LT1368 Oscillation Issues

[MatthewStevenson]

Hi,

I've been given the task of modifying a temperature cutoff circuit by employing the use of a 2 stage opamp circuit which consists of a voltage follower, followed by a feedback comparator circuit with hysteresis as attached in figure 1.

The issue is that if I arrange the circuit into a simple voltage follower as per figure 2, I get oscillation at the output of stage 1. If I changed the opamp to either an AD8062 or a TI part, and changed the resistor values accordingly, the oscillation would not present itself.

I simulated it on LTspice and it works as expected. With 2V at the non-inverting input, I get close to 2V at the output with the voltage follower arrangement in figure 2.

We are using this component on another part of the same board with no issues. Can anybody explain why this oscillation occurs and how to prevent it?

Thanks,
Matt

View attachment voltagefollower.bmpView attachment tempcutoff.bmp

 

[LvW]

Hi Matt,
according to the data sheet, the LT1368 should be compensated with 0.1 uF at the output pin. Perhaps this can improve the situation.

 

[MatthewStevenson]

Thanks,

I must have overlooked that sentence. I will test it out later but it seems that it is needed to compensate for the low slew rate so makes sense.

Regards,

Matt