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?
Reply by ●June 21, 20112011-06-21
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
Reply by Spehro Pefhany●June 21, 20112011-06-21
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�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.
Reply by Jon Kirwan●June 21, 20112011-06-21
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
Reply by Jon Kirwan●June 21, 20112011-06-21
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
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
Reply by ●June 21, 20112011-06-21
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