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


  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.


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    •  Analog Employees 
    on Dec 18, 2020 6:28 AM 3 months ago in reply to Urmi S

    Yes, the operation would be the same if the power flows from Vout to Vin, except now that FBIN (EA3) also monitors the input regulation while IMON_INP (EA5) set the constant current for that power flow.

    Buck-Boost operation is discussed in page 19. A2 and A5 are both used since Buck-Boost operates in cycle of Buck, Boost, and pass-through (M1-M4 switched on). Vc is the reference for the inner loop (with CSP-CSN voltage as the sampled switch current), which is derived from the resultant of six internal Error Amplifiers (outer loop).