quaternion
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ashish_chauhan said:Your choice of pass device (high vt ,low vt, regular) will also depend on the total leakage current spec you have. Otherwise there wont be much difference in the sizes of pass device supporting same amount of current.
If you need to have lower leakage go for high vt device.
quaternion said:So , the regular Vth seems to be my best choice as it leads to a simple design and lower leakage and at a little smaller size than low Vth one.
I think in normal LDO design the quiescent current will be larger than leakage ,isn't this true?
Also, I have a little question; why high voltage devices are named high gain ?(is this related to the process?)
winsonpku said:I think for the pass device, the low vth maybe a prefered choice
but this will add an extra mask and this will add the cost.
winsonpku said:I think it has much deffrence between high vt and low vt device.
I think for the pass device, the low vth maybe a prefered choice
but this will add an extra mask and this will add the cost.
high voltage devices may have large output resistace,
so they have high gain under the normal condition.
ashish_chauhan said:winsonpku said:I think it has much deffrence between high vt and low vt device.
I think for the pass device, the low vth maybe a prefered choice
but this will add an extra mask and this will add the cost.
high voltage devices may have large output resistace,
so they have high gain under the normal condition.
I won,t disagree to you but as I said in my previous post... choice depends on ur specs. If you are targetting a lower standby current... high vt shall be the preferred choice... keeping the stability at "no load " in mind.
by the way , who are you Engineer or student?
ashish_chauhan said:But, say when I need the reg to be functional and regulating for loads which can be below 100nA... i think you low vt device will make the error amp saturate and thus killing the loopgain and hence the complete regulating function.
In this case a high vt will be better as it will get shut before ur amp saturates.
ashish_chauhan said:I think you are not getting my point...
I agree that in case of large current load transients a low vt device will help in quick recovery...
But, say when I need the reg to be functional and regulating for loads which can be below 100nA... i think you low vt device will make the error amp saturate and thus killing the loopgain and hence the complete regulating function.
In this case a high vt will be better as it will get shut before ur amp saturates.
I ur case , if you check stability at no load you will not be able stablize the regulator without bleeding some extra current through ur pass device , which can be more than 1uA even. And when you target a spec of 2uA TOTAL current consumption u cannot afford 1uA thru pass device alone!!!
hope I made my point this time.
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