A circuit diagram was designed using LTspice, as shown in the attached picture.When the voltage on the TK/SS pin changes, so does the output voltage.Can you explain what the problem is?The circuit diagram did not observe the reference,Is there a problem with the design as shown in the picture?The customer says it is working well and wants proof of the problem.
The issue is due to the voltage divider network on the TK/SS pin. For LTM4620A, when the voltage on TK/SS pin is below 0.6V, the FB pin voltage will be regulated equal to the TK/SS voltage instead of the fixed 0.6V, as it is in soft-start state. After the voltage on TK/SS increases over 0.6V, the FB pin will be regulated at a fixed 0.6V, thus allowing the converter output voltage to be regulated at your desired value. In your setup, there is a 3:1 voltage divider between Vref and TK/SS, thus the voltage on TK/SS will be>= 0.6V only when Vref>=1.8V. This is why your output voltage will change according to Vref voltage (TK/SS voltage) when it is smaller than 1.8V and will be regulated at your desired value when Vref>=1.8V.
Hope this helps!
I was moved by your kind reply!
Finally, is the TK/SS and FB of LTM4638 in the same method?
Yes, the LTM4638 Track/SS and FB will operate similarly.