LTC1773EMS データシートの表示（PDF） - Linear Technology

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LTC1773EMS

Synchronous Step-Down DC/DC Controller

Linear Technology 

LTC1773

PIN FUNCTIONS

ITH (Pin 1): Error Amplifier Compensation Point. The

current comparator threshold increases with this control

voltage. Nominal voltage range for this pin is 0V to 1.2V.

Under high duty cycle and nearing current limit, ITH can

swing up to 2.4V.

RUN/SS (Pin 2): Combination of Soft-Start and Run

Control Inputs. A capacitor to ground at this pin sets the

ramp time to full current output. The time is approximately

0.8s/µF. Forcing this pin below 0.4V shuts down all the

circuitry.

SYNC/FCB (Pin 3): Multifunction Pin. This pin performs

three functions: 1) secondary winding feedback input, 2)

external clock synchronization and 3) Burst Mode opera-

tion or forced continuous mode select. For secondary

winding applications, connect to a resistive divider from

the secondary output. To synchronize with an external

clock, apply a TTL/CMOS compatible clock with a fre-

quency between 585kHz and 750kHz. To select Burst

Mode operation, tie SYNC/FCB to VIN. Grounding this pin

forces continuous operation.

VFB (Pin 4): Feedback Pin. Receives the feedback voltage

from an external resistive divider across the output. Do not

use more than 0.01µF of feedforward capacitance from FB

to the output.

GND (Pin 5): Ground Pin.

BG (Pin 6): Bottom Gate Driver of External N-Channel

Power MOSFET. This pin swings from 0V to VIN.

TG (Pin 7): Top Gate Driver of External P-Channel Power

MOSFET. This pin swings from 0V to VIN.

VIN (Pin 8) : Main Supply Pin. Must be closely decoupled

to GND (pin 5).

SENSE–(Pin 9): The Negative Input to the Current Com-

parator. A sense resistor between this pin and VIN sets the

peak current in the top switch. Connect this pin to the

source of the external P-Channel power MOSFET.

SW (Pin 10): Switch Node Connection to Inductor. This

pin connects to the drains of the external main and

synchronous power MOSFET switches.

W

FUNCTIONAL DIAGRA

0.4µA

SYNC/FCB 3

BURST Y

DEFEAT

X

OSC

Y = “0” ONLY WHEN X IS A CONSTANT “1”

SLOPE

COMP

8 VIN

0.4V

9 SENSE–

VFB 4

0.6V –

SYNC

DEFEAT

+

0.8V REF

UVLO

TRIP = 2.5V

SHUTDOWN

0.8V

FREQ

SHIFT

+

EA

–

1.5µA

2

RUN/SS

RURNU/SNO/ FT

SOFSTT-ASRTATRT

0.86V

–

OVDET

+

0.22V

ITH

1

0.8V –

FCB

+

Figure 2.

EN

–

50mV

SLEEP

+

BURST

COMP

–+

ICOMP

SQ

RQ

SWITCHING

LOGIC

AND

BLANKING

CIRCUIT

ANTI

SHOOT-THRU

IRCMP

7 TG

6 BG

10 SW

5 GND

1773 FD

1773fb

5

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