LTC3444 データシートの表示（PDF） - Linear Technology

部品番号

コンポーネント説明

メーカー

LTC3444

Micropower Synchronous Buck-Boost DC/DC Converter for WCDMA Applications

Linear Technology 

U

OPERATIO

Buck Region (VIN > VOUT)

Switch D is always on and switch C is always off during this

mode. When the internal control voltage, VCI, is above

voltage V1, Switch A is on. During the off time of switch A,

synchronous switch B turns on for the remainder of the

time. Switches A and B will alternate similar to a typical

synchronous buck regulator. As the control voltage in-

creases, the duty cycle of switch A increases until the

maximum duty cycle of the converter in buck mode

reaches DMAX_BUCK, given by:

DMAX_BUCK = 100% – D4SW

where D4SW = duty cycle % of the four switch range.

D4SW = (125ns • f) • 100 %

where f = operating frequency, Hz.

Beyond this point the “four switch,” or Buck-Boost region

is reached.

LTC3444

Buck-Boost or Four Switch (VIN ~ VOUT)

When the internal control voltage, VCI, is above voltage V2,

but below V3, switch pair AD remain on for duty cycle

DMAX_BUCK, and the switch pair AC begins to phase in.

As switch pair AC phases in, switch pair BD phases out

accordingly. When the VCI voltage reaches the edge of the

buck-boost range, at voltage V3, the AC switch pair

completely phase out the BD pair, and the boost phase

begins at duty cycle D4SW. The input voltage, VIN, where

the four switch region begins is given by:

VIN

=

1–

VOUT

(125ns

•

f)

V

The point at which the four switch region ends is given by:

VIN = VOUT(1–D) = VOUT(1–125ns • f) V

3444fb

11

Share Link: