How to decide the Amplitude of the Ramp in DC-DC converter?

[sudheer_vlsi]

Hello all,

How to decide the Amplitude of the Ramp in DC-DC converter? What is the problem if we choose very less amplitude or more amplitude? Is it going to create any problem on the PWM comparator or Error Amplifier specifications?
Please answer me.

 

[VVV]

Re: How to decide the Amplitude of the Ramp in DC-DC convert

The larger the ramp amplitude the better, since the circuit becomes less prone to noise pickup. (Volts are less sensitive than millivolts).

On the other hand, too large an amplitude will require an unreasonably high supply voltage. Threfore, an amplitude in the order of 2-3Vpp should be OK.

 

[sudheer_vlsi]

Re: How to decide the Amplitude of the Ramp in DC-DC convert

Hi VVV,

if the peak-peak amplitude of the ramp is too low,then i think its going to place stringent specification on the resolution of the comparator,because if the output of the converter changes,then its duty cycle has to be adjusted,which means error amplifier output has to be adjusted within that ramp amplitude and hence the comparator has to resolve very very small changes in the error amplifier output.
is my explanation correct?
Thanks for ur reply.

 

[VVV]

Re: How to decide the Amplitude of the Ramp in DC-DC convert

Yes, you are right, the smaller the ramp, the harder the task of the comparator.

 

[sudheer_vlsi]

Re: How to decide the Amplitude of the Ramp in DC-DC convert

Hi VVV,

If the amplitude of the ramp is more,then the error amplifier output swing must be high to get 0 to100% duty cycle.but it has some supply related problem.if the amplitude is too low,it will relax the swing of error amplifier.but sensitive to noise.This also can be considered in our designs,Right?