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1
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 50
A Full-Scale DAC Programming Current
s
Standard SPI Mode or Pulse Mode
s
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 35
A 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.
s
Notebook and Palmtop Computers
s
Portable Instruments
s
Retail Terminals
APPLICATIO
N
S
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 50
A full-
scale current output DAC. The DAC provides simple "bits-
to-lamp current control" and communicates in two inter-
DESCRIPTIO
N
U
TYPICAL APPLICATIO
N
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
750
L2
100
H
3
2
1
5
4
+
+
C7, 1
F
C1*
0.068
F
C5
1000pF
R2
220k
R3
100k
C3A
2.2
F
35V
C4
2.2
F
V
IN
3.3V
OR 5V
LT1186F TA01
C3B
2.2
F
35V
C2
27pF
3kV
+
Q2*
Q1*
SHUTDOWN
ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3A AND C3B.
MAKE 3CB ESR
0.5
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
0
A TO 50
A 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
2
LT1186F
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
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 ....................... 20V to V
CC
+ 0.3V
Junction Temperature (Note 1) ........................... 100
C
Operating Ambient Temperature Range
LT1186FC ............................................ 0
C to 100
C
LT1186FI .......................................... 40
C to 100
C
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec)................ 300
C
T
JMAX
= 100
C,
JA
= 100
C/W
LT1186FCS
LT1186FIS
ORDER PART
NUMBER
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
Consult factory for Industrial and Military grade parts.
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
CLK
CS
CCFL V
SW
BULB
BAT
ROYER
V
CC
I
OUT
D
OUT
D
IN
xSYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Q
Supply Current
3V
V
CC
6.5V, 1/2 Full-Scale DAC Output Current
q
6
9.5
mA
I
SHDN
SHUTDOWN Supply Current
SHUTDOWN = 0V, CCFL V
C
Open (Note 2)
35
70
A
SHUTDOWN Input Bias Current
SHUTDOWN = 0V, CCFL V
C
= Open
5
10
A
SHUTDOWN Threshold Voltage
q
0.45
0.85
1.2
V
f
Switching Frequency
Measured at CCFL V
SW
, I
SW
= 50mA,
175
200
225
kHz
I
CCFL
= 100
A, CCFL V
C
= Open
q
160
200
240
kHz
DC(MAX)
Maximum Switch Duty Cycle
Measured at CCFL V
SW
80
85
%
q
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
A
V
SW
= 30V, Measured at CCFL V
SW
40
A
I
CCFL
Summing Voltage
3V
V
CC
6.5V
0.425
0.465
0.505
V
q
0.385
0.465
0.555
V
I
CCFL
Summing Voltage for
I
CCFL
= 0
A to 100
A
5
15
mV
Input Programming Current
CCFL V
C
Offset Sink Current
CCFL V
C
= 1.5V, Positive Current Measured into Pin
5
5
15
A
CCFL V
C
Source Current for
I
CCFL
= 25
A, 50
A, 75
A, 100
A,
q
4.70
4.95
5.20
A/
A
I
CCFL
Programming Current
CCFL V
C
= 1.5V
T
J
< 0
C
q
4.60
4.95
5.20
A/
A
CCFL V
C
to DIO Current Servo Ratio
DIO = 5mA out of Pin, Measure I(V
C
) at CCFL V
C
= 1.5V
q
94
99
104
A/mA
CCFL V
C
Low Clamp Voltage
V
BAT
V
BULB
= BULB Protect Servo Voltage
q
0.1
0.3
V
CCFL V
C
High Clamp Voltage
I
CCFL
= 100
A
q
1.7
2.1
2.4
V
CCFL V
C
Switching Threshold
CCFL V
SW
DC = 0%
q
0.6
0.95
1.3
V
ELECTRICAL CHARACTERISTICS
T
A
= 25
C, V
CC
= SHUTDOWN = D
IN
= CS = 3.3V, BAT = Royer = BULB = 12V, I
CCFL
= CCFL V
SW
= Open, D
OUT
= Three-State, DIO = I
OUT
= CLK = GND, CCFL V
C
= 0.5V, unless otherwise specified.
3
LT1186F
T
A
= 25
C, V
CC
= SHUTDOWN = D
IN
= CS = 3.3V, BAT = Royer = BULB = 12V, I
CCFL
= CCFL V
SW
= Open, D
OUT
= Three-State, DIO = I
OUT
= CLK = GND, CCFL V
C
= 0.5V, unless otherwise specified.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
CCFL High-Side Sense Servo Current
I
CCFL
= 100
A, I(V
C
) = 0
A at CCFL V
C
= 1.5V
q
0.93
1.00
1.07
A
T
J
< 0
C
q
0.91
1.00
1.07
A
CCFL High-Side Sense Servo Current
BAT = 5V to 30V, I
CCFL
= 100
A,
0.1
0.16
%/V
Line Regulation
I(V
C
) = 0
A at CCFL V
C
= 1.5V
CCFL High-Side Sense Supply Current Current Measured into BAT and Royer Pins
q
50
100
150
A
BULB Protect Servo Voltage
I
CCFL
= 100
A, I(V
C
) = 0
A at CCFL V
C
= 1.5V,
q
6.5
7.0
7.5
V
Servo Voltage Measured between BAT and BULB Pins
BULB Input Bias Current
I
CCFL
= 100
A, I(V
C
) = 0
A at CCFL V
C
= 1.5V
5
9
A
I
LIM
CCFL Switch Current Limit
Duty Cycle = 50%
q
1.25
1.9
3.0
A
Duty Cycle = 75% (Note 3)
q
0.9
1.6
2.6
A
V
SAT
CCFL Switch On Resistance
CCFL I
SW
= 1A
q
0.6
1.0
I
Q
Supply Current Increase During
CCFL I
SW
= 1A
20
30
mA/A
I
SW
CCFL Switch On Time
DAC Resolution
8
Bits
DAC Full-Scale Current
V(I
OUT
) = 0.465V, Measured in SPI Mode
48.5
50
51.5
A
q
47.0
50
53.0
A
DAC Zero Scale Current
V(I
OUT
) = 0.465V, Measured in SPI Mode
200
nA
DAC Differential Nonlinearity
q
2.0
LSB
DAC Supply Voltage Rejection
3V
V
CC
6.5V, I
OUT
= Full Scale, V(I
OUT
) = 0.465V
q
2
4
LSB
Logic Input Current
0V
V
IN
V
CC
q
1
A
V
IH
High Level Input Voltage
V
CC
= 3.3V
q
1.9
V
V
CC
= 5V
q
2
V
V
IL
Low Level Input Voltage
V
CC
= 3.3V
q
0.45
V
V
CC
= 5V
q
0.80
V
V
OH
High Level Output Voltage
V
CC
= 3.3V, I
O
= 400
A
q
2.1
V
V
CC
= 5V, I
O
= 400
A
q
2.4
V
V
OL
Low Level Output Voltage
V
CC
= 3.3V, I
O
= 1mA
q
0.4
V
V
CC
= 5V, I
O
= 2mA
q
0.4
V
I
OZ
Three-State Output Leakage
V
CS
= V
CC
q
5
A
SERIAL INTERFACE (Notes 4, 5)
f
CLK
Clock Frequency
q
2
MHz
t
CKS
Setup Time, CLK
Before CS
q
150
ns
t
CSS
Setup Time, CS
Before CLK
q
400
ns
t
DV
CS
to D
OUT
Valid
See Test Circuits
q
150
ns
t
DS
Data in Setup Time Before CLK
q
150
ns
t
DH
Data in Hold Time After CLK
q
150
ns
t
DO
CLK
to D
OUT
Valid
See Test Circuits
q
150
ns
t
CKHI
CLK
High Time
q
200
ns
t
CKLO
CLK
Low Time
q
250
ns
t
CSH
CLK
Before CS
q
150
ns
t
DZ
CS
to D
OUT
In Hi-Z
See Test Circuits
q
400
ns
t
CKH
CS
Before CLK
q
400
ns
4
LT1186F
ELECTRICAL CHARACTERISTICS
T
A
= 25
C, V
CC
= SHUTDOWN = D
IN
= CS = 3.3V, BAT = Royer = BULB = 12V, I
CCFL
= CCFL V
SW
= Open, D
OUT
= Three-State, DIO = I
OUT
= CLK = GND, CCFL V
C
= 0.5V, unless otherwise specified.
The
q
denotes specifications which apply over the specified operating
temperature range.
Note 1: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LT1186FCS: T
J
= T
A
+ (P
D
)(100
C/W)
Note 2: Does not include switch leakage.
Note 3: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current is given by I
LIM
= 1.4(1.393 DC) for the
LT1186F due to internal slope compensation circuitry.
Note 4: Timings for all input signals are measured at 0.8V for a High-to-
Low transition and 2.0V for a Low-to-High transition.
Note 5: Timings are guaranteed but not tested.
TEMPERATURE (
C)
75
SUPPLY CURRENT (mA)
6
8
10
9
7
5
3
1
125
LT1186F G01
4
2
0
25
50
0
50
100
150
25
75
175
Supply Current
vs Temperature
TEMPERATURE (
C)
0
SHUTDOWN INPUT BIAS CURRENT (
A)
2
4
6
5
3
1
25
25
75
125
LT1186F G03
175
50
75
0
50
100
150
V
CC
= 5V
V
CC
= 3V
TEMPERATURE (
C)
75
SHUTDOWN CURRENT (
A)
60
8O
100
90
70
50
30
10
125
LT1186F G02
40
20
0
25
50
0
50
100
150
25
75
175
V
CC
= 5V
V
CC
= 3V
Shutdown Current
vs Temperature
Shutdown Input Bias Current
vs Temperature
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
Shutdown Threshold Voltage
vs Temperature
TEMPERATURE (
C)
0.6
SHUTDOWN THRESHOLD VOLTAGE (V)
0.8
1.0
1.2
1.1
0.9
0.7
25
25
75
125
LT1186F G04
175
50
75
0
50
100
150
TEMPERATURE (
C)
75
CCFL FREQUENCY (kHz)
220
240
125
LT1186F G05
200
180
160
25
25
75
175
210
230
190
170
100
50
0
50
150
Frequency vs Temperature
TEMPERATURE (
C)
75
CCFL MAXIMUM DUTY CYCLE (%)
87
91
95
93
89
85
81
77
125 150
LT1186F G06
83
79
75
25 0
50
25 50
75 100
175
Maximum Duty Cycle
vs Temperature
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
SERIAL INTERFACE (Notes 4, 5)
t
CSLO
CS
Low Time
f
CLK
= 2MHz
q
4550
ns
t
CSHI
CS
High Time
q
400
ns
5
LT1186F
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
TEMPERATURE (
C)
I
CCFL
SUMMING VOLTAGE (V)
0.53
0.52
0.51
0.50
0.49
0.48
0.47
0.46
0.45
0.44
0.43
0.42
0.41
0.40
0.39
0.38
25
25
75
125
LT1186F G07
175
50
75
0
50
100
150
I
CCFL
Summing Voltage
vs Temperature
I
CCFL
Summing Voltage
Load Regulation
I
CCFL
PROGRAMMING CURRENT (
A)
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10
40
80
120
160
LT1186F G08
200
20
0
60
100
140
180
T = 55
C
T = 25
C
T = 125
C
I
CCFL
SUMMING VOLTAGE (mV)
CCFL V
C
Source Current for
I
CCFL
Programming Current
vs Temperature
TEMPERATURE (
C)
4.80
CCFL V
C
SOURCE CURRENT FOR
I
CCFL
PROGRAMMING CURRENT (
A/
A)
4.90
4.85
5.00
4.95
5.10
5.05
25
25
75
125
LT1186F G10
175
50
75
0
50
100
150
I
CCFL
= 10
A
I
CCFL
= 50
A
I
CCFL
= 100
A
Negative DIO Voltage
vs Temperature
TEMPERATURE (
C)
75
NEGATIVE DIO VOLTAGE (V)
1.2
1.6
125
LT1186F G12
0.8
0.4
0
25
25
75
175
1.0
1.4
0.6
0.2
100
50
0
50
150
I(DIO) = 1mA
I(DIO) = 5mA
I(DIO) = 10mA
V
C
Sink Offset Current
vs Temperature
TEMPERATURE (
C)
3
CCFL V
C
SINK OFFSET CURRENT (
A)
1
1
0
2
10
9
6
8
7
5
3
2
4
75
125 150
25 0
50
25 50
75 100
175
CCFL V
C
= 0.5V
CCFL V
C
= 1.0V
CCFL V
C
= 1.5V
LT1186F G09
TEMPERATURE (
C)
75
CCFL V
C
DIO CURRENT SERVO RATIO (
A/mA)
101
103
125
LT1186F G13
99
97
95
25
25
75
175
100
102
98
96
100
50
0
50
150
I(DIO) = 1mA
I(DIO) = 5mA
I(DIO) = 10mA
V
C
to DIO Current Servo
Ratio vs Temperature
TEMPERATURE (
C)
75
1.7
CCFL V
C
HIGH CLAMP VOLTAGE (V)
1.8
2.0
2.1
2.2
2.4
50
50
100
LT1186F G15
1.9
2.3
25
150 175
25 0
75
125
V
C
High Clamp Voltage
vs Temperature
V
C
Low Clamp Voltage
vs Temperature
TEMPERATURE (
C)
0
CCFL V
C
LOW CLAMP VOLTAGE (V) 0.10
0.05
0.20
0.15
0.30
0.25
25
25
75
125
LT1186F G14
175
50
75
0
50
100
150
Positive DIO Voltage
vs Temperature
TEMPERATURE (
C)
0
POSITIVE DIO VOLTAGE (V)
0.4
0.2
0.8
0.6
1.2
1.0
25
25
75
125
LT1186F G11
175
50
75
0
50
100
150
I(DIO) = 1mA
I(DIO) = 5mA
I(DIO) = 10mA
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