LMC662: About LMC662 with voltage follower circuit.

user6018337

Part Number: LMC662
Other Parts Discussed in Thread: TLV9002

Hello.

I made a circuit with a voltage follower circuit with a single 5V power supply using LMC662.

When the input voltage exceeds about 3.5V, the output voltage jumps to 5V.

Is this suspected oscillation?

Can you tell me anything else to doubt?

Regards.

over 4 years ago

0 Bala Ravi over 4 years ago

TI__Expert 6625 points

Hi User,

This is happening because by applying an input voltage close to rail you're forcing the op amp to operate in the saturation region. To avoid this, you need to make sure to not violate the input common mode range of the op amp. LMC662 has an input common-mode range of (VCC - 1.9V) to (VEE - 0.4V). For your case of 5V supply; the input common mode range will be from 3.1V to -0.4V.

If your application requires a rail-to-rail input op amp, please refer to TLV9002.

Regards,

Bala Ravi

0 user6018337 over 4 years ago in reply to Bala Ravi

Prodigy 140 points

Hello,

Thank you for the reply.

Data sheet says "Rail to Rail", so my usage was not enough to pay attention to "Input common mode range".

I will promote the exchange to TLV9002.

Regards,

0 kai klaas69 over 4 years ago in reply to user6018337

Guru 140200 points

Hi,

the LMC662 can do Rail-to-Rail output voltage swing. Or by other words, It's a "RRO" OPAmp. But you need an OPAmp which can also handle Rail-to-Rail input voltage swing. This would be a "RRIO" OPAmp :-)

Kai

0 user6018337 over 4 years ago in reply to kai klaas69

Prodigy 140 points

hello kai

thank you for the explanation.
I understand the essence!

regards

0 Bala Ravi over 4 years ago in reply to user6018337

TI__Expert 6625 points

Hello User,

Please let us know if you need any additional rail-rail input/output part recommendations. I will go ahead and close this thread for now.

Regards,

Bala Ravi

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LMC662: About LMC662 with voltage follower circuit.