AN2389

Test environment and results

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Test environment and results

We used this buck-boost converter in the universal battery charger evaluation board

non-inverting buck-boost converter circuit mentioned in this application note. For simplicity,

this figure does not show all the connections.

Figure 6.

General circuit-based battery charger

Here some results are shown for charging the Li-ion battery using this converter in buck-

boost mode. The above charger is is intended for charging a single Li-ion or two NiMH in

series using a 5V supply input. Details on the implementation are given in AN2390 where

you can find results for NiMH batteries as well as for a charger used simply in buck

converter mode.

Some parameter values are as follows:

PWM1 and PWM2 = 16KHz.

of D1 is 95% and D2 is equal to 30%.

Then using the formulas given in Section 3:

Lmin = 21 uH (from equation 1) or 10 uH (from equation 2). So we should choose a value

larger than 21 uH.

Cmin = 70uF (from equation 3). So we need to choose a value higher than 70 uF.

In this example, L = 75 uH, C = 470 uF are taken, which are larger than the values

calculated using the formulas hence will support the application.

The following table shows some of the readings taken for different values of the duty cycles

D1 and D2.

PWM1

PWM2

C

d1

P-

P+

L

d2

SW2

SW1

Sense resistor

Battery