FEATURES
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LT3591
White LED Driver with
Integrated Schottky in
3mm
×
2mm DFN
DESCRIPTION
The LT
®
3591 is a fixed frequency step-up DC/DC converter
specifically designed to drive up to ten white LEDs in series
from a Li-Ion cell. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness
and eliminating the need for ballast resistors. 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,
allowing a simpler one wire LED connection. Traditional
LED drivers use a grounded resistor to sense LED current,
requiring a 2-wire connection to the LED string.
The high switching frequency allows the use of tiny induc-
tors and capacitors. A single pin performs both shutdown
and accurate LED dimming control. Few external compo-
nents are needed: open-LED protection and the Schottky
diode are all contained inside a low profile 3mm
×
2mm
DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
Drives Up to Ten White LEDs from a 3V Supply
High Side Sense Allows “One Wire Current Source”
Internal Schottky Diode
One Pin Dimming and Shutdown
80:1 True Color PWM
TM
Dimming Range
42V Open LED Protection
1MHz Switching Frequency
±5% Reference Accuracy
V
IN
Range: 2.5V to 12V
Requires Only 2.2µF Output Capacitor
Low Profile 8-Lead DFN Package
(3mm
×
2mm
×
0.75mm)
APPLICATIONS
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Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
TYPICAL APPLICATION
Li-Ion Driver for Ten White LEDs
SHUTDOWN AND
DIMMING CONTROL
CTRL
EFFICIENCY (%)
V
IN
3V TO 5V
22µH
SW
GND
1µF
V
IN
LT3591
LED
2.2µF
60
CAP
R
SENSE
10Ω
80
Conversion Efficiency
V
IN
= 3.6V
10 LEDs
75
70
65
55
0
5
10
LED CURRENT (mA)
15
20
3591 TA01b
3591 TA01a
3591f
1
LT3591
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
V
IN
1
GND 2
NC 3
SW 4
9
8 CTRL
7 LED
6 NC
5 CAP
Input Voltage (V
IN
) ................................................... 12V
CTRL Voltage ........................................................... 12V
SW Voltage .............................................................. 45V
CAP Voltage ............................................................. 45V
LED Voltage ............................................................. 45V
Operating Junction Temperature Range
(Note 2) ...............................................–40°C to 85°C
Maximum Junction Temperature ........................ 125°C
Storage Temperature Range...................–65°C to 150°C
DDB PACKAGE
8-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W
EXPOSED PAD (PIN 9) SHOULD BE CONNECTED TO PCB GROUND
ORDER PART NUMBER
LT3591EDDB
DDB PART MARKING
LCPG
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
LED Current Sense Voltage (V
CAP
– V
LED
)
CAP Pin Bias Current
LED Pin Bias Current
Supply Current
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
V
CTRL
for Full LED Current
V
CTRL
to Shut Down IC
V
CTRL
to Turn On IC
CTRL Pin Bias Current
CAP Pin Overvoltage Protection
Schottky Forward Drop
Schottky Leakage Current
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, V
CTRL
= 3V, unless otherwise specified.
CONDITIONS
V
CAP
= 24V, I
SW
= 300mA
V
CAP
= 36V, V
LED
= 35.8V
V
CAP
= 36V, V
LED
= 35.8V
V
CAP
= 24V, V
LED
= 23V
CTRL = 0V
0.75
92
●
●
MIN
2.5
190
TYP
200
40
20
4
9
1
94
800
200
0.1
MAX
210
80
40
5
11
1.2
UNITS
V
mV
µA
µA
mA
µA
MHz
%
mA
mV
500
I
SW
= 300mA
V
SW
= 24V
V
CAP
= 44V
●
5
50
µA
V
mV
mV
nA
1.5
100
100
40
42
0.8
4
44
●
●
V
V
µA
I
SCHOTTKY
= 200mA
V
R
= 30V
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 LT3591E is guaranteed to meet performance specifications
from 0°C to 85°C operating junction temperature range. Specifications
over the –40°C to 85°C operating junction temperature range are assured
by design, characterization and correlation with statistical process controls.
3591f
2
LT3591
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
(V
CESAT
)
500
SWITCH SATURATION VOLTAGE (mV)
SCHOTTKY FORWARD CURRENT (mA)
600
500
125°C
400
300
25°C
200
– 50°C
100
0
0
100 200 300 400 500 600 700 800
SWITCH CURRENT (mA)
3591 G01
T
A
= 25°C, unless otherwise specified.
Schottky Forward Voltage Drop
15
Shutdown Current (V
CTRL
= 0V)
SHUTDOWN CURRENT (µA)
400
25°C
12
300
125°C
9
– 50°C
25°C
125°C
200
– 50°C
100
6
3
0
0
0
200
400
600
800 1000
SCHOTTKY FORWARD DROP (mV)
1200
0
3
6
V
IN
(V)
9
12
3591 G03
3591 G02
Sense Voltage (V
CAP
– V
LED
)
vs V
CTRL
240
200
SENSE VOLTAGE (mV)
160
120
80
40
0
0
500
1000 1500 2000
V
CTRL
(mV)
2500
3000
– 50°C
25°C
125°C
45
Open-Circuit Output
Clamp Voltage
8
7
OUTPUT CLAMP VOLTAGE (V)
44
INPUT CURRENT (mA)
25°C
43
125°C
6
5
4
3
2
1
40
0
0
3
6
V
IN
(V)
3591 G04
3591 G05
Input Current in Output
Open Circuit
25°C
125°C
– 50°C
42
– 50°C
41
9
12
0
3
6
V
IN
(V)
9
12
3591 G06
Switching Waveform
V
SW
20V/DIV
V
CAP
50mV/DIV
I
L
200mA/DIV
V
IN
= 3.6V
500ms/DIV
FRONT PAGE
APPLICATION CIRCUIT
3591 G07
Transient Response
V
CAP
5V/DIV
V
CTRL
5V/DIV
I
L
500mA/DIV
V
IN
= 3.6V
1ms/DIV
FRONT PAGE
APPLICATION CIRCUIT
3591 G08
3591f
3
LT3591
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
(V
CTRL
= 3V)
6
5
QUIESCENT CURRENT (mA)
125°C
4
– 50°C
3
2
1
0
0
3
6
V
IN
(V)
9
12
3591 G09
T
A
= 25°C, unless otherwise specified.
Schottky Leakage Current
vs Temperature
15
SCHOTTKY LEAKAGE CURRENT (µA)
V
R
= 10V
V
R
= 16V
V
R
= 20V
Current Limit vs Temperature
1000
25°C
CURRENT LIMIT (mA)
800
12
600
9
400
6
200
3
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3591 G10
3591 G11
Open-Circuit Output Clamp
Voltage vs Temperature
45
8
7
44
INPUT CURRENT (mA)
6
5
4
3
2
1
40
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
Input Current in Output Open
Circuit vs Temperature
V
IN
= 3V
SWITCHING FREQUENCY (kHz)
1200
1150
1100
1050
1000
950
900
850
800
50
25
75
0
TEMPERATURE (°C)
100
125
Switching Frequency
vs Temperature
OUTPUT CLAMP VOLTAGE (V)
43
42
41
0
–50 –25
750
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3591 G12
3591 G13
3591 G14
Maximum Duty Cycle
vs Temperature
100
208
Sense Voltage (V
CAP
– V
LED
)
vs V
CAP
208
Sense Voltage (V
CAP
– V
LED
)
vs Temperature
MAXIMUM DUTY CYCLE (%)
98
SENSE VOLTAGE (mV)
204
25°C
125°C
196
– 50°C
SENSE VOLTAGE (mV)
204
96
200
200
94
196
92
192
192
90
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
188
5
10
15
20
V
CAP
(V)
25
30
35
3591 G16
188
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3591 G15
3591 G17
3591f
4
LT3591
PIN FUNCTIONS
V
IN
(Pin 1):
Input Supply Pin. Must be locally bypassed.
GND (Pin 2):
Ground Pin. Should be tied directly to local
ground plane.
SW (Pin 4):
Switch Pin. Minimize trace area at this pin to
minimize EMI. Connect the inductor at this pin.
CAP (Pin 5):
Output of the Driver. This pin is connected
to the cathode of internal Schottky. Connect the output
capacitor to this pin and the sense resistor from this pin
to the LED pin.
LED (Pin 7):
Connection Point for the Anode of the First
LED and the Sense Resistor. The LED current can be
programmed by :
I
LED
=
200mV
R
SENSE
CTRL (Pin 8):
Dimming and Shutdown Pin. Connect this
pin below 50mV to disable the driver. As the pin voltage
is ramped from 0V to 1.5V, the LED current ramps from
0 to I
LED
( = 200mV/R
SENSE
). The CTRL pin must not be
left floating.
Exposed Pad (Pin 9):
Ground. The Exposed Pad must
be soldered to PCB ground to achieve the rated thermal
performance.
BLOCK DIAGRAM
1
V
IN
PWM
COMP
DRIVER
A2
R
S
Q
Q1
OVERVOLTAGE
PROTECTION
R
4
SW
CAP
Σ
RAMP
GENERATOR
V
REF
1.25V
SHDN
OSCILLATOR
A1
R
C
START-UP
CONTROL
C
C
Figure 1. Block Diagram
3591f
+
+
–
+
+
A3
–
5
–
+
A = 6.25
–
LED
7
CTRL
8
2
GND
3591 F01
5
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