Searching suitable quadruple op amp as buffer for ADC

Wolfgang Schwarz

Other Parts Discussed in Thread: LMV324, LM7705, LMV844

Hello,
I searching a suitable rail to rail quadruple op amp with minimum offset and a negative rail swing very close to GND. I want to use two of them as buffers for an ADC (MCP3204).
I have a 5V single supply voltage and tried to use the LMV324 - but the output swing of the negative rail is about 50mV without 0V signal input.
That is to much for my application because it's a zero based measurement. Is there an opamp with better data for my application or what can i do instead?

Note:
I need rail to rail because i want to drive with the other two op amps two logic level Mosfets. In fact this capability is working with the LMV324

Best Regards
Wolfgang

over 6 years ago

0 Michael Steffes over 6 years ago

Guru 48395 points

Hello Wolfgang,

Not sure any RRO part actually goes to 0V with good linearity. There might be other devices that get closer than 50mV, but for true swing to ground consider the LM7705 which was intended precisely for this kind of thing. It is very low cost and can support multiple devices easily.

0 kai klaas69 over 6 years ago

Guru 140200 points

Hallo Wolfgang,

even if you will find an OPAmp which seems to fully go down to 0V at the output, the performance of OPAmp like open loop gain, settling time, etc. can heavily detoriate.

Have you thought about using the LM7705? It will generate a -0.232V negative supply voltage for the OPAmp and by this keep the OPAmp always in its linear range.

Kai

0 Wolfgang Schwarz over 6 years ago in reply to Michael Steffes

Prodigy 40 points

Hello Michael,
thanks for your answer. I will have a look at the LM7705.
Another idea was go away from RRO and use an other device without RRO capability with better offset. Make then the power supply for the op amp a little bit higher approx 8 or 9V. So i get enough headroom to drive the Mosfet and having no problems with my zero based measurement.
I still thinking what is the best way.
Wolfgang

0 kai klaas69 over 6 years ago in reply to Wolfgang Schwarz

Guru 140200 points

Hi Wolfgang,

what MOSFET? Can you show a schematic?

Kai

0 Wolfgang Schwarz over 6 years ago in reply to Wolfgang Schwarz

Prodigy 40 points

Hello Kai,
thanks for your advice.
If i use the LM7705 with a RRO op amp and with 5V single supply voltage, do you know a device with a pinout like the LMV324 but with a better offset voltage?

Wolfgang

0 kai klaas69 over 6 years ago in reply to Wolfgang Schwarz

Guru 140200 points

Hi Wolfgang,

have you had a look at the TI's products page?

www.ti.com/.../products.html

Kai

0 Wolfgang Schwarz over 6 years ago in reply to Wolfgang Schwarz

Prodigy 40 points

Hello again,
the Mosfet is a BUK954R8-60E. And it needs 3,9V Ugs for fully open in my application.

Wolfgang

0 Michael Steffes over 6 years ago in reply to Wolfgang Schwarz

Guru 48395 points

well Wolfgang, you might look at the LMV844

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Searching suitable quadruple op amp as buffer for ADC