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feiyue

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the wide input voltage range in dc-dc converter
Jul 28^th, 2007, 4:43pm

hi all,

I find that many commercial dc-dc converter product can tolerant wide input voltage range,such as 2.7v to 20v.I am curious that why they will not induce reliability issue for the controller and power transistors. For example,if we design the converter using 0.35um cmos technology,the nominal operation voltage is 3.3v,but if the operation voltage is 4.5v or higher,then the gate oxide of the digital circuits in controller and power transistors will break down. I am not sure whether my concern is correct.Does anybody have some ideas or explanation on it? I wish my question would not be too simple.:)

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Faisal

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Re: the wide input voltage range in dc-dc converte
Reply #1 - Jul 30^th, 2007, 7:23am

Hi,

In some process technologies there are more than one version of transistor. E,g there are Thicker oxide transistors (in addition to normal oxide transistor) which can stand higher gate voltages. Some fab processes offer transistors for high voltage applications e,g 32V etc.

If your process does not has such transistors.. then I think it would not be possible to design such a wide range dc_dc converter in such a technology.

Kind Regards,
Faisal Mateen

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feiyue Junior Member Offline Posts: 15	Re: the wide input voltage range in dc-dc converte Reply #2 - Jul 30^th, 2007, 10:24am hi Faisal, Thanks! if the input voltage is not so wide such as 3-5v,is it a good solution to implement a internal linear regulator to set a proper power supply for contrller IC ? then i think it maybe possible. I am not sure whether it is true.
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vivkr

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Re: the wide input voltage range in dc-dc converte
Reply #3 - Jul 31^st, 2007, 2:35am

Hi feiyue,

Sure, you can use a linear regulator for getting a fixed internal supply. Just keep in mind the additional design overhead, power consumption,
and the drop introduced by the regulator.

If your controller really needs a constant, ripple-free supply and you have no constraints on power consumption and/or have external components
available for filtering your supply (assuming ripple from controller), then it may work well for you. Usually though, it is advisable to design your
controller to be relatively insensitive to supply, especially if the supply does not vary much, as you say.

Regards
Vivek

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feiyue Junior Member Offline Posts: 15	Re: the wide input voltage range in dc-dc converte Reply #4 - Aug 1^st, 2007, 10:06pm hi Vivek, thank you very much for your suggestion! feiyue
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edwintsu

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Re: the wide input voltage range in dc-dc converte
Reply #5 - Sep 11^th, 2007, 4:53am

Hi all,

I have a similar question.

If the min. voltage range become lower , such as 1.8V, how to deal with it typically? (At corners of some process the sum of VTHN + |VTHP| is larger than the min. voltage.)

Use voltage boost circuit (charge pump) + voltage regulator to set the fixed internal voltage?

Thank you.

Edwin

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jordan76 New Member Offline Truth always lies in the details. Posts: 3 China	Re: the wide input voltage range in dc-dc converter Reply #6 - Nov 27^th, 2008, 11:41pm Hi edwintsu. In this case using voltage boost circuit (charge pump) + voltage regulator can be an option; often buck-boost converter can be better choice depending on your system spec: space, cost and efficiency etc. Truth always lies in the details regards, Jordan76
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