AN1330 datasheet(26/31 Pages) STMICROELECTRONICS

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Application ideas

AN1330

26/31

Application ideas

6.1

Positive buck-boost regulator

The device can be used to implement a step-up/down converter with a positive output

voltage. Figure 25 below shows the schematic diagram of this topology for an output voltage

of 12 V.

The input voltage can range from 5 V and 35 V. The output voltage is given by VO=VIN ·

D/(1-D), where D is duty cycle. The maximum output current is given by IOUT=1× (1-D). The

current capability is reduced by the term (1-D) and so, for example, with a duty cycle of 0.5,

the maximum output current deliverable to the load is 0.5 A. This is due to the fact that the

current flowing trough the internal power switch is delivered to the output only during the

OFF phase.

Figure 25.

Positive buck-boost regulator

6.2

Buck-boost regulator

In Figure 26, the schematic circuit for a standard buck-boost topology is shown. The output

voltage is given by VO = - VIN · D/(1-D). The maximum output current is equal to IOUT=1 · (1-

D), for the same reason as that of the up-down converter. An important thing to take into

account is that the ground pin of the device is connected to the negative output voltage.

Therefore, the device is subjected to a voltage equal to VIN-VO, that has to be lower than 36

V (the maximum operating input voltage).

Figure 26.

Buck-boost regulator

VIN=5V

10uF

25V

Ceramic

STPS2L25U

VCC

COMP

GND

OUT

INH

SYNC

VREF

L5970

4.7k

33uH

24k

2.7k

22nF

3.3V

100uF

16V

VOUT=12V/0.3A

220pF

STPS2L25U

STN4NE03L

Vin=5V Vout=12V

Iout=0.3A

Efficiency=76%

AN1330 Datasheet(PDF) 26 Page - STMicroelectronics

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