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BQ25703A: Deep discharge protection

Horv.joe
Prodigy 85 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQ25703

Hi, 

I'd like to use the Bq25703 in a 12V lead-acid charger / ups application, and I have some questions about it: 

My application's parameters: 

  • DC Input voltage: 12V (5A)
  • Battery: 2,3Ah 12V SLA
  • System voltage: 12V 
  • Mode: UPS

Is there a way to increase the "VVBAT_UVLOZ" - (Battery undervoltage threshold) value from 2,55V to 10,5V? Because the datasheet says "If only battery is present and the voltage is above VVBAT_UVLOZ, the BATFET turns on and connects battery to system" and I don't want to start the system when adapter isn't connected to the charger's input and the battery's voltage is under 10,5V - to avoid deep discharge the SLA battery. 

If it isn' possible, is there a way to manually switch off the BATFET with an i2c command, to disconnect it from the system, or I should use an additional battery monitor IC and a power FET in series with the BATFET to disconnect the battery when it's voltage drops below 10,5V ? 

Or could you recommend and other solution for these requirements? 

Thank you,
Joe 

 

  • 0
    TI__Guru 56650 points
    Battery FET has a body diode. Even, it is turned off. The body diode can still pass battery voltage to system.
    To disconnect system from battery, you need to add another FET. Yes. You should use an additional battery monitor IC and a power FET in series with the BATFET to disconnect the battery when it's voltage drops below 10,5V.