LINEAR TECHNOLOGY LT1186F Technical data

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LT1186F

DAC Programmable

CCFL Switching Regulator

(Bits-to-Nits

TM

)

FEATURES

■

Wide Battery Input Range: 4.5V to 30V

■

Grounded Lamp or Floating Lamp Configurations

■

Open Lamp Protection

■

Precision 50µA Full-Scale DAC Programming Current

■

Standard SPI Mode or Pulse Mode

■

DAC Setting Is Retained in Shutdown

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APPLICATIONS

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Retail Terminals

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DESCRIPTION

The LT®1186F is a fixed frequency, current mode, switch­ing 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 “bits­to-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 depend­ing on the DIN 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 shut­down 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 nar­row 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

TYPICAL APPLICATION

90% Efficient Floating CCFL with 1-Wire (Increment Only) Pulse Mode Control of Lamp Current

D1

BAT85

1

CCFL

CCFL V

LT1186F

C

BULB

BAT

ROYER

V

I

OUT

D

OUT

D

SW

CC

IN

PGND

2

I

CCFL

3

C7, 1µF

SHUTDOWN

FROM MPU

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

4

5

6

7

8

DIO

CCFL V

AGND

SHDN

CLK

CS

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CCFL BACKLIGHT APPLICATION CIRCUITS
CONTAINED IN THIS DATA SHEET ARE COVERED
BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING

16

15

14

13

V

C4

2.2µF

IN

3.3V
OR 5V

CURRENT GIVES

CCFL

12

11

10

9

+

0µA TO 50µA I
0mA TO 6mA LAMP CURRENT
FOR A TYPICAL DISPLAY.

UP TO 6mA

LAMP

C5

1000pF

R2
220k

R3
100k

FOR ADDITIONAL CCFL/LCD CONTRAST APPLICATION CIRCUITS,
REFER TO THE LT1182/83/84/84F DATA SHEET

10

321 5

+

C1*

0.068µF

Q2* Q1*

6

C3B

2.2µF
35V

L2
100µH

C2
27pF
3kV

4

D1

1N5818

L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
*DO NOT SUBSTITUTE COMPONENTS
COILTRONICS [phone]

L1

+

C3A

2.2µF

R1
750Ω

LT1186F • TA01

35V

BAT
8V TO 28V

1

LT1186F

WW

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ABSOLUTE MAXIMUM RATINGS

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PACKAGE/ORDER INFORMATION

VCC........................................................................... 7V

BAT, Royer, BULB .................................................. 30V

CCFL PGND

CCFL VSW............................................................... 60V

Shutdown ................................................................. 6V

I

Input Current .............................................. 10mA

CCFL

CCFL V

DIO Input Current (Peak, <100ms).................... 100mA

Digital Inputs ................................ –0.3V to VCC + 0.3V

Digital Outputs.............................. –0.3V to VCC + 0.3V

DAC Output Voltage ....................... –20V to VCC + 0.3V

Junction Temperature (Note 1)........................... 100°C

Operating Ambient Temperature Range

LT1186FC ............................................ 0°C to 100°C

LT1186FI ..........................................– 40°C to 100°C

Consult factory for Industrial and Military grade parts.

Storage Temperature Range ................ –65°C to 150°C

Lead Temperature (Soldering, 10 sec)................ 300°C

ELECTRICAL CHARACTERISTICS

TA = 25°C, VCC = SHUTDOWN = DIN = CS = 3.3V, BAT = Royer = BULB = 12V, I
= CLK = GND, CCFL VC = 0.5V, unless otherwise specified.

CCFL

TOP VIEW

1
2

I

CCFL

3

DIO

4

C

5

AGND

6

SHDN

7

CLK

8

CS

S PACKAGE

16-LEAD PLASTIC SO

T

= 100°C, θJA = 100°C/W

JMAX

= CCFL VSW = Open, D

U

W

U

ORDER PART

16

CCFL V

SW

15

BULB

14

BAT

13

ROYER

12

V

CC

11

I

OUT

10

D

OUT

9

D

IN

= Three-State, DIO = I

OUT

NUMBER

LT1186FCS
LT1186FIS

OUT

xSYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

I

SHDN

f Switching Frequency Measured at CCFL VSW, ISW = 50mA, 175 200 225 kHz

DC(MAX) Maximum Switch Duty Cycle Measured at CCFL V

BV Switch Breakdown Voltage Measured at CCFL V

Supply Current 3V ≤ VCC ≤ 6.5V, 1/2 Full-Scale DAC Output Current ● 6 9.5 mA
SHUTDOWN Supply Current SHUTDOWN = 0V, CCFL VC Open (Note 2) 35 70 µA
SHUTDOWN Input Bias Current SHUTDOWN = 0V, CCFL VC = Open 5 10 µA
SHUTDOWN Threshold Voltage ● 0.45 0.85 1.2 V

= 100µA, CCFL VC = Open ● 160 200 240 kHz

I

CCFL

SW

SW

Switch Leakage Current VSW = 12V, Measured at CCFL V

= 30V, Measured at CCFL V

V

SW

I

Summing Voltage 3V ≤ VCC ≤ 6.5V 0.425 0.465 0.505 V

CCFL

∆I

Summing Voltage for I

CCFL

∆Input Programming Current
CCFL VC Offset Sink Current CCFL VC = 1.5V, Positive Current Measured into Pin –5 5 15 µA

∆CCFL VC Source Current for I
∆I

Programming Current CCFL VC = 1.5V

CCFL

CCFL VC to DIO Current Servo Ratio DIO = 5mA out of Pin, Measure I(VC) at CCFL VC = 1.5V ● 94 99 104 µA/mA
CCFL VC Low Clamp Voltage V
CCFL VC High Clamp Voltage I
CCFL VC Switching Threshold CCFL VSW DC = 0% ● 0.6 0.95 1.3 V

= 0µA to 100µA515mV

CCFL

= 25µA, 50µA, 75µA, 100µA, ● 4.70 4.95 5.20 µA/µA

CCFL

< 0°C ● 4.60 4.95 5.20 µA/µA

T

J

– V

BAT

CCFL

= BULB Protect Servo Voltage ● 0.1 0.3 V

BULB

= 100µA ● 1.7 2.1 2.4 V

SW
SW

80 85 %

● 75 85 %

60 70 V

20 µA
40 µA

● 0.385 0.465 0.555 V

2

ELECTRICAL CHARACTERISTICS

LT1186F

TA = 25°C, VCC = SHUTDOWN = DIN = CS = 3.3V, BAT = Royer = BULB = 12V, I

= CCFL VSW = Open, D

CCFL

= Three-State, DIO = I

OUT

OUT

= CLK = GND, CCFL VC = 0.5V, unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNIT

CCFL High-Side Sense Servo Current I

CCFL High-Side Sense Servo Current BAT = 5V to 30V, I
Line Regulation I(V

CCFL High-Side Sense Supply Current Current Measured into BAT and Royer Pins ● 50 100 150 µA
BULB Protect Servo Voltage I

BULB Input Bias Current I

I

LIM

V
∆I

∆I

SAT

Q

SW

CCFL Switch Current Limit Duty Cycle = 50% ● 1.25 1.9 3.0 A

CCFL Switch On Resistance CCFL ISW = 1A ● 0.6 1.0 Ω
Supply Current Increase During CCFL ISW = 1A 20 30 mA/A

CCFL Switch On Time
DAC Resolution 8 Bits
DAC Full-Scale Current V(I

DAC Zero Scale Current V(I
DAC Differential Nonlinearity ● ±2.0 LSB
DAC Supply Voltage Rejection 3V ≤ VCC ≤ 6.5V, I
Logic Input Current 0V ≤ VIN ≤ V

V

IH

V

IL

V

OH

V

OL

I

OZ

High Level Input Voltage V

Low Level Input Voltage V

High Level Output Voltage V

Low Level Output Voltage V

Three-State Output Leakage V

SERIAL INTERFACE (Notes 4, 5)

f

CLK

t

CKS

t

CSS

t

DV

t

DS

t

DH

t

DO

t

CKHI

t

CKLO

t

CSH

t

DZ

t

CKH

Clock Frequency ● 2 MHz
Setup Time, CLK↓ Before CS↓ ● 150 ns
Setup Time, CS↓ Before CLK↑ ● 400 ns
CS↓ to D

Valid See Test Circuits ● 150 ns

OUT

Data in Setup Time Before CLK↑ ● 150 ns
Data in Hold Time After CLK↑ ● 150 ns
CLK↓ to D

Valid See Test Circuits ● 150 ns

OUT

CLK High Time ● 200 ns
CLK Low Time ● 250 ns
CLK↓ Before CS↑ ● 150 ns
CS↑ to D

In Hi-Z See Test Circuits ● 400 ns

OUT

CS↑ Before CLK↑ ● 400 ns

= 100µA, I(VC) = 0µA at CCFL VC = 1.5V ● 0.93 1.00 1.07 A

CCFL

< 0°C ● 0.91 1.00 1.07 A

T

J

= 100µA, 0.1 0.16 %/V

) = 0µA at CCFL VC = 1.5V

C

= 100µA, I(VC) = 0µA at CCFL VC = 1.5V, ● 6.5 7.0 7.5 V

CCFL

CCFL

Servo Voltage Measured between BAT and BULB Pins

= 100µA, I(VC) = 0µA at CCFL VC = 1.5V 5 9 µA

CCFL

Duty Cycle = 75% (Note 3)

) = 0.465V, Measured in SPI Mode 48.5 50 51.5 µA

OUT

) = 0.465V, Measured in SPI Mode 200 nA

OUT

= Full Scale, V(I

OUT

CC

= 3.3V ● 1.9 V

CC

= 5V ● 2V

V

CC

= 3.3V ● 0.45 V

CC

= 5V ● 0.80 V

V

CC

= 3.3V, IO = 400µA ● 2.1 V

CC

V

= 5V, IO = 400µA ● 2.4 V

CC

= 3.3V, IO = 1mA ● 0.4 V

CC

V

= 5V, IO = 2mA ● 0.4 V

CC

= V

CS

CC

) = 0.465V ● 24 LSB

OUT

● 0.9 1.6 2.6 A

● 47.0 50 53.0 µA

● ±1 µA

● ±5 µA

3

LT1186F

TEMPERATURE (°C)

0

SHUTDOWN INPUT BIAS CURRENT (µA)

2

4

6

5

3

1

–25 25 75 125

LT1186F • G03

175–50–75 0 50 100 150

VCC = 5V

VCC = 3V

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

ELECTRICAL CHARACTERISTICS

TA = 25°C, VCC = SHUTDOWN = DIN = CS = 3.3V, BAT = Royer = BULB = 12V, I

= CCFL VSW = Open, D

CCFL

= Three-State, DIO = I

OUT

OUT

= CLK = GND, CCFL VC = 0.5V, unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNIT
SERIAL INTERFACE (Notes 4, 5)

t

CSLO

t

CSHI

The ● denotes specifications which apply over the specified operating
temperature range.

Note 1: T
dissipation P

LT1186FCS: TJ = TA + (PD)(100°C/W)

Note 2: Does not include switch leakage.

CS Low Time f

= 2MHz ● 4550 ns

CLK

CS High Time ● 400 ns

Note 3: For duty cycles (DC) between 50% and 80%, minimum

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

guaranteed switch current is given by I
LT1186F due to internal slope compensation circuitry.

Note 4: Timings for all input signals are measured at 0.8V for a High-to-

= 1.4(1.393 – DC) for the

LIM

Low transition and 2.0V for a Low-to-High transition.
Note 5: Timings are guaranteed but not tested.

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

Supply Current
vs Temperature

10

9
8
7
6
5
4
3

SUPPLY CURRENT (mA)

2
1
0

–25–50 0 50 100 150

–75

TEMPERATURE (°C)

75

125

25

175

LT1186F • G01

Shutdown Current
vs Temperature

100

90
8O
70

60
50
40
30

SHUTDOWN CURRENT (µA)

20
10

0

–25–50 0 50 100 150

–75

VCC = 5V

VCC = 3V

75

25

TEMPERATURE (°C)

125

Shutdown Input Bias Current
vs Temperature

175

LT1186F • G02

Shutdown Threshold Voltage
vs Temperature

1.2

1.1

1.0

0.9

0.8

0.7

SHUTDOWN THRESHOLD VOLTAGE (V)

0.6

4

–25 25 75 125

TEMPERATURE (°C)

Maximum Duty Cycle

Frequency vs Temperature

240

230

220

210

200

190

CCFL FREQUENCY (kHz)

180

170

175–50–75 0 50 100 150

LT1186F • G04

160

–75

–50

–25

75

50

25

0

TEMPERATURE (°C)

100

125

150

LT1186F • G05

175

vs Temperature

W

TEMPERATURE (°C)

–3

CCFL V

C

SINK OFFSET CURRENT (µA)

–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 VC = 0.5V

CCFL VC = 1.0V

CCFL VC = 1.5V

LT1186F • G09

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

U

TYPICAL PERFORMANCE CHARACTERISTICS

I

Summing Voltage

CCFL

vs Temperature

0.53

0.52

0.51

0.50

0.49

0.48

0.47

0.46

0.45

0.44

0.43

SUMMING VOLTAGE (V)

0.42

CCFL

0.41

I

0.40

0.39

0.38
–25 25 75 125

TEMPERATURE (°C)

∆CCFL VC Source Current for
∆I

Programming Current

CCFL

vs Temperature

5.10

5.05

I

= 100µA

5.00

4.95

SOURCE CURRENT FOR

4.90

C

PROGRAMMING CURRENT (µA/µA)

4.85

∆CCFL V

CCFL

∆I

4.80

CCFL

I

= 50µA

CCFL

I

CCFL

–25 25 75 125

TEMPERATURE (°C)

175–50–75 0 50 100 150

LT1186F • G07

= 10µA

175–50–75 0 50 100 150

LT1186F • G10

I

Summing Voltage

CCFL

Load Regulation

5
4
3
2
1

0
–1
–2
–3

–4
–5

SUMMING VOLTAGE (mV)

–6

CCFL

–7

∆I

–8
–9

–10

I

T = 125°C

40 80 120 160

PROGRAMMING CURRENT (µA)

CCFL

Positive DIO Voltage
vs Temperature

1.2

1.0

0.8

0.6

0.4

POSITIVE DIO VOLTAGE (V)

0.2

0

I(DIO) = 1mA

–25 25 75 125

TEMPERATURE (°C)

T = –55°C

T = 25°C

I(DIO) = 10mA

I(DIO) = 5mA

LT1186F • G08

LT1186F • G11

LT1186F

VC Sink Offset Current
vs Temperature

20020060 100 140 180

Negative DIO Voltage
vs Temperature

1.6

1.4

1.2

1.0

0.8

0.6

0.4

NEGATIVE DIO VOLTAGE (V)

0.2

175–50–75 0 50 100 150

0

–75

–50

I(DIO) = 10mA

–25

25

0
TEMPERATURE (°C)

I(DIO) = 5mA

I(DIO) = 1mA

75

50

100

125

LT1186F • G12

150

175

VC to DIO Current Servo
Ratio vs Temperature

103

102

101

100

I(DIO) = 1mA

99

98

97

DIO CURRENT SERVO RATIO (µA/mA)

C

96

CCFL V

95

–75

–25

–50

TEMPERATURE (°C)

0

I(DIO) = 10mA

I(DIO) = 5mA

50

25

75

100

125

150

LT1186F • G13

175

VC Low Clamp Voltage
vs Temperature

0.30

0.25

0.20

0.15

0.10

LOW CLAMP VOLTAGE (V)

C

0.05

CCFL V

0

–25 25 75 125

TEMPERATURE (°C)

VC High Clamp Voltage
vs Temperature

175–50–75 0 50 100 150

LT1186F • G14

5