TPA3255 / TPA3251 / TPA3245 Rev.1B Final
In continuation / expansion of implementations based on the TPA3255 / TPA3251 / TPA3245 now the final approach of amplifier design for the Akita family. Differently to the past designs , the analog front end is now implemented on a dedicated circuit board powered by a balanced supply. This results in the ability to provide different approaches of signal input/suppl<. For example, it now is possible to directly feed the amplifier with I2S by i.e. a PCM5242 .
This post is in continuation to the following articles:
A first trial assembly before the boards were fitted.
2 boards with an AFE module each were built up. One was locally measured and valued, the other went to "Voltwide", member of the forum "stromrichter.org".
The supply of the AFE module (analog front end) and AVCC of TPA32XX is done by a LM5017 in flybuck configuration for +/-12V. The converter runs at approx. 850kHz, far outside of the audio spectrum.
Measured values / performance
Supply analog +/-AVCC
For the LM5017 in flybuck configuration there are these +/-AVCC ripple plots:
The RMS ripple is less than 10mV, without any ripple no COT would work. Related to +/-12V, the ripple is less than 0.1%. With additional 100n, the ripple at the AFE pinheader shows up as follows:
There's an additional RC filtering followed by a fedd-trough capacitor on the AFE module.
2mV ripple equals ro 0.017%, relative to AVCC = 12V. In the AFE related OPA1654 offer 30dB PSRR at 850kHz, with better than 65dB in the 20 kHz audio band.
The design delivers the following performance on 3.8Ohm load resistance:
Plots for 3.8Ohm load in BTL at PVCC = 51V, 600kHz AFE module with minimal PFFB at 1 kHz and for different frequencies:
Utilizing prefilter PBTL, connecting the TPA32XX outputs together right before the output filter, result in even lower values. The test setup:
Measurements taken with a load of 5.0Ohm connected at PVCC = 30V without PFFB and AFE module:
The following can be achieved with a load of 10.0Ohm:
In the same form factor (10x10cm), an LLC power supply module was developed by "Voltwide" which provides 50V for the powerstage and 12V AUX. A unit in 10x10x10cm results with the appropriate bolts.