LT8708: How does IC select (Constant current/ Constant Voltage) when used Li-ion Battery Charging Application

Hello,

  I am evaluating LT8708 for Li-ion Battery charging application. We require 2 modes of operation.

1. Constant Current Mode: For a 60V Battery lets say this mode starts when battery voltage is  37V. In this situation FBOUT and IMON_OP both Loops are active. FBOUT is set to have 63V and IMON_OP is set for 6A charging Current. How does it ensure that IMON_OP Error Amplifier dominates and IC works in CC Mode and not in CV Mode?

2. Constant Voltage Mode. After the battery is charged to 63V, only FBOUT error Amplifier must act to maintain battery voltage. This can be done as only FBOUT would be out of limit at this condition.

My confusion is how to ensure that IC operates in CC mode when Required? Do we need to disable the FBOUT Amplifier at that time? The examples in datasheet do not disable any of the Error Amplifiers, so what is the way to ensure its CC Mode operation when output voltage is below set limit.

Thanks

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  • +1
    •  Analog Employees 
    on Dec 17, 2020 11:45 PM 3 months ago

    Hi Urmi,

    When the FBOUT pin (E4) detects that Vout is below regulation, the compensation voltage, Vc, rises. (refer to page 23) The current will flow from Vin to Vout and it  would run in Constant Current mode with output current set by IMON_OP, until the FBOUT detects that you reach your CV level.

    So FBOUT would need to be active to sense the rise of your battery voltage while IMON_OP (E6) maintains the output constant current you desired at constant current mode.

    Regards,  

Reply
  • +1
    •  Analog Employees 
    on Dec 17, 2020 11:45 PM 3 months ago

    Hi Urmi,

    When the FBOUT pin (E4) detects that Vout is below regulation, the compensation voltage, Vc, rises. (refer to page 23) The current will flow from Vin to Vout and it  would run in Constant Current mode with output current set by IMON_OP, until the FBOUT detects that you reach your CV level.

    So FBOUT would need to be active to sense the rise of your battery voltage while IMON_OP (E6) maintains the output constant current you desired at constant current mode.

    Regards,  

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