LX1681 Microsemi Corporation, LX1681 Datasheet

LX1681

Manufacturer Part Number

LX1681

Description

VOLTAGE - MODE PWM CONTROLLERS

Manufacturer

Microsemi Corporation

Datasheet

1.LX1681.pdf (9 pages)

Current page: 1 of 9
Download datasheet (126Kb)

Rev. 1.0 5/99

H E

The LX1681/1682 are monolithic, pulse-

width modulator controller ICs. They are

designed to implement a flexible, low cost

buck (step-down) regulator supply with mini-

mal external components.

troller; the LX1682 has a synchronous driver

for higher efficiency.

means of a resistor divider to set the voltage

between 1.25V and 4.5V.

implemented without expensive current

sense resistors. Current is sensed using the

voltage drop across the R

— sensing is delayed for 1µs to eliminate

MOSFET ringing errors.

NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.

The LX1681 is a non-synchronous con-

The output voltage is adjustable by

Short-circuit current limiting can be

0.1µF

N F I N I T E

LX1681 N

N.C.

GND

LX1681

11861 W

O W E R

DS(ON)

TDRV

-S

1µF

YNCHRONOUS

of the MOSFET

ESTERN

12V

BOOST

D E S C R I P T I O N

O F

SET

I N

IRL3103S

Note: All surface-mount packages are available in Tape & Reel,

VENUE

0 to 70

PA C K A G E O R D E R I N F O R M A T I O N

append the letter "T" to part number. (i.e. LX1681CDMT)

N N O V A T I O N

(°C)

ONTROLLER

I N I T Y

, G

1500µFx3

5µH

MBR2545

average power to the power elements during

short-circuit conditions.

for optimal cost and space.

for optimal start-up performance.

LX1681/82 can be disabled by pulling the soft-

start pin to ground.

board space.

conversion, the LX1681/82 can also be used

for converting 12V to 5V, 3.3V or other

voltages with high efficiency, eliminating the

need for bulky heat sinks.

ARDEN

Hiccup-mode fault protection reduces

Switching frequency is fixed at 200kHz

Under-voltage lockout and soft-start

Small 8-pin SOIC packaging reduces

Optimized for 5V-to-3.3V or 5V-to-2.5V

P R O D U C T H I G H L I G H T

Non-Synchronous

1500µF

Synchronous

ROVE

I C R O E L E C T R O N I C S

Output

, CA. 92841, 714-898-8121, F

OUT

O L T A G E

0.1µF

R O D U C T I O N

Plastic SOIC

8-pin

LX1681CDM

LX1682CDM

GND

BDRV

The

LX1682 S

- M

LX1682

O D E

N C

TDRV

YNCHRONOUS

: 714-893-2570

1µF

P W M C

Fixed 200kHz Switching Frequency

Constant Frequency Voltage-Mode Control

Requires NO External Compensation

Hiccup-Mode Over-Current Protection

High Efficiency

Output Voltage Set By Resistor Divider

Under-Voltage Lockout

Soft-Start And Enable

Synchronous Rectification (LX1682)

Non-Synchronous Rectification (LX1681)

Small, 8-pin Surface Mount Package

5V to 3.3V Or Less Buck Regulators

FPGA Supplies

Microprocessor Chipset Supplies

(e.g. Camino, Whitney, etc.)

Rambus

Hard Disk Drives

Computer Add-on Cards

12V

BOOST

LX1681/1682

K E Y F E A T U R E S

A P P L I C A T I O N S

A T A

RIMM

SET

IRL3103S

ONTROLLER

O N T R O L L E R S

Supplies

1500µFx2

IRL3103S

5µH

H E E T

1500µF

OUT

Related parts for LX1681

LX1681 Summary of contents

Page 1

... (°C) DM Output A Non-Synchronous Synchronous Note: All surface-mount packages are available in Tape & Reel, append the letter "T" to part number. (i.e. LX1681CDMT CA. 92841, 714-898-8121, F VENUE ARDEN ...

Page 2

... N.C. / GND GND / BDRV TDRV DM PACKAGE (Top View) * Pin 3 = N.C. for LX1681, GND for LX1682 Pin 4 = GND for LX1681, BDRV for LX1682 = 5V 12V 25°C LX1681/1682 Min. Typ. Max. 1.237 1.25 1.262 1.231 1.269 170 190 230 1 ...

Page 3

... SET I RESET PWM Set V RESET UVLO Ramp Oscillator Hiccup FIGURE 1 — Block Diagram LX1681/1682 SET +12V V (5V TDRV L 4 BDRV 3 GND ...

Page 4

... resistor and the external capacitor set the time constant Pin Number LX1681 LX1682 1 ...

Page 5

... POWER UP and INITIALIZATION At power up, the LX1681/82 monitors the supply voltage to both the +5V and the +12V pins (there is no special requirement for the sequence of the two supplies). Before both supplies reach their under-voltage lock-out (UVLO) thresholds, the soft-start (SS) pin is held low to prevent soft-start from beginning ...

Page 6

... LX1681/1682 OUTPUT INDUCTOR The output inductor should be selected to meet the requirements of the output voltage ripple in steady-state operation and the inductor current slew-rate during transient. The peak-to-peak output voltage ripple is: ...

Page 7

... OUTPUT ENABLE The LX1681/82 FET driver outputs are driven to ground by pulling the soft-start pin below 0.3V. PROGRAMMING THE OUTPUT VOLTAGE The output voltage is sensed by the feedback pin (V -(t ...

Page 8

... The use of a dual Schottky diode in a single TO-220 package (e.g. the MBR2535) helps improve thermal dissipation. Operation From A Single Power Supply The LX1681/1682 needs a secondary supply voltage (V provide sufficient drive to the upper MOSFET. In many applica- tions with and a 12V (V ...

Page 9

... FIGURE 3 — Current Sensing Using Sense Resistor LX1682 GND BDRV TDRV SET FIGURE 4 — Bootstrap Circuit For 5V Only Operation LX1681/1682 SENSE V OUT OUT R ...

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