LT1186F_15 Datasheet, PDF (1/16 Pages) Linear Technology – DAC Programmable CCFL Switching Regulator

LT1186F
DAC Programmable
CCFL Switching Regulator
(Bits-to-Nits^TM)
FEATURES
s _{Wide Battery Input Range: 4.5V to 30V}
s _{Grounded Lamp or Floating Lamp Configurations}
s _{Open Lamp Protection}
s _{Precision 50µA Full-Scale DAC Programming Current}
s _{Standard SPI Mode or Pulse Mode}
s _{DAC Setting Is Retained in Shutdown}
U
APPLICATIONS
s _{Notebook and Palmtop Computers}
s _{Portable Instruments}
s _{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-
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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
D1
BAT85
C7, 1µF
SHUTDOWN
FROM MPU
1 _CCFL
PGND
2
I_CCFL
16
CCFL V_SW
15
BULB
3
DIO
14
BAT
4
LT1186F
13
CCFL V_C
ROYER
5
AGND
12
V_CC
6
SHDN
11
I_OUT
7
CLK
10
D_OUT
8 CS
D_IN 9
CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE COVERED
BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
C5
1000pF
R2
220k
UP TO 6mA
LAMP
C2
27pF
10 6
3kV
3
2 14
+ C3B
2.2µF
35V
V_IN
+
3.3V
C4 ^{OR 5V}
2.2µF
C1*
0.068µF
R3
100k _Q2*
Q1*
L1
5
L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
*DO NOT SUBSTITUTE COMPONENTS
COILTRONICS [phone]
BAT
+ C3A ^{8V TO 28V}
2.2µF
35V
R1
750Ω
L2
100µH
D1
1N5818
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.
LT1186F • TA01
FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,
REFER TO THE LT1182/83/84/84F DATA SHEET
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