[Moved]: Can power grid and voltage regulator coexist to provide 1.2V supply voltage

[zhangljz]

Hello,


I am designing a chip that during reset the current consumption is only several mA, after reset the current will burst to 200mA for 5ns ~ 100ns, then calm down again.

The technology is 0.13um CMOS, 1.2V core voltage. But the circuit is very sensitive to supply voltage variation. If I only use power grid, I am afraid the IR drop will affect the function.

I know voltage regulator will generate stable voltage, but I have no experience with this design. I am not sure if it will work for me.

And to be safe, if power grid and voltage regulator can cowork will be an good option. In this case, if voltage regulator fails, I still have power grid for power supplying.

Does anyone know if it is practical, and possible issues? Any suggestions?

Thank you

 

[csolis_GT]

Re: Can power grid and voltage regulator coexist to provide 1.2V supply voltage

Hey zhangljz,

Are you afraid of the IR drop only when the current ramps up to 200 mA? If so, a ceramic capacitor next to the power pin can provide that amount of current during the burst. A 1 uF cap will give you less than 20 mV supply variation for the worst case of the numbers you quoted. Actually, I would pay more attention to package parasitics, such as the bondwires of the package since for thos current swings at those speeds can create substancial ringing inside the chip. I would recommend finding info on package parasitics and simulate that.

As for having the power grip and regulator at the same time, the only impression I have is that you may have to be careful how to implement the control because they will be trying to regulate the same variable and they might fight each other. If the power grid is a solid 1.190 V, for example, how will the regulator respond/behave? It may want to source a lot of current but if you are not using that much current, where would it go?

Carlos

 

[mtwieg]

Re: Can power grid and voltage regulator coexist to provide 1.2V supply voltage

What resistance are you concerned about? So long as you're using adequate bondwires and metal for the supply rails of the IC, a few hundred milliamps shouldn't be a problem. Outside the IC, a small ceramic capacitor can easily handle the short current pulse. You shouldn't need any fancy voltage regulator.

 

[zhangljz]

Re: Can power grid and voltage regulator coexist to provide 1.2V supply voltage

Hi mtwieg,

The worst IR drop I expect is 20mv at 1.2V power supply, 200mA burst current. Will this be a tough target? I have no idea how to calculate the IR drop of the whole chip. I need to learn this.

 

[mtwieg]

Re: Can power grid and voltage regulator coexist to provide 1.2V supply voltage

I have no idea how to calculate the IR drop of the whole chip. I need to learn this.

Well you should probably start there, since if that drop is to high then things become difficult. If necessary you could use have a couple extra supply pins to act as kelvin sense terminals that are fed to an external regulator, allowing you to compensate for the IR drop inside the IC.