TDA1562Q low freq roll-off - diyAudio
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Old 9th November 2009, 04:47 PM   #1
DrLex is offline DrLex  Belgium
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Default TDA1562Q low freq roll-off

I'm looking into using the TDA1562Q. The datasheet only gives a concrete value for the high-frequency roll-off and states "The low frequency power roll-off is determined by the value of the electrolytic lift capacitors." Unfortunately there is no mention of what value is needed to obtain a certain frequency, or what the roll-off is for the 4700F caps shown in the application circuit.

Does anyone have an idea what would be a good value for C1 and C2 to get a -1dB roll-off at about 30Hz?

Or is there anything equivalent, i.e. another IC that can deliver a similar amount of power into a 4Ohm load on a supply up to 24V?
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Old 9th November 2009, 05:32 PM   #2
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The -1 dB point is more or less twice as high as the -3 dB point. The -3 dB point can be calculated with f = 1 / (2 x PI x R x C). R is 75 k according to the datasheet. 150 nF capacitors on each input should give you the desired roll-off.
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Old 9th November 2009, 06:43 PM   #3
DrLex is offline DrLex  Belgium
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Yes, that's for the input capacitors. But for this IC, the 'lift' capacitors C1 and C2 also affect the (power) bandwidth and I would like to know how. The datasheet for the similar TDA1560Q contains a table with values versus frequency, but the datasheet for the TDA1562Q doesn't.
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Old 9th November 2009, 09:42 PM   #4
gfiandy is offline gfiandy  United Kingdom
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Hi you could try the TDA7498 this will supply 60W into 6R on 24V at 10%. So theoretically it will supply 90W in 4R off the same supply - however due to extra losses in the PSU output inductors etc this theory never works but you will probably still get your 70W.

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Andrew
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Old 9th November 2009, 10:29 PM   #5
DrLex is offline DrLex  Belgium
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Thanks for the suggestion, that is indeed a chip with good-looking specs. Unfortunately it's only available in SMD. Last time I had to solder a chip with 0.65mm pitch I almost went crazy already, and it only had 10 pins. Something with 36 pins is out of the question. I have found some other class D chips like the TDF8599B or the TPA3120d2 which also look promising, but again in the same hobbyist-unfriendly packages.
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Old 10th November 2009, 03:17 PM   #6
DrLex is offline DrLex  Belgium
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I should have mentioned that the 4Ohm load is actually two 30W 8Ohm loads in parallel because I need to feed an identical signal to two speakers. In other words, two amps that can deliver 30W in 8Ohm are also OK. And behold: the TPA3122D2 delivers almost exactly that at 24V, and it is in PDIP. Gotta love TI!
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Old 10th November 2009, 07:42 PM   #7
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Quote:
Originally Posted by DrLex View Post
Yes, that's for the input capacitors. But for this IC, the 'lift' capacitors C1 and C2 also affect the (power) bandwidth and I would like to know how. The datasheet for the similar TDA1560Q contains a table with values versus frequency, but the datasheet for the TDA1562Q doesn't.
Step the up by the same ratio as the input capacitors. The datasheet gives 4700 F lift for 100 nF input. So for 150 nF input use 6800 F lift, for 220 nF input use 10000 F lift, etc.
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Old 8th December 2009, 02:37 PM   #8
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The TDA1562 apparently just has a higher current capability to handle 4 ohm loads. So ( boost ) supply capacitance should be about double that used for TDA1560Q.
The TDA1560Q says for -3dB at 10 Hz you need 4700uF and input cap of 560nF. As Pacificblue mentioned -1dB is about 2x the -3dB frequency.

So for -3dB at 15 Hz ( -1dB at 30 HZ ) you need about 370nF ( 0.39uF ) at the input and something between 4700 and 3300uF for the supply cap. This would need to be double at 4 ohms and so 10,000uF recomended by Pacificblue sounds appropriate.

I lost my TDA1560Q ! So I never got round to trying out my sub amp !
I bought a new TDA1560Q today ! Since Murphy is always around I will find the first TDA1560Q chip after all components are soldered on the board !
One day Murphy will be shot .
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Last edited by ashok; 8th December 2009 at 02:40 PM.
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