Linear Technology LT1786F Datasheet

LT1786F

SMBus Programmable

CCFL Switching Regulator

FEATURES

■

Wide Battery Input Range: 4.5V to 30V

■

Grounded Lamp or Floating Lamp Configurations

■

Open Lamp Protection

■

Precision 100µA Full-Scale DAC Programming Current

■

2-Wire SMBus Interface

■

Two Selectable SMBus Addresses

■

DAC Setting Is Retained in Shutdown

U

APPLICATIONS

■

Notebook and Palmtop Computers

■

Portable Instruments

■

Personal Digital Assistants

U

DESCRIPTION

The LT®1786F 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 6-bit 100µ A fullscale current output DAC. The DAC provides simple “bits-

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 40µ 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 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 switching 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.

, LTC and LT are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATION

90% Efficient Floating CCFL with 2-Wire SMBus Control of Lamp Current

D1

BAT85

1

CCFL PGND

2

I



CCFL

3

C7, 1µF

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 

4

5

6

7

8

DIO

CCFL V

AGND

SHDN

SMBSUS

ADR

LT1786F



C

CCFL V

ROYER

BULB

BAT

V

I

OUT

SCL

SDA

16



SW

15

14

13

12



CC

11



10

9

U

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



3V ≤ V

CC

≤ 6.5V

+

C4

2.2µF

TO SMBus HOST

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

C5

1000pF

R3

100k

CCFL

LAMP

10

321 5

R2 220k

CURRENT GIVES 

+

C1*

0.068µF

Q2* Q1*

L1 = COILTRONICS CTX210605 L2 = COILTRONICS CTX100-4 

*DO NOT SUBSTITUTE COMPONENTS COILTRONICS (561) 241-7876

L1



+

C3A

2.2µF

R1 750Ω

35V

BAT 8V TO 28V

6

C3B

2.2µF 35V

C2 27pF 3kV

4



L2 100µH

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

D1

1N5818

1786F TA01

1

LT1786F

WW

W

U

ABSOLUTE MAXIMUM RATINGS

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

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

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

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

I

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

CCFL

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 ..................... –15V to (VCC + 0.3V)

Junction Temperature (Note 1)............................ 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

U

PACKAGE/ORDER INFORMATION

TOP VIEW

16

CCFL V



SW

15

BULB

14

BAT

13

ROYER

12

V



CC

11

I



OUT

10

SCL

9

SDA

I

CCFL

CCFL V

AGND SHDN

ADR

1 2



3

DIO

4



C

5 6 7 8

S PACKAGE

16-LEAD PLASTIC SO

T

= 100°C, θJA = 100°C/W

JMAX

CCFL PGND

SMBSUS

Consult factory for Industrial and Military grade parts.

W

ORDER PART

NUMBER

LT1786FCS

ELECTRICAL CHARACTERISTICS

TA = 25°C, VCC = SHUTDOWN = SMBSUS = SCL = SDA = 3.3V, BAT = Royer = BULB = 12V, I DIO = I

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

ISUS SMBSUS Supply Current SMBSUS = 0V or Command Code Bit 7 = 1, ● 40 100 µA

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

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

OUT

Supply Current 3V ≤ VCC ≤ 6.5V, I

CCFL VC = Open (Note 2) SHUTDOWN Supply Current SHUTDOWN = 0V, CCFL VC = Open (Note 2) ● 150 300 µA SHUTDOWN Input Bias Current SHUTDOWN = 0V, CCFL VC = Open 5 10 µA SHUTDOWN Threshold Voltage ● 0.45 0.85 1.2 V

I

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

CCFL

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

VSW = 30V, Measured at CCFL V 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 CCFL High-Side Sense Servo Current I

= 0µA to 100µA 5 15 mV

CCFL

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

CCFL

– V

BAT

BULB

= 100µA ● 1.7 2.1 2.4 V

CCFL

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

CCFL

= 0µA ● 6 9.5 mA

OUT

SW

SW SW

= BULB Protect Servo Voltage ● 0.1 0.3 V

= CCFL VSW = Open,

CCFL

80 85 %

● 75 85 %

60 70 V

● 0.385 0.465 0.555 V

20 µA 40 µA

U

2

LT1786F

ELECTRICAL CHARACTERISTICS

TA = 25°C, VCC = SHUTDOWN = SMBSUS = SCL = SDA = 3.3V, BAT = Royer = BULB = 12V, I DIO = I

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNIT

I

LIM

V

SAT

∆I ∆I

SW

I

IN

V

IH

V

IL

V

OL

SMBus Timing (Notes 4, 5)

f

SMB

t

BUF

t

HD:STA

t

SU:STA

t

SU:STO

t

HD:DAT

t

SU:DAT

t

LOW

t

HIGH

t

f

t

r

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

OUT

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

CCFL

Servo Voltage Measured between BAT and BULB Pins

BULB Input Bias Current I

CCFL

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

Duty Cycle = 75% (Note 3)

CCFL Switch On Resistance CCFL ISW = 1A ● 0.6 1.0 Ω

Q

Supply Current Increase During CCFL ISW = 1A 20 30 mA/A CCFL Switch On Time

DAC Resolution 6 Bits DAC Full-Scale Current V(I

DAC Zero Scale Current V(I DAC Differential Nonlinearity ● ±0.1 ±1 LSB DAC Supply Voltage Rejection 3V ≤ VCC ≤ 6.5V, I Logic Input Current 0V ≤ VIN ≤ V High Level Input Voltage ADR ● VCC – 0.3 V

SMBSUS SCL, SDA

Low Level Input Voltage SMBSUS, ADR ● 0.8 V

SCL, SDA ● 0.6 V

Low Level Output Voltage I

OUT

I

OUT

SMB Operating Frequency ● 10 100 kHz Bus Free Time Between Stop and Start Condition ● 4.7 µs Hold Time After (Repeated) Start Condition ● 4.0 µs Repeated Start Condition Setup Time ● 4.7 µs Stop Condition Setup Time ● 4.0 µs Data Hold Time ● 300 ns Data Setup Time ● 250 ns Clock Low Period ● 4.7 µs Clock High Period ● 4.0 50 µs Clock/Data Fall Time ● 300 ns Clock/Data Rise Time ● 1000 ns

= 100µA, 0.1 0.16 %/V

) = 0µA at CCFL VC = 1.5V

C

CCFL

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

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

) = 0.465V 98 100 102 µA

OUT

) = 0.465V ● ±200 nA

OUT

CC

= Full Scale, V(I

OUT

) = 0.465V ● 0.2 2 LSB

OUT

= 3mA, SDA Only ● 0.4 V = 1.6mA, SMBSUS = 0V, Measured at SHDN Pin ● 0.4 V

= CCFL VSW = Open,

CCFL

● 0.9 1.6 2.6 A

● 96 100 104 µA

● ±1 µA

● 2.4 V

● 1.4 V

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

Note 1: T

is calculated from the ambient temperature TA and power

J

dissipation PD according to the following formula:

LT1786FCS: T

= TA + (PD)(100°C/W)

J

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

= 1.4(1.393 – DC) for the

LIM

LT1786F due to internal slope compensation circuitry. Note 4: Timings for all signals are referenced to V

and VIL signals.

IH

Note 5: These parameters are guaranteed by design and are not tested in production. Refer to the Timing Diagrams for additional information.

3

LT1786F

I

CCFL

PROGRAMMING CURRENT (µA)



5 4 3 2 1

0 –1 –2 –3 –4 –5

–6

–7

–8 –9

–10

40 80 120 160

1786 G09

20020060 100 140 180

T = –55°C

T = 25°C

T = 125°C

∆I

CCFL

SUMMING VOLTAGE (mV)

TEMPERATURE (°C)

–75

CCFL FREQUENCY (kHz)

220

240

125

1786 G06

200

180

160

–25

25

75

175

210

230

190

170

100

–50

0

50

150



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

25

TEMPERATURE (°C)

SHDN Input Bias Current vs Temperature

6

5

4

3

75

VCC = 5V

125

1786 G01

175

ISUS Current vs Temperature

100

SMBSUS = 0V

90

8O

70

60

50

ISUS (µA)

40 30 20 10

0

–25–55 –5 50 100 150

VCC = 5V

VCC = 3V

25

TEMPERATURE (°C)

SHDN Threshold Voltage vs Temperature

1.2

1.1

1.0

0.9

SHDN Supply Current vs Temperature

300

SHDN = 0V

270 240 210 180 150 120

90

SHDN SUPPLY CURRENT (µA)

60 30

75

125

1786 G02

0

–25–55 –5 50 100 150

VCC = 5V

VCC = 3V

25

TEMPERATURE (°C)

75

125

1786 G03

Frequency vs Temperature

2

1

SHDN INPUT BIAS CURRENT (µA)

0

Maximum Duty Cycle vs Temperature

95 93 91 89

87

85 83

81 79

CCFL MAXIMUM DUTY CYCLE (%)

77 75

–75

4

VCC = 3V

–25 25 75 125

TEMPERATURE (°C)

–25 0–50

25 50

TEMPERATURE (°C)

75 100

1786 G04

125 150

1786 G07

175–50–75 0 50 100 150

175

0.8

0.7

SHDN THRESHOLD VOLTAGE (V)

0.6 –25 25 75 125

TEMPERATURE (°C)

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)

1786 G05

1786 G08

175–50–75 0 50 100 150

I

Summing Voltage

CCFL

Load Regulation

175–50–75 0 50 100 150

W

TEMPERATURE (°C)

0

POSITIVE DIO VOLTAGE (V)

0.4

0.2

0.8

0.6

1.2

1.0

–25 25 75 125

1786 G12

175–50–75 0 50 100 150

I(DIO) = 1mA

I(DIO) = 5mA

I(DIO) = 10mA

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

1786 G15

175–50–75 0 50 100 150

TEMPERATURE (°C)

–75

BULB PROTECT SERVO VOLTAGE (V)

7.1

7.3

7.5

7.4

7.2

7.0

6.8

6.6

125 150

1786 G18

6.9

6.7

6.5 –25 0–50

25 50

75 100

175

I

CCFL

= 10µA

I

CCFL

= 50µA

I

CCFL

= 100µA

U

TYPICAL PERFORMANCE CHARACTERISTICS

LT1786F

VC Sink Offset Current vs Temperature

10

9 8 7 6 5

4

3 2

1

SINK OFFSET CURRENT (µA)

C

0

–1

CCFL V

–2

–3

–25 0–50

–75 125 150

CCFL VC = 1.5V

CCFL VC = 1.0V

CCFL VC = 0.5V

75 100

25 50

TEMPERATURE (°C)

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

0

–50

–75

I(DIO) = 10mA

I(DIO) = 5mA

I(DIO) = 1mA

–25

25

0

TEMPERATURE (°C)

75

50

100

125

150

1786 G13

175

1786 G10

175

∆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)

VC to DIO Current Servo Ratio vs Temperature

103

102

101

100

99

98

97

DIO CURRENT SERVO RATIO (µA/mA)

C

96

CCFL V

95

–75

I(DIO) = 1mA

–50

I(DIO) = 10mA

–25

25

0 TEMPERATURE (°C)

= 10µA

I(DIO) = 5mA

75

50

100

125

1786 G11

150

1786 G14

Positive DIO Voltage vs Temperature

175–50–75 0 50 100 150

VC Low Clamp Voltage vs Temperature

175

VC High Clamp Voltage vs Temperature

2.4

2.3

2.2

2.1

2.0

HIGH CLAMP VOLTAGE (V)

1.9

C

1.8

CCFL V

1.7 –75

–25

–50

0 TEMPERATURE (°C)

25

75 125

50

100

150

1786 G16

175

VC Switching Threshold vs Temperature

1.3

1.2

1.1

1.0

0.9

0.8

SWITCHING THRESHOLD VOLTAGE (V)

C

0.7

CCFL V

0.6 –75

–50

0

25

–25

TEMPERATURE (°C)

75 125

50

100

150

BULB Protect Servo Voltage vs Temperature

175

1786 G17

5

LT1786F

TEMPERATURE (°C)

0.940

CCFL HIGH-SIDE SENSE NULL CURRENT (A)

0.980

0.960

1.020

1.000

1.060

1.040

–25 25 75 125

1786 G21

175–50

–75

0 50 100 150

DUTY CYCLE (%)

0

CCFL V

SW

CURRENT LIMIT (A)

0.5

1.5

2.0

2.5

20

40

50 90

1786 G24

1.0

10 30

60

70

80

T = 25°C

T = 125°C

MINIMUM

T = 0°C

TEMPERATURE (°C)

–50–75

FULL-SCALE OUTPUT CURRENT (µA)

0–25 5025

75

100 125 150 175

1786 G26

104

103

102

101

100

99

98

97

96

V(I

OUT

) = 0.465V

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

BULB Input Bias Current vs Temperature

10

8

6

4

2

BULB INPUT BIAS CURRENT (µA)

0

–50

–25 0

–75 125 150

TEMPERATURE (°C)

25 50

75 100

High-Side Sense Null Current Line Regulation vs Temperature

0.160

0.140

0.120

0.100

0.080

0.060

0.040

0.020

CCFL HIGH-SIDE SENSE LINE REGULATI0N (%V)

0.000 –75

–50

–25

75

50

25

0 TEMPERATURE (°C)

100

125

1787 G19

150

1786 G22

175

High-Side Sense Supply Current vs Temperature

150 140 130 120

110

100

90 80 70 60

CCFL HIGH-SIDE SENSE SUPPLY CURRENT (µA)

50

–50

–75

0

–25

25 50

TEMPERATURE (°C)

75 100

VSW Sat Voltage vs Switch Current

1.0

0.9

0.8

0.7

0.6

0.5

SAT VOLTAGE (V)

0.4

SW

0.3

CCFL V

0.2

0.1 0

0.3

0

T = 25°C

0.9

0.6

SWITCH CURRENT (A)

125 150

T = –5°CT = 125°C

1.2

1786 G20

1787 G23

175

1.5

High-Side Sense Null Current vs Temperature

V

Current Limit vs Duty Cycle

SW

6

Forced Beta vs ISW on V

110 100

90 80 70 60 50

FORCED BETA

40 30 20 10

0

0.4

0.6

0.2 1.8

0

1.2

0.8

1.0

CCFL ISW (A)

1.4

SW

1.6

Full-Scale Output Current vs Temperature

2.0

1786 G25

Linear Technology LT1786F Datasheet

Specifications and Main Features

Frequently Asked Questions

User Manual