Buck Conveter Design Issues

[pjohn]

Hi, I am designing a Buck converter, which has the following requirements.

Vin = 12v-14v
Vout = 3.3v
I load = 160mA

I need some guidance and information regarding stability and phase margin.

I have different options for choosing the IC,

Option 1: ADP2302: 2A, 700KHz NonSynchronous Step-Down DC-DC Switching Regulator

Option 2: LM2841, 300 mA, 500KHz, Step-Down DC/DC Regulator

As my load only needs 160mA I would be tempted to go with Option2,LM2841, but LM2841 has Phase margin of 33 degree where as Option1, ADP2302 has phase margin of 66 degree to 56 degree over different x frequencies.

I do not exactly understand the role of phase margin in designing buck converter. If I go for option1, with better phase margin, will the device be okay to deliver me 160mA, despite being rated 2A, without any ripples in the system.

Please help me understand phase margin of buck converter and stability relation between IC current rating and load current requirements.

Thanks in advance

 

[huzuhong525]

Wikipedia has your want.

 

[pjohn]

I could not find any thing on wikipedia

 

[TekUT]

The question issued is very important regarding the power supply stability, I think you can also take a look into the National Semiconductor web site at this address:

**broken link removed**

on the right you can fill the form with your design data in order to have some help into the device selection and other things also regarding the stability of your design.

Could you please let me know from where came the two design outlined into your post? Do you've designed the Buck by using the State Space Averaging transfer function (Middlebrook) or by using some other way?

Bye
Pow

 

[FvM]

Looking at the step responses given in both datasheets, your statement about phase margin differences isn't understandable. I wonder, where you´got the numbers, and if the setup has been similar in both cases. Capacitor ESR is e.g. a parameter, that has a large impact on phase margin. Both switchers are intended for low part count designs, where you are stuck with the given fixed internal loop compensation. But I would assume, that it has been choosen reasonable for both chips.

I'm not used to ADI as a player on the switcher market, but National's Simple Switchers have been previously known to deserve the name.

 

[leo_o2]

LM2841 will have better efficiency. Phase Margin is OK.