LT3481 데이터 시트보기 (PDF) - Linear Technology

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LT3481

36V, 2A, 2.8MHz Step-Down Switching Regulator with 50µA Quiescent Current

Linear Technology 

LT3481

PIN FUNCTIONS

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

Schottky diode.

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 LT3481’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

LT3481 in shutdown mode. Tie to ground to shut down

the LT3481. Tie to 2.3V 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.

PG (Pin 6): The PG pin is the open collector output of an

internal comparator. PG remains low until the FB pin is

within 10% of the final regulation voltage. PG output is

valid when VIN is above 3.5V and RUN/SS is high.

BIAS (Pin 7): The BIAS pin supplies the current to the

LT3481’s internal regulator. Tie this pin to the lowest

available voltage source above 3V (typically VOUT). This

architecture increases efficiency especially when the input

voltage is much higher than the output.

FB (Pin 8): The LT3481 regulates the FB pin to 1.265V.

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

BIAS

7

INTERNAL 1.265V REF

–

+

RUN/SS

5

3

SLOPE COMP

RT

10

RT

SOFT-START

PG

6

1.12V

ERROR AMP

+

–

OSCILLATOR

300kHz–2.8MHz

GND

FB

11

8

R2

R1

SWITCH

LATCH

R

Q

S

DISABLE

BurstMode

DETECT

VC CLAMP

BD

1

BOOST

2

SW

3

C3

L1

D1

VOUT

C2

VC

9

CC

CF

RC

3481 BD

3481fb

7

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