LTC4013 CC+CV 10s4p Li-ion charger selectable charging current

Hi, 

I need to implement a buck battery charger for a 10s4p Li-ion pack, Vin 48VDC. with the additional requirement that Iout should be selectable from a MCU (i.e. conmuting between different programming resistors).

LTC4013 looks great, but one thing worries me: changing charging current for the LTC4013 means conmuting between different Rs resistors, which are in the high current branch, and makes it complex.

Is there any other way of implementing a CC+CV battery charger for 10s Li-Ion, with a LTC4013 or a DC DC Buck such as the LT3761 or the LT3796, allowing me to program the charging current from a MCU selecting between different resistors? 

I'm very newbie at power electronics, sorry about my ignorance.

Thanks

  • 0
    •  Analog Employees 
    on Jun 11, 2019 8:11 PM over 1 year ago

    Hello and welcome to the wonderful world of power electronics.

    You are correct that it is very difficult to swap out milliohm-range resistors during runtime. I do not have a good solution for doing so unless you plan to operate at fairly low current. You might consider one of our other chargers that allows you to set the output current in a different way. Unfortunately, in this high-voltage operating space, you are very limited in product options. Your only other option is LTC4020 which may be overkill here (it is buck-boost for one thing).

    However, LTC4020 does have an ILIMIT pin which can allow you to dynamically change the charge current.

    If you can lower your battery voltage requirement, you can increase your options for product selection.

    Since you are a self-proclaimed newbie to power, let me know before you go to fabricate your board and we can try to make sure we get the layout right the first time. This becomes very critical, especially in these high-power designs. Our demo board layouts are available online and can be copied as you desire.

    Regards,

    Zack

  • Hi Zack, thanks for your help. I really don't need to swap the resistors while the battery is charging, but only when the charger is idle (I.e. user removed the battery from charger). Do you think this may make possible to conmute between various Rs values from a MCU?

    Regarding LTC4020, I couldn't find the ILIMIT pin that would allow me to set the charge current dynamically.

    Regards,

    Sebastian

  • 0
    •  Analog Employees 
    on Jun 12, 2019 2:41 PM over 1 year ago in reply to SdeLeon

    Hi Sebastian,

    I should have said "in-circuit" rather than "during runtime". It makes no difference whether the charger is running or not - the underlying issue is that the RDS(on) of the FET used to swap the sense resistor value would be comparable with the sense resistance itself. If you have a higher-value sense resistor and a low-resistance FET then you may consider the impact negligible. What is your charge current?

    ILIMIT is pin 25 on LTC4020.

    Regards,

    Zack

  • Thanks again, Zack. Yeah, that's the problem. Charging current is up to 5A, so Rs value is quiet small. I'll do simulations with LTSpice and see.

    If you want, let's close this thread - and I'll try simulations with the LTC4013.

    Regards,

    Sebastian