AN2390 datasheet(2/42 Pages) STMICROELECTRONICS

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AN2390

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The evaluation board is powered from a 5 V supply. This supply is purposely chosen to show

the application of the modified buck-boost converter. This is because, while a buck converter

can be used to charge 2 cell NiMH battery from a 5 V supply, it is not generally suitable for

charging a 4.2 V Li-ion battery due to the presence of protection diodes and other

components which induce a voltage drop of around 1 V so you can not use a buck converter

in this case.

The modified non-inverting buck-boost converter circuit used in this application note needs

only one inductor and requires only an extra PWM signal compared to the kind of buck

converter that is normally used. By using the switches in different forms, this converter can

be used either as a buck converter or as a boost converter. Using the flexibility of the MCU,

this converter is capable of charging a wide variety of batteries as can be seen from the

evaluation board, where this converter has been used in buck converter mode to charge

NiMH batteries, while a combination of buck-boost converter and boost converter modes are

used to charge Li-ion batteries. For more details on the buck-boost converter, please refer to

AN2389.

AN2390 Datasheet(PDF) 2 Page - STMicroelectronics