LTC4079 enabled to charge super cap while load imposed to it.

Hi,

I'm using LTC4079 to charge a hybrid capacitor which supply wireless transmission circuits, by AC mains or renewable DC.

My question is whether LTC4079 can be enabled all the time when our product is switched on, even when the hybrid capacitor voltage is lower than the limit of LTC4079 re-charge and wireless transmission is activated, are there any negative impacts on LTC4079? Say, excessive current drain from BAT.

I don't find clear description on it, but my laptop are always used as both AC mains and battery are plugged at the same time.

Regards,

Dawei Ma

  • +1
    •  Analog Employees 
    on Dec 7, 2020 11:33 PM 1 month ago

    Hi Dawei,

    You mean to keep it in a "permanent charging" state so that it always outputs? Yes, there is a way.

    Instead of a capacitor on the TIMER pin, put a 3.3Mohm resistor from TIMER to GND. This will prevent the timer from ever timing out but will also disable C/10 termination. As a result, it remains in a permanent charging state.

    Regards,

    Zack

  • Zack,

    Not exactly, I consider to use auto-recharge feature and C/10 termination will be used, but I concern when LTC4079 is charging battery, is it OK to load current (wireless transmission enabled) from battery at the same time? Any impacts on BAT pin of LTC 4079?

    According to your description of permanent charging feature, it is OK to load current from battery when charging. 

    Regards,

    Ma Dawei

  • +1
    •  Analog Employees 
    on Dec 10, 2020 7:17 PM 1 month ago in reply to Dawei Ma

    It is ok to supply the load from the battery while it is being charged, but you should be aware of what that means from the charger's perspective.

    The charger is not aware of this and still limits the charge current to the programmed battery charge current.

    If your load is small in comparison, no problem. The battery will still be charged, just at a slower rate (since some of the charge current is going to the load instead).

    If your load current is greater than the charge current, the battery will be net discharging while being charged, so that could be an issue.

    Regards,
    Zack

  • Zack,

    The load current in my application is greater than programmed charge current.

    I don't care about the battery is not charged while load is activated, if it doesn't impose negative impacts on LTC4079, that's what I concern.

    In short, I can enable LTC4079 all the time while load is activated, auto-recharge feature and C/10 termination will be used.

    Regards,

    Ma Dawei

  • 0
    •  Analog Employees 
    on Dec 11, 2020 7:55 PM 1 month ago in reply to Dawei Ma

    Yes, that is correct and it sounds like you understand any complications you will run into.

    Regards,

    Zack