OPA551: OPA551

OPA551 -15V 02222024.TSC

Hi Yvan,

Yes, you may use OPA551 with a single supply. If you want to generate -15Vdc, you may implement something below or similar. Please pay attention to the input Vcm requirements. 

OPA551 -15V 02222024.TSC

If you have other questions, please let us know.

Best,

Raymond 

Thank you, but what I really needed to know was if the amplifier operates properly with just one power source.

Second query.

Is it stable with a gain of 1? Or is a gain of five preferable?

Hi Yvan,

OPA551 as the buff does not have great phase margin. The phase margin is approx. 47 degrees. Technically, it is ok, but if the output has any parasitic capacitance, the phase margin would be even less as a buffer. 

If the circuit configured in Gain = 3V/V, it may work out better with phase margin at approx. 60 degrees (do not use CF or 100nF feedback capacitor). If the output is driving capacitive load, it would require further loop compensation, which the same as Gain = 1V/V above. 

OPA551 -15V AC Analysis Gain3 02222024.TSC

Best,

Raymond

Hello,

First question:

We also use the OPA551 as a current generator as shown in the attached diagram.
The gain =0.1 and in relation to the phase margin of the OPA551, do we have a risk of oscillation (not found in simulation)?.

Second question

You can be sure that the amp works correctly with a single power supply. Section 9 of the datasheet contains recommendations, but there's nothing to indicate that it should work between V+ and GND.

Thank you for your help.

*****************************************************************************************

Power Supply Recommendations

For applications that do not require symmetrical output voltage swing, power-supply voltages do not need to be
equal. The OPA55x can operate with as little as 8 V between the supplies or with up to 60 V between the
supplies. For example, the positive supply could be set to 50 V with the negative supply at –10 V, or vice-versa.

Howland Current Pump With Buffer.docx

Hi Yvan,

DRUILHE yvan said:

The gain =0.1 and in relation to the phase margin of the OPA551, do we have a risk of oscillation (not found in simulation)?.

The constant current source/sink seem to be stable from the simulated modes. 

OPA551 Howland Ipump Stability Analysis 02232024.TSC

The step transient behaviors look good as well. 

OPA551 Step Transient behavior 02232024.TSC

DRUILHE yvan said:

Section 9 of the datasheet contains recommendations, but there's nothing to indicate that it should work between V+ and GND.

All our op amps are specified in these similar verbiage.

Most modern op amps do not require GND in order to work, where ground typically refers to as an earth or chassis reference. Modern amplifiers can work without GND (in a floating configuration). In other words, it can be boot strapped in a middle of higher voltage supply rail, as long as the following requirements are met. For instance, if OPA551 is used to operate within 100V supply rail, as long as (V+) - (V-) does not exceed 60Vdc (using zener or other voltage clamping device) and it does not violate the absolute max. ratings, the op amp will operate normally. 

If you have other questions, please let us know. 

Best,

Raymond