LINEAR TECHNOLOGY LT1186F Data Sheet

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LT1186F

DAC Programmable CCFL Switching Regulator (Bits-to-Nits TM) face modes including standard SPI mode and pulse mode.

FEATURES

On power-up, the DAC counter resets to half-scale and the

Wide Battery Input Range: 4.5V to 30V DAC configures to SPI or pulse mode depending on the CS Grounded Lamp or Floating Lamp Configurations signal level. In SPI mode, the system microprocessor Open Lamp Protection serially transfers the present 8-bit data and reads back the Precision 50µA Full-Scale DAC Programming Current previous 8-bit data. In pulse mode, the upper six bits of the Standard SPI Mode or Pulse Mode DAC configure as increment-only (1-wire interface) or DAC Setting Is Retained in Shutdown increment/decrement (2-wire interface) operation depend-

ing on the DIN signal level.

APPLICATIONS

The LT1186F control circuitry operates from a logic supply

Notebook and Palmtop Computers

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

Portable Instruments

voltage pin that operates from 4.5V to 30V. The LT1186F

Retail Terminals

draws 6m A typical quiescent current. An active low shut- down pin reduces total supply current to 35µA for standby

DESCRIPTION

operation and the DAC retains its last setting. A 200k Hz The LT®1186F is a fixed frequency, current mode, switch- switching frequency minimizes magnetic component size. ing regulator that provides the control function for Cold Current mode switching techniques with cycle-by-cycle Cathode Fluorescent Lighting (CCFL). The IC includes an limiting gives high reliability and simple loop frequency efficient high current switch, an oscillator, output drive compensation. The LT1186F is available in a 16-pin nar- logic, control circuitry and a micropower 8-bit 50µA full- row SO package.

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

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

to-lamp current control” and communicates in two inter- Bits-to-Nits is a trademark of Linear Technology Corporation. 1 Nit = 1 Candela/meter2

TYPICAL APPLICATION

90% Efficient Floating CCFL with 1-Wire (Increment Only) Pulse Mode Control of Lamp Current

CCFL BACKLIGHT APPLICATION CIRCUITS UP TO 6m A

D1 L1 = COILTRONICS CTX210605

CONTAINED IN THIS DATA SHEET ARE COVERED

BAT85 LAMP

BY U.S. PATENT NUMBER 5408162 L2 = COILTRONICS CTX100-4

AND OTHER PATENTS PENDING

3k V *DO NOT SUBSTITUTE COMPONENTS

CCFL C5 COILTRONICS (407) 241-7876

CCFL VSW L1

PGND 1000p F

ICCFL BULB

C3B 8V TO 28V

DIO BAT 2.2µF

LT1186F 35V

CCFL VC ROYER R1

AGND VCC 3.3V

C4 OR 5V

SHUTDOWN SHDN IOUT 2.2µF

FROM MPU CLK DOUT

CS DIN

ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3A AND C3B.

LT1186F • TA01

MAKE 3CB ESR ≥ 0.5Ω TO PREVENT DAMAGE TO THE LT1186F HIGH-SIDE SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON

C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKP-20 0µA TO 50µA ICCFL CURRENT GIVES FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS, 0m A TO 6m A LAMP CURRENT REFER TO THE LT1182/83/84/84F DATA SHEET

Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001

FOR A TYPICAL DISPLAY.