TEA1755LT

[madariagal]

On item 7.3.5 of the TEA1755 Specification, it says that "Under normal operating conditions, the converter regulates the output voltage. Vfbctrl varies between 0.77V at minium output power and 4.9V at maximum output power."

What are the events or conditions that will make Vfbctrl > 0.77V?

[madariagal]

The question should be "What are the events or conditions that will make Vfbctrl < 0.77?" and not Vfbctrl > 0.77

[TomasVaverka · Accepted solution]

Hi Lorenzo,

I am not very familiar with the TEA1755, but I had a look anyway:

 

Often during load step testing the regulation will give some overshoot, because of a small delay in reaction to an external event (current load step). If the output voltage becomes a bit too high because the current suddenly decreases from maximum to zero, the feedback will react by strongly reducing Vfbctrl (for lowest power level). It will show an “undershoot” below 0.77V for a short time that will hold the switching until the output voltage has dropped to near the regulation level again and the system continuous in Burst Mode operation.

In short: at load step / transients.

Best regards,

Tomas

[madariagal]

Hi Tomas,

Thank you very much for the insight. In a regular burst mode operation the Vfbctrl is somewhere around 2.5V with switching frequency of about 36kHz with burst frequency of around 600hz. The statements that you mentioned are all correct.

However, I am experiencing a strange behavior in the FBCTRL whenever I increase the load (from NL to a certain light load say 0.11A).

Here's the waveform.

As I increase the load, a [Sub-Burst mode frequency of 3.7Hz with 100ms FBCTRL blanking] appeared which causes the output to go unstable.

Is this a normal phenomenon?

Warm regards,

Lorenzo