Other Parts Discussed in Thread: PCM3168
Hey everyone, i got two questions about a combination of the PCM3168 and the TPA3251.
First one, using a direct connection only with a single set of DC-Blocking Caps should work as i think. The PCM has a dif-Output with 8Vpp, the TPA a gain of 10, therefore the PCM is able to drive the amplifier into clipping (assuming a +-36V output voltage over the speaker terminals), even so with 0,4V margin on the input.
--> The PCM is used without an additional second order lowpass, but only with a passive first order one.
Should be ok.
The interesting part is no the use of the AC Coupling. Both, the PCM as well as the TPA do use a DC-Bias at their respective terminals, so using an electrolytic capacitor (+ to input of TPA, - to output of PCM), might be possible, the Cap is then biased with around 1,4V. My question which arises now:
The Capacitor is not biased enough for a full voltage swing, assuming an instantaneous fullscale output of the PCM, 5V is applied on the negative terminal, whereas only 3,9V is applied to the positive one, resulting in a negative voltage of 1,1V. This may not be fully applicable to audio applications, but im afraid using an electrolytic like this might increase the THD strongly in the "zero crossing". Does anyone have experience here? Or someone of the TI Staff who can help out with some hints here?
Second Question here, since the TPA is supplied up to 30V, the input voltage margin now increases to 1V, and i want to use the remaining margin to apply some PFFB with only a small influence on the input.
--> i will be using the suggested network (R, CRC) of the latest appnotes for this, but i do not use an additional OPA between the PCM and the TPA, therefore i cannot fully take over the app-note. Can this result in a stability problem or any other problems? I cannot use an additional OPA in my application due to size restrictions.
Thanks alot,
best regards,
Lukas
Second one,