A couple of questions in regards to this chip
1)How do you connect more than 4 speakers to the device (we are looking at 6 speakers)
2)Can we use the output to drive a higher power amp section
You use 2 LM48901s.to achieve 5-8 speaker outputs. Each LM48901 has 4ch output - more channels requires additional devices. We support up to 4 LM48901s resulting in 16 speaker channel output.
For details about connections/programming please refer to the datasheet pages 43-44. http://www.ti.com/lit/ds/symlink/lm48901.pdf
There are 2 ways to do this.
1. Filter the class D output back to an analog signal. Then use analog input Class Ds of your output power requirements. We can reccomend a TI class D if you share your requirements.
2. Utilize the analog input of the LM48901. Then you can use the digital output (I2S) to go to external I2S input Class Ds We can reccomend a TI class D for this as well.
Thanks for the reply...In regards to Question #1 thanks for pointing out that page in the spec sheet. In regards to Question #2, we plan on using both the Analog inputs along with the I2S inputs so it seems the only option is Option #1 - filter the class D outputs back to an analog signal. Our power requirements are
We are also considering combining the Mid and Woofer to operate below 300 Hz. Also any suggestions on filtering out the Class D outputs would be very helpful
Take a look at TPA3110D2... It's a little below your power points, but CHEAP. Next up is TPA3100D2 which can do 20Wx2, but a lot more expensive.
As for the filtering, I'm not an expert on the LM part, but I'd assume if you used a resistor in series with each input, with a cap across them (on the chip side) forming a first order LPF you'd be set.
Audio Applications Engineering Manager
Dallas, TX USA
I would recommend a passive RLC low pass filter. Select a resistor value ~200-300ohms so you don't load down the 48901, but still allowing you to use reasonable inductor values to achive a desired -3dB rolloff around 60-90kHz. If noise is an issue, you may have to go to a higher order filter, or add an active filter circuit after the RLC.
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