WEBENCH® Tools/MC3403: MC3403DR Output Problem

User,

Is the measurement incorrect in simulation or incorrect with a real MC3403?
The output should be 4V

real mc3403

Be sure to check other pin voltages at the MC3403 pins, especially pins 2, 3, and 11.

11 is gnd so it is 0, 2. pin 2.64v 3. pin is 0.45v

User,

Thanks, that is helpful. Inverting input voltage is much greater than non-inverting input, therefore the correct response is for output to go low. For that to happen pin 11 must be low and it is low. Pin 2 voltage matches output voltage and feedback resistors so feedback is good. Pin 3 is 0.45V, is your input still 1V? That is a big difference.

So how often does this happen? Is it just one sample or many?
If you have not already done so, try changing the MC3403 IC with a fresh one. MC3403 is an old device, and ESD damage is possible.

hmm okay i will change it and let you know tomorrow. because i saw it just now the output never changes always 10v

Changed nothing. But i noticed this, ihe output of DAC121C085 is connected to mc3403 and if i read the output of  dac  then the output of mc3403 is become normal. What cause that ?

User,

Perhaps the physical contact of measuring caused a poor connection to become good.
Do you get the same result measuring at the DAC pin and the MC3403 pin?

I thought that too but it is not about poor connection i am sure. It is more likely dac needs a load and mc3403 doesnt do that. when i use multimeter dac sees a load and starts producing voltage