L6910GTR PDF资料下载(13/26 页)1.3 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDS

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参数资料

型号：	L6910GTR
厂商：	STMICROELECTRONICS
元件分类：	稳压器
英文描述：	1.3 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封装：	SO-16
文件页数：	13/26页
文件大小：	1046K
代理商：	L6910GTR

L6910G

20/26

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:

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:

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

OMAX

LIM

–

()

-----------------------

C1- C2

L6910/A

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

VOUT ( 5V 2.5A )

VCC

GND

VREF

OSC

OCSET

UGATE

PHASE

LGATE

PGND

PGOOD

VFB

-14

C13

GNDOUT

C12

C10

GNDIN

VCC (12V BUS)

EAREF

BOOT

C11

GNDCC