Choosing a power supply for an ST510A device

[jorge]

Posted on July 17, 2015 at 23:24

Hello,

I'm setting up a system with a STA309A DSP and a STA510A amplifier.

I'm expecting to connect two 8Ω loads with a maximum power of 50W each, but I can't find the graphics that show the estimated Power dissipation and the THD that I can expect at that level. The datasheet for other parts like the STA518A do have figures that allow me to calculate that. 

Is there an application note that describes how to calculate the required power supply for a specific power output?

 

[Nickname1623_O]

Posted on July 20, 2015 at 03:25

Hi Jorge ,

sorry, the applicaiton note is not available in ST website , but you can calculate it by following equation :

I peak = Vcc*MI/(Rload+2*Rdson)  ---- for BTL ,  current will go through two mosfet  , MI is modulation index , for STA309A , it would be 94% for calculation . for STA510A or STA518 , Rdson is 0.2.

P @ 1% THD =1/2 *((I peak)^2)*R load

P @ 10% THD = 1.28 * P@ 1% THD .

then for your applicaiton , if 50W output is for 10% THD , then the unclipping output would be 39W =( 50/1.28) , and the max peak current through  8 ohm load would be 3.125A .

so the Vcc  (supply voltage ) would be  27.9V = ( 3.125 *8.4/0.94).

considering the tolerance and loss in coil and trace , 28.5V would be enough for your target output power .

Thanks ,

YT

[jorge]

Posted on July 21, 2015 at 02:27

Hello YT,

Thanks for your very helpful response.

I'm looking at STA518A datasheet and I see in Figure 17 that at 39W, the power dissipation is about 9W. Does that mean that if I use a 28.5V power supply I would need it to be able to supply a current of approximately 9W/28.5V = 315mA?  Or am I missing something?

Thanks,

Jorge

[Nickname1623_O]

Posted on July 21, 2015 at 04:15

Hi Jorge ,

the fig 17 is output power vs dissipation power curve , when the output is 39W x2 , the power dissipated inside IC die is 9 W , the total power from power supply is 87W , means that the efficiency of power amplifier is around 90% =39*2/(9+39*2) .

so for 50W x2 output , the power supply should be able to deliver 112W to audio amplifier , and the supply voltage is 28.5V ,then the output current should be 3.93A .

then to reach the target output power ,the specification of your power supply should be 28.5V ,4A .

Thanks ,

YT

[jorge]

Posted on October 06, 2015 at 06:26

YT,

As always, your answers are spot on! A couple of additional questions come to mind:

1. If I switch to a STA311B and a STA516B using FFX mode, would that change the formulas and the values I need to use?

2. If I use the PSCorrect feature of the STA311B, how much improvement in the THD I can get?

Best regards,

Jorge Rivera

[Nickname1623_O]

Posted on October 22, 2015 at 09:12

hi Jorge ,

it will not changed with STA311B+STA516B soultion in FFX mode .

the PSC feature aimed to improve the noise from power supply with high output powr , you may get 0.8% improvement in lower audio band ( below 1Khz ) .

thanks ,

YT