cases.

    Table 2 – Receiver Truth Table, however, is not as simple and requires for the user to know that Vid = Rin+ -  Rin-, or the input voltage difference. Once the difference is worked out the truth table does lend itself to logic if Vid >= 100mV => H or Vid < -100mV => L, anything in between is considered high impedance (off).

    The datasheet does have a mistake in Table 2 - Receiver Truth Table, it should say Rin+ -  Rin-, which is probably what confused you. Thank you so much for catching this! 

    The table below shows that Rout does not follow Rin+ or Rin-, but rather the conditions on Vid discussed in Table 2. 

    I also saw that you mentioned Figure 6, which shows Rin- = 1.3V and Rin+ = 1.1V, this is another typo that should be Rin+ = 1.3 V and Rin- = 1.1 V, consequently Vid= 200mV. Figure 6 illustrates Rout going high (as is expected) since Vid>100mV and it is emphasizing the propagation delays. 

    I think the origin of the typos, by looking at the block diagram, is that the Rin+ and Rin- are switched for R1 but do not let this trick you, Vid = Rin+ - Rin-. 

    Thank you again for catching our mistakes, we will make sure to fix them in the next revision. 

    Hope this was helpful, 

    Carolina