AN2946 datasheet(18/38 Pages) STMICROELECTRONICS

18 / 38 page

Hardware design

AN2946

18/38

Doc ID 15473 Rev 2

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Stage 3:

In stage 3 when VBATTERY ≥ 14.3 V, the controller enters into floating charging, and Uba is

limited to 14.3 V. Figure 18 shows the battery voltage (Uba) and charging current (Iba) in

this stage.

Figure 18.

Battery voltage versus charging current

The result shows that with different charging currents, the battery voltage is kept at around

13.8 V and remains constant. Figure 19 and 20 show the typical current output from the

solar module and the current charged to the battery. Both currents are smooth and no large

current ripple is observed. In Figure 21 the inductor current waveform shows that the buck

converter works at continuous current mode. Peak-to-peak current (IL) ripple is around 0.7

A. Such a small current ripple requires a small output capacitor. The turn-off switching

voltage spike of the MOSFET (Vds) and diode (Vak) are very small in actuality.

Table 3.

Test results for different values of Vdc (R = 4.6 Ω)

Udc [V]

Usc [V]

Isc [A]

Uba [V]

Iba [A]

Charger

efficiency [%]

18.0

3.90

13.08

5.03

93.7

17.5

3.80

12.99

4.79

93.6

17.0

3.65

12.90

4.57

95.0

16.5

3.50

12.82

4.33

96.1

16.0

3.48

12.73

4.12

94.2

15.5

3.38

12.65

3.90

94.2

15.0

3.30

12.57

3.69

93.7

14.6

3.17

12.47

3.48

93.8

14.4

2.97

12.39

3.26

94.4

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