AVL Design With SIM908

Hi guys.i'm new in edaboard
I'm in designing car AVL with SIM908 module.I have a problem with power unit.The system powered with two power sources,external power from car and the other is internal 3.7 Li-Ion battery.The SIM908 has a built-in battery charger(Very Cool!).I want to connect the battery to VBAT pin and external voltage from switching regulator(LM2596T-ADJ) to VCHG pin of module.
The main power source of module and subsystem(micro,lcd,...) is internal battery and external power will charge the battery.
Everything is OK!
But...
The problem is when the battery is damaged or accidentally removed...
If in normal operation of system, internal battery removed,the system must be alive and work with external power.
Any body know about that the SIM908 power can be produced from VCHG pin?(The regulator circuit is designed for producing 2A current) or i have to design the hardware to switch the power source from internal battery to external power?
Thanks for your time.
Saeid

Use a TI BQ24073RGTT battery management chip to provide power to the SIM908.

Will run with or without the battery connected (will auto switch), will charge the battery, and provides outputs to indicate a) main power connected and b) battery is charging.

Azlan.

Batang said:

Use a TI BQ24073RGTT battery management chip to provide power to the SIM908.

Will run with or without the battery connected (will auto switch), will charge the battery, and provides outputs to indicate a) main power connected and b) battery is charging.

Azlan.

Click to expand...

Thanks to reply.
The datasheet of SIM908 says that the battery directly connected to module and no need to any charger IC!
All the information in SIM908 datasheet for power, is about voltage on VBAT pin. For example:The voltage on VBAT pin can't be reduced under 3.1V...
-> If i just connected the 5V charger to VCHG pin with no any buttery present on VBAT pin, the module can be operate?
-> The current burst that may need sometime, can be produced from VCHG pin(without any buttery on VBAT pin)?
That's my exactly ambiguity!
Thanks.

hi
1: module doesnt work when there is no power on vbat pin , means you have to connect a battery to vbat , even low charge one!
and also module doesnt work with only +5 volts on vchg pin! " battery has to be connected "
2:if you use Li poly battery , youre gonna need the charger IC as he said in former post!
i mean it ! in Li poly , charger ic is essential!
3:if you use li-ion battery , you can use sim908's insided charger
but its strongly recomended to put some protects in input power,bat:wink:

If i just connected the 5V charger to VCHG pin with no any buttery present on VBAT pin, the module will be on or not or it could damage the modem ?