I want to use the LTC3757 as booster (with a strong NMOST and diode). It's working and it's stable. But when I turn on the load the regulation will get unstable, because:
And now the problem: The half bridge outputs into a tank circuit with a resonance frequency of 150 kHz. And we get a DC load of approx. 0.5A and an AC load of 2A. So there is some energy fed bock into the capacitors. And in this case the regulation of the LTC3757 loses the stable point.
yellow: output ac current, 2A/divblue: output half bridgemagenta: switch voltage (unstable duty cycle)
What can I do? Making the control slower by putting some nF to the compensation network pin. Filtering the feedback voltage divider (I already use 10nF added to the feedback network to get a corner frequency of approx 3kHz)?
Best regards and thanks for the help!
It is normal when the load is switching. LTspice simulation should be able to show the exact behavior.
Ok, if this is normal, the LTC3757 is not a suitable part for this application. And, the simulation does not show a similar behaviour. At least during the first 10 ms.
Try removing all the components connected to the VC pin. Then place a 0.1uF between the VC pin and GND.
I already tried, it gets better: It's stable up to a load of 1.5A AC. Then it get's unstable.
Try cutting the sensing resistor value by half.