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1V regulator run from a single NiMH battery

Started by Unknown June 21, 2011
I need to supply a 1V to a the real time clock section of a Atmel
AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I
would like to use a single NiMH battery which has a max output of
1.4V. My problem is that most linear regulators use a 1.23V reference
so I am not sure what happens to the output voltage when the battery
voltage drops to 1.2V. Can anybody offer any advice or ideas
Thanks

Steve
On 21/06/2011 12:27, steve.jones@scannex.co.uk wrote:
> I need to supply a 1V to a the real time clock section of a Atmel > AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I > would like to use a single NiMH battery which has a max output of > 1.4V. My problem is that most linear regulators use a 1.23V reference > so I am not sure what happens to the output voltage when the battery > voltage drops to 1.2V. Can anybody offer any advice or ideas > Thanks > > Steve
There are loads of low dropout regulators which have a reference lower than 1.0V What's wrong with something like a LP5952TL-1.0? I would suggest a quick look through the likes of Digikey. -- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
On Tue, 21 Jun 2011 04:27:17 -0700 (PDT),
steve.jones@scannex.co.uk wrote:

>I need to supply a 1V to a the real time clock section of a Atmel >AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I >would like to use a single NiMH battery which has a max output of >1.4V. My problem is that most linear regulators use a 1.23V reference >so I am not sure what happens to the output voltage when the battery >voltage drops to 1.2V. Can anybody offer any advice or ideas
Ricoh R1100D101C LDO is an example: http://www.ricoh.com/LSI/product_power/vr_linear/r1100d/r1100d-e.pdf Spec'd at a max dropout of 30mV at 1mA output. I think you will be fine at 1.2V. Jon
On Tue, 21 Jun 2011 05:01:48 -0700, I wrote:

>On Tue, 21 Jun 2011 04:27:17 -0700 (PDT), >steve.jones@scannex.co.uk wrote: > >>I need to supply a 1V to a the real time clock section of a Atmel >>AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I >>would like to use a single NiMH battery which has a max output of >>1.4V. My problem is that most linear regulators use a 1.23V reference >>so I am not sure what happens to the output voltage when the battery >>voltage drops to 1.2V. Can anybody offer any advice or ideas > >Ricoh R1100D101C LDO is an example: > >http://www.ricoh.com/LSI/product_power/vr_linear/r1100d/r1100d-e.pdf > >Spec'd at a max dropout of 30mV at 1mA output. I think you >will be fine at 1.2V.
By the way, Atmel's own eval kit for your very cpu uses that regulator. I don't use Atmel so I just went there and looked up the part for VDDBU on the BOM. Easy. You should have done that much: http://atmel.com/dyn/resources/prod_documents/AT91SAM9G20-EK__KitsFiles.zip As another poster mentioned, there are others as well. Do you design, professionally? Jon
On Tue, 21 Jun 2011 04:27:17 -0700 (PDT), steve.jones@scannex.co.uk
wrote:

>I need to supply a 1V to a the real time clock section of a Atmel >AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I >would like to use a single NiMH battery which has a max output of >1.4V. My problem is that most linear regulators use a 1.23V reference >so I am not sure what happens to the output voltage when the battery >voltage drops to 1.2V. Can anybody offer any advice or ideas >Thanks > >Steve
BTW, 1.2V is not a very conservative value for dropout with a NiMH cell, particularly if your product must handle low ambient temperatures. 1.1 or 1.05V would be better. The Ricoh part that Jon mentioned has a worst case dropout voltage of 700mV at 1mA and 25&#2013266096;C (yes, the data sheet is misleading), so it could start to drop out at 1.724V in with 1mA load!, but, but at < 10uA it's _probably_ okay (up to you to check though). MOSFETs look like resistors, or better, so it should scale at least as well as 0.01mA/1mA * 700mV = 7mV.
On Jun 21, 1:31=A0pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
> On Tue, 21 Jun 2011 04:27:17 -0700 (PDT), steve.jo...@scannex.co.uk > wrote: > > >I need to supply a 1V to a the real time clock section of a Atmel > >AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I > >would like to use a single NiMH battery which has a max output of > >1.4V. My problem is that most linear regulators use a 1.23V reference > >so I am not sure what happens to the output voltage when the battery > >voltage drops to 1.2V. Can anybody offer any advice or ideas > >Thanks > > >Steve > > BTW, 1.2V is not a very conservative value for dropout with a NiMH > cell, particularly if your product must handle low ambient > temperatures. 1.1 or 1.05V would be better. > > The Ricoh part that Jon mentioned has a worst case dropout voltage of > 700mV at 1mA and 25=B0C (yes, the data sheet is misleading), so it could > start to drop out at 1.724V in with 1mA load!, but, but at < 10uA it's > _probably_ okay (up to you to check though). MOSFETs look like > resistors, or better, so it should scale at least as well as > 0.01mA/1mA * 700mV =3D 7mV. =A0
Yes, I looked at the ricoh part, but the 700mV drop out put me off, it uses a 1,23V reference I think so I was not sure what would happen when Vin=3D1V. I will see if I can get one and try it, but surely it is dependent on the turn on threshold of the output Mosfet which is not defined. Atmel uses a 3V6 battery which gets round the problem. The national part has too high a quiescent current, more than the circuit uses Thanks again Thanks
On Jun 21, 1:31=A0pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat>
wrote:
> On Tue, 21 Jun 2011 04:27:17 -0700 (PDT), steve.jo...@scannex.co.uk > wrote: > > >I need to supply a 1V to a the real time clock section of a Atmel > >AT91SAM9G20 at 9uA. This has a min input of 0.9V and a max of 1.1. I > >would like to use a single NiMH battery which has a max output of > >1.4V. My problem is that most linear regulators use a 1.23V reference > >so I am not sure what happens to the output voltage when the battery > >voltage drops to 1.2V. Can anybody offer any advice or ideas > >Thanks > > >Steve > > BTW, 1.2V is not a very conservative value for dropout with a NiMH > cell, particularly if your product must handle low ambient > temperatures. 1.1 or 1.05V would be better. > > The Ricoh part that Jon mentioned has a worst case dropout voltage of > 700mV at 1mA and 25=B0C (yes, the data sheet is misleading), so it could > start to drop out at 1.724V in with 1mA load!, but, but at < 10uA it's > _probably_ okay (up to you to check though). MOSFETs look like > resistors, or better, so it should scale at least as well as > 0.01mA/1mA * 700mV =3D 7mV. =A0
Yes, I looked at the Ricoh part, it appears to have a 1.23V voltage reference so I wondered what would happen when the battery voltage dropped below the refernce, and below the turn on voltage of the output MOSFET, or does its still look like a resistor?