For the DS1302 trickle charger settings description on page 7 of the datasheet, I'm unclear about the differences between connecting 1 vs. 2 diodes to the battery sources. I'm also unclear about the resistor selection as well as I'm not sure which resistance to pick to limit the charging current. Any comments would be much appreciated.

 

If you look on the datasheet for the equation they use to work out the 'trickle charge current' for the back up source....you can see that there are 8 possible current levels. Four resistors with one diode, and four resisotrs with 2(!) diodes. The diodes simply drop the supply voltage before it goes to the resistor, reducing the voltage across said resistor, therefore, reducing the current.

It all depends on your battery source. Pick a coin cell, and get the datasheet for it. Check the recommended charging currents...as as long as you don't go over the limits, you should be fine. As for 'supercaps', I don't see any reason at all to limit the current.

Theres also the question of power usage. The battery is only used as back up, to keep the RTC going, and to store the ram. But still, if it spends almost all its time in power down mode (running off battery) then when you DO give it a full supply thus charging the battery, you might want to jack up the current, otherwise it will hardly get charged. For example, if it is used for a datalogger..and it only powers up for a few seconds a few times a day? thats not much time to charge the battery.

Without more information, I can't help much.

Blueteeth

Note, I didn't want to say anything earlier but if you use a 'non rechargable' lithium coin cell..like the CR2032...don't charge it Just use a shottky doide to block current going into the battery

see: http://www.acmesystems.it/?id=105

personally, if you can, I would use a supercap just for the coolness factor.

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Inconsistency is the key to flexibility!

 

Thanks for the comment. I'm using this as a datalogger. However, I found out that the application of this chip is a datalogger that Vcc2 would always be on. I am using a CR2032 lithium ion coin cell that I don't think is rechargable. So I may skip coding the functions that are responsible for the settings altogether.

 

Yep, sounds about right.

Of course I would still use a small coin cell (non rechargable) in series with a diode and resistor (shottky diode, v-drop of 0.3, 1k resistor?) just to make sure you don't accidently end up trying to charge it. It'll be there just incase you lose power, so you won't have to set the time and date again....good precaution. (no power supply is completely 'uninterruptable').

So good luck! I'm also building a datalogger! But alas, its got tight restricitons on power uasage, so I better check that datasheet properly.

Blueteeth

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Inconsistency is the key to flexibility!

 

Do you have a schematic of how that is connected or would that be in a book called "The Art of Electronics"?

 

google the part number....then click 'images'. i found at least 30 schems.

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Inconsistency is the key to flexibility!

 

I tried googling for 1N5817, but can't find any images useful in terms of circuit. I have modeled a circuit as shown in http://imagebin.org/12690 , but not too sure if that's it.

 

that'll do just fine...its the same setup in the link I provided in a previous post. any shottky diode should do, as we're dealing with tiny current here.

edit: When I said 'google' the part number, I meant the DS1302
http://www.acmesystems.it/articles/0...ema_ds1302.gif

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Inconsistency is the key to flexibility!