According to the data sheet for the OPA2227P, the max supply voltage is 36V and the recommended operating conditions are +/-2.5 to +/-18. Is it okay to have a voltage supply of 24V to 0V (GND)? What are the pros and cons?
Also is -24V to 0 (GND) okay for this op amp?
Hi Rodney,
From the voltage supply perspective, the OPA2227 can be powered by a unipolar supply with +24V and 0V (GND). However, the circuit designer needs to be aware of the op-amp input and output voltage range, and headroom limitations to ensure the device operates properly within its linear range.
The OPA2227 input common-mode voltage range is delimited from (V-)+2V to (V+)-2V, or requires a headroom of 2V from the supply rails:
Similarly the OPAx227 output has to remain within its linear region. Looking at the OPAx227 open-loop gain (AOL) specification, the OPAx227 output swing is limited to (V-)+2V < OUT < (V+) - 2V from the supplies while driving a 10kOhm load:
For example, when using the OPA2227 in the buffer configuration (G=+1) while powered by a +24V unipolar supply, with a 10kOhm load, the op-amp supports signals +2V above GND, to a maximum of +22V.
You can also look at a rail-to-rail amplifier, such as the OPA2197, where the OPA2197 supports input common-mode just slightly above and below the supply rails, (V-) - 0.1V to (V+) + 0.1V, or input common mode of 100mV below and above the supply. However, even rail-to-rail amplifiers such as the OPA2197 still require headroom for output swing. The OPA2197 requires about ~300mV headroom from the rails with a 10kΩ load per the AOL specification, so it would support signals of +300mV above GND to +23.7V while powered with a +24V unipolar supply.
If the application requires to support a bipolar signal with voltage levels below GND, you will need to power the amplifier with a bipolar (+/-) supply.
Please review the TI Precision Labs Amp tutorial section 3.1 to 3.4. This TI Precision Labs - Op Amps Series training video addresses operational amplifier input and output limitations. The tutorial sessions discuss op amp common-mode input voltage, input and output voltage swing limitations, and show how to determine the source of circuit errors caused by these limitations.
https://training.ti.com/ti-precision-labs-op-amps-input-and-output-limitations-non-linear-behavior
Thank you and Regards,
Luis
HI Rodney,
When connecting the OPA2227 in the inverting configuration G=-1, powered with supplies V+ = 0V and V- = -24V, and connecting the non-inverting terminal to GND, the input common-mode is outside the input range specification. The input common-mode in this circuit is right at 0V (GND), same voltage as the positive (V+) supply.
The OPA2227 allowed input common-mode voltage is delimited from (V-)+2V to (V+)-2V, or essentially requires a headroom of 2V away from the supply rails:
A suggestion would be to power the amplifier with +/-15V bipolar supplies. Alternatively, asymmetrical supplies such as +5V and -24V can work as well, placing the amplifier with its input and output inside the linear range.
Thank you and Regards,
Luis
