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LT1786FCS#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
1
LT1786F
■
Grounded Lamp or Floating Lamp Configurations
■
Precision 100µA 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
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 40µA 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 150µA.
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.
The LT
®
1786F 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 6-bit 100µA full-
scale current output DAC. The DAC provides simple “bits-
■
Notebook and Palmtop Computers
■
Portable Instruments
■
Personal Digital Assistants
90% Efficient Floating CCFL with 2-Wire SMBus Control of Lamp Current
BAT
8V TO 28V
16
15
14
13
12
11
10
9
I
CCFL
DIO
CCFL V
C
AGND
SHDN
SMBSUS
ADR
CCFL V
SW
BULB
BAT
ROYER
V
CC
I
OUT
SCL
SDA
CCFL
PGND
LT1786F
LAMP
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
3V ≤ V
CC
≤ 6.5V
TO
SMBus
HOST
1786F 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 LT1786F HIGH-SIDE
SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON
C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKI OR MKP-20
= PANASONIC ECH-U
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
1
2
3
4
5
6
7
8
D1
1N5818
L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
*DO NOT SUBSTITUTE COMPONENTS
COILTRONICS (561) 241-7876
CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE COVERED
BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
SMBus
Programmable
CCFL Switching Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LT1786F
(Note 1)
V
CC
........................................................................... 7V
BAT, Royer, BULB .................................................. 30V
CCFL V
SW
............................................................... 60V
Shutdown ................................................................. 6V
I
CCFL
Input Current .............................................. 10mA
DIO Input Current (Peak, <100ms).................... 100mA
Digital Inputs .............................. –0.3V to (V
CC
+ 0.3V)
Digital Outputs............................ –0.3V to (V
CC
+ 0.3V)
DAC Output Voltage ..................... –15V to (V
CC
+ 0.3V)
Junction Temperature (Note 2)............................ 100°C
Operating Ambient Temperature Range..... 0°C to 70°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
LT1786FCS
ORDER PART
NUMBER
TOP VIEW
S PACKAGE
16-LEAD PLASTIC SO
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
CCFL PGND
I
CCFL
DIO
CCFL V
C
AGND
SHDN
SMBSUS
ADR
CCFL V
SW
BULB
BAT
ROYER
V
CC
I
OUT
SCL
SDA
T
JMAX
= 100°C, θ
JA
= 100°C/W
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
Supply Current 3V ≤ V
CC
≤ 6.5V, I
OUT
= 0µA ● 6 9.5 mA
ISUS SMBSUS Supply Current SMBSUS = 0V or Command Code Bit 7 = 1, ● 40 100 µA
CCFL V
C
= Open (Note 3)
I
SHDN
SHUTDOWN Supply Current SHUTDOWN = 0V, CCFL V
C
= Open (Note 3) ● 150 300 µA
SHUTDOWN Input Bias Current SHUTDOWN = 0V, CCFL V
C
= Open 5 10 µA
SHUTDOWN Threshold Voltage ● 0.45 0.85 1.2 V
f Switching Frequency Measured at CCFL V
SW
, I
SW
= 50mA, 175 200 225 kHz
I
CCFL
= 100µA, CCFL V
C
= Open ● 160 200 240 kHz
DC(MAX) Maximum Switch Duty Cycle Measured at CCFL V
SW
80 85 %
● 75 85 %
BV Switch Breakdown Voltage Measured at CCFL V
SW
60 70 V
Switch Leakage Current V
SW
= 12V, Measured at CCFL V
SW
20 µA
V
SW
= 30V, Measured at CCFL V
SW
40 µA
I
CCFL
Summing Voltage 3V ≤ V
CC
≤ 6.5V 0.425 0.465 0.505 V
● 0.385 0.465 0.555 V
∆I
CCFL
Summing Voltage for I
CCFL
= 0µA to 100µA515mV
∆Input Programming Current
CCFL V
C
Offset Sink Current CCFL V
C
= 1.5V, Positive Current Measured into Pin –5 5 15 µA
∆CCFL V
C
Source Current for I
CCFL
= 25µA, 50µA, 75µA, 100µA, ● 4.70 4.95 5.20 µA/µA
∆I
CCFL
Programming Current CCFL V
C
= 1.5V
CCFL V
C
to DIO Current Servo Ratio DIO = 5mA out of Pin, Measure I(V
C
) at CCFL V
C
= 1.5V ● 94 99 104 µA/mA
CCFL V
C
Low Clamp Voltage V
BAT
– V
BULB
= BULB Protect Servo Voltage ● 0.1 0.3 V
CCFL V
C
High Clamp Voltage I
CCFL
= 100µA ● 1.7 2.1 2.4 V
CCFL V
C
Switching Threshold CCFL V
SW
DC = 0% ● 0.6 0.95 1.3 V
CCFL High-Side Sense Servo Current I
CCFL
= 100µA, I(V
C
) = 0µA at CCFL V
C
= 1.5V ● 0.93 1.00 1.07 A
ABSOLUTE AXI U RATI GS
WWWU
PACKAGE/ORDER I FOR ATIO
UU
W
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= SHUTDOWN = SMBSUS = SCL = SDA = 3.3V,
BAT = Royer = BULB = 12V, I
CCFL
= CCFL V
SW
= Open, DIO = I
OUT
= GND, CCFL V
C
= 0.5V, unless otherwise specified.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1786F
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNIT
CCFL High-Side Sense Servo Current BAT = 5V to 30V, I
CCFL
= 100µA, 0.1 0.16 %/V
Line Regulation I(V
C
) = 0µA at CCFL V
C
= 1.5V
CCFL High-Side Sense Supply Current Current Measured into BAT and Royer Pins ● 50 100 150 µA
BULB Protect Servo Voltage I
CCFL
= 100µA, I(V
C
) = 0µA at CCFL V
C
= 1.5V, ● 6.5 7.0 7.5 V
Servo Voltage Measured between BAT and BULB Pins
BULB Input Bias Current I
CCFL
= 100µA, I(V
C
) = 0µA at CCFL V
C
= 1.5V 5 9 µA
I
LIM
CCFL Switch Current Limit Duty Cycle = 50% ● 1.25 1.9 3.0 A
Duty Cycle = 75% (Note 4)
● 0.9 1.6 2.6 A
V
SAT
CCFL Switch On Resistance CCFL I
SW
= 1A ● 0.6 1.0 Ω
∆I
Q
Supply Current Increase During CCFL I
SW
= 1A 20 30 mA/A
∆I
SW
CCFL Switch On Time
DAC Resolution 6 Bits
DAC Full-Scale Current V(I
OUT
) = 0.465V 98 100 102 µA
● 96 100 104 µA
DAC Zero Scale Current V(I
OUT
) = 0.465V ● ±200 nA
DAC Differential Nonlinearity ● ±0.1 ±1LSB
DAC Supply Voltage Rejection 3V ≤ V
CC
≤ 6.5V, I
OUT
= Full Scale, V(I
OUT
) = 0.465V ● 0.2 2 LSB
I
IN
Logic Input Current 0V ≤ V
IN
≤ V
CC
● ±1 µA
V
IH
High Level Input Voltage ADR ● V
CC
– 0.3 V
SMBSUS
● 2.4 V
SCL, SDA
● 1.4 V
V
IL
Low Level Input Voltage SMBSUS, ADR ● 0.8 V
SCL, SDA
● 0.6 V
V
OL
Low Level Output Voltage I
OUT
= 3mA, SDA Only ● 0.4 V
I
OUT
= 1.6mA, SMBSUS = 0V, Measured at SHDN Pin ● 0.4 V
SMBus Timing (Notes 5, 6)
f
SMB
SMB Operating Frequency ● 10 100 kHz
t
BUF
Bus Free Time Between Stop and Start Condition ● 4.7 µs
t
HD:STA
Hold Time After (Repeated) Start Condition ● 4.0 µs
t
SU:STA
Repeated Start Condition Setup Time ● 4.7 µs
t
SU:STO
Stop Condition Setup Time ● 4.0 µs
t
HD:DAT
Data Hold Time ● 300 ns
t
SU:DAT
Data Setup Time ● 250 ns
t
LOW
Clock Low Period ● 4.7 µs
t
HIGH
Clock High Period ● 4.0 50 µs
t
f
Clock/Data Fall Time ● 300 ns
t
r
Clock/Data Rise Time ● 1000 ns
Note 4: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current is given by I
LIM
= 1.4(1.393 – DC) for the
LT1786F due to internal slope compensation circuitry.
Note 5: Timings for all signals are referenced to V
IH
and V
IL
signals.
Note 6: These parameters are guaranteed by design and are not tested in
production. Refer to the Timing Diagrams for additional information.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LT1786FCS: T
J
= T
A
+ (P
D
)(100°C/W)
Note 3: Does not include switch leakage.
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= SHUTDOWN = SMBSUS = SCL = SDA = 3.3V,
BAT = Royer = BULB = 12V, I
CCFL
= CCFL V
SW
= Open, DIO = I
OUT
= GND, CCFL V
C
= 0.5V, unless otherwise specified.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20

LT1786FCS#TRPBF

Mfr. #:
Buy LT1786FCS#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators SMBus Progmable CCFL Sw Reg
Lifecycle:
New from this manufacturer.
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