FEATURES
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LT3498
20mA LED Driver and
OLED Driver with Integrated
Schottky in 3mm x 2mm DFN
DESCRIPTION
The LT
®
3498 is a dual output boost converter featuring a
2.3MHz PWM LED Driver and PFM OLED Driver. It includes
an internal power switch and Schottky diode for each
driver. Both converters can be independently shut down
and modulated. This highly integrated power solution is
ideal for dual display electronic devices.
The 2.3MHz step-up converter is designed to drive up to six
white LEDs in series from a Li-Ion cell. The device features
a unique high side LED current sense that enables the part
to function as a “one-wire” current source—one side of the
LED string can be returned to ground anywhere. Traditional
LED drivers use a grounded resistor to sense LED current,
requiring a 2-wire connection to the LED string.
The PFM OLED driver is a low noise boost converter that
features a novel control technique.* The converter controls
power delivery by varying both the peak inductor current
and switch off time. This technique results in low output
voltage ripple, as well as, high efficiency over a wide load
range. The off time of the switch is not allowed to exceed a
fixed level, guaranteeing a switching frequency that stays
above the audio band.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Patent Pending
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Dual Output Boost for Dual Display Devices
Drives Up to Six White LEDs and OLED/LCD Bias
Internal Power Switches and Schottky Diodes
Independent Dimming and Shutdown
200mV High Side Sense on LED Driver Allows
“One-Wire Current Source”
Wide Input Voltage Range: 2.5V to 12V
Wide Output Voltage Range: Up to 32V
2.3MHz PWM Frequency for LED Driver
PFM for OLED Driver is Non-Audible Over Entire
Load Range
Open LED Protection (27V Maximum on CAP1 Pin)
OLED Output Disconnect
Available in 12-Pin DFN Package
1mm Tall Solution Height
APPLICATIONS
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Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
TYPICAL APPLICATION
Li-Ion to Six White LEDs and OLED/LCD Bias
80
V
IN
= 3V TO 5V
4.7µF
0.47µF
OLED Efficiency
75
70
EFFICIENCY (%)
16V
24mA
V
IN
= 3.6V
V
OUT2
= 16V
LOAD FROM V
OUT2
400
350
300
POWER LOSS (mW)
250
200
150
100
15µH
1µF
10Ω
CAP1 SW1
V
IN
15µH
SW2 CAP2 V
OUT2
65
60
55
50
45
40
0.1
POWER LOSS
FROM V
OUT2
1
10
LED CURRENT (mA)
10µF
LT3498
LED1
20mA
CTRL1
OFF ON
SHUTDOWN
AND
DIMMING
CONTROL
3498 TA01
GND1
GND2
CTRL2
OFF ON
SHUTDOWN
AND
CONTROL
FB2
2.21MΩ
50
0
100
3498 TA01b
3498f
1
LT3498
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
PACKAGE/ORDER INFORMATION
TOP VIEW
LED1 1
CTRL1 2
GND1 3
GND2 4
CTRL2 5
FB2 6
13
12 CAP1
11 SW1
10 V
IN
9 SW2
8 CAP2
7 V
OUT2
Input Voltage (V
IN
) ....................................................12V
CTRL1 and CTRL2 Voltage ........................................12V
FB2 Voltage ..............................................................2.5V
V
OUT2
Voltage ...........................................................32V
SW1 and SW2 Voltage ..............................................32V
CAP1 and CAP2 Voltage ............................................32V
LED1 Voltage ............................................................32V
Operating Junction Temperature Range ...–40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range...................–65°C to 150°C
DDB PACKAGE
12-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 160°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3498EDDB
DDB PART MARKING
LCQF
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
Minimum Operating Voltage
Maximum Operating Voltage
Supply Current (LED Off, OLED Off)
Supply Current (LED On, OLED Off)
Supply Current (LED Off, OLED On)
Supply Current (LED On, OLED On)
V
CTRL1
for Full LED Current
V
CTRL2
for Full OLED Brightness
V
CTRL1
or V
CTRL2
to Turn On I
C
V
CTRL1
and V
CTRL2
to Shut Down I
C
CTRL1, CTRL2 Pin Bias Current
LED Driver
LED Current Sense Voltage (V
CAP
– V
LED
)
CAP1, LED1 Pin Bias Current
V
CAP1
, V
LED1
Common Mode Minimum Voltage
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 3V, V
CTRL1
= V
CTRL2
= 3V.
CONDITIONS
MIN
2.5
12
V
IN
= 3V, V
CTRL1
= 0V, V
CTRL2
= 0V
V
IN
= 3V, V
CTRL1
= 3V, V
CTRL2
= 0V, V
CAP1
= 24V,
V
LED1
= 23V
V
IN
= 3V, V
CTRL1
= 0V, V
CTRL2
= 3V, V
FB2
= 3V
V
IN
= 3V, V
CTRL1
= 3V, V
CTRL2
= 3V, V
CAP1
= 24V,
V
LED1
= 23V
●
TYP
MAX
UNITS
V
V
µA
mA
µA
mA
V
mV
8
1.6
230
1.65
1.5
125
10
2
280
2.05
●
●
75
100
mV
nA
V
CAP1
= 24V, I
SW
= 200mA
V
CAP1
= 16V, V
LED1
= 16V
●
190
200
20
210
30
2.5
2.8
mV
µA
V
MHz
%
mA
mV
3498f
●
1.8
88
300
2.3
90
425
250
●
I
SW
= 200mA
2
LT3498
ELECTRICAL CHARACTERISTICS
PARAMETER
Switch Leakage Current
CAP1 Pin Overvoltage Protection
Schottky Forward Voltage
Schottky Reverse Leakage
OLED Driver
Feedback Voltage
Feedback Resistor
Minimum Switch Off Time
Minimum Switch Off Time
Maximum Switch Off Time
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Schottky Forward Voltage
Schottky Reverse Leakage
PMOS Disconnect V
CAP2
– V
OUT2
CTRL2 to FB2 Offset
Maximum Shunt Current
I
SW2
= 200mA
V
SW2
= 16V
I
SCHOTTKY2
= 100mA
V
REVERSE2
= 20V
I
OUT2
= 10mA, V
CAP2
= 5V
V
CTRL2
= 0.5V
V
FB2
= 1.3V
250
8
220
15
After Start-Up
During Start-Up (Note 4)
V
FB2
= 1.5V
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 3V, V
CTRL1
= V
CTRL2
= 3V.
CONDITIONS
V
SW1
= 16V
26
I
SCHOTTKY1
= 100mA
V
REVERSE1
= 20V
V
CTRL2
= 3V (Note 3)
●
●
MIN
TYP
0.1
27
0.8
MAX
5
28
6
UNITS
µA
V
V
µA
V
kΩ
ns
µs
1.18
177
1.215
182
150
1
1.25
186
15
180
20
300
260
0.1
800
30
400
5
2
µs
mA
mV
µA
mV
µA
mV
mV
µA
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 LT3498 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C junction
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
Internal reference voltage is determined by finding V
FB2
voltage
level which causes quiescent current to increase 20µA above “Not
Switching” level.
Note 4:
If CTRL2 is overriding the internal reference, start-up mode
occurs when V
FB2
is less then half the voltage on CTRL2. If CTRL2 is not
overriding the internal reference, start-up mode occurs when V
FB2
is less
then half the voltage of the internal reference.
3498f
3
LT3498
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Current
(V
CTRL1
= V
CTRL2
= 0V)
15
SWITCH SATURATION VOLTAGE (mV)
T = –50°C
500
T = –50°C
SCHOTTKY FORWARD CURRENT (mA)
450
400
350
300
250
200
150
100
50
0
0
2
4
6
V
IN
(V)
8
10
12
1635 G07
T
A
= 25°C, unless otherwise specified.
LED Schottky Forward
Voltage Drop
400
350
T = 125°C
300
250
200
150
100
50
0
0
200
400
T = –50°C
T = 25°C
LED Switch Saturation
Voltage (V
CESAT1
)
SHUTDOWN CURRENT (µA)
12
9
T = 125°C
6
T = 25°C
T = 25°C
T = 125°C
3
0
0
50
100 150 200 250 300 350 400
SWITCH CURRENT (mA)
3498 G02
800
600
SCHOTTKY FORWARD DROP (mV)
1000
3498 G03
Sense Voltage (V
CAP1
– V
LED1
)
vs V
CTRL1
240
200
SENSE VOLTAGE (mV)
160
120
80
40
0
0
500
1000
V
CTRL1
(mV)
1500
2000
3498 G04
Sense Voltage (V
CAP1
– V
LED1
)
vs Temperature
206
206
Sense Voltage (V
CAP1
– V
LED1
)
vs V
CAP1
T = 25°C
T = –50°C
T = 125°C
SENSE VOLTAGE (mV)
202
SENSE VOLTAGE (mV)
202
198
198
T = 125°C
T = 25°C
194
194
T = –50°C
190
190
186
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
186
0
5
15
10
CAP1 VOLTAGE (V)
20
25
3498 G06
3498 G05
LED Current Limit
vs Temperature
500
29
Open Circuit Output
Clamp Voltage
6
5
T = –50°C
T = 25°C
27
T = 150°C
INPUT CURRENT (mA)
28
4
3
Input Current in Output
Open Circuit
CURRENT LIMIT (mA)
450
OUTPUT CLAMP VOLTAGE (V)
T = 150°C
T = 25°C
T = –50°C
400
2
1
350
26
300
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
25
0
0
2
4
6
V
IN
(V)
8
10
12
3498 G08
2
4
6
V
IN
(V)
8
10
12
3498 G09
3498 G07
3498f
4
LT3498
TYPICAL PERFORMANCE CHARACTERISTICS
LED Switching Frequency
vs Temperature
2.6
LED SWITCHING FREQUENCY (MHz)
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
SWITCH SATURATION VOLTAGE (mV)
300
SCHOTTKY FORWARD CURRENT (mA)
T = 125°C
250
T = –50°C
200
150
100
50
0
T = 25°C
T
A
= 25°C, unless otherwise specified.
OLED Schottky Forward
Voltage Drop
400
350
T = 125°C
300
250
200
T = 25°C
150
100
T = –50°C
50
0
0
200
800 1000
600
SCHOTTKY FORWARD DROP (mV)
400
1200
OLED Switch Saturation
Voltage (V
CESAT2
)
0
50
250
100
150
200
SWITCH CURRENT (mA)
300
3498 G10
3498 G11
3498 G12
V
OUT2
vs V
CTRL2
(V
OUT2
= 16V)
18
16
OUTPUT VOLTAGE CHANGE (%)
14
V
OUT2
VOLTAGE (V)
12
10
8
6
4
2
0
0
500
1500
1000
CTRL2 VOLTAGE (V)
2000
3498 G13
V
OUT2
vs Temperature
(V
OUT2
= 16V)
6
2.0
1.5
3
V
OUT2
VOLTAGE CHANGE (%)
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1.0
0.5
0
–0.5
–1.0
–1.5
–6
–50
–2.0
V
OUT2
Load Regulation
0
–3
0
10
40
30
LOAD CURRENT (mA)
20
50
3498 G15
3498 G14
OLED Minimum
Switching Frequency
80
70
SWITCHING FREQUENCY (kHz)
60
50
40
30
20
10
0
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
SWITCHING FREQUENCY (kHz)
1200
1000
800
600
400
200
0
OLED Switching Frequency
vs Load Current
600
PEAK INDUCTOR CURRENT (mA)
0.1
1
10
LOAD CURRENT (mA)
100
3498 G17
Peak Inductor Current
550
500
450
400
350
300
250
200
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
3498 G16
3498 G18
3498f
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