LT1942
Quad DC/DC Converter
for Triple Output TFT Supply
Plus LED Driver
FEATURES
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■
■
■
■
■
■
■
■
■
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■
DESCRIPTIO
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)
The LT
®
1942 is a highly integrated quad switching regu-
lator 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.
APPLICATIO S
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■
Poly-Silicon TFT Displays
Amorphous Silicon TFT Displays
TFT Bias and White LED Backlight Power Supply
V
IN
3V TO 4.2V
0.22µF
698k
V
ON
10V
2mA
10k
0.22µF
V
OFF
–10V
2mA
665k
47µH
47µH
0.1µF
0.22µF
100k
PGND23
V
OUT3
NFB2
D2
SW2
SHDN SGND/
CTRL4 AGND
SS1
SS4
0.1µF
0.1µF
LT1942
D3
FB3
SW3
22µH
22µH
V
CC
SW1
FB1
PGND14
PGOOD
SW4
D4
LED1
LED2
FB4
CT
0.1µF
4.99Ω
1942 TA01
CMDSH-3
301k
4.7pF
4.7µF
100k
33µH
V
IN
V
IN
SHUTDOWN
LED CONTROL
U
Si2301BDS
1M
AV
DD
5V
40mA
4.7µF
20mA
20mA
1942fa
U
1
LT1942
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
CC
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
OUT3
Voltage ......................................................... 36V
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
PGND14
SW2
SW1
SW4
V
CC
ORDER PART
NUMBER
LT1942EUF
18 LED1
17 LED2
24 23 22 21 20 19
PGND23 1
SW3 2
D3 3
V
OUT3
4
FB3 5
NFB2 6
7
8
9 10 11 12
25
D2
16 D4
15 FB4
14 FB1
13 PGOOD
UF PART
MARKING
1942
AGND
SS1
SHDN
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W,
θ
JC
= 4.3°C/W
EXPOSED PAD (PIN 25) IS SGND
(MUST BE SOLDERED TO PCB)
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.
ELECTRICAL CHARACTERISTICS
PARAMETER
Quiescent Current
Input Voltage Range
AV
DD
Feedback Voltage
AV
DD
Feedback Pin Bias Current (FB1)
AV
DD
Feedback Voltage for Power Good Signal
V
OFF
Feedback Voltage
V
OFF
Feedback Pin Bias Current (NFB2)
V
ON
Feedback Voltage
V
ON
Feedback Pin Bias Current (FB3)
LED Feedback Voltage
LED Feedback Pin Bias Current (FB4)
LED Feedback Voltage with Dimming
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
SHDN
= V
IN
, unless otherwise noted. (Note 2)
CONDITIONS
V
SHDN
= 3.3V, V
CTRL4
= 0V, Not Switching
V
SHDN
= V
CTRL4
= 0V, In Shutdown
V
CC
Pin
FB1 Pin
FB1 Pin (Note 3)
FB1 Pin Voltage as a Percent of Nominal Voltage
NFB2 Pin
NFB2 Pin (Note 3)
FB3 Pin
FB3 Pin (Note 3)
FB4 Pin, V
CTRL4
= 3.3V
FB4 Pin (Note 3)
FB4 Pin, V
CTRL4
= 1V
85
●
●
●
●
●
●
CTRL4
SS4
CT
MIN
TYP
7
0
MAX
10
1
16
1.275
60
100
–140
60
1.275
60
210
60
105
UNITS
mA
µA
V
V
nA
%
mV
nA
V
nA
mV
µA
mV
2.6
1.225
95
–160
1.225
190
1.25
15
97
–150
25
1.25
25
200
20
95
2
U
1942fa
W
U
U
W W
W
LT1942
ELECTRICAL CHARACTERISTICS
PARAMETER
LED1-LED2 Current Matching
LED1 Voltage
LED2 Voltage
LED1, LED2 Maximum Current
LED1, LED2 Leakage Current
AV
DD
Maximum Duty Cycle
V
OFF
Maximum Duty Cycle
V
ON
Maximum Duty Cycle
LED Maximum Duty Cycle
AV
DD
Switch Current Limit at Minimum DC (SW1)
AV
DD
Switch Current Limit at Maximum DC (SW1)
V
OFF
Switch Current Limit at Minimum DC (SW2)
V
OFF
Switch Current Limit at Maximum DC (SW2)
V
ON
Switch Current Limit at Minimum DC (SW3)
V
ON
Switch Current Limit at Maximum DC (SW3)
LED Switch Current Limit at Minimum DC (SW4)
LED Switch Current Limit at Maximum DC (SW4)
V
OFF
Schottky Diode Forward Drop
V
OFF
Schottky Diode Leakage Current
V
ON
Schottky Diode Forward Drop
V
ON
Schottky Diode Leakage Current
LED Schottky Diode Forward Drop
LED Schottky Diode Leakage Current
Switching Frequency
SHDN Pin Current
CTRL4 Pin Current
SW1-SW4 leakage Current
SW1 V
CESAT
SW2 V
CESAT
SW3 V
CESAT
SW4 V
CESAT
SS1 Charging Current
SS4 Charging Current
SHDN Input Voltage High
SHDN Input Voltage Low
CTRL4 Input Voltage High
CTRL4 Input Voltage Low
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
SHDN
= V
IN
, unless otherwise noted. (Note 2)
CONDITIONS
Current Into Each Pin = 20mA, V
LED1
= V
LED2
Current Into Each Pin = 20mA, |V
LED1
-V
LED2
| = 1V
20mA Into Pin, V
LED2
= 2V, FB4 = 0
20mA Into Pin, V
LED1
= 2V, FB4 = 0
Into Either Pin, V
LEDX
< 1.5V, FB4 = 0
V
SHDN
= 0V, V
LEDX
= 45V
SW1 Pin
SW2 Pin
SW3 Pin
SW4 Pin
SW1 Pin (Note 4)
SW1 Pin (Note 4)
SW2 Pin (Note 4)
SW2 Pin (Note 4)
SW3 Pin (Note 4)
SW3 Pin (Note 4)
SW4 Pin (Note 4)
SW4 Pin (Note 4)
D2 Pin, I = 60mA
D2 Pin, V
D2
= –36V
D3 Pin, I = 60mA
V
D3
= 36V, SW3 = 0V, Output Disconnect PNP Off
I = 250mA
V
D4
= 36V, SW4 = 0V
V
SHDN
= 3V
V
SHDN
= 0V
V
CTRL4
= 3V
V
CTRL4
= 0V
V
SWX
= 36V
I
SW1
= 100mA (Note 5)
I
SW2
= 40mA (Note 5)
I
SW3
= 40mA (Note 5)
I
SW4
= 400mA (Note 5)
V
SS
= 0.5V
V
SS
= 0.5V
1
1
1
0.4
0.25
0.1
●
●
●
●
MIN
TYP
0
1
1
1
MAX
1.5
2.5
1.2
1.2
1
UNITS
%
%
V
V
mA
µA
%
%
%
%
35
88
75
75
88
150
80
50
30
50
30
550
450
93
86
86
93
200
140
80
60
80
60
750
600
0.65
1
0.65
1
0.75
1
0.8
●
●
●
250
200
110
90
110
90
900
850
mA
mA
mA
mA
mA
mA
mA
mA
V
µA
V
µA
V
µA
MHz
µA
nA
µA
nA
µA
mV
mV
mV
mV
µA
µA
V
V
V
V
1
70
20
30
–60
0.01
200
150
150
280
3
3
1.2
100
30
60
–150
1
300
250
250
400
5
5
1942fa
3
LT1942
ELECTRICAL CHARACTERISTICS
PARAMETER
PGOOD Leakage Current
PGOOD Sink Current
CT Charging Current
CT Reference Voltage
V
OUT3
Leakage Current
V
OUT3
Source Current
Minimum D3/V
OUT3
Operating Voltage
D4 LED Open-Circuit Voltage
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
SHDN
= V
IN
, unless otherwise noted. (Note 2)
CONDITIONS
PGOOD NPN Off, V
PGOOD
= 5V
PGOOD NPN On, V
PGOOD
= 1V
0.5
MIN
TYP
0
0.7
12
0.8
Output Disconnect PNP Off, D3 = 36V, V
OUT
= 0V
Output Disconnect PNP On, D3 = 3V, V
OUT
= 2.5V
Minimum D3 Voltage for Proper Output
Disconnect PNP Operation
38
10
0
15
3
42
44
1
MAX
0.1
UNITS
µA
mA
µA
V
µA
mA
V
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
temperature range are assured by design, characterization and correlation
with statistical controls.
Note 3:
Current flows out of the pin.
Note 4:
Current limit guaranteed by design and/or correlation to static test.
Note 5:
V
CESAT
100% tested at wafer level.
TYPICAL PERFOR A CE CHARACTERISTICS
V
FB1
Voltage
1.28
1.27
VOLTAGE (mV)
VOLTAGE (V)
–149
–150
–151
–152
–153
–154
1.25
1.24
1.23
1.22
–40 –20
VOLTAGE (V)
1.26
40
20
60
0
TEMPERATURE (°C)
4
U W
80
1942 G01
NFB2 Voltage
–145
–146
–147
–148
1.27
1.26
1.25
1.24
1.23
1.28
V
FB3
Voltage
100
–155
–40
–20
40
20
0
60
TEMPERATURE (°C)
80
100
1.22
–40 –20
40
20
60
0
TEMPERATURE (°C)
80
100
1942 G02
1942 G01
1942fa
LT1942
TYPICAL PERFOR A CE CHARACTERISTICS
FB4 Voltage
210
208
206
204
200
V
FB4
(mV)
T
A
= –40°C
150
T
A
= 85°C
100
50
0
–20
40
20
0
60
TEMPERATURE (°C)
80
100
OSCILLATOR FREQUENCY (kHz)
V
FB4
(mV)
202
200
198
196
194
192
190
–40
Quiescent Current
10.0
9.5
QUIESCENT CURRENT (mA)
SW1 SATURATION VOLTAGE (mV)
9.0
DELAY TIME (ms)
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
–40
–20
40
20
0
60
TEMPERATURE (°C)
80
100
SW2 Saturation Voltage
400
SW2 SATURATION VOLTAGE (mV)
T
A
= 25°C
SW3 SATURATION VOLTAGE (mV)
300
250
200
150
100
50
0
0
10
40
30
SW2 CURRENT (mA)
20
50
60
1942 G10
300
250
200
150
100
50
0
0
10
40
30
SW3 CURRENT (mA)
20
50
60
1942 G10
SW4 SATURATION VOLTAGE (mV)
350
U W
1942 G04
V
FB4
vs CTRL4
300
250
1200
1100
1000
900
800
700
Oscillator Frequency
T
A
= 25°C
0
0.5
1
1.5
2
CTRL4 (V)
2.5
3
1942 G05
600
–40 –20
40
20
60
0
TEMPERATURE (°C)
80
100
1942 G06
CT Timer Delay Time
10
9
8
7
6
5
4
3
2
1
0
–40
–20
40
20
0
60
TEMPERATURE (°C)
80
100
C
T
= 0.1µF
600
500
400
300
200
100
0
SW1 Saturation Voltage
T
A
= 25°C
0
25
50 75 100 125 150 175 200
SW1 CURRENT (mA)
1942 G09
1942 G07
1942 G08
SW3 Saturation Voltage
400
350
T
A
= 25°C
800
700
600
500
400
300
200
100
0
SW4 Saturation Voltage
T
A
= 25°C
0
100 200 300 400 500 600 700 800
SW4 CURRENT (mA)
1942 G12
1942fa
5
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