On chip Buck Boost DC2DC -transistor realibility issue

[vovan76]

Hi
I going to design on chip Buck Boost DC2DC convertor
Vin=3.3V Vout=1.7-4.5V
Transitor ,wchich I have is only for 3.3V voltage
How I can design this Dc2Dc for Vout=4.5V
What is the topology for this designs
Thanks

 

[dick_freebird]

You'd have to look at making cascode stacked switches
to divide the voltage. That in turn probably needs at
least a twin-well process as well as some refernces
for the guard gates. I've done a design this way (on
SOI) that works well. You need to be sure the voltage
division keeps top and bottom devices, both safe for
Vgs, Vds, Vgb, ... rules. The large Miller kick is a good
challenge for the cascode scheme.

 

[willi65]

Hi

did u have any schematic of ur Design? i can u help when i see the drawing..wich PWM u take? normaly when u have low input voltage u have using an booster for the supply voltage for the PWM Controller..,and better use LL Mosfet..


Willi

Added after 8 minutes:

Hi

u can look the attached schematic (sorry for German lang)
this an PoL DC-DC from 3V Input voltage and 1V Output Voltage with 30A..(the power stage only of the Master have two slave)

willi

 

[Colbhaidh]

If the 4.5V is on chip, then you cannot use the 3.3V transistor which will have a maximum rating of 3.6V. This is due to hot carrier reliability of the 3.3V MOSFETs. To use 4.5V you will need to use custom high voltage transistors that the Foundry may offer.

 

[diy.technodict]

If you do not wish to use transistor use MAX756 ic.it has preset pins for 3.3 v and 5v and a switching frequency of 500khz.