LX1684CD-TR MICROSEMI [Microsemi Corporation], LX1684CD-TR Datasheet

LX1684CD-TR

Manufacturer Part Number

LX1684CD-TR

Description

Voltage-Mode PWM Controller

Manufacturer

MICROSEMI [Microsemi Corporation]

Datasheet

1.LX1684CD-TR.pdf (12 pages)

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Rev. 1.0c, 2005-03-08

mode pulse-width modulator controller.

It is designed to implement a flexible,

low cost buck (step-down) regulator

supply with a minimal of external

components.

driver for higher efficiency and is

optimized to provide 12V to 3.3V or

12V to 2.5V regulation. It also can be

used to convert 5V or 3.3V to voltages

as low as 1.25V.

175kHz for optimal cost and space.

Short-circuit current limiting can be

implemented without expensive current

sense resistors.

with the positive side of the current

sense comparator brought out (CSP) to

allow it to be referenced to the topside

FET.

IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com

The LX1684 is a monolithic, voltage-

The LX1684 has a synchronous

Switching frequency is fixed at

Similar to the LX1682 in function but

Optional 12V only circuit

or equivalent

LM78L05

12V

P R O D U C T H I G H L I G H T - T Y P I C A L 1 2 V T O 3 . 3 V A P P L I C A T I O N

VCC

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

0 to 70

Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1684CD-TR)

100 Ohm

165 Ohm

(°C)

D E S C R I P T I O N

0.1µF

Css

drop across the R

this sensing is delayed for 1µs to

eliminate

Hiccup-mode fault protection reduces

average power to the power elements

during short-circuit conditions.

are

performance. Pulling the soft-start pin to

ground can disable the LX1684.

combined with low profile, low ESR

capacitors, and TO-252 packaged FETs

results in a high efficiency converter in a

small board area. In most cases PCB

copper can accomplish necessary heat

sinking and no bulky additional heat

sinks are required.

small electrolytic capacitors can be used

reducing the overall converter cost.

Current is sensed using the voltage

Under-voltage lockout and soft-start

If a low profile design is not required

Synchronous

P A C K A G E O R D E R I N F O

The small 14-pin SOIC packaging,

Integrated Products Division

provided

UTPUT

Microsemi

CSP

GND

PGND

BDR

MOSFET

for

DS(ON)

VCC

TDR

VC1

optimal

RoHS Compliant / Pb-free Transition DC: 0440

of the MOSFET

ringing

RSET

Voltage-Mode PWM Controller

3.3K

1µF

Plastic SOIC

14-PIN

start-up

errors.

RODUCTION

5817SMT

LX1684CD

SUB45N

SUB45N05-

05-20L

0.1µF

20L

L1 is a powdered

iron toroid

10µH

ATA

12V to 3.3V Or Less Buck

Regulators

3.3/5V to 2.5V Or Less Buck

Regulators

Hard Disk Drives

Computer Add-on Cards

Fixed 175kHz 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

Small, 14-pin Surface Mount

Package

12V

10%

K E Y F E A T U R E S

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

820µF,

16V

HEET

1500µF

6.3V

VOUT

3.3V

10A

LX1684

Page 1

Related parts for LX1684CD-TR

LX1684CD-TR Summary of contents

Page 1

... Ohm Optional 12V only circuit T (° Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1684CD-TR) Copyright © 2000 Rev. 1.0c, 2005-03-08 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Voltage-Mode PWM Controller ® ...

Page 2

Supply Voltage (V ) ...................................................................................... 18V C1 Supply Voltage (V ...

Page 3

TM Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C otherwise noted. Test conditions: V =5V Parameter REFERENCE Reference Voltage OSCILLATOR Frequency Ramp Amplitude ERROR AMPLIFIER Input Resistance CURRENT SENSE Current Set V TRIP ...

Page 4

Com VCSP RESET TRIP SET 320k 20k 1 - Error Com plifier RESET Com pensation V REF R SS Hiccup Hiccup ...

Page 5

TM GENERAL DESCRIPTION The LX1684 is a voltage-mode pulse-width modulation controller integrated circuit. The internal oscillator and ramp generator frequency is fixed at 175kHz. The devices have internal compensation, so that no external compensation is required. POWER UP AND INITIALIZATION ...

Page 6

TM 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: V ESR = RIPPLE where ( ...

Page 7

TM SOFT-START CAPACITOR (continued) The capacitor current to follow the SS-pin voltage is OUT = = OUT OUT where C is the output capacitance. The typical value of C OUT should be ...

Page 8

TM FET SELECTION (continued) Synchronous Rectification – Lower MOSFET The lower pass element can be either a MOSFET or a Schottky diode. The use of a MOSFET (synchronous rectification) will result in higher efficiency, but at higher cost than using ...

Page 9

TM R1 300 Ohm R2 Css 100 Ohm 0.1µF Figure 3 R1 150 Ohm R2 Css 50K Ohm 0.1µF C3 Panasonic EEF-UE0D271R 270uF 3A 15mOhm ESR C4 Panasonic EEF-UE0J151R 150uF 3A 18mOhm ESR Copyright © 2000 Rev. 1.0c, 2005-03-08 11861 ...

Page 10

TM EFFICENCY VS. OUTPUT CURRENT 1.00 0.95 0.90 0.85 0.80 0.75 0. Output Current (A) OUTPUT VOLTAGE VS. TEMPERATURE 3.34 3.33 3.32 3.31 3.30 3.29 3. Temperature (°C) OUTPUT VOLTAGE ...

Page 11

Note: 1. Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side. Lead dimension shall not include solder coverage. Copyright © 2000 Rev. 1.0c, 2005-03-08 11861 Western ...

Page 12

TM PRODUCTION DATA – Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not ...

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