LT1786FCS#TRPBF Linear Technology, LT1786FCS#TRPBF Datasheet

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LT1786FCS#TRPBF

Manufacturer Part Number
LT1786FCS#TRPBF
Description
IC SW REG CCFL SMBUS PROG 16SOIC
Manufacturer
Linear Technology
Datasheet

Specifications of LT1786FCS#TRPBF

Applications
Converter, CCFL
Voltage - Input
4.5 ~ 30 V
Number Of Outputs
1
Operating Temperature
0°C ~ 70°C
Mounting Type
Surface Mount
Package / Case
16-SOIC (3.9mm Width)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Voltage - Output
-

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FEATURES
DESCRIPTIO
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 6-bit 100 A full-
scale current output DAC. The DAC provides simple “bits-
TYPICAL APPLICATIO
APPLICATIO S
Notebook and Palmtop Computers
Portable Instruments
Personal Digital Assistants
Grounded Lamp or Floating Lamp Configurations
Precision 100 A Full-Scale DAC
Programming Current
2-Wire SMBus Interface
DAC Setting Is Retained in Shutdown
Wide Battery Input Range: 4.5V to 30V
Open Lamp Protection
Two Selectable SMBus Addresses
®
C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKI OR MKP-20
Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001
ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3A AND C3B.
MAKE 3CB ESR 0.5 TO PREVENT DAMAGE TO THE LT1786F HIGH-SIDE
SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON
1786F is a fixed frequency, current mode, switch-
SHUTDOWN
C7, 1 F
BAT85
D1
U
U
1
2
3
4
5
6
7
8
I
DIO
CCFL V
AGND
SHDN
SMBSUS
ADR
CCFL
PGND
CCFL
LT1786F
C
90% Efficient Floating CCFL with 2-Wire SMBus Control of Lamp Current
CCFL V
= PANASONIC ECH-U
ROYER
BULB
I
SDA
BAT
SCL
V
OUT
U
SW
CC
16
15
14
13
12
11
10
9
CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE COVERED
BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
+
C4
2.2 F
TO
SMBus
HOST
3V V
6.5V
CC
0 A TO 50 A I
0mA TO 6mA LAMP CURRENT
FOR A TYPICAL DISPLAY.
1000pF
100k
C5
CCFL
to-lamp-current control” and communicates using the
2-wire SMBus serial interface. The LT1786F acts as an
SMBus slave device using one of two selectable SMBus
addresses set by the address pin ADR.
On Power-up, the DAC output current assumes midrange
or zero scale, depending on the logic state of the ADR
pin.The entire IC can be shut down through the SMBSUS
pin or by setting the SHDN bit = 1 in the SMBus command
byte. Digital data for the DAC output current is retained
internally and the supply current drops to 40 A for standby
operation. The active low SHDN pin disables the CCFL
control circuitry, but keeps the DAC alive. Supply current
in this operating mode drops to 150 A.
The LT1786F control circuitry operates from a logic supply
voltage of 3.3V or 5V. The IC also has a battery supply pin
that operates from 4.5V to 30V. The LT1786F draws 6mA
typical quiescent current. A 200kHz switching frequency
minimizes magnetic component size. Current mode switch-
ing techniques with cycle-by-cycle limiting gives high
reliability and simple loop frequency compensation. The
LT1786F is available in a 16-pin narrow SO package.
R3
CCFL Switching Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation.
CURRENT GIVES
R2
220k
Q2*
3
SMBus Programmable
10
0.068 F
LAMP
+
C1*
2
L2
100 H
FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,
REFER TO THE LT1182/83/84/84F DATA SHEET
6
C3B
2.2 F
35V
Q1*
1
C2
27pF
3kV
4
1N5818
D1
5
L1
L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
*DO NOT SUBSTITUTE COMPONENTS
COILTRONICS (561) 241-7876
R1
750
1786F TA01
+
C3A
2.2 F
35V
LT1786F
BAT
8V TO 28V
1

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LT1786FCS#TRPBF Summary of contents

Page 1

... The LT1786F is available in a 16-pin narrow SO package. , LTC and LT are registered trademarks of Linear Technology Corporation. CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THIS DATA SHEET ARE COVERED BY U.S. PATENT NUMBER 5408162 ...

Page 2

LT1786F ABSOLUTE AXI U RATI GS (Note 1) V ........................................................................... 7V CC BAT, Royer, BULB .................................................. 30V CCFL V ............................................................... 60V SW Shutdown ................................................................. 6V I Input Current .............................................. 10mA CCFL DIO Input Current (Peak, < 100ms).................... ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T BAT = Royer = BULB = 12V CCFL V CCFL SYMBOL PARAMETER CCFL High-Side Sense Servo Current Line Regulation CCFL High-Side Sense Supply Current Current Measured into BAT and ...

Page 4

LT1786F W U TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Temperature –75 – 50 – 100 125 150 175 TEMPERATURE ( C) 1786 G01 SHDN Input ...

Page 5

W U TYPICAL PERFORMANCE CHARACTERISTICS V Sink Offset Current C vs Temperature 10 9 CCFL CCFL CCFL –1 –2 ...

Page 6

LT1786F W U TYPICAL PERFORMANCE CHARACTERISTICS BULB Input Bias Current vs Temperature –75 – 50 – 100 125 150 TEMPERATURE ( C) 1787 G19 High-Side Sense Null Current Line Regulation ...

Page 7

... The regulator provides a separate analog ground and power ground to isolate high current ground paths from low current signal paths. Linear Technology recommends the use of star-ground layout techniques. I (Pin 2): This pin is the input to the CCFL lamp current CCFL programming circuit ...

Page 8

LT1786F PIN FUNCTIONS AGND (Pin 5): This is the low current analog ground the negative sense terminal for the internal 1.24V refer- ence and the I summing voltage in the LT1786F. CCFL Connect low current ...

Page 9

PIN FUNCTIONS ROYER (Pin 13): This pin connects to the center-tapped primary of the Royer converter and is used with the BAT pin in a floating-lamp configuration where lamp current is controlled by sensing Royer primary-side converter ...

Page 10

LT1786F W BLOCK DIAGRAM LT1786F SMBus Programmable CCFL Switching Regulator 6 SHDN SHUTDOWN + CCFL – V1 0.465V 2 I CCFL SCL 10 SMBus INTERFACE SDA 9 8 ADR 10 V BAT UNDER- THERMAL 2.4V VOLTAGE SHUTDOWN ...

Page 11

DIAGRA S t BUF SDA SCL t STOP START SMBus Write Byte Protocol, with SMBus Address = 0101101B, Command Byte = 0XXXXXXXB and Data Byte = 111111XXB ADR SMBUS ADDRESS 0 SDA 0 1 ...

Page 12

LT1786F U U APPLICATIONS INFORMATION battery drain. Additionally, all components, including PC board and hardware, usually must fit within the LCD enclosure with a height restriction of 5mm to 10mm. The CCFL regulator drives an inductor that acts as a ...

Page 13

U U APPLICATIONS INFORMATION value (see Block Diagram). A STOP condition is optional. The command code and data byte are defined with the following format: Command Code Data Byte SHDN ...

Page 14

LT1786F U U APPLICATIONS INFORMATION LT1786F SMBus Lookup Tables SMBus Address Byte Table ADR DECIMAL BINARY HEX GND 90 0101101 0101100 58 CC Bit 0 (LSB) in the SMBus Address is the Write Bit = 0 SMBus ...

Page 15

U U APPLICATIONS INFORMATION Simplified Lamp Current Programming A programming block in the LT1786F controls lamp current, permitting either grounded lamp or floating lamp configurations. Grounded configurations control lamp current by directly controlling one-half of actual lamp current and converting ...

Page 16

... This capacitor charges up when the system is first pow- ered by the battery pack wall adapter. The amount of current delivered at start-up can be very large if the total impedance in this path is small and the voltage source has high current capability. Linear Technology recommends pin provides stable loop com- C ...

Page 17

... Every aspect of the design is interrelated and any design change requires complete re-evaluation for all other critical design param- eters. Linear Technology has engineered one of the most complete test and evaluation setups for backlight designs and understands the issues and tradeoffs in achieving a compact, efficient and economical customer solution ...

Page 18

LT1786F U TYPICAL APPLICATION Dual Transformer CCFL Power Supply Space constraints may dictate utilization of two small transformers instead of a single, larger unit. Although this approach is somewhat more expensive, it can solve space problems and offers other attractive ...

Page 19

... FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...

Page 20

... SPI or Pulse Mode Programmable Peak Current Limit 1.5A, 500kHz Multiple Lamp Capability, No Lamp Flicker, Precision Maximum and Minimum Lamp Currents Maximize Lamp Life 1786fa LT/CP 0801 1.5K REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1998 ...

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