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LT1186

Description
DAC Programmable CCFL Switching Regulator(Bits-to-NitsTM)
File Size207KB,16 Pages
ManufacturerLinear ( ADI )
Websitehttp://www.analog.com/cn/index.html
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LT1186 Overview

DAC Programmable CCFL Switching Regulator(Bits-to-NitsTM)

LT1186F
DAC Programmable
CCFL Switching Regulator
(Bits-to-Nits
TM
)
FEATURES
s
s
s
s
s
s
APPLICATIONS
s
s
s
face modes including standard SPI mode and pulse mode.
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 D
IN
signal level.
Notebook and Palmtop Computers
Portable Instruments
Retail Terminals
DESCRIPTION
The LT
®
1186F is a fixed frequency, current mode, switch-
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 50µA full-
scale current output DAC. The DAC provides simple “bits-
to-lamp current control” and communicates in two inter-
TYPICAL APPLICATION
90% Efficient Floating CCFL with 1-Wire (Increment Only) Pulse Mode Control of Lamp Current
D1
BAT85
CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE COVERED
BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
1
2
3
C7, 1µF
4
5
SHUTDOWN
FROM MPU
6
7
8
CCFL
PGND
I
CCFL
DIO
CCFL V
SW
BULB
BAT
16
15
14
R2
220k
C5
1000pF
3
2
1
C3B
2.2µF
35V
R1
750Ω
4
5
UP TO 6mA
LAMP
10
6
C2
27pF
3kV
L1
L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
*DO
NOT SUBSTITUTE COMPONENTS
COILTRONICS (407) 241-7876
BAT
8V TO 28V
LT1186F
13
CCFL V
C
ROYER
AGND
SHDN
CLK
CS
V
CC
I
OUT
D
OUT
12
11
10
D
IN
9
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
0µA TO 50µA I
CCFL
CURRENT GIVES
C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKP-20
0mA TO 6mA LAMP CURRENT
Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001
FOR A TYPICAL DISPLAY.
U
U
U
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 35µA 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Bits-to-Nits is a trademark of Linear Technology Corporation. 1 Nit = 1 Candela/meter
2
+
+
C3A
2.2µF
35V
+
V
IN
3.3V
C4 OR 5V
2.2µF
C1*
0.068µF
R3
100k
Q2*
Q1*
L2
100µH
D1
1N5818
LT1186F • TA01
FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,
REFER TO THE LT1182/83/84/84F DATA SHEET
1

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