AN2389

Application in battery charger

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4

Application in battery charger

We can use the modified non-inverting buck-boost converter in a combination of different

modes as required by the application.

4.1

Theory of operation

The DC-DC converter uses a combination of buck-boost converter and boost converter

mode to charge the Li-ion battery. In case of Li-ion, the constant current constant voltage

(CC CV) charging algorithm is used to charge the battery. Here we have chosen the input

voltage just enough to show the functionality of the converter in buck-boost mode and boost

mode.

Initially the converter works in Buck-Boost converter mode to charge the battery in constant

current mode by keeping the duty cycle of PWM2 constant and varying the duty cycle of

PWM1. As soon as there is an overflow condition for the duty cycle of PWM1. The converter

switches from buck-boost converter mode to boost converter mode. And then duty cycle of

PWM2 is varied to follow the algorithm while SW1 remains in ON condition. Following

section shows the software flow chart for this combination.