LT1377CS8 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT1377CS8

500kHz and 1MHz High Efficiency 1.5A Switching Regulators

Linear Technology 

LT1372/LT1377

PIN FUNCTIONS

VC (Pin 1): The Compensation pin is used for frequency

compensation, current limiting and soft start. It is the

output of the error amplifier and the input of the current

comparator. Loop frequency compensation can be per-

formed with an RC network connected from the VC pin to

ground.

FB (Pin 2): The Feedback pin is used for positive output

voltage sensing and oscillator frequency shifting. It is the

inverting input to the error amplifier. The noninverting

input of this amplifier is internally tied to a 1.245V

reference. Load on the FB pin should not exceed 250µA

when the NFB pin is used. See Applications Information.

NFB (Pin 3): The Negative Feedback pin is used for

negative output voltage sensing. It is connected to the

inverting input of the negative feedback amplifier through

a 100k source resistor.

S/S (Pin 4): Shutdown and Synchronization Pin. The S/S

pin is logic level compatible. Shutdown is active low and

the shutdown threshold is typically 1.3V. For normal

operation, pull the S/S pin high, tie it to VIN or leave it

floating. To synchronize switching, drive the S/S pin be-

tween 600kHz and 800kHz (LT1372) or 1.2MHz to 1.6MHz

(LT1377).

VIN (Pin 5): Bypass input supply pin with 10µF or more. The

part goes into undervoltage lockout when VIN drops below

2.5V. Undervoltage lockout stops switching and pulls the

VC pin low.

GND S (Pin 6): The ground sense pin is a “clean” ground.

The internal reference, error amplifier and negative feed-

back amplifier are referred to the ground sense pin. Con-

nect it to ground. Keep the ground path connection to the

output resistor divider and the VC compensation network

free of large ground currents.

GND (Pin 7): The ground pin is the emitter connection of

the power switch and has large currents flowing through it.

It should be connected directly to a good quality ground

plane.

VSW (Pin 8): The switch pin is the collector of the power

switch and has large currents flowing through it. Keep the

traces to the switching components as short as possible to

minimize radiation and voltage spikes.

BLOCK DIAGRAM

S/S

SHUTDOWN

DELAY AND RESET

VIN

LOW DROPOUT

2.3V REG

SYNC

OSC

LOGIC

100k

NFB

50k

+

NFBA

–

5:1 FREQUENCY

SHIFT

COMP

FB

1.245V

REF

GND SENSE

–

EA

+

IA

VC

AV ≈ 6

SW

ANTI-SAT

DRIVER

SWITCH

0.08Ω

GND LT1372 • BD

5

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