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Looking for a battery charging IC to supply 5V and act as a "UPS"

Craig Easdale
Expert 2170 points
Other Parts Discussed in Thread: BQ25600, BQ25606, BQ24040

Hello,

I have a requirement for a new project to be able to keep itself alive for a short while in the event of an external power failure. At the moment I am using an encapsulated DCDC converter to provide 5V to the system. This 5V is then also used to deliver 3.3V via a LDO. 

I'm fairly happy with the current DCDC converter, so I was wondering if a one-chip solution existed that would allow me to charge a battery from this regulated 5V supply, and maintain the 5V output using the battery as the source if that failed. The maximum current this would have to deliver is ~350mA.

In order to reduce the design time and deliver a reliable solution quickly I was hoping to find a highly integrated solution. Can anyone make a recommendation for a part that might fit my requirements here?

  • 0
    TI__Mastermind 21590 points

    Hello Craig,
    What is the charge voltage of the battery you plan on using?

    Also would you require 5V on the output even if powered by battery alone? This would require a buck boost charger.

  • 0 in reply to Raheem
    Expert 2170 points
    Hi Raheem,

    I was likely going to use a single lithium-ion cell, so probably 3.7v or 4.2v maximum.

    And yes, I would need both the 5v and 3.3v rails to continue to function when powered by the battery alone. I know I'll need a boost converter to achieve this from the battery voltage, but I hoped that perhaps an integrated solution my exist.
  • 0
    TI__Guru**** 166176 points
    Craig,

    Most of TI's newer switching, buck based chargers have OTG mode in which the charger runs the buck converter in reverse, as a boost converter, and provides 5V at the output. The bq25600 family might work for you. If you don't have a host processor, I suggest looking at the bq25606 standalone version. With OTG pin pulled high, following a short delay after VBUS=5V is removed, the charger will provide 5V back to VBUS from the battery. The challenge will be providing 5V power during this delay. Perhaps a large capacitor in the system?
  • 0 in reply to Jeff F
    Expert 2170 points
    How short a delay in the power feeding back through to VBUS is there likely to be?

    I do have a host controller, but I'd like to keep the solution as simple as possible to reduce any additional development time so the bq25606 might be ideal if this delay isn't too significant/can be compensated for with a large capacitor as you suggest.
  • 0 in reply to Craig Easdale
    Expert 2170 points

    Looking for a follow up on this.

    I can't find any timing information regarding the possible delay to the power returning. The system could see peak currents of 200mA, so if the delay is much longer than a few milliseconds then it might not be feasible.

    Additionally, if I wanted to use the non-standalone I2C version of the part would it function just as the standalone version does by default?

  • 0 in reply to Jeff F
    Expert 2170 points

    Hi, It's been 3 days since I last heard from anyone about this. I really really need some answers to guide my design ASAP.

    Thanks.

     

  • 0 in reply to Craig Easdale
    TI__Guru**** 166176 points

    Craig,

    The standalone part works like a host controlled part in default, except you use external components to set charge current, battery regulation voltage, input current limit and also do not have access the status/fault registers.

    I will have to test on the bench in order to determine the exact delay time but it is likely in the 30ms time range.

  • 0 in reply to Jeff F
    TI__Guru**** 166176 points
    Craig,

    Based on my bench testing, the bq25606 does not automatically enter OTG when VBUS is removed. It requires OTG to be toggled. This can be achieved with a simple circuit that pulls OTG pin high when VBUS drops but the 40ms delay (unloaded, longer if loaded) is too long for your application. So, I recommend a battery charger (BQ24040 1A charger), powered by 5V, with battery tied to a 5-V boost converter and 200mA, 3.3V LDO combo (TPS61120RSA). You can diode OR the 5V supply and the output of the boost converter.