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Li-Ion (Lithium) Battery - Charger and protection ICs ???

Jeferson Pehls
Expert 1170 points
Other Parts Discussed in Thread: BQ24040, BQ24090
Hi.

I am designing a power supply where I will also need to use a backup battery.
The choosen battery type was a Li-Ion (Lithium) type, which has a nominal cell voltage of 3.7V .
I have little experience with battery chargers and protection circuits (using dedicated ICs).

--> I searching for dedicated charger ICs and I think MCP73812 from Microchip is a good choice to do the automatic charge control.
Using a MCP73812 I am able to ENABLE/DISABLE and ADJUST the charge current through an external bias resistor.

--> I was also searching for a Li-Ion battery protection IC, to "disconnect" the BATT from the circuit in situations of under-voltage (over-discharge) and over-voltage (over-charge). I found this IC model on Digikey: S-8241ABKMC-GBKT2G. 
This IC (S-8241ABKMC-GBKT2G) controls two MOSFETs who are connected between the Li-Ion battery and the circuit's power supply.


The S-8241ABKMC-GBKT2G IC works similar to that:

1) It is powered from the Li-Ion battery and its current consumption is very very low, just some microamperes or less, when in power-down mode. 

2) When the BATT voltage goes below 2.5V, it "opens" the MOSFET switch, preventing the BAT to continue supplying current to the circuit. It "closes" the MOSFET switch again only when the BATT voltage goes above 2.9V. This is a good idea, using a small voltage hysteresis between OPENING and CLOSING the MOSFET switch, preventing oscilations.

3) When the BATT is in charge process and its voltage reaches 4.325V, the S-8241ABKMC-GBKT2G "opens" the MOSFET switch, preventing the BAT to continue charging and being "over-charged". S-8241ABKMC-GBKT2G "closes" the MOSFET switch again only when the BAT voltage goes below 4.075V. This is a good idea, using a small voltage hysteresis beetwenn OPENING and CLOSING the MOSFET switch, preventing oscilations.

4) S-8241ABKMC-GBKT2G has two digital outputs to control two mosfets, one for under-volge and another for over-voltage cases. So using just the under-voltage output, we could use this same IC to protect battery circuits who uses NiMh (more than one cell in series) backup batteries. 


- MCP73812 -->> Simple, Miniature Single-Cell, Fully Integrated Li-Ion / Li-Polymer Charge Management Controller
- S-8241ABKMC-GBKT2G -->> BATTERY PROTECTION IC FOR 1-CELL PACK


DATASHEETS HERE:
http://ww1.microchip.com/downloads/en/DeviceDoc/22036b.pdf
http://datasheet.sii-ic.com/en/battery_protection/S8241_E.pdf


SOMEBODY RECOMMEND ME ANOTHER ICs for LI-ION BATTERY AUTOMATIC CHARGE AND FOR PROTECTION (OVER-VOLTAGE AND UNDER-VOLTAGE) ???
I don't want to use Lead-Acid, NiCd or NiMh battery anymore. Just Li-Ion from now on hehehe.

Help?
  • 0
    TI__Mastermind 36110 points

    You might want to consider a charger that provides temperature qualification to ensure the battery is only charged when its temperature is within acceptable charging range, typically 0deg C to 45 deg C.  This requires a temperature sense pin.  You might also need a charger that allows higher power dissipation.  Your chosen charger says it's capable of 500mA, however with Vin=5V and Vout =3.7V, the power dissipation will be Pd=(5V-3.7V)*0.5A=0.65W.  The SOT-25 thetaJA is 230 degC/W which means it will have a temperate rise of 230degC/W*0.65W = 149.5 deg C.  This is not possible.  The Texas Instruments battery charger, bq24040 provides the temperatrue sensing as well as a theta JA of 60deg C/W which is only a 39 deg C temperature rise under the same conditions.  If you need power path, there are other ICs that provide that functionality.  TI has many chargers to choose from.  You probably need a linear standalone battery charger. You can select one by going to www.ti.com, clicking on Power Management and then clicking on Battery Charge Management.  Also consider contacting your local distributor for additional assistance in selecting the right IC for your application.  If you don't know your local distributor, you can find them by contacting TI's Product Information Center by clicking on "contact technical support" from www.ti.com.

  • 0 in reply to Matthew Day
    Expert 1170 points 
    Hi.

    The goal is to recharge the batteries within a 100 to 200mA range.

    The BATT will be rarely used to supply current to the circuit (just one day of the week), so there is no need of a fast charge and the power dissipation over the IC will be much lower than you calculated.

    And also, bq24040 and bq24041 are very hard to find, even on Digikey (there are fewer quantity than most of other ICs that do the same job)
    I always bought from Digikey, even in high quantity
    

    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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                          TI__Mastermind
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    Also look at bq24090.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                 	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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