Question on Trickle Charge DS1302 and an ML2430 Lithium

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I am designing some devices to track my machines capacity utilization data. I am using a tiny2313, a FM24C64 Fram memory chip and a DS1302.

The battery I plan to use is a ML2430 Lithuium
.5ma charge, constant voltage charge 3.1 +-0.15V

I am using the latest CodeVision C compiler that has a library for this parts communication.

The Fram needs 5VDC. I plan to use a larger battery to run the device for up to 30 days minimum. If I use a LDO regulator to power the tiny2313 and the DS1302 at 3.1V and a second LDO regulator to power the Fram at 5V.

Should I use a single diode and 2k resistor for the Trickle charge connection to the ML2430? I have some Shottky diodes I can use. Should I bump the voltage to the DS1302 so that the output of the trickle charger reaches 3.1V ?

After a bit more reading, I see the diode and resistors are internal to the DS1302 and set by software.

EDIT....
So it looks like i could use a regulator to power vcc2 at 3.8VDC and select 1 diode and 2k resistor to get 3.1V charge maximum at 1.9ma Once I looked at connecting it up adding a diode and resistor did not make much sense.

:roll:

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Moving to general electronics.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I did not realise that FRAM needed 5V.

Surely the simplest arrangement is to use a 23F256 SPI SRAM. And battery backup. i.e. one single 3.3V system.

Your RTC, AVR, SRAM will all function with 2.5V - 3.6V supplies e.g. your battery.

Mind you, you could use FRAM and 5V mains power. The application simply stops without mains power. The Lithium battery only supplies backup power to the RTC.

David.

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I did look at the new Fram chips, I actually have the 256 surface mount chips and indeed they run at 3.3V. I also have a bunch of through hole FM24C64 and they do use 5V. (they are old) so I initially was looking at just the 5V spec. I did make boards that will use both since I have all the components. At least the box of lithium batteries will be put to use. It will make it easier to just change the main battery without having to re input the current date and time.

I am just going to pull the data using the usart and another reader board to read each board at the first of the month. I can then upload the data to my main computer on the com port. I have a bunch of 800ma lithium battery packs at 7.4V for the main power. I am only making 8 of them.

So I will use the 3.3VDC regulator for the 3.3v fram and the AVR and use another 5VDC regulator for the Fram that needs the 5V since I don't have enough of the 256 chips. I guess I can't let the 5V chips go to waste, trying to help the environment by using up existing components. :wink: