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LT1186F
DAC Programmable
CCFL Switching Regulator
(Bits-to-Nits
TM
)
FEATURES
■
Wide Battery Input Range: 4.5V to 30V
■
Grounded Lamp or Floating Lamp Configurations
■
Open Lamp Protection
■
Precision 50µA Full-Scale DAC Programming Current
■
Standard SPI Mode or Pulse Mode
■
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-
ing on the D
IN
signal level.
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.
■
Notebook and Palmtop Computers
■
Portable Instruments
■
Retail Terminals
APPLICATIONS
U
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-
DESCRIPTION
U
TYPICAL APPLICATION
U
, 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
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
I
CCFL
DIO
CCFL V
C
AGND
SHDN
CLK
CCFL V
SW
BULB
BAT
ROYER
V
CC
I
OUT
D
OUT
CCFL
PGND
CS
LT1186F
LAMP
UP TO 6mA
10
6
L1
R1
750Ω
L2
100µH
321 5
4
+
+
C7, 1µF
C1*
0.068µF
C5
1000pF
R2
220k
R3
100k
C3A
2.2µF
35V
C4
2.2µF
V
IN
3.3V
OR 5V
LT1186F • TA01
C3B
2.2µF
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
0µA TO 50µA I
CCFL
CURRENT GIVES
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
D
IN
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
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