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TLC2274: Question about opamp's feature and rail to rail

Shen Zed
Prodigy 225 points
Part Number: TLC2274
Other Parts Discussed in Thread: OPA4991, TL3474, OPA4191, OPA4192, OPA2156

Hi, I usually used TLC2274 for op-amp as buffer circuit.

(Connecting In- to Out. Gain = 1)

I want to use more faster slew rate op-amp with rail to rail.

. 

So I searched in the TI Hompage,

And I found there are some different kinds of rail to rail features as below.

1. In to V-

2. In, Out

3. In to V-, Out.

.

TLC2274 has rail to rail feature as In to V-, Out.

Here are my questions. 

.

1. What is different between In to V-, Out  //  In to V-  //  In, Out.

.

2. And what is High cload drive mean?

.

   I want to use same feature as TLC2274 and more slew rate. (going to use as just buffer circuit. connecting V- to Out directly)

3. And please, Could you recommend any op amp that has faster slew rate the TLC2274 and has same feature?  (4ch, 2ch, 1ch don't care)

.

Thanks.

  • 0
    Guru 140200 points

    Hi Shen,

    "In" means that the input voltage range is from rail to rail, or by ther words, from "V- to V+".

    "In to V-" means that "V-" is included but not "V+". For the TLC2274 this means that the input voltage should stay 1.5V away from "V+". Or by other words, for the TLC2274 the input voltage range is "V- to V+ -1.5V".

    "Out" means that the output voltage swing is from rail to rail.

    "High Cload Drive" means that the OPAmp can drive bigger capacitive loads compared to standard OPAmps before becoming unstable. Sometimes it can also mean that the isolation resistor needed for stable operation with a big capacitive load can be smaller than with a standard OPAmp.

    See also figure 57 of datasheet of TLC2274.

    Kai

  • 0
    TI__Guru 55491 points

    Hi Zed

    1. What is different between In to V-, Out  //  In to V-  //  In, Out


    In, Out means Rail-to-Rail Input/Output or RRIO = In, Out, example is OPA4991 in the table

    In to V-, Out  means the input Vcm can be as low was V- only, and output is Rail-to-Rail Output, example is TLC2274 in the table

    In to V- means the input Vcm can be as low as V- only, example is TL3474 in the table

    .https://www.ti.com/lit/an/sloa039a/sloa039a.pdf?ts=1596113415042&ref_url=https%253A%252F%252Fwww.google.com%252F

    2. And what is High cload drive mean?

    Cload means capacitive load at the op amp's output. Any capacative load at op amp's output can potential introduce another pole within a feedback loop. Ideally, op amp roll off at -20dB/decade. A second pole within the feedback loop will introduce -40dB/decade roll off, which it may create instability in the closed loop. Large Cload means that the op amp stability is not affected without further compensation. Here High Cload is a relative term, may be in an order of 1nf range. 

    I want to use same feature as TLC2274 and more slew rate. (going to use as just buffer circuit. connecting V- to Out directly)

    3. And please, Could you recommend any op amp that has faster slew rate the TLC2274 and has same feature?  (4ch, 2ch, 1ch don't care)

    How about OPA4192, OPA4191 or OPA2156? We have many op amps that can meet >3.6V/usec. If you provide me the op amp's application and cost requirements, I can do a refined search.  

    Best,

    Raymond

  • 0 in reply to kai klaas69
    Prodigy 225 points

    Thanks for the detailed answer. Very helpful to me.

  • 0 in reply to Shen Zed
    Guru 140200 points

    You are welcome :-)

    Kai