Hello,
my custopmer is searching for a battery backup solution for a processor module. Normally the board is supplied by a power supply. In case of a power down the battery should switch over and power the system. The processor module needs 5V/1.5A. The battery is allowed to charge slowly.
Requirements:
- battery should buffer the module for 2hr
- battery: 2-cell = 7.2V, 2.9Ah.
- Vin can be 24V or 5V
- Quick charging is not needed
Regards, Holger
Hi Holger,
If you are looking for a switch to disconnect the backup battery from the rest of the system, then a load switch (such as the TPS22810) can be used to disconnect the battery from the system until it is needed.
If you are looking for a way to charge the battery, then perhaps the battery chargers group can help you out here. WEBENCH also has a pretty nifty tool for deigning a battery charging application here:
.
I'll move this post to the battery chargers forum to see what recommendations they can give for charging the 2s battery.
Thanks,
Alek Kaknevicius
To charge 2 LiIon series from 5V you need a boost circuit.
To charge 2S LiIon from 24V you need a buck.
To create 5V from 2S LiIon you need to buck.
The easiest path for a 2S seems to be using the 24Vin to charge the 2S, then buck from the 2S to make 5V.
However a 1S2P would give as much energy as a 2S1P and be easier to implement.
Using 5Vin, you can Linearly charge the battery slowly.
For some ideas take a look at ------
High Efficiency Backup Power Supply
This is a SuperCap backup system using a TPS25940A switch with a TPS63030 buck boost.
In this design the TPS63030 operates bidirectionally, charges the Supercap from 5Vin and discharges it to make 5Vsys.
24-V AC Power Stage With Wide Vin Converter and Battery Backup Reference Design for Smart Thermostat
Automotive eCall Power Supply Reference Design with Low Intermediate Voltage
I drew up the circuit below based off 1S2P.
This should perform the function you need.
TPS22963 switches with reverse blocking
BQ24040 Linear charger
TPS61253 boost
Some logicto control
Is it possible to use 1S2P?
If not then we need to look at charging a 2S pack from 24V and discharging it with a buck.
The load switches in my document would still be needed.
For a 2S1P configuration I think this will work.
BQ24703 Charger with System Power Selector, can perform the function of ORing the battery and 24Vin.
This will pass Vin, 24V, to the buck converter, then connect seamlessly the battery to the buck converter when 24Vin is gone.
It is what this device was intended for.
See if this would work in your design;
