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LM25007: LM25007 Switching power supply does not start if a rpre-bias voltage of 2.5V is applied to the output.

Mathias Gabler
Prodigy 10 points

Part Number: LM25007

After the LM25007 switching power supply, customer have a 3.3V LDO to generate the voltage for their microcontroller. These can be fed to an external power supply or just about the LM25007 switching power supply. If they externally supply their microcontroller comes somewhere a pre-bias voltage of 2.5V on the output of the LM25007 switching power supply and then the LM25007 switching power supply does not start.

I have tried Solution No. 3 from Application Note AN-2129 Boot Capacitor Regulation in LM25007 Constant-On-Time (COT) Converter. This solution works fine, but the output ripple without the assembly with the 50K and the 10V Zener diode in my design is about 20mV. After the assembly with the 50K and the 10V Zener diode I have an output ripple of 120mV.


This high output ripple is too high for us, we need the low ripple.

Has anyone on the forum other ways to get in spite of pre-bias voltages to start the power supply?
Or a solution to minimize the high ripple after the solution from the application Note?


Best Regards

Mathias