Hello,

i'm doing a project that has a SMPS to step-up a couple AA to 5V.
The SMPS is a TI TL499A. Has a linear and switch regulator inside the
package.

The project transmits pre-recorded audio from a ISD recording chip, through
a 2-pole low-pass pre-amplifier @~4kHz.
The other sound source is a ~1kHz PWM from the PIC, that is also
pre-amplified by a 2-pole low-pass @~1.2kHz, to smooth the wave.

And i still get noise of the SMPS on my audio output.
The audio noise from the ISD is like a smooth crackling (frying).
The audio noise from the PWM is of a very high frequency.
The audio noise is proportional to the switching freq of the SMPS. The lower
the batteris, the noisier the audio get.

When i power the circuit through the Linear regulator inside the chip, all
the switching noise disappears. Its very clean.

Does someone have an idea of what i can do/should improve on my design ?
Any ideas welcome, thanks.

Kind regards,

Antonio Sergio Sena




-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist