designing multiple o/p regulator

Hi all
I want to design a multiple o/p buck converter

3.3v at 2A
5V at 500ma
1.9 v at 1A
1.2 v at 1.5 A
2.5v at 1 A

i gone through various companies ic's

in most of the ic's to generate voltage less than 5 v it requires max of 7V

My input supply voltage is 12v

I thought of using 12 to 5 v converter module from TI at 6A as a primary step down stage .

i have a doubt that if i put a switched regulator on the o/p of the 5 v regulator module it will create any problem or not as the module itself is switching type

And iam confused in selecting other regulators, as there are many single and dual regulators from various vendors.

And about the switching frequency good to use higher or lower frequency switching ic’s

Important - I need this for a DSP and FPGA power.

Please give suggestions :idea: .

I don't think, in your case, it is a good idea to create an intermediate voltage of 5V ..

Have a look at this option:
**broken link removed** (3A, or 2575 for 1A)
These regulators can be fed directly from +12V ..
For 3.3V you can select LM2576-3.3V.
For 5V and less then 1A, you can select LM2575-5.0V.
For other voltages you can select LM2576/5-ADJ (stands for sdjustable) and, using one additional regulator per voltage required, adjust them as follows: 2.5V, 1.9V and 1.2V ..
Regards,
IanP

IanP said:

I don't think, in your case, it is a good idea to create an intermediate voltage of 5V ..

Have a look at this option:
h**p://www.national.com/ds/LM/LM2576.pdf (3A, or 2575 for 1A)
These regulators can be fed directly from +12V ..
For 3.3V you can select LM2576-3.3V.
For 5V and less then 1A, you can select LM2575-5.0V.
For other voltages you can select LM2576/5-ADJ (stands for sdjustable) and, using one additional regulator per voltage required, adjust them as follows: 2.5V, 1.9V and 1.2V ..
Regards,
IanP

Click to expand...

Thanks IanP for your suggestion that IC Regulator you suggested works on 52Khz i feel it is low and i don’t know its effect on the supplies ripples and it needs 100uH(bulky) inductor. i need low noise regulators for DSP processor power supply with size consideration.

1. generation a 5V from 12V simply by 7805, this 5V will not be the source for 500mA output. it's just a power for those PWM regulator 's controller.

2. use PWM regulators like SEMTECH 1485 or 1486, which are buck (step down) converter from 12V to 5/3.3/2.9/1.5/1.2, and the switching freq. can be larger than 300kHz, which need only small inductors, ( < 5uH ) in ur application

Btrend said:

1. generation a 5V from 12V simply by 7805, this 5V will not be the source for 500mA output. it's just a power for those PWM regulator 's controller.

Click to expand...

Why it is needed as the pwm controllers (most of them) will have a small regulator inside for powering its ckts.

Btrend said:

2. use PWM regulators like SEMTECH 1485 or 1486, which are buck (step down) converter from 12V to 5/3.3/2.9/1.5/1.2, and the switching freq. can be larger than 300kHz, which need only small inductors, ( < 5uH ) in ur application

Click to expand...

that controller you suggested is good it looks like a clone of TI buck controllers(easily available through distributers).

as I know, due to CMOS process limitation, PWM controller are usually operating in low voltage range (4.5 to 5.5V), if embedded regulator, it require high voltage process (12V regulate to 5V), which need more mask, and more cost.
Anyway, if u find one which has internal regulator, then u can surely bypass 7805.
But SEMTECH 1485 has no internal regulator.

puviarasu said:

3.3v at 2A
5V at 500ma
1.9 v at 1A
1.2 v at 1.5 A
2.5v at 1 A

Click to expand...

This is how I would do it:

From the 12V input, create a 5V rail capable of 5A with the Intersil ISL6522 buck regulator.

From the 5V rail, create a 3.3V rail capable of 5.5A with the switching regulator portion of the Intersil HIP6521.

Utilizing the three linear regulator controllers integrated in the HIP6521, create the 2.5V, 1.9V and 1.2V rails derived from the 3.3V rail.

Thanks "out to lunch", i dint know about that ic manufacturer. Your way of deriving the voltages feels good logically. I am going through intersil's products many of them feels useful, i still have one doubt it is good to use a switching regulator at the output of another switching regulator?
And what should be those regulators operating frequency?

You should have no problems with cascading switching regulators, it is done all the time. The only place you may have a problem is if there is an IC with two switching regulators and both of them sharing the same clock. This would cause both regulators to fire the control or synch fet at the same time. Most mfgs of regulator ICs would phase shift the clock for the second regulator in the IC, though, so even then you wouldn't have a problem.

Switching frequency is up to you. The higher you go in frequency, the smaller some of the devices can be but there are always trade offs in price, efficiency, response, etc.

Is there is any relation for the switching frequency and output noise on the power

And for ADC it is better to linear power regulator than switched?

And there is any relation of switching frequency for multi stage ie if i use one to step-down from 12v to 5v and another to step-down from 5v to 3.3v.