LTC1266-33 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LTC1266-33

Synchronous Regulator Controller for N- or P-Channel MOSFETs

Linear Technology 

LTC1266

LTC1266-3.3/LTC1266-5

W

FU CTIO AL DIAGRA Pin 10 Connection Shown for LTC1266-3.3 and LTC1266-5; Changes Create LTC1266

–

LBIN 13

LB

VIN

1.25V

REFERENCE

+

14 LBOUT

SIGNAL

GROUND

12

SLEEP

PWR VIN 2

3 PINV

1 TDRIVE

16 BDRIVE BINH 4

15 PGND

SENSE+

SENSE –

9

8

ADJUSTABLE

VERSION

VFB

10

V

R

Q

S

S

VTH2

VTH1

–

C

– + VTRIP

VOS

5pF

13k

T

+

MAX

ON-TIME

ITH 7

G

100k

1.265V

CONTROL

6

CT

OFF-TIME

CONTROL

VIN

SENSE

–

VFB

ENABLE

PINV

SHDN 11 REFERENCE 5 VIN

1266 FD

U

OPERATIO

The LTC1266 series uses a current mode, constant off-

time architecture to synchronously switch an external pair

of power MOSFETs. Operating frequency is set by an

external capacitor at the timing capacitor Pin 6.

The output voltage is sensed by an internal voltage divider

connected to SENSE –, Pin 8, (LTC1266-3.3 and LTC1266-

5) or external divider returned to VFB, Pin 10, (LTC1266).

A voltage comparator V, and a gain block G, compare the

divided output voltage with a reference voltage of 1.265V.

To optimize efficiency, the LTC1266 automatically switches

between two modes of operation, burst and continuous.

The voltage comparator is the primary control element

when the device is in Burst Mode operation, while the gain

block controls the output voltage in continuous mode.

During the switch ON cycle in continuous mode, current

comparator C monitors the voltage between Pins 8 and 9

connected across an external shunt in series with the

inductor. When the voltage across the shunt reaches its

threshold value, the topside driver output is switched to

turn off the topside MOFSET (Power VIN for P-channel or

ground for N-channel). The timing capacitor connected to

Pin 6 is now allowed to discharge at a rate determined by

the off-time controller. The discharge current is made

proportional to the output voltage (measured by Pin 8) to

model the inductor current, which decays at a rate which

is also proportional to the output voltage. While the timing

capacitor is discharging, the bottom-side drive output is

switched to power VIN to turn on the bottom-side

N-channel MOSFET.

7

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