LINEAR TECHNOLOGY LT1942 Technical data

FEATURES

■

Triple Output TFT Supply with Built-In
Power Sequencing

■

Integrated White LED Backlight Driver

■

Integrated Schottky Diodes

■

Active Ballast Circuitry Ensures Precise Current
Matching in White LEDs

■

Low Noise 1MHz Fixed Frequency Operation

■

2.6V to 16V Input Voltage Range

■

Soft-Start Limits Inrush Current

■

TFT Supply Output Voltages Independently Set
(Not Charge Pump Derived)

■

Power Good and Output Disconnect for TFT Supply

■

Built-In LED Dimming Capability

■

Open LED Protection for LED Driver

■

24-Lead QFN Package (4mm × 4mm)

U

APPLICATIO S

■

Poly-Silicon TFT Displays

■

Amorphous Silicon TFT Displays

LT1942

Quad DC/DC Converter

for Triple Output TFT Supply

Plus LED Driver

U

DESCRIPTIO

The LT®1942 is a highly integrated quad switching regu­lator designed to provide all necessary power supply
functions for TFT displays, including the white LED
backlight driver. The TFT supply incorporates two boost
and one inverting DC/DC converters. The TFT supply
output voltages are independently set, unlike charge
pump solutions which have many limitations. Power
sequencing for the TFT supply is built into the part and is
user programmable.

The LED driver is a boost DC/DC converter that can be
independently controlled. The LED driver has built-in
dimming control for precise control of LED current. An 8:1
dimming range is achieved by adjusting the CTRL4
voltage.The user can elect to drive a single string or two
strings of LEDs. An LED ballast circuit is included to
precisely match the LED currents if two strings of LEDs are
used. Soft-start is built into the LED driver as well as the
primary TFT supply.

The LT1942 is available in a low profile (0.75mm) 24-lead
QFN (4mm × 4mm) package.

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

All other trademarks are the property of their respective owners.

V

3V TO 4.2V

V
10V

2mA

V

OFF

–10V

2mA

IN

ON

SHUTDOWN

LED CONTROL

10k

0.22µF

665k

TFT Bias and White LED Backlight Power Supply

CMDSH-3

22µH

0.22µF

698k

100k

0.1µF

D3 SW3

FB3

PGND23

V

OUT3

NFB2

D2

SW2

SHDN

CTRL4

0.22µF

47µH

47µH

V

IN

22µH

SGND/

AGND

V

CC

PGND14

LT1942

SS1 SS4 CT

0.1µF

SW1

FB1

PGOOD

SW4

LED1

LED2

FB4

4.99Ω

V

4.7pF

4.7µF

IN

301k

100k

33µH

D4

0.1µF0.1µF

Si2301BDS

1M

4.7µF

AV

DD

5V
40mA

20mA 20mA

1942 TA01

1942fa

1

LT1942

PACKAGE/ORDER I FOR ATIO

UU

W

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

VCC Voltage............................................................. 16V

SW1, SW2, SW3 Voltage .......................... –0.4V to 36V

SW4.......................................................... –0.4V to 45V

FB1, FB3 Voltage ................................................... 2.5V

FB4 Voltage ....................................................... 400mV

NFB2 Voltage ................................................... –200mV

SHDN Voltage ......................................................... 10V

CTRL4 Voltage ........................................................ 16V

SS1, SS4 Voltage .................................................. 1.5V

Current Into D2 ......................................................... 1A

D2 Voltage ............................................................ –36V

Current Out of D3 ..................................................... 1A

D3 Voltage .............................................................. 36V

Current Out of D4 ..................................................... 4A

D4 Voltage .............................................................. 45V

LED1, LED2 Voltage ............................................... 45V

Current Into LED1, LED2 ..................................... 35mA

PGOOD Voltage ...................................................... 16V

V

Voltage ......................................................... 36V

OUT3

CT Current ........................................................... ±1mA

Maximum Junction Temperature ......................... 125°C

Operating Temperature Range (Note 2) .. – 40°C to 85°C

Storage Temperature Range ................ –65°C to 125°C

TOP VIEW

ORDER PART

NUMBER

SW2D2VCCPGND14

24 23 22 21 20 19

PGND23

1

SW3

2

D3

3

V

4

OUT3

FB3

5

NFB2

6

7 8 9

SHDN

CTRL4

24-LEAD (4mm × 4mm) PLASTIC QFN

T

JMAX

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts specified with wider operating temperature ranges.

UF PACKAGE

= 125°C, θJA = 37°C/W, θJC = 4.3°C/W
EXPOSED PAD (PIN 25) IS SGND

(MUST BE SOLDERED TO PCB)

25

10 11 12

CT

AGND

SW1

SS1

SW4

SS4

LT1942EUF

18

LED1

LED2

17

D4

16

FB4

15

FB1

14

13

PGOOD

UF PART

MARKING

1942

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Quiescent Current V

Input Voltage Range VCC Pin

AVDD Feedback Voltage FB1 Pin

AVDD Feedback Pin Bias Current (FB1) FB1 Pin (Note 3) 15 60 nA

AVDD Feedback Voltage for Power Good Signal FB1 Pin Voltage as a Percent of Nominal Voltage

V

Feedback Voltage NFB2 Pin –160 –150 –140 mV

OFF

V

Feedback Pin Bias Current (NFB2) NFB2 Pin (Note 3) 25 60 nA

OFF

VON Feedback Voltage FB3 Pin 1.225 1.25 1.275 V

VON Feedback Pin Bias Current (FB3) FB3 Pin (Note 3) 25 60 nA

LED Feedback Voltage FB4 Pin, V

LED Feedback Pin Bias Current (FB4) FB4 Pin (Note 3) 20 60 µA

LED Feedback Voltage with Dimming FB4 Pin, V

V

SHDN

SHDN

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 3.3V, V

A

= 3.3V, V
= V

CTRL4

CTRL4

CTRL4

= 0V, Not Switching

CTRL4

= 0V, In Shutdown

= 3.3V

= 1V 85 95 105 mV

= VIN, unless otherwise noted. (Note 2)

SHDN

●

●

●

2.6 16 V

●

1.225 1.25 1.275 V

●

95 97 100 %

●

190 200 210 mV

710 mA
01 µA

1942fa

2

LT1942

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 3.3V, V

A

= VIN, unless otherwise noted. (Note 2)

SHDN

PARAMETER CONDITIONS MIN TYP MAX UNITS

LED1-LED2 Current Matching Current Into Each Pin = 20mA, V

Current Into Each Pin = 20mA, |V

LED1 Voltage 20mA Into Pin, V

LED2 Voltage 20mA Into Pin, V

LED1, LED2 Maximum Current Into Either Pin, V

LED1, LED2 Leakage Current V

SHDN

= 0V, V

= 2V, FB4 = 0 1 1.2 V

LED2

= 2V, FB4 = 0 1 1.2 V

LED1

< 1.5V, FB4 = 0 35 mA

LEDX

= 45V

LEDX

= V

LED1

LED1-VLED2

LED2

0 1.5 %

| = 1V 1 2.5 %

●

1 µA

AVDD Maximum Duty Cycle SW1 Pin 88 93 %

V

Maximum Duty Cycle SW2 Pin 75 86 %

OFF

VON Maximum Duty Cycle SW3 Pin 75 86 %

LED Maximum Duty Cycle SW4 Pin 88 93 %

AVDD Switch Current Limit at Minimum DC (SW1) SW1 Pin (Note 4) 150 200 250 mA

AVDD Switch Current Limit at Maximum DC (SW1) SW1 Pin (Note 4) 80 140 200 mA

V

Switch Current Limit at Minimum DC (SW2) SW2 Pin (Note 4) 50 80 110 mA

OFF

V

Switch Current Limit at Maximum DC (SW2) SW2 Pin (Note 4) 30 60 90 mA

OFF

VON Switch Current Limit at Minimum DC (SW3) SW3 Pin (Note 4) 50 80 110 mA

VON Switch Current Limit at Maximum DC (SW3) SW3 Pin (Note 4) 30 60 90 mA

LED Switch Current Limit at Minimum DC (SW4) SW4 Pin (Note 4) 550 750 900 mA

LED Switch Current Limit at Maximum DC (SW4) SW4 Pin (Note 4) 450 600 850 mA

V

Schottky Diode Forward Drop D2 Pin, I = 60mA 0.65 V

OFF

V

Schottky Diode Leakage Current D2 Pin, VD2 = –36V

OFF

●

1 µA

VON Schottky Diode Forward Drop D3 Pin, I = 60mA 0.65 V

VON Schottky Diode Leakage Current VD3 = 36V, SW3 = 0V, Output Disconnect PNP Off

●

1 µA

LED Schottky Diode Forward Drop I = 250mA 0.75 V

LED Schottky Diode Leakage Current VD4 = 36V, SW4 = 0V

●

1 µA

Switching Frequency 0.8 1 1.2 MHz

SHDN Pin Current V

CTRL4 Pin Current V

SW1-SW4 leakage Current V

SW1 V

CESAT

SW2 V

CESAT

SW3 V

CESAT

SW4 V

CESAT

= 3V

SHDN

= 0V 20 30 nA

V

SHDN

= 3V

CTRL4

V

= 0V –60 –150 nA

CTRL4

= 36V

SWX

I

= 100mA (Note 5) 200 300 mV

SW1

I

= 40mA (Note 5) 150 250 mV

SW2

I

= 40mA (Note 5) 150 250 mV

SW3

I

= 400mA (Note 5) 280 400 mV

SW4

●

●

●

70 100 µA

30 60 µA

0.01 1 µA

SS1 Charging Current VSS = 0.5V 1 3 5 µA

SS4 Charging Current VSS = 0.5V 1 3 5 µA

SHDN Input Voltage High 1V

SHDN Input Voltage Low 0.4 V

CTRL4 Input Voltage High 0.25 V

CTRL4 Input Voltage Low 0.1 V

1942fa

3

LT1942

TEMPERATURE (°C)

–40

VOLTAGE (V)

1.26

1.27

1.28

20 60

1942 G01

1.25

1.24

–20 0

40 80 100

1.23

1.22

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 3.3V, V

A

= VIN, unless otherwise noted. (Note 2)

SHDN

PARAMETER CONDITIONS MIN TYP MAX UNITS

PGOOD Leakage Current PGOOD NPN Off, V

PGOOD Sink Current PGOOD NPN On, V

= 5V 0 0.1 µA

PGOOD

= 1V 0.5 0.7 mA

PGOOD

CT Charging Current 12 µA

CT Reference Voltage 0.8 V

V

Leakage Current Output Disconnect PNP Off, D3 = 36V, V

OUT3

V

Source Current Output Disconnect PNP On, D3 = 3V, V

OUT3

Minimum D3/V

Operating Voltage Minimum D3 Voltage for Proper Output 3 V

OUT3

= 0V 0 1 µA

OUT

= 2.5V 10 15 mA

OUT

Disconnect PNP Operation

D4 LED Open-Circuit Voltage 38 42 44 V

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The LT1942 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating

Note 3: Current flows out of the pin.
Note 4: Current limit guaranteed by design and/or correlation to static test.
Note 5: V

100% tested at wafer level.

CESAT

temperature range are assured by design, characterization and correlation
with statistical controls.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

V

FB1

1.28

1.27

1.26

1.25

VOLTAGE (V)

1.24

1.23

1.22
–40

Voltage

–20 0

40 80 100

20 60

TEMPERATURE (°C)

1942 G01

NFB2 Voltage V

–145

–146

–147

–148

–149

–150

–151

VOLTAGE (mV)

–152

–153

–154

–155

–40

–20

0

40

20

TEMPERATURE (°C)

60

80

100

1942 G02

Voltage

FB3

4

1942fa

UW

TEMPERATURE (°C)

–40

OSCILLATOR FREQUENCY (kHz)

1000

1100

1200

20 60

1942 G06

900

800

–20 0

40 80 100

700

600

SW1 CURRENT (mA)

0

0

SW1 SATURATION VOLTAGE (mV)

100

200

300

400

50

100

200150 175

1942 G09

500

600

25

75

125

TA = 25°C

SW4 CURRENT (mA)

0

SW4 SATURATION VOLTAGE (mV)

300

400

500

300

700

1942 G12

200

100

0

100 200 500

600

400

600

700

800

800

TA = 25°C

TYPICAL PERFOR A CE CHARACTERISTICS

LT1942

FB4 Voltage V

210

208

206

204

202

(mV)

200

FB4

V

198

196

194

192

190

–40

–20

0

40

20

TEMPERATURE (°C)

60

80

100

1942 G04

300

250

200

(mV)

150

FB4

V

100

vs CTRL4 Oscillator Frequency

FB4

TA = –40°C

T

A

50

0

0

0.5

1 1.5 2

CTRL4 (V)

TA = 25°C

= 85°C

2.5 3

1942 G05

Quiescent Current CT Timer Delay Time SW1 Saturation Voltage

10.0

9.5

9.0

8.5

8.0

7.5

7.0

6.5

QUIESCENT CURRENT (mA)

6.0

5.5

5.0
–40

–20

0

TEMPERATURE (°C)

40

20

60

80

100

1942 G07

10

CT = 0.1µF

9

8

7

6

5

4

DELAY TIME (ms)

3

2

1

0

–40

–20

40

20

0

TEMPERATURE (°C)

80

100

1942 G08

60

400

TA = 25°C

350

300

250

200

150

100

SW2 SATURATION VOLTAGE (mV)

50

0

10 20 40

0

30

SW2 CURRENT (mA)

SW3 Saturation VoltageSW2 Saturation Voltage SW4 Saturation Voltage

400

TA = 25°C

350

300

250

200

150

100

SW3 SATURATION VOLTAGE (mV)

50

0

10 20 40

50

60

1942 G10

0

30

SW3 CURRENT (mA)

50

60

1942 G10

1942fa

5