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LOW-COST DOUBLE LI-ION BATTERY CHARGER USING ST6255C/ST6265C MCU

In this demo, L = 150 µH and C = 220 µF so the cut-off frequency is 876 Hz. The PWM fre-

quency is fixed at ~30 kHz. This way, charging voltage ripple is minimized.

If

α is the PWM positive duty cycle in A, the mean value of V

-

α)*(-V

Example with the evaluation board hardware:

For the maximum current to apply (600 mA), typical values are:

tery voltage is 4.2 V. In this case, the required duty cycle is ~98%. These values show that the

range of duty cycles is fully used, which improves PWM resolution.

Let us now consider the whole charging time. At this scale,

α, I

The above equation helps to understand how

α evolves during this time.

α decreases gradually in order to reduce I

2.2 PWM SIGNAL SWITCHING GENERATION

The ST6255C only provides one PWM signal. Switching the signal from one slot to another is

done through the E_FRONT and E_REAR signals, generated by standard output pins. It is

less expensive to implement the AND function using NPN transistors than with AND gates.

S

bat

D

d

sat

CE

ply

sup

bat

R

V

V

V

V

V

I

−

−

−

⋅

α

−

+

−

⋅

α

=

1