OPA187: OPA187 is a rail-to-rail amplifier but the output voltage swing are +/-3V

Danilo A.

Mastermind 25555 points

Part Number: OPA187
Other Parts Discussed in Thread: OPA188

Hi Team,

We have received this inquiry from our customer,

I don't understand the OPA187's output voltage swing vs output current. Is it a rail-to-rail amplifier?

This is the OPA188's, it clearly show that it is an rail-to-rail amplifier, but the OPA187's diagram makes me confused

It seem's that the max output voltage is +-3V

Thank you for your support!

Regards,

Danilo

over 2 years ago

0 Michael Steffes over 2 years ago

Guru 48185 points

Well Danilo,

These output stages are physical defices with their own internal resistance. As you ask them to deliver more current that IR drop in the output devices adds to the required headroom for linear operation - this is called a claw curve and this performance metric is included in the newer models. This I/O swing issue comes up so much, both Bruce Trump and I tried to address in seperate articles,

https://e2e.ti.com/blogs_/archives/b/thesignal/posts/swinging-close-to-ground-single-supply-operation

And then a planet analog article on this topic,

https://www.planetanalog.com/input-and-output-voltage-range-issues-for-high-speed-amplifiers-insight-1/

0 Raymond Zhang1 over 2 years ago

TI__Guru 51701 points

Hi Danilo,

Is it a rail-to-rail amplifier?

Yes, OPA187 is RRO amplifier as the datasheet presented when R_load = 10kΩ that is connected to Vout = mid supply of Vs or 0.5Vs.

OPA187 presents the Output Voltage Swing vs. Output current under different test conditions. The Figure 11 is referenced to maximum supply voltage in OPA188, while OPA187 in Figure 10 is referenced to Vs = ± 2.75Vdc (missing the actual Vs test conditions, which is mentioned in Michael's recommended articles).

If you have additional questions, please let us know.

Best,

Raynibd

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OPA187: OPA187 is a rail-to-rail amplifier but the output voltage swing are +/-3V