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DS1337 RTC Backup Battery

Hello All,

Would like to use a DS1337 RTC in an app and would like to have a 3V Li
backup battery. Vdd is 3.3V. Can I just use two schottky diodes to
protect the Li Bat? (BTW, DS1337 doesn't have a b/u battery
connection.)

Like so:

Vdd
|
|
V
_
|
-----DS1337 Pwr
|
_
^
|
|
Li Bat

Thanks,

John
 
E

Eeyore

Jan 1, 1970
0
Hello All,

Would like to use a DS1337 RTC in an app and would like to have a 3V Li
backup battery. Vdd is 3.3V. Can I just use two schottky diodes to
protect the Li Bat? (BTW, DS1337 doesn't have a b/u battery
connection.)

Like so:

Vdd
|
|
V
_
|
-----DS1337 Pwr
|
_
^
|
|
Li Bat

Safety regs mean that you have to have 2 series diodes from the Lithium battery
IIRC. Think what would happen if one went short !

If worried about the volt drop, maybe you could replace one with a mosfet ?

Graham
 
Safety regs mean that you have to have 2 series diodes from the Lithium battery
IIRC. Think what would happen if one went short !

What's a little fire? UL is a bunch of pessimists!
If worried about the volt drop, maybe you could replace one with a mosfet ?

Can't picture that. What would it look like?

Thanks for the common sense that I appear to be missing.

John
 
E

Eeyore

Jan 1, 1970
0
What's a little fire? UL is a bunch of pessimists!

I know a guy who used to run STC's compliance labs. They set one off intentionally.
Talk about brown trousers ! Even though it was in a bell jar.

Can't picture that. What would it look like?

Gate driven by main power detect.

Thanks for the common sense that I appear to be missing.

YW.

Graham
 
I know a guy who used to run STC's compliance labs. They set one off intentionally.
Talk about brown trousers ! Even though it was in a bell jar.

My day job is airplane/helicopter pilot. We use to use lithium
batteries for night vision goggles. Until people started making the
mistake of putting them in their pockets and helmet bags unprotected. I
know of at least one AH-64 Apache that was brought down by a itty bitty
battery that caught fire in a helmet bag in a storage compartment.

Respect lithium batteries....
 
M

martin.shoebridge

Jan 1, 1970
0
Presumably you have in mind one of those coin cells - CR2032 etc. I can't
see a fire hazard with those.... The 1377 will run for years on one of
those....
 
E

Eeyore

Jan 1, 1970
0
martin.shoebridge said:
Presumably you have in mind one of those coin cells - CR2032 etc. I can't
see a fire hazard with those....

If it's a lithium battery it can explode/catch fire. Lauda Air lost an airliner
it's believed on account of a cargo of defective lithium coin cell batteries !

Graham
 
L

laodao

Jan 1, 1970
0
Vdd
|
|
V
_
|
-----DS1337 Pwr
|
_
^
| resister
|
Li Bat


I think there should be a resister between Li Bat and the diode. it
will be no problem if the two diodes have a short.
 
J

James Beck

Jan 1, 1970
0
If it's a lithium battery it can explode/catch fire. Lauda Air lost an airliner
it's believed on account of a cargo of defective lithium coin cell batteries !

Graham
A cargo is surely a LOT more than a single coin cell on a PCB.
I guess I had better keep an eye on all of those old motherboards we
have laying around. One could go up at any moment.

Jim
 
D

David Collier

Jan 1, 1970
0
basically any 2 components in series will be OK, though to avoid
charging you'd want one to be a diode in this cct. a 100R will drop less
than a diode will IIRC

David
 
D

David Collier

Jan 1, 1970
0
*Subject:* DS1337 RTC Backup Battery
*From:* [email protected]
*Date:* 16 Aug 2006 11:54:42 -0700

Hello All,

Would like to use a DS1337 RTC in an app and would like to have a 3V

other RTCs in the range have a separate battery pin, and are UL rated
without external components... that's why they exist.

David
 
other RTCs in the range have a separate battery pin, and are UL rated
without external components... that's why they exist.

I understand, but try finding one that has:

SOIC footprint (and not a gazillion pins)
Has an alarm INT (not just a time of day alarm either)
Is available in prototyping quantities
Is I2C (I had to settle for SPI)

etc.

etc.
 
D

dalai lamah

Jan 1, 1970
0
Un bel giorno [email protected] digitò:
I understand, but try finding one that has:

SOIC footprint (and not a gazillion pins)
Has an alarm INT (not just a time of day alarm either)
Is available in prototyping quantities
Is I2C (I had to settle for SPI)

etc.

etc.

Several ST RTC have these characteristics, see for example M41T80M6E. Even
Digikey sells them.

You can always find an alternative to Maxim parts, and if you don't, it
means that your design is flawed.
 
D

David Collier

Jan 1, 1970
0
*Subject:* Re: DS1337 RTC Backup Battery
*From:* [email protected]
*Date:* 17 Aug 2006 11:54:10 -0700


I understand, but try finding one that has:

SOIC footprint (and not a gazillion pins)
Has an alarm INT (not just a time of day alarm either)
Is available in prototyping quantities
Is I2C (I had to settle for SPI)

etc.

http://www.standardics.philips.com/literature/leaflets/i2c/pdf/pcf8563.pca
8565.pcf8583.pdf

pcf8583 ???

don't ask me where to buy it though!

ah! RS stock number 296-683

David
 
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