TSU101 Op. Amp. operation problem

[DKarl.4]

Hi All,

I have used ​TSU101 op. amp.as a comparator in my design. Output of opamp is used to drive relay through mosfet. My problem is when i connect power supply to my board o/p of comparator change for fraction of second and again work correctly as per design. My question is why op. amp switch it's states initially when powered up.

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Thank You.​

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[Pierre SENNEQUIER]

Hi,

Would you please have a scope capture including the power supply, the inputs and output of the op amp ?

Before the op amp reaching its operating condition (during power up), there is no guarantee of its output state.

Also, depending on the shape of your output signal, could it be related to the slew rate of the op amp ? (as it is not a comparator, its switching time is much longer)

Best Regards,

Pierre

[DKarl.4]

Hi,

I have captured all the waveform you have mentioned.

There is small change in o/p when power-up you can observe it. Output switch to 0V for around 200ms. We are not getting why this is happening.

Pl. see the circuit: here, +VIN3 = 12V.

What can be done for the solution? & why it is happening?

Thank You,

Dipesh

[Pierre SENNEQUIER]

Hi Dipesh,

At the beginning (below ~1V), the output is high and follows the power supply which is below the guaranteed minimum operating range.

Then the output is low because the voltage on the non inverting pin is lower than the reference voltage on the inverting pin.

During that period of time, IN+=0.38x3.3VDC and IN-=1.19V (from the moment when the input ESD protection diode is not conducting).

So, the output remains low until 3.3VDC=1.19/0.38=3.13V, which is what you get in your waveform.

It means that the observed behavior is normal.

Thanks and regards,

Pierre