LTC1877 データシートの表示（PDF） - Linear Technology

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LTC1877

High Efficiency Monolithic Synchronous Step-Down Regulator

Linear Technology 

LTC1877

PIN FUNCTIONS

RUN (Pin 1): Run Control Input. Forcing this pin below

0.4V shuts down the LTC1877. In shutdown all functions

are disabled drawing <1µA supply current. Forcing this pin

above 1.2V enables the LTC1877. Do not leave RUN

floating.

ITH (Pin 2): Error Amplifier Compensation Point. The

current comparator threshold increases with this control

voltage. Nominal voltage range for this pin is from 0.5V

to 1.9V.

VFB (Pin 3): Feedback Pin. Receives the feedback voltage

from an external resistive divider across the output.

GND (Pin 4): Ground Pin.

SW (Pin 5): Switch Node Connection to Inductor. This pin

connects to the drains of the internal main and synchro-

nous power MOSFET switches.

VIN (Pin 6): Main Supply Pin. Must be closely decoupled

to GND, Pin 4.

SYNC/MODE (Pin 7): External Clock Synchronization and

Mode Select Input. To synchronize with an external clock,

apply a clock with a frequency between 400kHz and

700kHz. To select Burst Mode operation, tie to VIN. Ground-

ing this pin selects pulse skipping mode. Do not leave this

pin floating.

PLL LPF (Pin 8): Output of the Phase Detector and Control

Input of Oscillator. Connect a series RC lowpass network

from this pin to ground if externally synchronized. If

unused, this pin may be left open.

W

FUNCTIONAL DIAGRA

PLL LPF

8

SYNC/MODE

7

BURST

DEFEAT Y

X

Y = “0” ONLY WHEN X IS A CONSTANT “1”

SLOPE

COMP

VCO

OSC

VIN

0.8V

0.6V –

3

+

VFB

FREQ

SHIFT

VREF +

0.8V

– EA

gm = 0.5m Ω

VIN SLEEP

VIN

VIN

RUN

1

0.8V REF

–

OVDET

0.85V +

SHUTDOWN

0.45V

2 ITH

– EN SLEEP

+

BURST

SQ

RQ

RS LATCH

SWITCHING

LOGIC

AND

BLANKING

CIRCUIT

ICOMP

ANTI

SHOOT-

THRU

IRCMP

6 VIN

6Ω

5 SW

4 GND

1877 BD

6

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