OPA548: OPA548 works with bipolar power supply

user5363809

Part Number: OPA548

Hi support:

OPA548 works with bipolar power supply (+9V and -2.5V), the schematic diagram is as follows

Question 1:

When the output voltage of OPA548 is higher than V2, the op-amp shows positive voltage and current, that is, in source mode, it can output normally;

When the output voltage of OPA548 is lower than V2, the op-amp shows positive voltage and negative current, that is, in sink mode, it can not work normally, and it beats back and forward when it is put on shutdown and current limiting output;

The above schematic diagram remains unchanged. Change -2.5V to direct grounding, and it can work normally in sink mode.

How to realize source or sink mode according to the above schematic diagram under the condition of bipolar power supply?

Problem two:

The connection of the enable terminal is shown in the figure above. Under a single power supply, the operational amplifier can be switched on and off.

However, under the condition of bipolar power supply, the switch on and switch off control cannot be realized normally.

Under bipolar power supply, does the control enable terminal need special treatment?

over 3 years ago

0 Raymond Zhang1 over 3 years ago

TI__Guru* 76461 points

Hi user5363809,

The attached schematic is not going to be stable while driving the capacitive load directly. The phase margin is only approx. 13 degree. Please let me know your design requirements so that we can fix it. Op amps do not like to drive large capacitive load directly and it will introduce a 2nd pole inside of the feedback loop and make the feedback loop unstable.

The 0.1uF capacitor should be connected after the 10Ω series resistor, but it is necessary to check the phase margin with an actual load. What is the load and driving application?

How to realize source or sink mode according to the above schematic diagram under the condition of bipolar power supply?

The op amp feedback loop will make sure the output is following the input for a given gain. In addition to the OPA548's input and output requirements, also see the datasheet, the output voltage swing is a function of source or sink current.

For V3 = 3V, Vp = 6V, Vp > Vo, this is a current source mode, where Iout = (Vp - Vo)/R5 = (6-4)/10=200.5mA.

If Vin = -0.5V, Vp = -1V, this is a current sink mode per the configuration, where Iout = (Vp - Vo)/R5 = (-1 -4)/10 = -0.5 A. Please see the Iout and the current flow direction, which is negative or inward.

OPA548 E2E 06302022.TSC

However, under the condition of bipolar power supply, the switch on and switch off control cannot be realized normally.

Under bipolar power supply, does the control enable terminal need special treatment?

It is not clear what the Vo voltage is described in the above conditions.

I will assume that the OPA548 is powered with 9V/-2.5V rails and E/S is disable the op amp's output in the following discussion.

When E/S is in disable status, the output stage is disconnected from the load. For single or dual supply voltages, you need to implement current steering schottky diodes as shown in Figure 38. The ESD protection diodes are designed at the output of OPA548, where the output pins are required to be protected with the external current steering schottky diodes (turned on faster than the OPA548's output ESD protection diodes).

Regarding to the output E/S pin, you need to follow the datasheet and voltage status logic to enable or disable the OPA548's output.

If you have additional questions, please let me know.

Best,

Raymond

0 Raymond Zhang1 over 3 years ago in reply to Raymond Zhang1

TI__Guru* 76461 points

Hi user5363809,

I am going to close this inquiry.

If you have additional questions, please let me know.

Best,

Raymond

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OPA548: OPA548 works with bipolar power supply