Cadence simulations for switching regulator

[chviswanadh]

Hello,

Please help me out with what type of analysis to choose for verifying the following specifications of a switching regulator

Efficiency

Load Regulation

Line Regulation

Input voltage Range

Output Voltage Rande

Start up time

Load Current

Switching frequency


The design is a Current mode control continuos off time PWM controlled Buck regulator. Please somebody help me with this

Thanks
Kasi

 

[jluhzw]

For the Efficiency , Load Regulation , Line Regulation,
you should do the transient simulation.You can make the input voltage vary to measure the output voltage variation to attain the line regulation.
You also can make the load current vary to measure the output voltage variation to attain the load regulation. In fact , i think you should only choose the tranisent to verify all the specifications
Lucks!

 

[chviswanadh]

Hi jluhzw,

Thanks for ur reply. I have a doubt doing the transient response. While checking the line regulation we need to make a step change in the input voltage and is the same with the load regulation we need to make a step chane in the output current. how can we do that in transient analysis???

Hope u got my problem.

Thanks
Kasi

 

[jluhzw]

hello
for line regulation, Change your power supply for the pwl or pulse soures.
For load regulation, Change your load current in the following way. You can take
advantage the bipolar as the switcher to control the load current. For different
load currents, you turn on the different loads. May be some loads is 100mA, the
other loads is 10mA, 1mA and .1mA, if you like. The every load current quantity is determined by the resistance which is series with the load's bipolar. When you want to turn on the load, you can make the bipolar base voltage high, the other bipolar' bases voltage is low.
Sorry ,I have drawed the schematic ,but it could not be loaded here.

 

[chviswanadh]

Hi jluhzw,

Thanks for the information. I can understand what u are telling. U meant to say that i need to put a sort of resistance bank isn't it???
On the same terms how can I calculate the switching frequency.

Thanks
Kasi

 

[max0412]

To test dynamic response and line /load regulation. In spice you can do this in several ways.Placing a current source at your output with a time delay is another way.The way I'm doing it here is how I've done it in the school lab. (see attacment)

The settings on the VPULSE sources will depend on your particular application.

This is a basic linear regulator but it can be applied to your SMPS.

To find the switching frequency it is just 1/(T ON + T OFF) of your SWITCH.

Do you mean continous conduction mode ? Not continous off time. Is this a fixed frequency or variable frequency desighn (constant on or off time).

V out is 30V U3 switches on at TD=0.15m.Basically shorting out R6 and I out jumps to 30V/(R8 +U3 RDSon).RDSon can be neglected here.LOAD transient from 250mA to 3A.

The LINE transient is just a pulse source with an intial condtion of V2=36V for a PW=0.1m then it drops to V2=31V. LINE transient from 36V to 31v.

 

[chviswanadh]

Hello max,

Thanks for the reply. I meant to say continuous conduction mode constant off time.
At the top level of the design how can u find the on time and off time of the regulator?

Thanks
Kasi

 

[max0412]

The time integral of the inductor voltage over one full period must be zero.In other words the area under the VL(on) (Area A) waveform equals the area under the VL(off)(Area B) waveform.Inductor volt/second balance.So straight from the buck converter gain formula :
(ccm)
A=B
VL(on)*ton = VL(off)*toff

(V(in)-V(sw)-V(out))*t(on) = (V(out)+V(D))*t(off)

So just sovle for t(on) if t(off) is fixed then.

t(on)=(V(out)+V(D))*t(off)/(V(in)-V(sw)-V(out))

V(D)=diode voltage drop.For sync rectification use FET I*Rdson.
V(sw)= Mosfet volt drop I*Rdson

If you are using a "constant off time" controller t(off) is fixed by desighn.

 

[chviswanadh]

Hi max,

Thanks for the reply. Can u get me some material on constant off time regulator.

Thanks
Kasi

 

[max0412]

Using a UC384x Controller for "constant off time".

https://www.venable.biz/tp-05.pdf

Analogs (kester& Erisiman)
Good general ref on SMPS,INCLUDES "CONSTANT OFF TIME"

https://www.analog.com/UploadedFiles/Associated_Docs/84245885Power_sect3.PDF

A couple of controllers.

https://www.analog.com/UploadedFiles/Data_Sheets/54177831ADP3171_a.pdf

**broken link removed**

A new one from Allegro

**broken link removed**

This should provide you with enough information to refine your searching.The above was found using Google in about ten minutes.

You should also search the forum for SMPS related material.There is a massive amount of information available here and using good searching techniques on search engines.

Good luck
max0412

 

[andy2000a]

sometime I use transformer & inductor in hspice
will cause not convergence
or simulation need very very logn time for get
stable Power vcc ( like PWM booster)