Author Topic: LDOs with low input voltage shutdown?  (Read 2020 times)

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Offline cksa

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LDOs with low input voltage shutdown?
« on: July 25, 2010, 01:13:20 pm »
Hi,

I was wondering how people normally design a linear regulator in a battery powered situation. For most linear regulators, let's say this one regulates to 3V. If the input voltage is say 2.5V, the output of this regulator will also be 2.5V. Surely this is a common problem? I want a regulator that automatically shutsdown completely when the output falls out of regulation (i.e. battery is low, and not to over discharge the battery). What are such linear regulators called? And if a particular regulator does not have this feature, how can I roll my own onto a standard regulator?
 

Offline cksa

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Re: LDOs with low input voltage shutdown?
« Reply #1 on: July 25, 2010, 01:21:26 pm »
Well the CORE of my problem is that

1) I am operating a device from a single cell lithium polymer battery, using a linear regulator, regulating to 3V.
2) I do not want to over discharge this battery
3) How can I ensure that I do not over discharge this battery?

Thanks
 

Online Zero999

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Re: LDOs with low input voltage shutdown?
« Reply #2 on: July 25, 2010, 03:52:19 pm »
You need brownout protection.

By the way you were wrong earlier when you said when the input is 2.5V, the output will be 2.5V, in reality it will be significantly lower, unless you're using a top of the range LDO regulator.
 

Offline jahonen

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Re: LDOs with low input voltage shutdown?
« Reply #3 on: July 25, 2010, 04:01:19 pm »
You might consider using a regulator with a "power not good"-flag, and then shut the regulator down when this condition is indicated.

Regards,
Janne
 

Online Zero999

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Re: LDOs with low input voltage shutdown?
« Reply #4 on: July 25, 2010, 05:54:18 pm »
That would work but they're a couple of things that I'd be concerned about.

Ideally the power not good and disable flags should both be active low that way you should be able to just connect them together and it will work. You'll probably need a resistor and capacitor to the disable flag to ensure it it gets high pulse when the power is applied.
 


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