width considerations for MOSFET switch

Thread Starter

arunkps

Joined Jan 28, 2014
16
What are the Width Length design considerations for the switch MOSFET (PMOS or NMOS) in synchronous buck converter?
 

Thread Starter

arunkps

Joined Jan 28, 2014
16
Hi,

Sorry, for the delay and it is because of my internet problem. Meanwhile, people presumed about my absence.

Ok, here I give the detail. Basically I am designing a synchronous buck converter and have planned to do a layout in 180nm in Cadence. Initially, when I simulated a simple buck converter power stage in Cadence, I faced problem in the switching section i.e., both HSS (High Side Switch) and LSS (Low Side Switch). So when I tried to simulate a MOSFET (PMOS or NMOS) alone, I noticed that the MOSFET not acting as switch until I increased the width of the MOSFET to enormous value (100um). It is my understanding from the simulations; that inorder to act the MOSFET as switch, the width should be made very large such that the ON resistance become very small and the VDS ON will be very less and the complete input voltage can be seen at the output of the MOSFET.
My simulations files are there for your reference. However the simulations are of the asynchronous buck converter.

The designed component values are for the spec
vin=1.8v
vout=500mv
Load current=1mA
switching frequency=1MHz
output Iripple=100uA
Output Vripple=500uv

Please help me in simulating this power stage.
 

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Thread Starter

arunkps

Joined Jan 28, 2014
16
Hi,

Sorry, for the delay and it is because of my internet problem. Meanwhile, people presumed about my absence.

Ok, here I give the detail. Basically I am designing a synchronous buck converter and have planned to do a layout in 180nm in Cadence. Initially, when I simulated a simple buck converter power stage in Cadence, I faced problem in the switching section i.e., both HSS (High Side Switch) and LSS (Low Side Switch). So when I tried to simulate a MOSFET (PMOS or NMOS) alone, I noticed that the MOSFET not acting as switch until I increased the width of the MOSFET to enormous value (1000um). It is my understanding from the simulations; that in order to act the MOSFET as switch, the width should be made very large such that the ON resistance become very small and the VDS ON will be very less and the complete input voltage can be seen at the output of the MOSFET.
My simulations files are there for your reference. However the simulations are of the asynchronous buck converter.

The designed component values are for the spec
vin=1.8v
vout=500mv
Load current=1mA
switching frequency=1MHz
output Iripple=100uA
Output Vripple=500uv

Please help me in simulating this power stage.
 

Attachments

Thread Starter

arunkps

Joined Jan 28, 2014
16
Hi,

Attachment in the buck converter circuit. I have designed the component values to get Vo of 500 mv. I will be thankful, if you can simulate it in 180nm (preferably CADENCE).
 

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