MC34709 Li Cell Charger

[MarkRoy]

Hello,

I am using the MC34709 in a design.   We are using a 3.0V rechargeable lithium cell to backup the RTC on the MC34709.    I was wondering if there were any parameters or ratings on the charger circuit since it seems to be poorly documented in the datasheet.  The datasheet only lists the parameters of Table 19.   All of the values in this table are only "Typical" values and there are no minimums or maximums listed.    For example for safety reasons I would like to know what the maximum charge current is.    Also, is there any kind of reverse charge protection built in to the charger?

If a user accidentally installs the battery in reverse, what will happen?  Will this damage the MC34709?  Will it attempt to reverse charge the cell causing leakage or worse damage to the cell?

If there are no protections for reverse polarity then I may need to use a permanent battery instead to remove the possibility of user error.

Regards,

Mark Roy

[igorpadykov]

Hi Mark

Table 19 is only available official data.

Regarding "If a user accidentally installs the battery in reverse", battery will

be shorted to internal ESD diode (max. allowable current about 2mA).

Best regards

chip

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[MarkRoy]

Thanks Chip,

So are you saying then that the ESD diode would be able to handle a reverse battery? 

Or would this kill the ESD diode?

If I put a low voltage schottky diode from LICELL (pin M2) to the cell, would this fix the problem of reverse charging or would the charger then have problems correctly sensing the voltage?

Regards,

Mark Roy

[igorpadykov]

Hi Mark

yes installing diode will definitely

fix the problem of reverse battery connection.

Best regards

chip