Problem in using DS1210 : at power up

[Henry A. Park]

Hello

I took DS1210s to make SRAM to NVRAM as commonly used.
Pin 2(VCCO) was connected to SRAM's power layer in PCB board, and Pin
4(VBAT 1) was connected to Battery(3.6V). Other pins was connected as
recommendation.
Most of applications were normally operated - when power off, it keeps
SRAM power layer to data retention level very well.

But some of them didn't go as usual way.
The Problem was at power-up; when 5V power is turned on, VBAT pin is
pulled high(5V) without any reason. Clearly, VBAT is connected to 3.6V
BATTERY. But more complicated than this is that fresh battery doesn't
seem to happen this(it were only poor batteries which were used more
than 8 months although retain normal voltage). I thought DS1210 may
use shortening/recharging protection circuit at VBAT input as
specified DS1321, but now I think that it might not. How could this
happen? This phenomenon has corrupted entire board process at
power-on.

And tried more cases. VBAT floating, it also showed 5V when power-on.
Two battery connected parallely to VBAT: also high.

To put together, there was only one case when DS1210 operating
normally - one good battery.
When VBAT is connected to poor battery or 2 good battery in parallel,
or is floated, then it may be pulled high.

I couldn't find clue because Dallas doesn't offer any schematics nor
block diagrams of DS12XX.
Are there anyone who suffered same phenomenon like my case?

Park

 

[Pwillard]

I imagine that the schematics of the DS1210 would look a lot like...
http://pdfserv.maxim-ic.com/en/an/app004.pdf since I presume that a
DS1210 NVRAM is like a sealed DS1213 solution... I'm guessing, but
studying the DS1213 might give you some clues.

Pete Willard