1

LT1186F

DAC Programmable

CCFL Switching Regulator

(Bits-to-Nits

FEATURES

s

Wide Battery Input Range: 4.5V to 30V

s

Grounded Lamp or Floating Lamp Configurations

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Open Lamp Protection

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Precision 50

µA Full-Scale DAC Programming Current

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Standard SPI Mode or Pulse Mode

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DAC Setting Is Retained in Shutdown

face modes including standard SPI mode and pulse mode.

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

DAC configures to SPI or pulse mode depending on the CS

signal level. In SPI mode, the system microprocessor

serially transfers the present 8-bit data and reads back the

previous 8-bit data. In pulse mode, the upper six bits of the

DAC configure as increment-only (1-wire interface) or

increment/decrement (2-wire interface) operation depend-

The LT1186F control circuitry operates from a logic supply

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

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

draws 6mA typical quiescent current. An active low shut-

down pin reduces total supply current to 35

µA for standby

operation and the DAC retains its last setting. A 200kHz

switching frequency minimizes magnetic component size.

Current mode switching techniques with cycle-by-cycle

limiting gives high reliability and simple loop frequency

compensation. The LT1186F is available in a 16-pin nar-

row SO package.

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Notebook and Palmtop Computers

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Portable Instruments

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Retail Terminals

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 8-bit 50

µA full-

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

to-lamp current control” and communicates in two inter-

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

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

BAT

8V TO 28V

16

15

14

13

12

11

10

9

DIO

AGND

SHDN

CLK

BULB

BAT

ROYER

CCFL

PGND

CS

LT1186F

LAMP

UP TO 6mA

10

6

L1

R1

750

Ω

L2

100

µH

32

1

5

4

+

+

C7, 1

µF

C1*

0.068

µF

C5

1000pF

R2

220k

R3

100k

C3A

2.2

µF

35V

C4

2.2

µF

3.3V

OR 5V

LT1186F • TA01

C3B

2.2

µF

35V

C2

27pF

3kV

+

Q2*

Q1*

SHUTDOWN

ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3A AND C3B.

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

Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001

0

0mA TO 6mA LAMP CURRENT

FOR A TYPICAL DISPLAY.

FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,

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

D1

BAT85

FROM MPU

1

2

3

4

5

6

7

8

D1

1N5818

L1 = COILTRONICS CTX210605

L2 = COILTRONICS CTX100-4

*DO NOT SUBSTITUTE COMPONENTS

COILTRONICS (407) 241-7876

CCFL BACKLIGHT APPLICATION CIRCUITS

CONTAINED IN THIS DATA SHEET ARE COVERED

BY U.S. PATENT NUMBER 5408162

AND OTHER PATENTS PENDING