L6910G データシートの表示（PDF） - STMicroelectronics

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L6910G

ADJUSTABLE STEP DOWN CONTROLLER WITH SYNCHRONOUS RECTIFICATION

STMicroelectronics 

L6910G

9 APPLICATION IDEA 2: POSITIVE BUCK-BOOST REGULATOR 3V TO 13.2V

INPUT / 5V 2.5A OUTPUT

In some applications the input voltage changes in a very wide range while the output must be regulated to a

fixed value. In this case a Buck-Boost topology can be required in order to keep the output voltage in regulation.

The schematic below shows how to implement a Buck-Boost regulating 5V at the output from both 3.3V and 5V

and 12V input buses.

In a Buck-Boost topology the current is delivered to the output during the OFF phase only. So, for a given current

limit, the maximum output current depends strongly on the duty cycle. Assuming a 100% efficiency and neglect-

ing the current ripple across the inductor, the relationship betweent the current limit and the maximum output

current is the following:

IOMAX = ILIM ⋅ (1 – D)

Where ILIM is the current limit and D is the duty cycle of the application.

The worst case is with DMAX. Since, in a Buck-Boost application, D is given by the following formula:

D = -V----I-N--V---+--O---V----O---

The worst case is with VINMIN.

Obviously, since the efficiency is lower than 100% and the ripple is usually not negligible, the maximum output

current is always lower than the value calculated in the above formula

Figure 28. Positive buck-boost regulator 3V to 13.2V input / 5V 2.5A Output Circuit

VIN (3.3V-5V-12V BUSES)

GNDIN

VCC (12V BUS)

GNDCC

G1

R7

C6

C8

C7

R1

C3

D1

BOOT

12

VCC

15

OCSET

3

11

C5

10

GND

7

U1

14

SS

4 L6910/A 13

OSC

2

9

EAREF

8

5

1

6

C4

UGATE

PHASE

LGATE

PGND

PGOOD

VREF

C9

R5

C10

C1- C2

Q1

L1

Q4

Q2

D2

Q3

C13- 14

C12

R3

R4 C11

VOUT ( 5V 2.5A )

R2

GNDOUT

R6

20/26

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