FEATURES
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LTC3524
Adjustable TFT Bias Supply
with WLED Driver
DESCRIPTION
The LTC
®
3524 is an integrated BIAS and white LED power
converter solution for small/medium-sized polysilicon thin
film transistor (TFT) liquid crystal (LCD) display panels.
The device operates from a single Lithium-Ion/polymer
battery or any voltage source between 2.5V and 6V.
A 1.5MHz synchronous boost converter generates a pro-
grammable low noise, high efficiency 25mA TFT supply
of up to 6.0V. Regulated, low ripple charge pumps are
used to generate up to +20V and –20V at 2mA. Output
sequencing is internally controlled to insure proper
initialization and rapid discharge of the LCD panel in
shutdown.
A second 1.5MHz boost converter powers one or two LED
strings with up to five series elements each. LED current
and display brightness can be controlled over a wide range
using analog or digital means up to 25mA.
The LTC3524 is offered in the 4mm
×
4mm 24-pin QFN
package, minimizing the total solution footprint.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Generates Three Adjustable, Low Noise Rails for
Small/Medium TFT Displays
Drives Up to Ten White LEDs
LED Dimming and Open-Circuit Protection
Controlled Power-Up/Power-Down Sequencing
1.5MHz Fixed Frequency, Low Noise Operation
V
IN
Range 2.5V to 6V, V
OUT
Range 3V to 6V
TFT Supply Efficiency Up to 90%
LED Supply Efficiency Up to 78%
Two Independantly Enabled LED Strings
200 to 1 True Color PWM
TM
Dimming
Tiny External Solution
24-Lead QFN Package (4mm
×
4mm
×
0.75mm)
APPLICATIONS
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PDAs, Palmtop Computers
Digital Still and Video Cameras
Handheld GPS
Portable Instrument Displays
Portable Media Players
TYPICAL APPLICATION
+5V, –7.5V, +12.5V, 8 LED Power Supply
+
–
+5V
25mA
10μF
+10V
0.47μF
0.1μF
+12.5V
2mA
0.47μF
220k
2M
FBH
CH
+
CH
–
GND CN
+
0.1μF
VN
324k
1M
FBVO
VNIN
V2x
C2
+
C2
–
VH
LED1
LTC3524
PROG
ELED2
ELED1
ELCD
FBN
1M
–7.5V
2mA
0.47μF
100k for 20mA
470k
V
IN
V
OUT
60
5
100
Li-Ion
2.2μF
SW1
10μH
V
IN
3.3μH
SW2
VLED
LED2
10μF
90
EFFICIENCY (%)
LCD Bias and LED Efficiency
V
IN
= 3.6V, V
OUT
= 5V, 8 LEDs
V
IN
= 3.6V
LCD
80
LED
V
OUT
70
15
20
10
V
OUT
OR LED STRING CURRENT (mA)
25
3524 TA01b
0.1μF
3524 TA01a
3524f
1
LTC3524
ABSOLUTE MAXIMUM RATINGS
(Referred to GND)
PIN CONFIGURATION
TOP VIEW
ELED1
ELED2
PROG
VLED
LED1
18 LED2
17 CH
–
16 CH
+
25
15 VH
14 FBH
13 FBN
7
C2
+
8
V2x
9 10 11 12
VN
IN
CN
+
NC
VN
V
IN
, SW1, V
OUT
, C2
–
....................................... –0.3 to 7V
ELCD, ELED1, ELED2, PROG ......................... –0.3 to 7V
FBN, FBH, FBVO ............................................. –0.3 to 7V
V2x, C2
+
, CH
–
.............................................. –0.3 to 13V
LED1, LED2, VLED, SW2 ............................. –0.3 to 22V
VN
IN
, VH, CH
+
, CN
+
...................................... –0.3 to 21V
VN .............................................................. –21 to +0.3V
Operating Temperature Range (Note 2) ...–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
24 23 22 21 20 19
ELCD 1
V
IN
2
FBVO 3
V
OUT
4
SW1 5
C2
–
6
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) MUST BE SOLDERED TO PCB
AND CONNECTED TO GND
ORDER INFORMATION
LEAD FREE FINISH
LTC3524EUF#PBF
LEAD BASED FINISH
LTC3524EUF
TAPE AND REEL
LTC3524EUF#TRPBF
TAPE AND REEL
LTC3524EUF#TR
PART MARKING
3524
PART MARKING
3524
PACKAGE DESCRIPTION
24-Lead (4mm
×
4mm) Plastic QFN
PACKAGE DESCRIPTION
24-Lead (4mm
×
4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Voltage Range
V
IN
Quiescent Supply Current LCD
V
IN
Quiescent Supply Current LED
V
OUT
Quiescent Supply Current LCD
V
IN
Quiescent Current Shutdown
Switching Frequency
Maximum Duty Cycle
V
OUT
Boost Regulator
FBVO Regulation Voltage
V
OUT
Adjust Range
See Note 3
CONDITIONS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 3.6V, V
OUT
= 5.1V, T
A
= 25°C, unless otherwise noted.
MIN
●
SW2
TYP
200
4
250
.02
MAX
6.0
UNITS
V
μA
mA
μA
2.5
ELCD = 1.5V, ELED1,2 = GND
ELCD = GND, ELED1,2 = 1.5V (LED1 and LED2 Open)
ELCD = 1.5V, ELED1,2 = GND
ELCD = ELED1,2 = GND
LED and LCD Boosts
LED and LCD Boosts
●
2
2
μA
MHz
%
1
85
1.20
3.0
1.5
94
1.225
1.25
6.0
V
V
3524f
2
LTC3524
ELECTRICAL CHARACTERISTICS
PARAMETER
Switch Current Limit
Charge Pumps
V2x Output Voltage
Output Impedance V2x
V2x Maximum Operating Voltage
VH Output Voltage (Quadrupler)
Output Impedance (2X + Quadrupler)
FBH Regulation Voltage
VH Maximum Operating Voltage
VN Output Voltage
FBN Regulation Voltage
Output Impedance VN (2X + VN)
VN Minimum Operating Voltage
Switching Frequency Charge Pumps
V2x to VN Delay
VN to VH Delay
LED Boost
LED1,2 Current Accuracy
SW2 Maximum Current Limit
SW2 V
CESAT
Logic Inputs
ELED1, ELED2 , ELCD Thresholds
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3524E is guaranteed to meet specifications from 0°C to
85°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization, and statistical process controls.
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 3.6V, V
OUT
= 5.1V, T
A
= 25°C, unless otherwise noted.
CONDITIONS
MIN
100
Load on V2x = 250μA
Flying Capacitors = 0.1μF
(Note 3)
Load = 250μA (FBH = 1V)
Flying Capacitors = 0.1μF
●
TYP
150
10
250
12
20
1200
MAX
UNITS
mA
V
Ω
V
V
Ω
1.15
1.225
20
–9.7
1.30
V
V
(Note 3)
Load on VN = 250μA, VN
IN
= 10.2V, External Schottkys
●
0.94
1
650
–20
94
2
2
1.06
V
Ω
V
KHz
ms
ms
Flying Capacitor = 0.1μF
(Note 3)
(Note 4)
(Note 4)
R
PROG
= 100k
I
SW
= 350mA
0.4
18
500
20
700
350
0.8
22
mA
mA
mV
1.2
V
Note 3:
Specification is guaranteed by design and not 100% tested in
production.
Note 4:
Measured from point at which VN crosses –V
OUT
to point at which
CH
+
starts switching.
3524f
3
LTC3524
TYPICAL PERFORMANCE CHARACTERISTICS
LCD Boost Efficiency
vs Load Current
100
L = 10μH
V
OUT
= 5V
85
L = 4.7μH
80
80
EFFICIENCY (%)
EFFICIENCY (%)
75
70
65
60
55
3
4
3.5
V
IN
(V)
4.5
5
3524 G02
T
A
= 25°C, unless otherwise noted.
4 LEDs per String Efficiency
vs V
IN
and LED Current
85
L = 4.7μH
LED Efficiency vs V
IN
90
EFFICIENCY (%)
80
75
70
V
IN
= 5
V
IN
= 4.2
V
IN
= 3.6
V
IN
= 3.1
V
IN
= 2.5
0
10
40
30
20
50
V
OUT
CURRENT (mA)
60
70
60
70
PER STRING:
5 LEDs
4 LEDs
3 LEDs
2 LEDs
V
IN
= 5
V
IN
= 4.2
V
IN
= 3.6
V
IN
= 3.1
V
IN
= 2.5
5
10
15
20
LED CURRENT (mA)
25
3524 G03
50
65
2.5
3524 G01
LED1 String Current vs V
IN
and Number of LEDs
22.0
21.5
21.0
CURRENT (mA)
20.5
20.0
19.5
19.0
18.5
18.0
2.5
3
3.5
V
IN
(V)
3524 G04
LED2 String Current
vs V
IN
and Number of LEDs
22.0
21.5
21.0
V2X VOLTAGE (V)
CURRENT (mA)
20.5
20.0
19.5
19.0
18.5
5
18.0
2.5
3
3.5
V
IN
(V)
3524 G05
V2X Output Voltage
vs V2X Load Current
10.0
9.5
PER STRING:
5 LEDs
4 LEDs
3 LEDs
2 LEDs
4
4.5
PER STRING:
5 LEDs
4 LEDs
3 LEDs
2 LEDs
4
4.5
5
9.0
8.5
0
1
4
3
V2X LOAD CURRENT (mA)
2
5
3524 G06
VH Voltage vs VH and
VN Load Current (FBH = 0V)
20
VN = 0mA
19
VH VOLTAGE (V)
VN = 1mA
–VN VOLTAGE (V)
9.0
8.5
8.0
VN = 2mA
10.0
9.5
VN Voltage vs VN and
VH Load Current (FBN = 1.3V)
8.0
7.5
VH = 1mA
VOLTAGE (V)
7.0
6.5
6.0
5.5
5.0
7.5
4.5
V
OUT
, |VN|, and VH/2
Regulation Overtemperature
|VN|
VH = 0mA
VH/2
18
VH = 2mA
17
V
OUT
16
0
0.5
1.5
1
VH LOAD CURRENT (mA)
2
3524 G07
7.0
0
0.5
1
1.5
VN LOAD CURRENT (mA)
2
3524 G09
4.0
–40
–15
35
TEMPERATURE (°C)
10
60
85
3524 G10
3524f
4
LTC3524
TYPICAL PERFORMANCE CHARACTERISTICS
LCD Bias Sequencing
VH
T
A
= 25°C, unless otherwise noted.
SW1 Voltage and 10μH Inductor
Current at 25mA Load
LCD Bias Sequencing
VH
V
OUT
SW1
2V/DIV
5V/DIV
V2X
VN
V
OUT
5V/DIV
VN
I
LCD
BOOST INDUCTOR CURRENT
200mA/DIV
I
LCD
BOOST
INDUCTOR
CURRENT
50mA/DIV
200ns/DIV
3524 G13
5ms/DIV
3524 G11
5ms/DIV
3524 G12
SW1 Voltage and 10μH Inductor
Current at 5mA Load
SW2
200mV/DIV
SW1
2V/DIV
I
LCD
BOOST
INDUCTOR
CURRENT
200mA/DIV
SW2
5V/DIV
SW2 Voltage and 4.7μH Inductor
Current at 20mA
LED Initial Start-Up Waveforms
I
LED
BOOST
INDUCTOR
CURRENT
V
LED
5V/DIV
LED1
LED2
500mV/DIV
I
LCD
BOOST
INDUCTOR
CURRENT
50mA/DIV
200ns/DIV
3524 G14
200ns/DIV
3524 G15
50μs/DIV
3524 G16
LED Burst Dimming Waveforms
LED1 and SW2
E
LED1
AND
E
LED2
I
LED
BOOST
INDUCTOR
LED1
SW2
12V
10V/DIV
10V/DIV
5V/DIV
200mA/DIV
E
LED1
AND
E
LED2
I
LED
BOOST
INDUCTOR
V
LED
LED2
LED Burst Dimming Waveforms
LED2 and VLED
5V/DIV
200mA/DIV
12.5V
12V
10V/DIV
10V/DIV
500μs/DIV
3524 G17
500μs/DIV
3524 G18
3524f
5
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