LT1786F Linear Technology, LT1786F Datasheet

LT1786F

Manufacturer Part Number

LT1786F

Description

SMBus Programmable CCFL Switching Regulator

Manufacturer

Linear Technology

Datasheet

1.LT1786F.pdf (20 pages)

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APPLICATIONS

DESCRIPTION

The LT

ing regulator that provides the control function for Cold

Cathode Fluorescent Lighting (CCFL). The IC includes an

efficient high current switch, an oscillator, output drive

logic, control circuitry and a micropower 6-bit 100 A full-

scale current output DAC. The DAC provides simple “bits-

FEATURES

TYPICAL

Notebook and Palmtop Computers

Portable Instruments

Personal Digital Assistants

Wide Battery Input Range: 4.5V to 30V

Grounded Lamp or Floating Lamp Configurations

Open Lamp Protection

Precision 100 A Full-Scale DAC

Programming Current

2-Wire SMBus Interface

Two Selectable SMBus Addresses

DAC Setting Is Retained in Shutdown

C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKI OR MKP-20

Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001

ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3A AND C3B.

MAKE 3CB ESR 0.5 TO PREVENT DAMAGE TO THE LT1786F HIGH-SIDE

SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON

1786F is a fixed frequency, current mode, switch-

SHUTDOWN

C7, 1 F

APPLICATION

BAT85

DIO

CCFL V

AGND

SHDN

SMBSUS

ADR

CCFL

PGND

CCFL

LT1786F

90% Efficient Floating CCFL with 2-Wire SMBus Control of Lamp Current

= PANASONIC ECH-U

CCFL V

ROYER

BULB

SDA

BAT

SCL

OUT

CCFL BACKLIGHT APPLICATION CIRCUITS

CONTAINED IN THIS DATA SHEET ARE COVERED

BY U.S. PATENT NUMBER 5408162

AND OTHER PATENTS PENDING

2.2 F

SMBus

HOST

3V V

6.5V

0 A TO 50 A I

0mA TO 6mA LAMP CURRENT

FOR A TYPICAL DISPLAY.

1000pF

100k

CCFL

to-lamp-current control” and communicates using the

2-wire SMBus serial interface. The LT1786F acts as an

SMBus slave device using one of two selectable SMBus

addresses set by the address pin ADR.

On Power-up, the DAC output current assumes midrange

or zero scale, depending on the logic state of the ADR

pin.The entire IC can be shut down through the SMBSUS

pin or by setting the SHDN bit = 1 in the SMBus command

byte. Digital data for the DAC output current is retained

internally and the supply current drops to 40 A for standby

operation. The active low SHDN pin disables the CCFL

control circuitry, but keeps the DAC alive. Supply current

in this operating mode drops to 150 A.

The LT1786F control circuitry operates from a logic supply

voltage of 3.3V or 5V. The IC also has a battery supply pin

that operates from 4.5V to 30V. The LT1786F draws 6mA

typical quiescent current. A 200kHz switching frequency

minimizes magnetic component size. Current mode switch-

ing techniques with cycle-by-cycle limiting gives high

reliability and simple loop frequency compensation. The

LT1786F is available in a 16-pin narrow SO package.

CURRENT GIVES

CCFL Switching Regulator

, LTC and LT are registered trademarks of Linear Technology Corporation.

220k

Q2*

0.068 F

SMBus Programmable

LAMP

C1*

100 H

FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,

REFER TO THE LT1182/83/84/84F DATA SHEET

C3B

2.2 F

35V

Q1*

27pF

3kV

1N5818

L1 = COILTRONICS CTX210605

L2 = COILTRONICS CTX100-4

*DO NOT SUBSTITUTE COMPONENTS

COILTRONICS (561) 241-7876

750

1786F TA01

C3A

2.2 F

35V

BAT

8V TO 28V

LT1786F

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