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Original question:

TLV170: TLV170/171/172 Reduced performance for full rail to rail input.

TLV170: Full output swing characterization

Ryanton
Prodigy 85 points
Part Number: TLV170
Other Parts Discussed in Thread: OPA170, LM7705, TLV771

I'd like to know if there is a full characterization of the "voltage output swing from rail" by RL value. The datasheet only characterizes this by RL=10k but does guarantee this over the operating temperature. In my application I am measuring ~39mV output voltage to the rail. The spec calls out 200mV to the V- rail at RL=10k. Is there a chart that characterizes this? I would like to use this part in my design, but I need a guarantee that I am operating within spec or if I just have a high performing batch of TLV170s.

  • 0
    Guru 47535 points

    Hey Ryanton, 

    The 200mV headroom is what you will need to observe as a worst case negative rail headroom, 

    This TLV170 is a stripped down (support and specs) version ofthe OPA170. While that datasheet isn,t much clearer, there is apparently a big effort to update these older models where the newest files show key performance tests, here is the pertinent plot from the new model file for the OPA170

    If you need that 39mV output on I am guessing single supply and ground, use the LM7705 - intended for exactly this requirement

  • 0 in reply to Michael Steffes
    Prodigy 85 points

    Yes sir, single supply and ground. Thanks for the recommendation, but I need to operate at +12V and looking for a SOT23-5 package. My RL application is 100kOhm. Is there data that defines the V- to rail output voltage at this RL value?

  • 0 in reply to Ryanton
    Prodigy 85 points

    Looking at the OPA170 spec, I would be ok if the TLV170 could be defined for IL sinking as well. If you could define IL for 500uA, that would be perfect. I could even handle 1mA if it is favorable.

  • 0 in reply to Ryanton
    Guru 47535 points

    So the changes in going to the TLV170 is to considerably relax a lot of the DC test limits, including output swing. While few devices might be any worse than OPA170 - those can ship with the much worse headrooms in the TLV170 datasheet. So the basic issue is you need single 12V supply RR out where the negative headroom is < 39mV - keep in mind if you have gain, the feedback is a load as well. On paper, the no load negative supply headroom TLV771 "over temp" will not make that. The OPA170 output swing with that Aol caveat shows about 0.35V. That is one common test of output swing limits, re-test Aol at the spec limit - so the OPA170 probably sets up the output at 0.35V from rails and retests that the Aol is still real good (DC gain accuracy). That is normally a 25C test but that spec line is over temp, so undoubtedly a sim. 

    Most of the degradations appears to be the over temp headroom, if you don't have that to consider, might make it. 

  • 0 in reply to Michael Steffes
    Prodigy 85 points

    The maximum output voltage to negative rail I need to stay under is 70mV across the operating temperature. Is it possible to request this data from the TLV170 to verify my application? Define the output voltage swing from rail across operating temperature for IL=500uA?

  • 0 in reply to Ryanton
    Guru 47535 points

    Topologically, if you are sourcing that current from the upper side of the output stage, it should probably be ok, but on paper, the TLV170 does not support that, 

    Unlikely you will get a special spec - but the product line will need to reply

  • 0 in reply to Michael Steffes
    TI__Guru*** 140126 points

    Hello Ryanton,

    I'll reverse engineer the specification in previous post for you. Sinking VOL is 200mV with +/-18V supply; load is 10k to mid supply. Therefore load current is at least (18V-0.2V)/10k = 1.78mA. This is equivalent to a 200mV/1.78mA = 112.4 ohms output on resistance. With a 0.5mA sink current the worst case VOL would be 112.4 ohms * 0.5mA = 56.2mV

    For lower Vs voltage, on resistance can be higher, but I expect no difference between 12V and 36V supply. For multi channel op amps, having some channel(s) at high sink current can raise the internal V- voltage, so that the VOL of other channel(s) can be elevated some even at no sink current.