rechargeable battery backup circuit for GSM.GPRS module

[Wajiduddaim]

HI

i m making a circuit of GSM/GPRS module SIM868 according to this **broken link removed**.
but i have a problem with VRTC (backup battery).if there is rechargeable battery will module will charge it, if yes then afrer fully charge, will module auto stop it?
if module didnt charge the battery the which circuit is suitable and which battery is recommended.

Battery info from DataSheet

6.3. Backup Power of GNSS
Power source (such as battery or LDO) connected to VRTC pin will help the GNSS chipset keep its internal RTC running while the main power source is turned off, this will help to short the cold start time. The voltage should be kept between 2.3~4.3V, and the typical value is 3.0V.

 

[KlausST]

Hi,

Often used:
* a 3V coin cell (do not enable charging)
* a capacitor or goldcap (enable charging)
* an LDO (do not enable charging) .. no backup function

Klaus

 

[BradtheRad]

There's nothing wrong with wanting to combine a charging circuit in your power supply. However consider that it may be simpler to have the battery provide power continually, and let the charger send whatever amount of juice replenishes the battery. Regulate the supply voltage so it never goes above a level which is safe for the battery.

Notice that most of the time the supply is the primary source of electrons, and those electrons pass right by the battery. The battery sits idle most of the time accepting a few mA of trickle current.

Steering diodes may be added, for a measure of protection.

The above setup requires care in design and adjustment. However it takes more effort to create a combination power supply and charging module, which must decide what to do: whether to power a circuit, or charge a battery, or stop charging, or whatever.

 

[KlausST]

Hi,

Just to clarify:
It's the Vrtc with a typ. current of 8uA.

Usually you won't use a LiIon battery (or similar) for this.

Klaus