Hi all,
I have designed a push-pull converter using the LT3999 controller. During testing, I monitored the UVLO, SS, and SWA pins using an oscilloscope.
I observed that although switching at the SWA pin begins when the UVLO voltage reaches approximately 1.25 V, the soft-start capacitor connected to the SS pin begins charging when the UVLO voltage is approximately 0.62 V.
My understanding was that the internal circuitry would become active only after the UVLO threshold had been reached. In the LTspice simulation, the SS pin begins sourcing current when the UVLO voltage reaches 1.25 V. However, this does not appear to be the case in the physical circuit.
Could you please confirm whether this behavior is expected, or whether it may indicate an issue with the circuit?
I look forward to your response.
Thank you in advance.