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TDA7492P Load Impedence

max2
Associate

‎2015-05-08 02:17 PM

Posted on May 08, 2015 at 23:17

Hello, I am designing an Audio Amplifier that is capable of connecting to 4 ohm, 6 ohm and 8 ohm speakers. I need to be able to run at an output of 25W at 25V so I decided to go with the TDA7492P. For reference, I have puchased the 50W and 20W Evaluation Boards and everything is great so far.

Question: The reference design of the 20W Amp shows the following image.

0690X00000602eRQAQ.jpg

BUT! The 20W Evaluation Board has a 33uH Inductor and a 220nF Capacitor and it claims to work from 4-8ohms at the top of the design and further on down in the datasheet it says 6-8 ohms. This has me very confused and I would like some clarification. According to the picture above, This should only support 8 Ohms. Otherwise the other loads will be much louder.

If I use a 220nF Cap with a 33uH inductor, will I get my design to work equally from 4-8 ohms or will I need 3 different set ups to support 4, 6 and 8 ohms?

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Nickname1623_O
Associate II

‎2015-05-10 06:21 PM

Posted on May 11, 2015 at 03:21

hello engineer X ,

the filter LC parameter will affect frequency response of class D amplifier ,due to the filter is LCR filter in fact. so when the load impedance had been changed , the LC parameters should be changed to provide a flat response within audio band. if you used LC fitler for 8 ohm , and connected 4 ohm load,  you will found 2~3 dB attenuation around 20Khz . so if you'd like to support 4~8 ohm load , it's better to choose LC parameters for 6 ohm load .

and another  improtant thing is output current capability of amplifier , if you are going to deliver 25W 1%THD @ 4 ohm load , 16 V  supply is enough , but if you are using 8 ohm load , it's better to provide 22V supply .

due to TDA7492P is slug down package , so the disspation power will be transferred to ambnient from PCB, in case you need to deliver high output power continously , it's better to choose TDA7492 , it's slug up version and external heatsink willl help to keep IC runing with high output power .

thanks to consider ST device .

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