LTC3524EUF-TR [Linear]
Adjustable TFT Bias Supply with WLED Driver; 可调TFT偏置电源， WLED驱动器
| 型号： | LTC3524EUF-TR |
| 厂家： | 
Linear |
| 描述： | Adjustable TFT Bias Supply with WLED Driver |
| 文件： | 总16页 (文件大小：259K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3524
Adjustable TFT Bias Supply
with WLED Driver
FEATURES
DESCRIPTION
The LTC®3524 is an integrated BIAS and white LED power
convertersolutionforsmall/medium-sizedpolysiliconthin
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.
■
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
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.
■
V Range 2.5V to 6V, V
IN
Range 3V to 6V
OUT
■
■
■
■
■
■
TFT Supply Efficiency Up to 90%
LED Supply Efficiency Up to 78%
Two Independantly Enabled LED Strings
200 to 1 True Color PWMTM Dimming
Tiny External Solution
24-Lead QFN Package (4mm × 4mm × 0.75mm)
A second 1.5MHz boost converter powers one or two LED
strings with up to five series elements each. LED current
anddisplaybrightnesscanbecontrolledoverawiderange
using analog or digital means up to 25mA.
APPLICATIONS
■
PDAs, Palmtop Computers
■
Digital Still and Video Cameras
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.
■
Handheld GPS
Portable Instrument Displays
■
■
Portable Media Players
TYPICAL APPLICATION
LCD Bias and LED Efficiency
VIN = 3.6V, VOUT = 5V, 8 LEDs
+5V, –7.5V, +12.5V, 8 LED Power Supply
100
90
80
70
60
V
IN
= 3.6V
+
–
10μH
3.3μH
2.2μF
Li-Ion
10μF
SW1
V
SW2
VLED
IN
LCD
LED
+5V
25mA
V
OUT
LED2
10μF
1M
324k
220k
FBVO
VNIN
V2x
LED1
+10V
PROG
100k for 20mA
ELED2
ELED1
ELCD
+
LTC3524
C2
0.47μF
0.1μF
–
V
IN
C2
470k
1M
+12.5V
2mA
VH
FBN
V
OUT
15
20
5
25
10
0.47μF
2M
V
OR LED STRING CURRENT (mA)
–7.5V
2mA
OUT
FBH
VN
3524 TA01b
+
–
+
CH
CH GND CN
0.47μF
0.1μF
0.1μF
3524 TA01a
3524f
1
LTC3524
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Referred to GND)
TOP VIEW
–
V , SW1, V , C2 ....................................... –0.3 to 7V
IN
OUT
ELCD, ELED1, ELED2, PROG ......................... –0.3 to 7V
FBN, FBH, FBVO............................................. –0.3 to 7V
24 23 22 21 20 19
+
–
V2x, C2 , CH .............................................. –0.3 to 13V
LED1, LED2, VLED, SW2 ............................. –0.3 to 22V
ELCD
1
2
3
4
5
6
18 LED2
–
V
CH
CH
17
16
IN
+
+
+
VN , VH, CH , CN ...................................... –0.3 to 21V
FBVO
IN
25
VN.............................................................. –21 to +0.3V
Operating Temperature Range (Note 2) ...–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
V
OUT
15 VH
FBH
SW1
14
13 FBN
–
C2
7
8
9 10 11 12
UF PACKAGE
24-LEAD (4mm × 4mm) PLASTIC QFN
T
= 125°C, θ = 37°C/W
JA
JMAX
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
PACKAGE DESCRIPTION
TEMPERATURE RANGE
–40°C to 85°C
24-Lead (4mm × 4mm) Plastic QFN
PACKAGE DESCRIPTION
PART MARKING
3524
TEMPERATURE RANGE
–40°C to 85°C
24-Lead (4mm × 4mm) Plastic QFN
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 The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VIN = 3.6V, VOUT = 5.1V, TA = 25°C, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
●
Input Voltage Range
2.5
6.0
V
V
V
V
Quiescent Supply Current LCD
Quiescent Supply Current LED
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
200
4
μA
IN
mA
μA
IN
Quiescent Supply Current LCD
250
.02
1.5
94
OUT
Quiescent Current Shutdown
2
2
μA
IN
Switching Frequency
Maximum Duty Cycle
LED and LCD Boosts
1
MHz
%
LED and LCD Boosts
85
V
OUT
Boost Regulator
●
FBVO Regulation Voltage
Adjust Range
1.20
3.0
1.225
1.25
6.0
V
V
See Note 3
V
OUT
3524f
2
LTC3524
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C. VIN = 3.6V, VOUT = 5.1V, TA = 25°C, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Switch Current Limit
100
150
mA
Charge Pumps
V2x Output Voltage
Load on V2x = 250μA
Flying Capacitors = 0.1μF
(Note 3)
10
250
12
V
Ω
V
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
Load = 250μA (FBH = 1V)
Flying Capacitors = 0.1μF
20
V
Ω
V
1200
1.225
20
●
●
1.15
0.94
1.30
1.06
(Note 3)
Load on VN = 250μA, VN = 10.2V, External Schottkys
–9.7
1
V
V
IN
FBN Regulation Voltage
Output Impedance VN (2X + VN)
VN Minimum Operating Voltage
Switching Frequency Charge Pumps
V2x to VN Delay
Ω
Flying Capacitor = 0.1μF
(Note 3)
650
–20
94
V
KHz
ms
ms
(Note 4)
(Note 4)
2
VN to VH Delay
2
LED Boost
LED1,2 Current Accuracy
SW2 Maximum Current Limit
R
= 100k
18
20
22
mA
mA
mV
PROG
500
700
350
SW2 V
I
SW
= 350mA
CESAT
Logic Inputs
●
ELED1, ELED2 , ELCD Thresholds
0.4
0.8
1.2
V
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 3: Specification is guaranteed by design and not 100% tested in
production.
Note 4: Measured from point at which VN crosses –V
CH starts switching.
to point at which
OUT
+
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.
3524f
3
LTC3524
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
LCD Boost Efficiency
vs Load Current
4 LEDs per String Efficiency
vs VIN and LED Current
LED Efficiency vs VIN
100
90
80
70
60
50
85
80
75
70
65
85
80
L = 10μH
OUT
L = 4.7μH
L = 4.7μH
V
= 5V
75
70
65
60
55
PER STRING:
5 LEDs
V
V
V
V
V
= 5
V
V
V
V
V
= 5
IN
IN
IN
IN
IN
IN
IN
IN
IN
IN
= 4.2
= 3.6
= 3.1
= 2.5
= 4.2
= 3.6
= 3.1
= 2.5
4 LEDs
3 LEDs
2 LEDs
0
10
20
V
30
40
50
60
70
5
10
15
20
25
2.5
3
3.5
V
4
4.5
5
CURRENT (mA)
LED CURRENT (mA)
(V)
OUT
IN
3524 G01
3524 G02
3524 G03
LED1 String Current vs VIN
and Number of LEDs
LED2 String Current
vs VIN and Number of LEDs
V2X Output Voltage
vs V2X Load Current
22.0
21.5
21.0
20.5
22.0
21.5
21.0
20.5
10.0
9.5
9.0
8.5
20.0
19.5
20.0
19.5
PER STRING:
PER STRING:
5 LEDs
19.0
18.5
18.0
19.0
18.5
18.0
5 LEDs
4 LEDs
3 LEDs
2 LEDs
4 LEDs
3 LEDs
2 LEDs
3
3.5
4.5
3
3.5
4.5
1
2
4
2.5
5
2.5
5
0
5
4
4
3
V
IN
(V)
V
(V)
IN
V2X LOAD CURRENT (mA)
3524 G04
3524 G05
3524 G06
VOUT, |VN|, and VH/2
Regulation Overtemperature
VH Voltage vs VH and
VN Load Current (FBH = 0V)
VN Voltage vs VN and
VH Load Current (FBN = 1.3V)
20
19
18
17
16
8.0
7.5
7.0
6.5
10.0
9.5
|VN|
VN = 0mA
VN = 1mA
VH = 0mA
VH = 1mA
9.0
8.5
VH/2
VN = 2mA
6.0
5.5
VH = 2mA
8.0
7.5
7.0
V
OUT
5.0
4.5
4.0
0
0.5
1
1.5
2
–15
10
TEMPERATURE (°C)
60
–40
85
35
0
0.5
1
1.5
2
VH LOAD CURRENT (mA)
VN LOAD CURRENT (mA)
3524 G07
3524 G10
3524f
4
LTC3524
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
SW1 Voltage and 10μH Inductor
Current at 25mA Load
LCD Bias Sequencing
LCD Bias Sequencing
VH
VH
SW1
2V/DIV
V
OUT
V2X
5V/DIV
5V/DIV
V
OUT
VN
VN
I
BOOST
LCD
INDUCTOR
CURRENT
50mA/DIV
I
BOOST INDUCTOR CURRENT
LCD
200mA/DIV
3524 G11
3524 G12
3524 G13
5ms/DIV
5ms/DIV
200ns/DIV
SW1 Voltage and 10μH Inductor
Current at 5mA Load
SW2 Voltage and 4.7μH Inductor
Current at 20mA
LED Initial Start-Up Waveforms
I
BOOST
SW2
LED
INDUCTOR
CURRENT
200mV/DIV
500mV/DIV
5V/DIV
SW1
2V/DIV
I
BOOST
INDUCTOR
CURRENT
200mA/DIV
LCD
V
LED
LED1
LED2
I
BOOST
SW2
5V/DIV
LCD
INDUCTOR
CURRENT
50mA/DIV
3524 G14
3524 G16
3524 G15
200ns/DIV
200ns/DIV
50μs/DIV
LED Burst Dimming Waveforms
LED1 and SW2
LED Burst Dimming Waveforms
LED2 and VLED
E
AND
LED2
E
AND
LED2
LED1
5V/DIV
5V/DIV
LED1
E
E
I
BOOST
INDUCTOR
I
BOOST
LED
INDUCTOR
LED
200mA/DIV
200mA/DIV
12.5V
12V
12V
V
LED
LED1
10V/DIV
10V/DIV
10V/DIV
10V/DIV
SW2
LED2
3524 G17
3524 G18
500μs/DIV
500μs/DIV
3524f
5
LTC3524
PIN FUNCTIONS
V (Pin 2): Common Input Supply for LCD Bias and White
IN
and the (–) side of the boost (V , VLED) filter capaci-
OUT
LED Boost Converters. This pin must be locally bypassed
with a minimum of 2.2μF.
tors, and the (–) side of the charge pump outputs (V2x,
VH, VN) filter capacitors. PCB ground must be soldered
to the Exposed Pad for proper operation.
GND/Exposed Pad (Pin 25): Signal and Power Ground for
theLTC3524.Provideashort,directPCBpathbetweenGND
LCD BIAS PIN FUNCTIONS
+
ELCD (Pin 1): Enable Input for the LTC3524’s LCD Cir-
cuits. LCD bias supplies are actively discharged to GND
when ELCD is low through internal pull down devices. An
optional RC network on ELCD provides a slower ramp-up
of the LCD boost converter inductor current during start-
up (soft-start). Shutdown mode is activated by driving
ELCD, ELED1, and ELED2 low. Shutdown disables all IC
functions and reduces quiescent current from the battery
to less than 2μA.
C2 (Pin 7): Charge pump doubler flying capacitor posi-
tive node. The charge pump doubler flying capacitor is
+
–
+
connected between C2 and C2 . The voltage on C2 will
alternate between V
and V2x at an approximate 50%
OUT
dutycyclewhilethechargepumpisoperating. Usea0.1μF
X5R type ceramic capacitor for best results.
V2x (Pin 8): Charge Pump Doubler Output and Input to
the Charge Pump Quadrupler. This output generates 2X
OUT
type ceramic capacitor. C2 and C2 should be left open
and V2x connected to V
to generate VH or VN.
V
. V2x should be bypassed to GND with a 0.47μF X5R
+
–
FBVO (Pin 3): Feedback Pin for the V
Switcher. Refer-
OUT
ence voltage is 1.225V. Connect resistive divider tap here
with minimum trace area.
if the doubler is not needed
OUT
VN (Pin 9): Positive Voltage Input for the Charge Pump
R1
R2
⎛
⎞
IN
VOUT = 1.225 1+
(See Block Diagram)
⎜
⎝
⎟
⎠
Inverter. The charge pump inverter can generate a regu-
lated negative voltage up to the voltage applied to VN .
IN
V
(Pin 4): Main Output of the LCD Boost Regulator
Connect VN to V , V2x, or VH. If VN is connected
OUT
IN
OUT
IN
and Input to the Voltage Doubler (2X) Stage. Bypass
to VH, external diodes and a capacitor are required for
V
with a low ESR, ESL ceramic capacitor (X5R type)
sequencing (see the Applications Information section).
OUT
between 4.7 and 22μF.
CN+ (Pin 10): Charge Pump Inverter Flying Capacitor
SW1 (Pin 5): Synchronous Boost Switch. Connect a
4.7μH-15μH inductor between SW1 and V . Keep PCB
Positive Node. The charge pump inverter flying capacitor
+
is connected between CN and external Schottky diodes
IN
+
trace lengths as short and wide as possible to reduce EMI
and voltage overshoot. If the inductor current falls to zero,
the PMOS synchronous rectifier is turned off to prevent
reverse charging of the inductor and an internal switch
(see Typical Application figures). The voltage on CN will
alternate between GND and VN at an approximate 50%
IN
dutycyclewhiletheinvertingchargepumpisoperating.Use
a 0.1μF X5R type ceramic capacitor for best results.
connects SW1 to V to reduce EMI.
IN
NC (PIN 11): No Connect. This pin should be connected
to GND.
–
C2 (Pin6):Chargepumpdoublerflyingcapacitornegative
node. The charge pump doubler flying capacitor is con-
VN (Pin 12): Negative Charge Pump Converter Output.
+
–
–
nected between C2 and C2 . The voltage on C2 will alter-
VN can be regulated down to approximately –VN volts
IN
nate between GND and V
at an approximate 50% duty
OUT
depending on where VN is connected. VN should be
IN
cycle while the charge pump is operating. Use a 0.1μF
X5R type ceramic capacitor for best results.
bypassed to GND with at 0.47μF or larger X5R type ce-
ramic capacitor.
3524f
6
LTC3524
LCD BIAS PIN FUNCTIONS
FBN (Pin 13): Feedback Pin for the VN Charge-Pump
Output. Reference voltage is 1.0V. Connect the resistive
up to 2mA to a load. VH should be bypassed to GND with
a 0.47μF X5R type ceramic capacitor. Connect V2x to
divider tap between V
trace area.
and VN here with minimum
V
for applications requiring a regulated voltage less
OUT
OUT
than 2X V
.
OUT
+
−R6 V
− 1
(
)
CH (Pin 16): Charge Pump Quadrupler Flying Capacitor
OUT
VN =
+ 1 (See Block Diagram)
Positive Node. The charge pump quadrupler (4X) flying
R5
+
–
capacitor is connected between CH and CH . The voltage
+
FBH (Pin 14): Feedback Pin for the VH Charge-Pump
Output. Reference voltage is 1.225V. Connect resistive
divider tap here with minimum trace area.
onCH willalternatebetweenV2xandVHatanapproximate
50% duty cycle while the charge pump is operating. Use
a 0.1μF X5R type ceramic capacitor for best results.
–
R3
R4
⎛
⎞
CH (Pin 17): Charge Pump Quadrupler (4X) Flying Ca-
VH = 1.225 1+
(See Block Diagram)
–
⎜
⎝
⎟
⎠
pacitor Negative Node. The voltage on CH will alternate
between GND and V2x at an approximate 50% duty cycle
while the charge pump is operating. Use a 0.1μF X5R type
ceramic capacitor for best results.
VH(Pin15):ChargePumpQuadruplerOutput.Thisoutput
can be regulated to 4X V and is capable of delivering
OUT
WHITE LED DRIVER PIN FUNCTIONS
LED2 (Pin 18): Output for Second LED String. Connect
up to five white LEDs between LED2 (anode) and GND
(cathode). For best current matching and efficiency use
the same number of white LEDs in both strings.
frequency (ie., 500Hz). Driving ELCD, ELED1, and ELED2
low initiates shutdown mode which disables all IC func-
tions and reduces quiescent current from the battery to
less than 2μA.
LED1 (Pin 19): Output for First LED String.
PROG (Pin 23): A single resistor (RPROG) between
PROG and GND sets the current in the LED strings. LED
current in mA is programmed by:
VLED (Pin 20): Output of the LED Switcher. Bypass VLED
with a low ESR, ESL ceramic capacitor (X5R type) of at
least 1μF. Keep PCB trace lengths as short and wide as
possible to minimize EMI and voltage overshoot.
6
⎛
⎞
2 × 10
R
ILED1= ILED2 =
mA
⎜
⎟
⎝
⎠
PROG
SW2 (Pin 21): White LED Boost Switch. Connect a 3.3-
A 100K resistor programs 20mA in each string. Analog
dimming can be implemented by connecting a second
resistor between PROG and a control voltage.
15μH inductor between SW2 and V . This is the collector
IN
of the internal NPN power switch. Connect an external
Schottky diode between SW2 and VLED. Keep PCB trace
lengths as short and wide as possible to minimize EMI
and voltage overshoot.
ELED1 (Pin 24): Enable and Pulse Dimming Control Input
for the LED1 String. For applications with five or fewer
LEDs, better efficiency is achieved by operating a single
LED string. For example, ELED1 = 1, ELED2 = 0, LED2 left
open circuit and the LED string connected to LED1.
ELED2 (Pin 22): Enable and PWM Dimming Control Input
for the LED2 String. The LED2 string is disabled when this
pin is grounded. Digital dimming can be implemented
by driving the ELED2 pin between 0V and >1.2V at low
3524f
7
LTC3524
BLOCK DIAGRAM
2.5V TO 6V
4.7μH
10μH
5
2
21
SW1
V
SW2
IN
VBEST
VLED
20
+5V
4
STRING ENABLE
LED CURRENT
SHARING
V
OUT
10μF
HIGH
VOLTAGE
PWM BOOST
CONVERTER
SHDN
R1
1M
SYNCHRONOUS
PWM BOOST
CONVERTER
OVP
LED1
19
LED2
18
R2
324k
FBVO 1.225V
3
PROG
23
RPROG
+
V
C2
IN
OUT
7
6
8
CHARGE
PUMP
DOUBLER
–
ANALOG DIMMING
C2
ELED2
22
ELED1
ENABLE/PULSE DIM LED2 STRING
ENABLE/PULSE DIM LED1 STRING
LCD BIAS ENABLE
V2x
SHUTDOWN WHEN
ELCD= ELED1= ELED2= 0V
+10V
OUT
CHARGE
PUMP
SEQUENCER
24
ELCD
SHDN
1
9
OSCILLATOR
CONTROL
VNIN
V2x
+
CN
IN
IN
+
–
CH
10
NC
11
16
REGULATED
CHARGE
REGULATED
CHARGE
PUMP
CH
VH
PUMP
17
15
QUADRUPLER
INVERTER
+12.5V
VN
12
OUT
–7.5V
OUT
SHDN
R3
2M
SHDN
10μF
R6
1M
R4
220k
R5
470k
FBH 1.225V
FBN
13
14
1V
GND,
EXPOSED PAD
V
OUT
25
3524 BD
3524f
8
LTC3524
OPERATION
The LTC3524 is a highly integrated power converter
intended for small to medium-sized TFT LCD display
modules. The part generates the required bias voltages
for the LCD panel as well as regulated current for one or
two white LED backlight strings. The LCD bias and white
LED boost converters are powered from a common input
voltage between 2.5V and 6V and share a 1.5MHz oscil-
lator, allowing tiny inductors and capacitors to be used.
The LCD bias supply and each white LED string can be
independently enabled and a low current shutdown mode
(<2μA) is activated when all outputs are disabled.
during shutdown to avoid loading the input power source.
Soft-start produces a controlled ramp of the converter
input current during start-up, greatly reducing the burden
on the input power source. Very low operating quiescent
current and synchronous operation allow for greater than
90% conversion efficiency.
V
IN
R
SS
1M
ELCD
The LCD bias includes a synchronous PWM boost con-
verter that can be programmed between 3.0V and 6.0V.
C
SS
6.8nF
This output (V ) is used as the main LCD supply and to
OUT
power three charge pump converters. The charge pump
circuits operate at one-sixteenth the boost frequency
(about94kHz).Thegeneratedoutputvoltagesareinternally
sequenced to insure proper initialization of the LCD panel.
A digital shutdown input (ELCD) rapidly discharges each
generated output voltage to provide a near instantaneous
turn-off of the LCD display.
3524 F01
Figure 1. 1ms Soft-Start with 3.6V VIN
Soft-start operation provides a gradual increase in the
current drawn from the input power source during initial
start-up of the LCD bias boost converter. The rate at which
the input current will increase is set by two external com-
The white LED driver circuitry consists of a PWM boost
converter with an internal low loss NPN power switch and
externalSchottkydiode.TheLEDboostoutput(VLED)can
power as many as ten white LEDs at up to 25mA. LED cur-
rent is programmable and current in each string matched
with an internal loop. PWM dimming can be implemented
through the enable pins (ELED1 and ELED2) to extend the
dimming range of the application.
ponents (R and C ) connected to ELCD (refer to Figure
SS
SS
2). Upon initial application of power the voltage on ELCD
will increase relative to the time constant R × C . After
SS
SS
one time constant, ELCD will rise to approximately 63.2%
of the voltage on V . From 0V to approximately 0.65V on
IN
ELCD, no switching will occur because the threshold is
0.65V (typ). From 0.65V to 1V the maximum switch pin
current capability of the LTC3524 will gradually increase
from near 0A to the maximum current limit.
LCD Bias Boost Converter
A synchronous boost converter is used to generate the
main analog LCD bias supply for the TFT display. The
converter utilizes current mode control and includes
internally set control loop and slope compensation for
optimized performance and a simple design. Only an
LCD Bias Charge Pumps
The LTC3524 uses three internal charge pump circuits to
generate low current, high voltage outputs typically used
tobiastheLCDgatedrive.Thethreechargepumpsinclude
a doubler, quadrupler, and inverting configuration. Each
charge pump requires two small external capacitors, one
totransfercharge, andoneforfiltering. Thechargepumps
feature fixed frequency operation for high efficiency and
lowest noise performance. The charge pump converters
operate at one-sixteenth the boost converter frequency.
inductor, output capacitor and V
programming resis-
OUT
tors at FBVO are required to complete the design of the
25mA boost. The 1.5MHz operating frequency produces
very low output ripple and allows the use of small low
profile inductors and tiny external ceramic capacitors.
The boost converter also disconnects its output from V
IN
3524f
9
LTC3524
OPERATION
The doubler is internally connected to V
a voltage of approximately 2X V
has its input connected to V2x and output to VH. The regu-
lated VH voltage is programmed at FBH and can be set to
produce a voltage up to 4X V . The maximum voltage
VH can source depends on charge pump loading and the
output impedance of the doubler and quadrupler stages
(see Typical Performance Characteristics).
and generates (V2x) to begin operation toward its final goal of 2X V
.
OUT
OUT
at V2x. The quadrupler
Approximately 2ms later, the charge pump inverter (VN)
begins operation toward its programmed value. When the
VN has reached approximately 50% of its final value, a
2ms (nominal) timeout period begins. At the conclusion
of the 2ms timeout period, the charge pump quadrupler
(VH) is allowed to begin operation.
OUT
OUT
During the initial power-up sequence, the charge pumps
The inverting charge pump has its input at VN and
run at half speed. If VN is connected to VH, a diode-OR
IN
IN
output at VN. Regulated VN voltage is set at FBN and can
circuit is needed between V2x, VH, and VN (see the
Typical Applications) to ensure proper sequencing.
IN
be programmed to a minimum negative voltage of VN
IN
minus diode drops. VN can be connected to V , V2x,
IN
OUT
When ELCD is brought low, internal transistors discharge
the outputs in an orderly fashion. As shown in Figure 2,
VN and V2x are initially discharged, followed by VH, fol-
or VH depending on the negative voltage value required
for the application. Efficiency is improved by using the
lowest voltage possible on VN . As with the other charge
IN
lowed by V . V
must be discharged before the part
OUT OUT
pump outputs, the maximum negative voltage that VN can
maintain will depend on loading. Two Schottky diodes are
required to complete the negative charge pump as shown
on the front page and applications circuits.
can enter low current shutdown mode (ELCD, ELED1,
ELED2 must be low, as well).
White LED Boost Driver
LCD BIAS Sequencing
The white LED driver portion of the LTC3524 consists of
a nonsynchronous, fixed frequency, current mode boost
converter that generates the voltage required for one or
two LED strings. The converter has an internal feedback
loop and slope compensation circuitry, reducing external
components and simplifying the design. As with the LCD
bias boost converter, the 1.5MHz operation allows tiny
external components to be used. The boost converter
Referring to the following text and Figure 2, the LTC3524
power-upanddischargesequenceisexplained.Wheninput
power is applied and ELCD is active, the boost converter
initializes and charges its output towards the final pro-
grammed value. When the boost converter output (V
hasreachedapproximately90%ofitsfinalvalue,aninternal
signal is asserted which allows the charge pump doubler
)
OUT
VH
VH
V2x
V2x
V
OUT
V
OUT
ELCD
ELCD
TIME
VN
VN
3524 F02
Figure 2. LCD Power-Up and Power-Down Timing Diagram
3524f
10
LTC3524
OPERATION
output voltage is not set to a fixed voltage, but rather
controlled to produce the programmed current in the
LED strings. The output (VLED) is rated for a maximum
of 21V which will support two strings of up to five series
LED in most cases.
A 0V to 3V V
with R
= 300k and R
= 150k will
SUM
SUM
PROG
produce LED currents between 3mA and 20mA.
V
0V – 3V
SUM
R
SUM
300k
The boost output is used to power one or two white LED
strings with a common ground. If only one string is en-
abled (ELED1 or ELED2) the voltage on that string (LED1
or LED2) will be controlled to regulate the LED current
set at the PROG pin. The voltage on VLED will be slightly
greater due to the overhead needed for the internal sense
element and share circuitry. For example, a single string
application with four white LEDs programmed at 20mA
would require 14.4V on LED1 if the forward drop on each
LED is 3.6V. The voltage on VLED may need to be 15V to
support the drops on the internal share circuitry. For ap-
plications with five or fewer LED elements, a single-string
operation will provide better efficiency.
PROG
R
PROG
150k
3524 F03
Figure 3. Analog Dimming Circuit Using VSUM
True Color PWM Dimming:
PWM dimming can be implemented by enabling and dis-
abling the LED strings with ELED1 and ELED2. A PWM
frequency between 100Hz and 500Hz is generally recom-
mended to get wide dimming range while operating at a
frequency faster than the eye can detect. For best results,
the LCD bias portion of the device should be enabled (to
keep the device out of shutdown) and ELED1 and ELED2
should be driven with a common low frequency PWM
signal.PWMdimmingwaveformsareshownintheTypical
Performance Characteristics section of this datasheet.
If both strings are enabled, the boost output (VLED)
will generate the voltage required to regulate current in
the higher voltage string. Voltage on the lower string is
controlled by the internal share circuit to provide the pro-
grammedcurrent.TheLTC3524achievescurrentmatching
between the strings while minimizing the voltage drop
between VLED and the higher voltage string (to maintain
high efficiency). For example, an application with four
LEDs on LED1 and five LEDs on LED2 is programmed for
The achievable dimming range is dependant on the PWM
dimming frequency (F
) and the settling time of the
SETTLE
PWM
LED strings when enabled (T
). The minimum duty
20mA (R
= 100k). In this instance, assuming a 3.6V
PROG
cycle (or light output) that the strings can be controlled
forward drop, LED1 is 14.4V, LED2 is 18V, and VLED is
18.6V. The drop between VLED and LED1 is 4V at 20mA,
resulting in lower efficiency. For this reason, it is recom-
mended when possible to keep the number of LEDs in
each string matched.
to is given by:
MinDuty = F
• T
SETTLE
PWM
For example, if the settling time is 50μS and the PWM
frequency is 100Hz, the minimum duty cycle is 0.5%
which corresponds to a 200:1 dimming range.
Analog Dimming:
The LTC3524’s white LED driver allows both analog and
PWM dimming to be implemented. Analog dimming
provides a lower noise solution but a reduced dynamic
range. Analog dimming can be implemented by resis-
tively summing a current into the PROG pin. The LED
Open LED:
The LTC3524 has internal over voltage protection in the
event that one of the white LED strings becomes open
circuited. If VLED reaches 24V (nominal) due to an open
circuit on either string, the boost converter will regulate
at 24V while current in the remaining string (if enabled)
is controlled to the programmed value.
string currents with R
, V
, and R
will be:
PROG SUM
SUM
⎛
⎝
⎞
⎠
1.225V 1.225V − VSUM
ILED = 1625 •
+
⎜
⎟
R
RSUM
PROG
3524f
11
LTC3524
APPLICATIONS INFORMATION
Inductor Selection
will have the highest maximum current and lowest DCR).
Shielded inductor series parts are in bold text.
3.3μH to 15μH inductors are recommended for use with
the LTC3524’s two boost converters. The synchronous
LCD bias boost inductor should have a saturation current
The V input capacitor should be an X5R type of at least
IN
2.2μF using a low impedance connection to the battery.
TheVLEDoutputcapacitorshouldbeX5Rtypeandatleast
1μF for analog dimming and 4.7μF for PWM dimming.
(I )ratingofatleast150mA,wherethenonsynchronous
SAT
white LED boost inductor should have a rating of at least
600mA. In most applications, the inductor value for the
LCD bias will be larger (10μH to 15μH) to prevent opera-
tion in deep discontinuous mode. The inductor value for
the white LED can be smaller (3.3μH to 6.8μH), since it
operates at higher currents. Ferrite core materials are
strongly recommended for their superior high frequency
performance characteristics. Inductors meeting these
requirements are listed in Table 1. The maximum current
and DCR ranges in the table correspond to the respec-
tive Inductance range (for example, the 3.3μH inductor
The V
capacitor should also be an X5R type between
OUT
2.2μF and 10μF. A larger capacitor (10μF) should be used
if lower output ripple is desired or the output load required
is close to the 25mA maximum.
+
–
The charge pumps require flying capacitors (C2 to C2 ,
+
+
–
CN ,andCH toCH )thatshouldbeatleast0.1μFtoobtain
specified performance. Ceramic X5R types are strongly
recommended for their low ESR and ESL and capacitance
vs bias voltage stability. The filter capacitors on V2x, VN,
Table 1. Recommended Inductors
MAXIMUM
DIMENSIONS
(mm)
(L × W × H)
L
CURRENT
(mA)
PART
(μH)
DCR (Ω)
MANUFACTURER
ME3220
LP03010
MSS4020
3.3-15
3.3-10
3.3-15
1300-700
950-570
1100-440
0.14-0.52
0.2-0.52
0.09-0.33
3.2 × 2.5 × 2.0
3.0 × 3.0 × 1.0
4.0 × 4.0 × 2.0
Coil Craft
www.coilcraft.com
SD3112
3.3-15
970-405
0.16-0.65
3.1 × 3.1 × 1.2
Cooper
www.cooperet.com
MIP3226D
3-10
1000-200
0.1-0.16
3.2 × 2.6 × 1.0
FDK
www.fdk.com
LQH32CN
LQH2MC
4.7-15
4.7-15
650-300
300-200
0.15-0.58
0.8-1.6
3.2 × 2.5 × 1.5
2 × 1.6 × 0.9
Murata
www.murata.com
CDRH3D16
CDRH2D14
3.3-15
3.3-12
1100-520
820-420
0.09-0.41
0.12-0.32
3.8 × 3.8 × 1.8
3.2 × 3.2 × 1.5
Sumida
www.sumida.com
NR3010
NR3015
3.3-15
3.3-15
750-400
1200-560
0.16-0.74
0.1-0.36
3.0 × 3.0 × 1.0
3.0 × 3.0 × 1.5
Taiyo Yuden
www.t-yuden.com
3524f
12
LTC3524
APPLICATIONS INFORMATION
and VH should be at least 0.47μF. Please be certain that
the capacitors used are rated for the maximum voltage
withadequatesafetymargin. RefertoTable2foralisting
of capacitor vendors.
Printed Circuit Board Layout Guidelines
High-speed operation of the LTC3524 demands care-
ful attention to PCB layout. You will not get advertised
performance with a careless layout. Figure 4 shows the
recommended component placement for a double layer
PCB. The bottom layer is used as a common ground plane
except for the VN trace.
Table 2. Capacitor Vendor Information
Supplier
AVX
Phone
Website
(803) 448-9411
(714) 852-2001
(408) 544-5200
(800) 368-2496
(847) 803-6100
www.avxcorp.com
www.murata.com
Murata
Samsung
Taiyo Yuden
TDK
www.sem.samsung.com
www.t-yuden.com
www.component.tdk.com
ELCD ELED1 ELED2
SCHOTTKY DIODE
L2
LAYOUT NOTES:
LIGHT GREY TOP LAYER
WHITE LEDs
VIA TO BOTTOM GROUND PLANE.
GROUND PLANE FILLS BOTTOM
*
*KEEP R
AWAY FROM SW2 TRACES
PROG
ELED1 PROG ELED2
24 23 22
SW2
21
VLED
20
LED1
19
WHITE LEDs
ELCD
1
LED2
18
GND
TOP VIEW
COMPONENT AND IC SIZES
NOT TO SCALE
–
V
2
CH
V
IN
IN
17
GND
R1
+
FBVO
3
CH
16
L1
V
VH
15
OUT
V
OUT
4
VH
GND
SW1
5
FBH
14
–
C2
6
FBN
13
+
+
C2
7
V2x
8
VN
9
CN
10
NC
11
VN
12
IN
SCHOTTKY
DIODE
VN
3524 F04
Figure 4. Suggested Layout Two Layer Board (Not to Scale)
3524f
13
LTC3524
TYPICAL APPLICATIONS
Li-Ion to +5V, 25mA, +16V, 1mA, –13V, 1mA TFT LCD Power Supply + 10 White LEDs
+
–
2.2μF
SW1
Li-Ion
10μH
4.7μH
10μF
V
IN
SW2
VLED
+5V, 25mA
V
OUT
LED2
1M
10μF
324k
LED1
FBVO
V2x
100k FOR 20mA
+10V
PROG
ELED2
ELED1
ELCD
LTC3524
0.47μF
0.47μF
+
REQUIRED
C2
V
VH
IN
FOR LCD BIAS
SEQUENCING
WHEN |VN| > V2X
0.1μF
–
C2
VNIN
FBN
V2x
+16V, 1mA
VH
287k
V
OUT
0.47μF
2M
165k
0.47μF
1M
–13V, 1mA
FBH
VN
+
–
+
CH
CH GND CN
0.1μF
0.1μF
3524 TA02a
100
90
80
70
60
LCD (V
)
)
IN
4.2
3.6
3.1
4.2
LED (V
IN
3.6
3.1
5
10
15
20
25
V
OUT
OR LED STRING CURRENT (mA)
3524 TA02b
3524f
14
LTC3524
PACKAGE DESCRIPTION
UF Package
24-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1697)
0.70 0.05
4.50 0.05
3.10 0.05
2.45 0.05
(4 SIDES)
PACKAGE OUTLINE
0.25 0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
R = 0.115
PIN 1 NOTCH
R = 0.20 TYP OR
0.35 × 45° CHAMFER
0.75 0.05
4.00 0.10
(4 SIDES)
TYP
23 24
PIN 1
TOP MARK
(NOTE 6)
0.40 0.10
1
2
2.45 0.10
(4-SIDES)
(UF24) QFN 0105
0.200 REF
0.25 0.05
0.00 – 0.05
0.50 BSC
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3524f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3524
TYPICAL APPLICATION
3NiMH or NiCD to +3.3V, 25mA, +10V, 1mA, –5V, 1mA TFT LCD Power Supply + 6 White LEDs
COILCRAFT
MSS4020 SERIES
+
–
10μH
4.7μH
100
90
80
70
60
50
2.2μF
SW1
3 NiMH
OR NiCD
10μF
V
SW2
VLED
IN
LCD (V
)
IN
3.1V
2.5V
+3.3V, 25mA
V
OUT
LED2
3.1V
510k
10μF
2.5V
301k
LED1
LED (V
)
IN
FBVO
V2x
100k FOR 20mA
+6.6V
0.47μF
LTC3524
LCD (V
)
PROG
IN
3.6V
3.6V
ELED2
ELED1
+
C2
0.1μF
V
ELCD
VNIN
IN
–
C2
V2x
5
10
15
20
25
+10V, 1mA
232k
VH
V
OR LED STRING CURRENT (mA)
V
OUT
FBN
VN
OUT
3524 TA03b
0.47μF
2M
0.47μF
604k
165k
–5V, 1mA
FBH
+
–
+
CH
CH GND CN
PHILIPS
PMEG3005
0.1μF
0.1μF
3524 TA03a
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
: 2.6V to 16V, V
LT1942
Quad DC/DC Converter for Triple Output TFT Supply Plus
LED Driver
V
= 36V, I = 7mA, I = < 1μA,
OUT(MAX) Q SD
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4mm × 4mm QFN-24 Package
LT1947
3MHz, 30V Adjustable Output TFT-LCD
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Triple Switching Regulator
V
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3mm × 3mm QFN-16 Package
LT3465/LT3465A
LT3466/LT3466-1
LT3471
Constant-Current, 1.2MHz/2.7MHz High Efficiency White
LED Boost Regulator with Integrated Schottky Diode
V
IN
: 2.7V to 16V, V = 34V, I = 1.9mA, I = < 1μA,
OUT(MAX)
Q
SD
ThinSOTTM Package
: 2.7V to 24V, V
Dual Constant-Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
V
IN
= 40V, I = 5mA, I = < 16μA,
OUT(MAX) Q SD
3mm × 3mm DFN-10 Package
: 2.4V to 16V, V = 40V, I = 2.5mA, I = < 1μA,
OUT(MAX) Q SD
Dual Output, Boost/Inverter, 1.3A I , 1.2MHZ, High
V
IN
SW
Efficiency Boost-Inverting DC/DC Converter
3mm × 3mm DFN-10 Package
LT3491
Constant-Current, 2.3MHz, High Efficiency White LED Boost
Regulator with Integrated Schottky Diode
V
IN
: 2.5V to 12V, V = 27V, I = 2.6mA, I = < 8μA,
OUT(MAX)
Q
SD
2mm × 2mm DFN-6 SC70 Package
LT3494/LT3494A
LT3497
40V, 180mA/350mA Micropower Low Noise Boost Converter
with Output Disconnect
V
IN
: 2.3V to 16V, V = 40V, I = 65μA, I = < 1μA,
OUT(MAX)
Q
SD
3mm × 2mm DFN-8 Package
Constant-Current, 2.3MHz, Dual High Efficiency White LED
Boost Regulator with Integrated Schottky Diode for 12 LEDs
V
IN
: 2.5V to 10V, V = 32V, I = 6mA, I = < 12μA,
OUT(MAX)
Q
SD
3mm × 2mm DFN-10 Package
LT3591
Constant-Current, 1MHz, High Efficiency White LED Boost
Regulator with Integrated Schottky Diode
V
IN
: 2.5V to 12V, V = 40V, I = 4mA, I = < 9μA,
OUT(MAX)
Q
SD
3mm × 2mm DFN-8 Package
ThinSOT is a trademark of Linear Technology Corporation.
3524f
LT 0208 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 2008
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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