LTC6373 Output Amplifier Supply

Hi,

the LTC6373 has a nice option with the V+OUT pin for the supply of the output amplifier, where one can have a high supply voltage like +-15V for the input amplifiers in order to have a large input voltage range, and have a lower supply voltage for the output amplifiers in order to protect the inputs of the ADC driven by the differential amplifier.

Unfortunately, the IC somehow misses the complementary V-OUT pin.

Was this option omitted during the chip design, or is the V-OUT node just bonded down to the V- pad because of lack of a 14th package pin?

If the latter is the case, will there be a version with the V-OUT brought out to a pin using a different package with more available pins?

Best Regards,
Gerd

Parents
  • 0
    •  Analog Employees 
    on Oct 18, 2020 12:40 PM 1 month ago

    Hi Gerd,

    Upon checking with the primary contact for the LTC6373. A separate output negative supply wouldn't add much in terms of functionality, because the LTC6373 already have the capability to shift the output common mode voltage via the Vocm pin.

    The LTC6373 is a fully differential output, which is why the two outputs will always be symmetrical around Vocm; therefore, it's not possible for one output to swing more than the other. 

    May I know the reason why you're looking for a separate V-OUT pin? Or do you have any specific application in mind for this kind of use case?

    Thanks,
    Donnie

Reply
  • 0
    •  Analog Employees 
    on Oct 18, 2020 12:40 PM 1 month ago

    Hi Gerd,

    Upon checking with the primary contact for the LTC6373. A separate output negative supply wouldn't add much in terms of functionality, because the LTC6373 already have the capability to shift the output common mode voltage via the Vocm pin.

    The LTC6373 is a fully differential output, which is why the two outputs will always be symmetrical around Vocm; therefore, it's not possible for one output to swing more than the other. 

    May I know the reason why you're looking for a separate V-OUT pin? Or do you have any specific application in mind for this kind of use case?

    Thanks,
    Donnie

Children
  • The LTC6373 is a fully differential output, which is why the two outputs will always be symmetrical around Vocm; therefore, it's not possible for one output to swing more than the other. 

    So if the more positive output goes into limitation because of the V+OUT voltage, the other output will also saturate, so that the common mode output voltage does not deviate from VOCM?

    Also if the more negative output goes into limitation because of V-, the more positive output would be limited accordingly even if there would be enough voltage at V+OUT for the more positive output to go higher?

    May I know the reason why you're looking for a separate V-OUT pin? Or do you have any specific application in mind for this kind of use case?

    There are two purposes for a separate V-OUT pin:

    1. Saving power consumption and heat generation, because you can apply like +-5V or 0V to +5V for the output stage for ADCs with such input voltage ranges while being able to supply +-15V for the input stage to accommodate an according wide input voltage range.

    2. Decoupling the power supplies for the input stage from the ones for the output stage. So the output current would not be drawn from the same supplies that power the input stage which would reduce possible influence from the load current/resistance towards the input signal.

    Another interesting point would be a possible availability of this amplifier in a gull wing package (like a TSSOP 14, where there also would be a 14th pin available for a V-OUT input in case that was available on the chip level but being bonded to the die pad together with the V- pin in the DFN package).
    Although the DFN packages having the advantage of being smaller than a gull wing package with comparable pin count, the DFN packages are more susceptible regarding temperature cycling because of no lead being there to take the thermo-mechanical strain.
    So for applications with according reliability requirements a gull wing package would have great benefit.