LT3990 데이터 시트보기 (PDF) - Linear Technology

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LT3990

62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes

Linear Technology 

LT3990

Pin Functions (DFN, MSOP)

FB (Pin 1/Pins 1, 2): The LT3990 regulates the FB pin to

1.21V. Connect the feedback resistor divider tap to this

pin. The two FB pins on the MSE package are connected

internally and provide a redundant path for the feedback

divider. Tie the divider to both pins.

EN/UVLO (Pin 2/Pin 4): The part is in shutdown when this

pin is low and active when this pin is high. The threshold

voltage is 1.21V going up with 32mV of hysteresis. Tie

to VIN if shutdown feature is not used. The EN/UVLO

threshold is accurate only when VIN is above 4.2V. If VIN

is lower than 4.2V, ground EN/UVLO to place the part in

shutdown.

VIN (Pin 3/Pin 6): The VIN pin supplies current to the

LT3990’s internal circuitry and to the internal power switch.

This pin must be locally bypassed.

GND (Pins 4, 5, Exposed Pad Pin 11/Pin 8, Exposed

Pad Pin 17): Ground. The exposed pad must be soldered

to the PCB.

SW (Pin 6/Pin 9): The SW pin is the output of an internal

power switch. Connect this pin to the inductor.

BOOST (Pin 7/Pin 11): This pin is used to provide a drive

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

NPN power switch.

BD (Pin 8/Pin 13): This pin connects to the anode of the

boost diode. This pin also supplies current to the LT3990’s

internal regulator when BD is above 3.2V.

PG (Pin 9/Pin 14): The PG pin is the open-drain output of

an internal comparator. PG remains low until the FB pin

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

when VIN is above 4.2V and EN/UVLO is high.

RT (Pin 10/Pin 16): A resistor is tied between RT and

ground to set the switching frequency.

NC (Pins 3, 5, 7, 10, 12, 15, MSOP Only): No Connects.

These pins are not connected to internal circuitry and must

be left floating to ensure fault tolerance.

Block Diagram

VIN

C1

VIN

1.21V

+

EN/UVLO –

INTERNAL 1.21V REF

SHDN

RT

RT

PG

1.09V

+

ERROR

AMP

–

–

+

SLOPE COMP

OSCILLATOR

200kHz TO 2.2MHz

VC

Burst Mode

DETECT

SWITCH LATCH

R

Q

S

BD

DBOOST

BOOST

SW

DCATCH

C3

L1

C2

VOUT

GND

R2

FB

R1

3990 BD

3990f



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