UC1901-SP: UC1901-SP

Hey Paul,

Unfortunately it was determined that we were unable to give the data asked for offline.

Thanks,
Daniel

Daniel, I am doing some detailed analysis of the circuit using this part, I have a few questions

1. What happens if the feedback input voltage is lower than that of the worst case ic. internal reference voltage, for example my worst case feedback voltage is 1.36V compared to 1,45V worst case internal reference voltage.

2. since the duty cycle and switching frequency is fixed, how does the ic. response to the feedback voltage that is above or lower the internal referenced voltage

3. How does the referenced voltage tolerance impact the output drive voltage with the added temperature tolerance, will the output drive voltage be increased or decreased due to the added tolerance impact.  

Hey Paul,

1. The way you would use this part is a closed loop converter correct? Thus whatever control device should try to bring them as close as possible. How would your control device handle this?

2. Its done through amplitude modulation.

3. The output drive voltage changes in general as this is amplitude modulation. The graph you are referring to is the peak swing which doesnt have much to do with reference voltage tolerance.

How are you currently using this part?
This part is best seen as an error amplifier with a amplitude modulated output.

Thanks,
Daniel

I am using the part to drive a transformer, used to cross the ground boundary to close the loop, I have a 5V output with a 4% tolerance, I am using 0.1% resistors in the FB divider. The method I am implementing is very similar to the examples in https://www.ti.com/lit/ds/symlink/uc1901.pdf?ts=1712620883411, fig. 4. 

I have corner cases where my FB voltage exceeds the 1.515V reference voltage, I observe that the model will not run when I exceed this FB voltage, what happens in that case? 

1. The way you would use this part is a closed loop converter correct? Thus whatever control device should try to bring them as close as possible. How would your control device handle this?

   ***The part is being used in a FB closed loop for an isolated Forward converter, if I exceed the max ref voltage per the datasheet, does the part simple rails out to max amplitude voltage? also what if I am lower. 

2. Its done through amplitude modulation.

****What is the peak amplitude and what drives/controls it 

3. The output drive voltage changes in general as this is amplitude modulation. The graph you are referring to is the peak swing which doesn't have much to do with reference voltage tolerance.

****What does the refence voltage control?, because in the model, if this exceeds the max reference voltage, it will not run, or rather the output voltage across the ground boundary, the output of the transformer is 0Volts 

****Does my FB voltage have to be within the range of the reference voltage range displayed on the datasheet or the model is simply broken, that is why it will not run outside this range.

This is a replica of my implementation, I need a secondary voltage to regulate a reference of 2.5V, how can I drive the amplitude to increase the drive voltage?

Hey Paul,

I would look at this for reference:
https://www.ti.com/tool/TIDA-070002

You can just bias the voltage on the secondary side to help.

Thanks,
Daniel

Daniel, this is identical to how I am using this part, but I am required to perform some detailed analysis and really need these questions answered.

I have corner cases where my FB voltage exceeds the 1.515V reference voltage, I observe that the model will not run when I exceed this FB ref voltage, what happens in that case? 

1. The way you would use this part is a closed loop converter correct? Thus whatever control device should try to bring them as close as possible. How would your control device handle this?

   ***The part is being used in a FB closed loop for an isolated Forward converter, if I exceed the max ref voltage per the datasheet, does the part simple rails out to max amplitude voltage? also what if I am lower. 

2. Its done through amplitude modulation.

****What is the peak amplitude and what drives/controls it 

3. The output drive voltage changes in general as this is amplitude modulation. The graph you are referring to is the peak swing which doesn't have much to do with reference voltage tolerance.

****What does the refence voltage control?, because in the model, if this exceeds the max reference voltage, it will not run, or rather the output voltage across the ground boundary, the output of the transformer is 0Volts 

****Does my FB voltage have to be within the range of the reference voltage range displayed on the datasheet or the model is simply broken, that is why it will not run outside this range.

Hey Paul,

I observe that the model will not run when I exceed this FB ref voltage, what happens in that case? 

The model is unfortunately not great.

Does the part simple rails out to max amplitude voltage? also what if I am lower. 

The part's amplitude will move up and down with the error amplifier output.
The error amplifier output will move up and down with the reference voltage.

What is the peak amplitude and what drives/controls it?

Its listed in the datasheet and its variation with temp.

Thanks,
Daniel

Daniel, Can you please take a swing at the model to see why it would work when the vref tolerance is exceeded, can you have someone from your model development to look at it.

Thanks 

Hey Paul,

This particular model model was created before standard model validation procedures were adopted. it may not have been validated for your operating conditions as the results it is producing do not appear to be valid.

Unfortunately you will not be able to use the model to validate what you are trying to test.

Thanks,
Daniel