WEBENCH® Tools/TPS54160A: TPS54160A

Hi

No. 20 equation is Compensator DC gain,the open loop DC gain is around A0*Adc(equation 14)

Thanks

Daniel Li

hi Daniel Li,

Thanks for the reply,

Taking the following value :

vout=3.3v       Iout=1.5A       Rload=Vout/Iout = 2.2       gmps=6 A/V       gmea=97 uA/V       Ro=100Mohms (calculated from datasheet)

R2= 10Kohms      R1=31.6Kohms

Now when i calculate the low freq gain as suggested by Daniel i got Gain= 89.76dB .

But it's not matching with the webench stimulation value which is 75.31dB and it keep on changing when i change components value other then the value mention above.

I have also noticed that on changing Cc value in stimulation from 1nF to 4.7nF low frequency gain changes from 84.37dB to 75.31dB.

So the question arise here is that  does low frequency gain value depend upon Cc?

Hi 

you DC gain will be right at 0.1Hz, there is a pole in the compensator which equal to 1/(2*pi*Cc*Ro), based on you setting, 1nF with 100Mohm, the pole is at 1.59Hz, so at 10Hz, the gain will decrease 15.96dB, which is 89.76-15.96=73.7dB.

you can also check 4.7nF, based on rough esimation, it will be reduce -13dB at 10hmz compare to 1nF

hi Daniel,

thanks for the reply,

But still i am not getting your answer.

I am calculating it as follow:

pole at 1.59Hz converting it to radian/sec i.e (2*3.14*1.59 = 9.99 rad/sec) and now using the formula 

dc gain = 20log(A0*Adc) - 20log(9.99) [ as we have a pole at w=9.99 so -20dB slope]

dc gain = 89.76 -19.9 = 69.7dB

I am not getting 15.96dB what am i doing wrong can you please explain.

Thank you.

HI 

you don't need change to radian. For 1nF, 100Mohm, the pole at 1.59Hz, you are check the gain at 10Hz, the gain will decrease by 20dB from 1.59Hz, so at 10Hz, it will decrease 20log(1.59/10)=-15.972

Thanks

Hi Daniel

Thanks for the reply

I got what you have done but why are we calculating gain at 10hz is there any specific reason?

Also by taking 4.7nf  and 100Mohms i got pole at 0.334hz and at 10hz i am getting -29.52dB which doesn't match your answer of -13dB.

And also i have done stimulation on webench using the above described value and i am getting 84.37dB when i use Cc = 1nf, Ro=100Mohms and 75.31dB when i use Cc = 4.7nf , Ro= 100Mohms.

Previously i was using the following formula to calculate DC gain

DC gain = 20log(Ao*Adc) - 20log(w(rad/sec) of pole)

And then used formula suggested by you as

Dc gain = 20log(Ao*Adc) - 20log(freq of pole/10hz)

But using both of this formula i am not able to get the value that is nearer to the stimulation value on webench.

What am i doing wrong? Is their anything that plays a vital role in this calculation and i am missing it.