LT3685E 데이터 시트보기 (PDF) - Linear Technology

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LT3685E

36V, 2A, 2.4MHz Step-Down Switching Regulator

Linear Technology 

LT3685

PIN FUNCTIONS

BD (Pin 1): This pin connects to the anode of the boost

Schottky diode. BD also supplies current to the internal

regulator.

BOOST (Pin 2): This pin is used to provide a drive

voltage, higher than the input voltage, to the internal bipolar

NPN power switch.

SW (Pin 3): The SW pin is the output of the internal power

switch. Connect this pin to the inductor, catch diode and

boost capacitor.

VIN (Pin 4): The VIN pin supplies current to the LT3685’s

internal regulator and to the internal power switch. This

pin must be locally bypassed.

RUN/SS (Pin 5): The RUN/SS pin is used to put the

LT3685 in shutdown mode. Tie to ground to shut down

the LT3685. Tie to 2.5V or more for normal operation. If

the shutdown feature is not used, tie this pin to the VIN

pin. RUN/SS also provides a soft-start function; see the

Applications Information section.

SYNC (Pin 6): This is the external clock synchronization

input. Ground this pin when SYNC function is not used. Tie

to a clock source for synchronization. Clock edges should

have rise and fall times faster than 1μs. See synchronizing

section in Applications Information.

PG (Pin 7): The PG pin is the open collector output of an

internal comparator. PG remains low until the FB pin is

within 11% of the final regulation voltage. PG output is

valid when VIN is above 3.6V and RUN/SS is high.

FB (Pin 8): The LT3685 regulates the FB pin to 0.790V.

Connect the feedback resistor divider tap to this pin.

VC (Pin 9): The VC pin is the output of the internal error

amplifier. The voltage on this pin controls the peak switch

current. Tie an RC network from this pin to ground to

compensate the control loop.

RT (Pin 10): Oscillator Resistor Input. Connecting a resistor

to ground from this pin sets the switching frequency.

Exposed Pad (Pin 11): Ground. The Exposed Pad must

be soldered to PCB.

BLOCK DIAGRAM

VIN

4 VIN

C1

INTERNAL 0.79V REF

RUN/SS

5

–

+

S

SLOPE COMP

RT

10

RT

SYNC

6

SOFT-START

PG

7

ERROR AMP

0.7V

+

–

OSCILLATOR

200kHz–2.4MHz

GND

FB

11

8

R2

R1

SWITCH

LATCH

R

Q

S

VC CLAMP

BD

1

BOOST

2

SW

3

C3

L1

D1

VOUT

C2

VC

9

CC

CF

RC

3685 BD

3685fb

7

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