Hello,
I am trying do get basic functionality of this IC following pdf datasheet and online Designer tool as calculator, but looks like it cant maintain constant voltage and ~1V at FB pin. FB pin keeps at ~1V only when there is no load. When connect any load, LED, or some resistor of ~4 Ohms, output voltage drops and stays there, and FB pin voltage drops, of course. For example, in my case with this values (on picture) of components, I get, no load output voltage ~6.8V and FB pin is ~1V; when connect 3.9 Ohm resistor as a load, output drops to 3,6V. Input is Li Ion battery, voltage ~4V. Should not this IC keeps output voltage constant (as can be seen in MPSmart simulator for MP3429 spice model)? Input and output capacitors are tantal.
and here is pcb, designed following pdf datasheet suggestions with some small simple modification:
Big fan of demo boards, they can save you days and days. do you have one?
Hi dosentnd,
Schematic & PCB looks good overall.
There could be several things to consider here if the output is unstable at lighter loads, is this problem occurring at all loads, did you try checking that?
Sometimes, the converter may become unstable and oscillate when there is insufficient load, changing the output voltage.
What is your battery current? Is it a good quality battery?
Can you share some of the waveforms from your oscilloscope such as Input & Output voltage, inductor current, Switch node voltage, output ripple, so that it will be helpful for me to interpret what is happening exactly ?
How does your inductor design look likes? I hope the inductor is not saturating.
In the mean time, I would recommend to start adding a couple of ceramic capacitors at the input & output along with a single electrolytic capacitor of 10uF for extra filtering purpose & stability which has low ESR values.
Regards,
Adhish
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