tda8945s audio amp

Discussion in 'The Projects Forum' started by smoking 555, Nov 26, 2008.

  1. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    does any body know what capacitors go where on the 8945s audio amp? I looked at the data sheet and its greek to me? do i have to use the 1.5nf caps or can i substitute them with something else? i just need to use it for a audio amp signal in and singal out louder. I cant upload a pic of the data sheet its in pdf and there is something screwed up with my pdf viewer. also should i have to ground pin 6 and pin 7?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    The TDA8945 has an output of only 11.5 watts at clipping into 8 ohms when its supply is 18V. If the supply voltage is less then the output power is less.

    The voltage gain is 52 times so an attenuator is needed if it is fed from the output of another power amplifier.

    The datasheet shows a 10uF capacitor from pin 6 to ground as a ripple filter.
    It shows the pin 7 MODE pin at half the supply voltage by two resistors for muting while the IC is turned on or off to prevent Plop noises, and pin 7 is at the supply voltage for operation.

    The datasheet shows a single 1.5nf capacitor between pin 4 and pin 5, two 220nF input capacitors, a 100nF supply bypass capacitor ands a 1000uF capacitor in the power supply's output.
     
  3. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    "It shows the pin 7 MODE pin at half the supply voltage by two resistors for muting while the IC is turned on or off to prevent Plop noises, and pin 7 is at the supply voltage for operation." ------can I just connect pin 7 to the supply voltage? not too concerned about the plop noise.


    "The datasheet shows a single 1.5nf capacitor between pin 4 and pin 5, two 220nF input capacitors."

    I cant figure out the 220nf caps how does that work? I'm trying to swap out the lm386 for a bigger amp that runs on 6 volts.
     
  4. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    I can hear the sounds but its very quiet I think its stuck in mute mode. how can i get this thing to start barking?
     
  5. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    found out the problem. i just dont have enough power to run the 8945. after giving it 7 volts dc it got louder but just barely. does any one of a good replacement for the lm386 that has more power, and can run at 5 volts well? is it possible to hook 2 lm386 together and boost output wattage?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    I looked at the NXP datasheet for your amplifier; it infers that pin 7 needs to be <0.5v to get the amp into operate mode which is opposite of what AudioGuru suggests.

    I don't know if AudioGuru is mistaken or the NXP datasheet is in error. The standby mode documentation on that same sheet doesn't quite jive with mute and operate mode info.
     
  7. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    I can get it to operate by taking pin 7 and grounding it. but it isnt very loud at all. I'm hitting it with about 7 volts. according to the data sheet it says that in mute mode it will produce "no audio output." so i know its operational because it is putting out sound just very quiet. is there a better amp that runs on 5 to 7 volts and puts out 5-10 watts?
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The datasheet for the TDA8945 shows a minimum supply voltage of 6V and an output power at clipping into 8 ohms of only 0.7W.
    The datasheet for the LM386 shows a 6V supply and an output power at clipping into 8 ohms of only 0.2W.
    If two LM386 amps are bridged then they get hot and they cannot deliver enough current for a higher power output.

    A TDA2822M is a bridged amp in a small 8-pins package. Its output into 8 ohms at clipping is 1.1W whan its supply is only 6V.

    A bigger speaker is much more sensitive than a tiny speaker.
    Amplifiers produce much more power output when their supply voltage is higher.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Fig. 13 in the same NXP datasheet confirms that if pin 7 is held high, the amp is in standby; at 50% Vcc it's muted, at <0.5v it's in operate.

    See the attached; lower left corner. If C1 from the uC is a logic high, the base of the NPN transistor is pulled high, which shorts pin 7 to GND.
     
  10. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    that explains why it only works when its grounded. it looks like the TDA2822M might be my only choice.
     
  11. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    is there another chip that is more common? just checked digikey and I'ld have to buy about 1000 or so. thats not good.
     
  12. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    just checked digikey its a nonstocked item. i would have to pick up about 1000 of them. thats not good. is there any other amp chip options?
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    There are many places to buy parts.
    Newark has 181 in stock of the TDA2822M for $.48US each. The minimum order is 1.
     
  14. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    very cool!! the TDA2822M has a total of 4 inputs would i just have to use one set? or could i just jump pins together? the lm386 makes pretty good noise but like you said .2 watts compared to 1.1 watts seems a huge improvement. is there an easy way to put this into my circuit? I'm looking at the application data and its mind numbing.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Look at Fig. 2; test bridge circuit.

    Replace RL with your speaker.

    Note that C1 is 10uF and C2 is 10nF (0.01uF)
     
  16. smoking 555

    Thread Starter Member

    Sep 21, 2008
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    ok thats the way I'll go. thanks audio guru. and a special thanks to you sgt wookie for helping me through this project from begining to end!!! just one last question on the TDA2822M whould i have to build r2,r3, and c4 and c5?
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    Why do you ask?
    The amplifier won't work properly without them.
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    R2/C4 and R3/C5 comprise what are known as Boucherot cells to supress high frequency oscillations that might otherwise occur.

    See this Wiki entry:
    http://en.wikipedia.org/wiki/Boucherot_cell
     
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