LT1186F
DAC Programmable
CCFL Switching Regulator
(Bits-to-Nits
TM
)
FEATURES
s
s
s
s
s
s
APPLICATIONS
s
s
s
face modes including standard SPI mode and pulse mode.
On power-up, the DAC counter resets to half-scale and the
Wide Battery Input Range: 4.5V to 30V
DAC configures to SPI or pulse mode depending on the CS
Grounded Lamp or Floating Lamp Configurations
signal level. In SPI mode, the system microprocessor
Open Lamp Protection
serially transfers the present 8-bit data and reads back the
Precision 50µA Full-Scale DAC Programming Current
previous 8-bit data. In pulse mode, the upper six bits of the
Standard SPI Mode or Pulse Mode
DAC configure as increment-only (1-wire interface) or
DAC Setting Is Retained in Shutdown
increment/decrement (2-wire interface) operation depend-
ing on the D
IN
signal level.
Notebook and Palmtop Computers
Portable Instruments
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-
TYPICAL APPLICATION
90% Efficient Floating CCFL with 1-Wire (Increment Only) Pulse Mode Control of Lamp Current
D1
BAT85
CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE COVERED
BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
1
2
3
C7, 1µF
CCFL
PGND
I
CCFL
DIO
CCFL V
SW
BULB
16
15
R2
220k
C5
1000pF
3
2
1
C3B
2.2µF
35V
R1
750Ω
4
5
UP TO 6mA
LAMP
10
6
C2
27pF
3kV
L1
L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
*DO
NOT SUBSTITUTE COMPONENTS
COILTRONICS (407) 241-7876
BAT
8V TO 28V
14
BAT
LT1186F
4
13
CCFL V
C
ROYER
5
AGND
SHDN
CLK
CS
V
CC
I
OUT
D
OUT
12
11
10
SHUTDOWN
FROM MPU
6
7
8
D
IN
9
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
0µA TO 50µA I
CCFL
CURRENT GIVES
C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKP-20
0mA TO 6mA LAMP CURRENT
Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001
FOR A TYPICAL DISPLAY.
U
U
U
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/meter
2
+
+
C3A
2.2µF
35V
+
V
IN
3.3V
C4 OR 5V
2.2µF
C1*
0.068µF
R3
100k
Q2*
Q1*
L2
100µH
D1
1N5818
LT1186F • TA01
FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,
REFER TO THE LT1182/83/84/84F DATA SHEET
1
LT1186F
ABSOLUTE
MAXIMUM
RATINGS
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
PACKAGE/ORDER INFORMATION
TOP VIEW
CCFL PGND 1
I
CCFL
2
DIO 3
CCFL V
C
4
AGND 5
SHDN 6
CLK 7
CS 8
16 CCFL V
SW
15 BULB
14 BAT
13 ROYER
12 V
CC
11 I
OUT
10 D
OUT
9
D
IN
ORDER PART
NUMBER
LT1186FCS
LT1186FIS
S PACKAGE
16-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 100°C/W
Consult factory for Industrial and Military grade parts.
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.
xSYMBOL PARAMETER
I
Q
I
SHDN
Supply Current
SHUTDOWN Supply Current
SHUTDOWN Input Bias Current
SHUTDOWN Threshold Voltage
f
DC(MAX)
BV
Switching Frequency
Maximum Switch Duty Cycle
Switch Breakdown Voltage
Switch Leakage Current
I
CCFL
Summing Voltage
∆I
CCFL
Summing Voltage for
∆Input
Programming Current
CCFL V
C
Offset Sink Current
∆CCFL
V
C
Source Current for
∆I
CCFL
Programming Current
CCFL V
C
to DIO Current Servo Ratio
CCFL V
C
Low Clamp Voltage
CCFL V
C
High Clamp Voltage
CCFL V
C
Switching Threshold
Measured at CCFL V
SW
, I
SW
= 50mA,
I
CCFL
= 100µA, CCFL V
C
= Open
Measured at CCFL V
SW
q
CONDITIONS
3V
≤
V
CC
≤
6.5V, 1/2 Full-Scale DAC Output Current
SHUTDOWN = 0V, CCFL V
C
Open (Note 2)
SHUTDOWN = 0V, CCFL V
C
= Open
q
q
q
MIN
TYP
6
35
5
MAX
9.5
70
10
1.2
225
240
UNITS
mA
µA
µA
V
kHz
kHz
%
%
V
0.45
175
160
80
75
60
0.85
200
200
85
85
70
Measured at CCFL V
SW
V
SW
= 12V, Measured at CCFL V
SW
V
SW
= 30V, Measured at CCFL V
SW
3V
≤
V
CC
≤
6.5V
q
20
40
0.425
0.385
0.465
0.465
5
–5
q
q
q
q
q
q
0.505
0.555
15
15
5.20
5.20
104
0.3
2.4
1.3
I
CCFL
= 0µA to 100µA
CCFL V
C
= 1.5V, Positive Current Measured into Pin
I
CCFL
= 25µA, 50µA, 75µA, 100µA,
CCFL V
C
= 1.5V
T
J
< 0°C
DIO = 5mA out of Pin, Measure I(V
C
) at CCFL V
C
= 1.5V
V
BAT
– V
BULB
= BULB Protect Servo Voltage
I
CCFL
= 100µA
CCFL V
SW
DC = 0%
5
4.95
4.95
99
0.1
2.1
0.95
4.70
4.60
94
1.7
0.6
µA/µA
µA/µA
µA/mA
V
V
V
2
U
W
U
U
W W
W
µA
µA
V
V
mV
µA
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.
SYMBOL
PARAMETER
CCFL High-Side Sense Servo Current
CCFL High-Side Sense Servo Current
Line Regulation
BULB Protect Servo Voltage
BULB Input Bias Current
I
LIM
V
SAT
∆I
Q
∆I
SW
CCFL Switch Current Limit
CCFL Switch On Resistance
Supply Current Increase During
CCFL Switch On Time
DAC Resolution
DAC Full-Scale Current
DAC Zero Scale Current
DAC Differential Nonlinearity
DAC Supply Voltage Rejection
Logic Input Current
V
IH
V
IL
V
OH
V
OL
I
OZ
f
CLK
t
CKS
t
CSS
t
DV
t
DS
t
DH
t
DO
t
CKHI
t
CKLO
t
CSH
t
DZ
t
CKH
High Level Input Voltage
Low Level Input Voltage
High Level Output Voltage
Low Level Output Voltage
Three-State Output Leakage
Clock Frequency
Setup Time, CLK↓ Before CS↓
Setup Time, CS↓ Before CLK↑
CS↓ to D
OUT
Valid
Data in Setup Time Before CLK↑
Data in Hold Time After CLK↑
CLK↓ to D
OUT
Valid
CLK High Time
CLK Low Time
CLK↓ Before CS↑
CS↑ to D
OUT
In Hi-Z
CS↑ Before CLK↑
See Test Circuits
See Test Circuits
See Test Circuits
3V
≤
V
CC
≤
6.5V, I
OUT
= Full Scale, V(I
OUT
) = 0.465V
0V
≤
V
IN
≤
V
CC
V
CC
= 3.3V
V
CC
= 5V
V
CC
= 3.3V
V
CC
= 5V
V
CC
= 3.3V, I
O
= 400µA
V
CC
= 5V, I
O
= 400µA
V
CC
= 3.3V, I
O
= 1mA
V
CC
= 5V, I
O
= 2mA
V
CS
= V
CC
V(I
OUT
) = 0.465V, Measured in SPI Mode
q
CONDITIONS
I
CCFL
= 100µA, I(V
C
) = 0µA at CCFL V
C
= 1.5V
T
J
< 0°C
BAT = 5V to 30V, I
CCFL
= 100µA,
I(V
C
) = 0µA at CCFL V
C
= 1.5V
q
q
q
q
MIN
0.93
0.91
TYP
1.00
1.00
0.1
MAX
1.07
1.07
0.16
150
7.5
9
3.0
2.6
1.0
30
UNIT
A
A
%/V
µA
V
µA
A
A
Ω
mA/A
Bits
CCFL High-Side Sense Supply Current Current Measured into BAT and Royer Pins
I
CCFL
= 100µA, I(V
C
) = 0µA at CCFL V
C
= 1.5V,
Servo Voltage Measured between BAT and BULB Pins
I
CCFL
= 100µA, I(V
C
) = 0µA at CCFL V
C
= 1.5V
Duty Cycle = 50%
Duty Cycle = 75% (Note 3)
CCFL I
SW
= 1A
CCFL I
SW
= 1A
50
6.5
100
7.0
5
q
q
q
1.25
0.9
1.9
1.6
0.6
20
8
48.5
47.0
50
50
51.5
53.0
200
±2.0
µA
µA
nA
LSB
LSB
µA
V
V
V(I
OUT
) = 0.465V, Measured in SPI Mode
q
q
q
q
q
q
q
q
q
q
q
q
2
1.9
2
4
±1
0.45
0.80
2.1
2.4
0.4
0.4
±5
2
150
400
150
150
150
150
200
250
150
400
400
V
V
V
V
V
V
µA
MHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
SERIAL INTERFACE (Notes 4, 5)
q
q
q
q
q
q
q
q
q
q
q
q
3
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.
SYMBOL
t
CSLO
t
CSHI
PARAMETER
CS Low Time
CS High Time
CONDITIONS
f
CLK
= 2MHz
q
q
MIN
4550
400
TYP
MAX
UNIT
ns
ns
SERIAL INTERFACE (Notes 4, 5)
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current
vs Temperature
10
9
SHUTDOWN CURRENT (µA)
8
90
8O
70
60
50
40
30
20
10
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G02
SHUTDOWN INPUT BIAS CURRENT (µA)
SUPPLY CURRENT (mA)
7
6
5
4
3
2
1
0
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G01
Shutdown Threshold Voltage
vs Temperature
1.2
240
SHUTDOWN THRESHOLD VOLTAGE (V)
1.1
CCFL FREQUENCY (kHz)
1.0
0.9
0.8
0.7
0.6
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G04
CCFL MAXIMUM DUTY CYCLE (%)
4
U W
Shutdown Current
vs Temperature
100
6
5
4
3
2
1
Shutdown Input Bias Current
vs Temperature
V
CC
= 5V
V
CC
= 3V
V
CC
= 5V
V
CC
= 3V
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G03
Frequency vs Temperature
95
93
91
89
87
85
83
81
79
77
0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G05
Maximum Duty Cycle
vs Temperature
230
220
210
200
190
180
170
160
–75 –50 –25
75
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G06
LT1186F
TYPICAL PERFORMANCE CHARACTERISTICS
I
CCFL
Summing Voltage
vs Temperature
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
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G07
CCFL V
C
SINK OFFSET CURRENT (µA)
∆I
CCFL
SUMMING VOLTAGE (mV)
I
CCFL
SUMMING VOLTAGE (V)
∆CCFL
V
C
Source Current for
∆I
CCFL
Programming Current
vs Temperature
5.10
∆CCFL
V
C
SOURCE CURRENT FOR
∆I
CCFL
PROGRAMMING CURRENT (µA/µA)
I(DIO) = 10mA
0.8
0.6
0.4
0.2
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G11
NEGATIVE DIO VOLTAGE (V)
5.05
POSITIVE DIO VOLTAGE (V)
5.00
4.95
4.90
4.85
I
CCFL
= 100µA
I
CCFL
= 50µA
I
CCFL
= 10µA
4.80
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G10
V
C
to DIO Current Servo
Ratio vs Temperature
CCFL V
C
DIO CURRENT SERVO RATIO (µA/mA)
103
CCFL V
C
LOW CLAMP VOLTAGE (V)
CCFL V
C
HIGH CLAMP VOLTAGE (V)
102
101
100
99
98
97
96
95
–75 – 50 –25
0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G13
I(DIO) = 10mA
I(DIO) = 1mA
I(DIO) = 5mA
U W
I
CCFL
Summing Voltage
Load Regulation
5
4
3
2
1
0
–1
–2
–3
–4
–5
–6
–7
–8
–9
–10
0
V
C
Sink Offset Current
vs Temperature
10
9
8
7
6
5
4
3
2
1
CCFL V
C
= 0.5V
0
–1
–2
–3
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G09
CCFL V
C
= 1.5V
T = –55°C
CCFL V
C
= 1.0V
T = 25°C
T = 125°C
20 40 60 80 100 120 140 160 180 200
I
CCFL
PROGRAMMING CURRENT (µA)
LT1186F • G08
Positive DIO Voltage
vs Temperature
1.2
1.0
I(DIO) = 5mA
1.6
1.4
Negative DIO Voltage
vs Temperature
I(DIO) = 10mA
1.2
1.0
0.8
0.6
0.4
0.2
0
–75 –50 –25
0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G12
I(DIO) = 5mA
I(DIO) = 1mA
I(DIO) = 1mA
V
C
Low Clamp Voltage
vs Temperature
0.30
0.25
0.20
0.15
0.10
0.05
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G14
V
C
High Clamp Voltage
vs Temperature
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1186F • G15
5
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