LT3491 - White LED Driver in SC70 with Integrated Schottky

LT3491
White LED Driver with
Integrated Schottky in SC70
and 2mm × 2mm DFN
DESCRIPTIO
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FEATURES
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Drives Up to Six White LEDs from a 3V Supply
High Side Sense Allows “One Wire Current Source”
Internal Schottky Diode
One Pin Dimming and Shutdown
27V Open LED Protection
2.3MHz Switching Frequency
±5% Reference Accuracy
VIN Range: 2.5V to 12V
Requires Only 1µF Output Capacitor
Wide 300:1 True Color PWMTM Dimming Range
8-Lead SC70 Package
Low Profile 6-Lead DFN Package
(2mm × 2mm × 0.75mm)
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APPLICATIO S
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Cellular Phones
PDAs, Handheld Computers
Digital Cameras
MP3 Players
GPS Receivers
The 2.3MHz switching frequency allows the use of tiny
inductors and capacitors. A single pin performs both
shutdown and accurate LED dimming control. Few external components are needed: open-LED protection and the
Schottky diode are all contained inside the tiny SC70 and
2mm × 2mm DFN packages. With such a high level of
integration, the LT3491 provides a high efficiency LED
driver solution in the smallest of spaces.
, LTC, LT and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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The LT®3491 is a fixed frequency step-up DC/DC converter
specifically designed to drive up to six 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.
TYPICAL APPLICATIO
Efficiency
Li-Ion Driver for Four White LEDs
SHUTDOWN AND
DIMMING CONTROL
80
VIN = 3.6V
4 LEDs
75
CTRL
VIN
L1
10µH
70
CAP
RSENSE
10Ω
LT3491
SW
LED
GND
C2
1µF
C1
1µF
EFFICIENCY (%)
VIN
3V TO 5V
65
60
55
50
45
40
0
3491 TA01a
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK316BJ105ML
L1: MURATA LQH32CN100
5
10
15
20
LED CURRENT (mA)
3491 TA01b
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LT3491
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ABSOLUTE
RATI GS (Note 1)
Input Voltage (VIN) .................................................
SW Voltage .............................................................
CAP Voltage ............................................................
CTRL Voltage ..........................................................
12V
32V
32V
12V
LED Voltage ............................................................ 32V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Maximum Junction Temperature ......................... 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10sec, SC-70) ......... 300°C
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PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
6 CTRL
VIN 1
GND 2
7
SW 3
8 CAP
7 LED
6 CTRL
5 VIN
SW 1
GND 2
GND 3
GND 4
5 LED
4 CAP
SC8 PACKAGE
8-LEAD PLASTIC SC70
DC PACKAGE
6-LEAD (2mm × 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 270°C/ W
TJMAX = 125°C, θJA = 102°C/W, θJC = 20°C/ W
EXPOSED PAD (PIN 7) SHOULD BE CONNECTED TO PCB GROUND
ORDER PART NUMBER
DC PART MARKING
ORDER PART NUMBER
DC PART MARKING
LT3491EDC
LCHJ
LT3491ESC8
LBXQ
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
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3V, VCTRL = 3V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
TYP
MAX
UNITS
200
210
mV
2.5
LED Current Sense Voltage (VCAP – VLED)
VCAP = 30V
CAP, LED Pin Bias Current
VCAP = 16V, VLED = 16V
●
190
V
40
µA
2.5
V
2.6
8
4
10
mA
µA
2.8
MHz
20
VCAP, VLED Common Mode Minimum Voltage
Supply Current
VCAP = 16V, VLED = 15V, CTRL = 3V
CTRL = 0V
Switching Frequency
1.8
2.3
Maximum Duty Cycle
●
88
92
%
Switch Current Limit
●
260
350
mA
Switch VCESAT
ISW = 200mA
200
Switch Leakage Current
VSW = 16V
0.1
VCTRL for Full LED Current
VCAP = 30V
●
●
µA
50
mV
1.5
V
VCTRL to Shut Down IC
VCTRL to Turn On IC
mV
5
100
CTRL Pin Bias Current
mV
100
●
CAP Pin Overvoltage Protection
Schottky Forward Drop
ISCHOTTKY = 100mA
Schottky Leakage Current
VR = 20V
26
27
nA
28
V
4
µA
0.8
V
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LT3491
ELECTRICAL CHARACTERISTICS
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 LT3491E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
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TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified)
Switch Saturation Voltage (VCESAT)
250
200
150
100
50
0
0
50
350
300
250
200
150
100
200
400
800 1000
600
SCHOTTKY FORWARD DROP (mV)
160
120
80
40
0
3
6
9
3491 G03
Input Current in Output Open
Circuit
6
5
29
28
27
26
25
2000
4
3
2
1
0
3
0
6
9
12
0
VIN (V)
VCTRL (mV)
3
6
VIN (V)
9
12
3491 G06
3491 G05
3491 G04
Transient Response
Switching Waveform
VSW
10V/DIV
VCAP
5V/DIV
VCAP
50mV/DIV
VCTRL
5V/DIV
IL
100mA/DIV
IL
200mA/DIV
VIN = 3.6V
200ns/DIV
FRONT PAGE
APPLICATION CIRCUIT
12
VIN (V)
INPUT CURRENT (mA)
OUTPUT CLAMP VOLTAGE (V)
200
SENSE VOLTAGE (mV)
1200
30
1500
3
Open-Circuit Output Clamp
Voltage
240
1000
6
3491 G02
Sense Voltage (VCAP – VLED)
vs VCTRL
500
9
0
0
3491 G01
0
12
50
0
100 150 200 250 300 350 400
SWITCH CURRENT (mA)
SHUTDOWN CURRENT (µA)
SCHOTTKY FORWARD CURRET (mA)
SWITCH SATURATION VOLTAGE (mV)
15
400
300
0
Shutdown Current (VCTRL = 0V)
Schottky Forward Voltage Drop
350
3491 G07
VIN = 3.6V
1ms/DIV
FRONT PAGE
APPLICATION CIRCUIT
3491 G08
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LT3491
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TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified)
Switching Current Limt
vs Duty Cycle
Quiescent Current (VCTRL = 3V)
3.0
15
450
400
SCHOTTKY LEAKAGE CURRENT (µA)
25°C
2.5
350
CURRENT LIMIT (mA)
QUIESCENT CURRENT (mA)
Schottky Leakage Current
vs Temperature
2.0
1.5
1.0
300
250
200
150
100
0.5
50
0
0
3
6
VIN (V)
9
30
50
60
70
DUTY CYCLE (%)
40
3491 G09
100
4
3
2
0
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
100
3491 G12
120
80
–50°C
25°C
85°C
0
0
500
1000
VCTRL (mV)
1500
2.05
2.00
1.95
–50
125
2000
50
25
0
75
TEMPERATURE (°C)
100
212
212
208
208
204
200
204
200
196
196
192
125
Sense Voltage (VCAP – VLED)
vs Temperature
5
10
15
20
25
VCAP (V)
3491 G15
–25
3419 G14
SENSE VOLTAGE (mV)
SENSE VOLTAGE (mV)
200
40
2.10
Sense Voltage (VCAP – VLED)
vs VCAP
240
100
2.15
3491 G13
Sense Voltage (VCAP – VLED)
vs VCTRL
160
75
Switching Frequency
vs Temperature
1
50
25
0
75
TEMPERATURE (°C)
0
25
50
TEMPERATURE (°C)
3491 G11
SWITCH FREQUENCY (MHz)
INPUT CURRENT (mA)
OUTPUT CLAMP VOLTAGE (V)
26
–25
–25
VIN = 3V
5
29
25
–50
3
2.20
6
27
6
Input Current in Output Open Circuit
vs Temperature
30
28
9
3491 G10
Open-Circuit Output Clamp Voltage
vs Temperature
SENSE VOLTAGE (mV)
90
80
12
0
–50
0
12
VR = 10V
VR = 16V
VR = 20V
3491 G16
192
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3491 G17
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LT3491
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PI FU CTIO S (SC70/DFN)
SW (Pin 1/Pin 3): Switch Pin. Minimize trace area at this
pin to minimize EMI. Connect the inductor at this pin.
GND (Pins 2, 3, 4/Pin 2): Ground Pins. All three pins
should be tied directly to local ground plane.
VIN (Pin 5/Pin 1): Input Supply Pin. Must be locally
bypassed.
CTRL (Pin 6/Pin 6): 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 ILED ( = 200mV/RSENSE). The CTRL pin must not
be left floating.
LED (Pin 7/Pin 5): Connection Point for the Anode of the
First LED and the Sense Resistor. The LED current can be
programmed by :
ILED =
200mV
RSENSE
CAP (Pin 8/Pin 4): 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.
EXPOSED PAD (NA/Pin 7): The Exposed Pad should be
soldered to the PCB ground to achieve the rated thermal
performance.
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BLOCK DIAGRA
5
1
VIN
SW
PWM
COMP
–
CAP
8
DRIVER
A2
R
+
S
Q1
Q
OVERVOLTAGE
PROTECTION
+
Σ
R
A3
–
RAMP
GENERATOR
+
OSCILLATOR
A1
RC
START-UP
CONTROL
+
+
–
VREF
1.25V
SHDN
A = 6.25
–
LED
7
CC
CTRL
6
PIN NUMBERS CORRESPOND TO THE 8-PIN SC70 PACKAGE
GND
PINS 2, 3, 4
3491 F01
Figure 1. Block Diagram
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LT3491
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OPERATIO
The LT3491 uses a constant frequency, current mode
control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the
Block Diagram in Figure 1.
At power up, the capacitor at the CAP pin is charged up to
VIN (input supply voltage) through the inductor and the
internal Schottky diode. If CTRL is pulled higher than
100mV, the bandgap reference, the start-up bias and the
oscillator are turned on. At the start of each oscillator
cycle, the power switch Q1 is turned on. A voltage proportional to the switch current is added to a stabilizing ramp
and the resulting sum is fed into the positive terminal of the
PWM comparator, A2. When this voltage exceeds the level
at the negative input of A2, the PWM logic turns off the
power switch. The level at the negative input of A2 is set by
the error amplifier A1, and is simply an amplified version
of the difference between the VCAP and VLED voltage and
the bandgap reference. In this manner the error amplifier,
A1, sets the correct peak current level in inductor L1 to
keep the output in regulation. The CTRL pin is used to
adjust the LED current. The LT3491 enters into shutdown
when CTRL is pulled lower than 50mV.
Minimum Output Current
The LT3491 can drive a 3-LED string at 2mA LED current
without pulse skipping using the same external components shown in the application circuit on the front page of
this data sheet. As current is further reduced, the device
will begin skipping pulses. This will result in some low
frequency ripple, although the average LED current remains regulated down to zero. The photo in Figure 2
details circuit operation driving three white LEDs at 2mA
load. Peak inductor current is less than 60mA and the
regulator operates in discontinuous mode, meaning the
inductor current reaches zero during the discharge phase.
After the inductor current reaches zero, the SW pin
exhibits ringing due to the LC tank circuit formed by the
inductor in combination with the switch and the diode
capacitance. This ringing is not harmful; far less spectral
energy is contained in the ringing than in the switch
transitions.
IL
50mA/DIV
VSW
10V/DIV
VIN = 4.2V
ILED = 2mA
3 LEDs
200ns/DIV
3491 F02
Figure 2. Switching Waveforms
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LT3491
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APPLICATIO S I FOR ATIO
INDUCTOR SELECTION
A 10µH inductor is recommended for most LT3491 applications. Although small size and high efficiency are major
concerns, the inductor should have low core losses at
2.3MHz and low DCR (copper wire resistance). Some
small inductors in this category are listed in Table 1. The
efficiency comparison of different inductors is shown in
Figure 3.
Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information
on their entire selection of ceramic parts.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
(800) 368-2496
www.t-yuden.com
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
Table 1. Recommended Inductors
L
(µH)
DCR
(Ω)
CURRENT
RATING
(mA)
LQH32CN100K53
LQH2MCN100K02
10
10
0.3
1.2
450
225
Murata
www.murata.com
SD3112-100
10
0.446
550
Cooper
www.cooperet.com
1001AS-100M
(TYPE D312C)
10
0.48
460
Toko
www.toko.com
CDRH2D11
CDRH2D14
10
10
0.5375
0.294
280
700
Sumida
www.sumida.com
PART
VENDOR
80
OVERVOLTAGE PROTECTION
The LT3491 has an internal open-circuit protection circuit.
In the cases of output open circuit, when the LEDs are
disconnected from the circuit or the LEDs fail open circuit,
VCAP is clamped at 27V (typ). The LT3491 will then switch
at a very low frequency to minimize input current. The VCAP
and input current during output open circuit are shown in
the Typical Performance Characteristics. Figure 4 shows
the transient response when the LEDs are disconnected.
75
EFFICIENCY (%)
70
IL
200mA/DIV
65
60
VIN = 3.6V
4 LEDs
FRONT PAGE
APPLICATION CIRCUIT
MURATA LQH2MCN100K02
MURATA LQH32CN100K53
TOKO 10001AS-100M
SUMIDA CDRH2D11
SUMIDA CDRH2D14
55
50
45
40
35
30
0
5
10
15
LED CURRENT (mA)
VCAP
10V/DIV
20
3491 F03
VIN = 3.6V
CIRCUIT OF
FRONT PAGE
APPLICATION
500µs/DIV
3491 F04
LEDs DISCONNECTED
AT THIS INSTANT
Figure 4. Output Open-Circuit Waveform
Figure 3. Efficiency Comparison of Different Inductors
CAPACITOR SELECTION
INRUSH CURRENT
The small size of ceramic capacitors make them ideal for
LT3491 applications. Use only X5R and X7R types because they retain their capacitance over wider temperature
ranges than other types such as Y5V or Z5U. A 1µF input
capacitor and a 1µF output capacitor are sufficient for
most applications.
The LT3491 has a built-in Schottky diode. When supply
voltage is applied to the VIN pin, an inrush current flows
through the inductor and the Schottky diode and charges
up the CAP voltage. The Schottky diode inside the LT3491
can sustain a maximum current of 1A.
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LT3491
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APPLICATIO S I FOR ATIO
For low DCR inductors, which is usually the case for this
application, the peak inrush current can be simplified as
follows:
IPK =
α=
ILED (mA)
VIN – 0.6
⎛ α π⎞
• exp ⎜ – • ⎟
⎝ ω 2⎠
L•ω
r
2 •L
ω=
Table 4. RSENSE Value Selection for 200mV Sense
5
40
10
20
15
13.3
20
10
DIMMING CONTROL
There are three different types of dimming control circuits.
The LED current can be set by modulating the CTRL pin
with a DC voltage, a filtered PWM signal or directly with a
PWM signal.
1
r2
–
L • C 4 • L2
where L is the inductance, r is the DCR of the inductor and
C is the output capacitance.
Table 3 gives inrush peak currents for some component
selections.
Table 3. Inrush Peak Currents
VIN (V)
r (Ω)
L (µH)
COUT (µF)
IP (A)
4.2
0.3
10
1.0
1.06
4.2
1.2
10
1.0
0.86
4.2
0.58
15
1.0
0.83
4.2
1.6
15
1.0
0.68
PROGRAMMING LED CURRENT
The feedback resistor (RSENSE) and the sense voltage
(VCAP – VLED) control the LED current.
The CTRL pin controls the sense reference voltage as
shown in the Typical Performance Characteristics. For
CTRL higher than 1.5V, the sense reference is 200mV,
which results in full LED current. In order to have accurate
LED current, precision resistors are preferred (1% is
recommended). The formula and table for RSENSE selection are shown below.
RSENSE =
RSENSE (Ω)
Using a DC Voltage
For some applications, the preferred method of brightness
control is a variable DC voltage to adjust the LED current.
The CTRL pin voltage can be modulated to set the dimming
of the LED string. As the voltage on the CTRL pin increases
from 0V to 1.5V, the LED current increases from 0 to ILED.
As the CTRL pin voltage increases beyond 1.5V, it has no
effect on the LED current.
The LED current can be set by:
ILED ≈
200mV
, when VCTRL > 1.5V
RSENSE
ILED ≈
VCTRL
, when VCTRL < 1.25V
6.225 • RSENSE
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics.
200mV
ILED
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LT3491
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APPLICATIO S I FOR ATIO
Using a Filtered PWM Signal
A filtered PWM signal can be used to control the brightness of the LED string. The PWM signal is filtered (Figure
5) by a RC network and fed to the CTRL pin.
The corner frequency of R1, C1 should be much lower than
the frequency of the PWM signal. R1 needs to be much
smaller than the internal impedance of the CTRL pin which
is 10MΩ (typ).
PWM
10kHz TYP
LT3491
R1
100k
C1
0.1µF
CTRL
level Si2302 MOSFET can be used since its source is
connected to ground. The PWM signal is applied to the
CTRL pin of the LT3491 and the gate of the MOSFET. The
PWM signal should traverse between 0V to 2.5V, to ensure
proper turn on and off of the driver and the NMOS
transistor Q1. When the PWM signal goes high, the LEDs
are connected to ground and a current of ILED = 200mV/
RSENSE flows through the LEDs. When the PWM signal
goes low, the LEDs are disconnected and turn off. The
MOSFET ensures that the LEDs quickly turn off without
discharging the output capacitor which in turn allows the
LEDs to turn on faster. Figure 7 shows the PWM dimming
waveforms for the circuit in Figure 6.
3491 F05
VIN
3V TO 5V
L1
10µH
Figure 5. Dimming Control Using a Filtered PWM Signal
VIN
SW
Direct PWM Dimming
Changing the forward current flowing in the LEDs not only
changes the intensity of the LEDs, it also changes the
color. The chromaticity of the LEDs changes with the
change in forward current. Many applications cannot
tolerate any shift in the color of the LEDs. Controlling the
intensity of the LEDs with a direct PWM signal allows
dimming of the LEDs without changing the color. In
addition, direct PWM dimming offers a wider dimming
range to the user.
Dimming the LEDs via a PWM signal essentially involves
turning the LEDs on and off at the PWM frequency. The
typical human eye has a limit of ~60 frames per second. By
increasing the PWM frequency to ~80Hz or higher, the eye
will interpret that the pulsed light source is continuously on.
Additionally, by modulating the duty cycle (amount of “ontime”), the intensity of the LEDs can be controlled. The color
of the LEDs remains unchanged in this scheme since the
LED current value is either zero or a constant value.
Figure 6 shows a Li-Ion powered driver for four white
LEDs. Direct PWM dimming method requires an external
NMOS tied between the cathode of the lowest LED in the
string and ground as shown in Figure 6. A simple logic
CAP
C1
1µF
RSENSE
10Ω
LT3491
LED
GND
CTRL
2.5V
0V
C2
1µF
PWM
FREQ
Q1
Si2302
100k
3491 F06
Figure 6. Li-Ion to Four White LEDs with Direct PWM Dimming
ILED
20mA/DIV
IL
200mA/DIV
PWM
5V/DIV
VIN = 3V
4 LEDs
2ms/DIV
3491 F07
Figure 7. Direct PWM Dimming Waveforms
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LT3491
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APPLICATIO S I FOR ATIO
The time it takes for the LED current to reach its programmed value sets the achievable dimming range for a
given PWM frequency. For example, the settling time of
the LED current in Figure 7 is approximately 30µs for a 3V
input voltage. The achievable dimming range for this
application and 100Hz PWM frequency can be determined
using the following method.
Example:
down to 100mV. The use of both techniques together
allows the average LED current for the four LED application to be varied from 20mA down to less than 20µA.
Figure 9 shows the application for dimming using both
analog dimming and PWM dimming. A potentiometer
must be added to ensure that the gate of the NMOS
receives a logic-level signal, while the CTRL signal can be
adjusted to lower amplitudes.
ƒ = 100Hz, t SETTLE = 30µs
tPERIOD =
1
1
=
= 0.01s
ƒ 100
100Hz
1kHz
t
0.01s
Dim Range = PERIOD =
= 300 : 1
t SETTLE 30µs
Min Duty Cycle =
10kHz
t SETTLE
30µs
• 100 =
• 10
00 = 0.3%
tPERIOD
0.01s
1
10
The dimming range can be further extended by changing
the amplitude of the PWM signal. The height of the PWM
signal sets the commanded sense voltage across the
sense resistor through the CTRL pin. In this manner both
analog dimming and direct PWM dimming extend the
dimming range for a given application. The color of the
LEDs no longer remains constant because the forward
current of the LED changes with the height of the CTRL
signal. For the four LED application described above, the
LEDs can be dimmed first, modulating the duty cycle of the
PWM signal. Once the minimum duty cycle is reached, the
height of the PWM signal can be decreased below 1.5V
1000
PWM DIMMING RANGE
Duty Cycle Range = 100% → 0.3% at 100Hz
The calculations show that for a 100Hz signal the dimming
range is 300 to 1. In addition, the minimum PWM duty
cycle of 0.3% ensures that the LED current has enough
time to settle to its final value. Figure 8 shows the dimming
range achievable for three different frequencies with a
settling time of 30µs.
100
3491 F08
Figure 8. Dimming Range Comparison
of Three PWM Frequencies
VIN
3V TO 5V
L1
10µH
VIN
SW
C1
1µF
CAP
RSENSE
10Ω
LT3491
LED
GND
CTRL
C2
1µF
2.5V
PWM
FREQ
0V
Q1
Si2302
100k
3491 F09
Figure 9. Li-Ion to Four White LEDs with Both
PWM Dimming and Analog Dimming
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LT3491
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APPLICATIO S I FOR ATIO
LOW INPUT VOLTAGE APPLICATIONS
BOARD LAYOUT CONSIDERATIONS
The LT3491 can be used in low input voltage applications.
The input supply voltage to the LT3491 must be 2.5V or
higher. However, the inductor can be run off a lower
battery voltage. This technique allows the LEDs to be
powered off two alkaline cells. Most portable devices have
a 3.3V logic supply voltage which can be used to power the
LT3491. The LEDs can be driven straight from the battery,
resulting in higher efficiency.
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
proper layout of high frequency switching paths is essential. Minimize the length and area of all traces connected to
the switching node pin (SW). Keep the sense voltage pins
(CAP and LED) away from the switching node. Place COUT
next to the CAP pin. Always use a ground plane under the
switching regulator to minimize interplane coupling. Recommended component placement is shown in Figure 11.
Figure 10 shows three LEDs powered by two AA cells. The
battery is connected to the inductor and the chip is
powered off a 3.3V logic supply voltage.
SHUTDOWN AND
DIMMING CONTROL
3.3V
CTRL
C1
0.1µF
2 AA CELLS
2V TO 3.2V
VIN
L1
10µH
CAP
RSENSE
10Ω
LT3491
SW
LED
C2
2.2µF
GND
C1
1µF
3491 F10
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK325BJ225ML
L1: MURATA LQH32CN100
Figure 10. 2 AA Cells to Three White LEDs
CIN
CTRL
LED
RSENSE
VIN
GND
5
4
6
3
7
2
CIN
VIN
CTRL
L1
1
1
8
2
SW
COUT
6
L1
3
GND
7
5
LED
4 CAP
SW
CAP
COUT
RSENSE
GND
3491 F11
(A) SC70 PACKAGE
(B) DFN PACKAGE
Figure 11. Recommended Component Placement
3491fa
11
LT3491
U
TYPICAL APPLICATIO S
Li-Ion Driver for One White LED
Efficiency
60
C2
1µF
50
EFFICIENCY (%)
RSENSE
10Ω
LED
VIN
3V TO 5V
CAP
VIN
L1
10µH
SW
45
40
35
30
25
LT3491
C1
1µF
VIN = 3.6V
55
SHUTDOWN
AND
DIMMING
CONTROL
CTRL
GND
20
15
10
3491 TA07a
5
0
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK316BJ105ML
L1: MURATA LQH32CN100
3491 TA07b
Li-Ion Driver for Two White LEDs
Efficiency
70
C2
1µF
EFFICIENCY (%)
60
LED
CAP
VIN
L1
10µH
LT3491
SW
C1
1µF
VIN = 3.6V
65
RSENSE
10Ω
VIN
3V TO 5V
20
10
15
LED CURRENT (mA)
SHUTDOWN
AND
DIMMING
CONTROL
CTRL
GND
55
50
45
40
35
30
25
3491 TA08a
0
10
5
20
15
LED CURRENT (mA)
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK316BJ105ML
L1: MURATA LQH32CN100
3491 TA08b
Efficiency
2-Cell Li-Ion Driver for Torch and Flash Mode LED Control
80
C2
4.7µF
VIN
6V TO 9V
75
D1
FLASH MODE
ILED = 200mA V
CTRL
1.5V
LED
L1
10µH
VIN
C1
1µF
70
65
60
LT3491
CTRL
VCTRL
680mV TORCH MODE
ILED = 100mA
EFFICIENCY (%)
RSENSE
1Ω
CAP
ILED = 100mA
SW
55
GND
3491 TA09a
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN LMK212BJ475MG
D1: AOT-2015 HPW1751B
L1: MURATA LQH32CN100
50
6
6.5
7
7.5
VIN (V)
8
8.5
9
3491 TA09b
3491fa
12
LT3491
U
TYPICAL APPLICATIO S
12V to One White LED at 200mA
Efficiency
C2
4.7µF
75
RSENSE
1Ω
C3
1µF
EFFICIENCY (%)
PVIN
12V
80
D1
CAP
VIN
3V
LED
L1
15µH
VIN
SHUTDOWN
AND
DIMMING
CONTROL
C1
1µF
LT3491
70
65
60
SW
55
3491 TA02a
50
CTRL
GND
0
C1, C3: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN LMK316BJ475ML
D1: LUXEON EMITTER LXHL-BWO2
L1: MURATA LQH32CN150
3491 TA02b
12V to Two White LEDs at 200mA
Efficiency
C2
4.7µF
90
85
RSENSE
1Ω
C3
1µF
D1
CAP
VIN
3V
LED
L1
15µH
VIN
SHUTDOWN
AND
DIMMING
CONTROL
C1
1µF
LT3491
CTRL
EFFICIENCY (%)
PVIN
12V
20 40 60 80 100 120 140 160 180 200
LED CURRENT (mA)
80
75
70
SW
65
3491 TA03a
60
GND
0
C1, C3: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN LMK316BJ475ML
D1: LUXEON EMITTER LXHL-BWO2
L1: MURATA LQH32CN150
20 40 60 80 100 120 140 160 180 200
LED CURRENT (mA)
3491 TA03b
3491fa
13
LT3491
U
TYPICAL APPLICATIO S
Li-Ion Driver for Three White LEDs
SHUTDOWN AND
DIMMING CONTROL
80
CTRL
70
VIN
L1
10µH
C1
1µF
CAP
RSENSE
10Ω
LT3491
SW
VIN = 3.6V
3 LEDs
75
LED
C2
1µF
GND
EFFICIENCY (%)
VIN
3V TO 5V
Efficiency
65
60
55
50
45
40
35
3491 TA04a
0
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK316BJ105ML
L1: MURATA LQH32CN100
2
4
3491 TA04b
Li-Ion Driver for Five White LEDs
Efficiency
80
SHUTDOWN AND
DIMMING CONTROL
70
C1
1µF
CAP
RSENSE
10Ω
LT3491
SW
LED
C2
1µF
GND
EFFICIENCY (%)
VIN
L1
10µH
VIN = 3.6V
5 LEDs
75
CTRL
VIN
3V TO 5V
6 8 10 12 14 16 18 20
LED CURRENT (mA)
65
60
55
50
45
40
35
0
3491 TA05a
2
4
6 8 10 12 14 16 18 20
LED CURRENT (mA)
3491 TA05b
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK316BJ105ML
L1: MURATA LQH32CN100
3491fa
14
LT3491
U
PACKAGE DESCRIPTIO
SC8 Package
8-Lead Plastic SC70
(Reference LTC DWG # 05-08-1639 Rev Ø)
0.30
MAX
0.50
REF
PIN 8
1.80 – 2.20
(NOTE 4)
1.00 REF
INDEX AREA
(NOTE 6)
1.80 – 2.40 1.15 – 1.35
(NOTE 4)
2.8 BSC 1.8 REF
PIN 1
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.10 – 0.40
0.15 – 0.27
8 PLCS (NOTE 3)
0.50 BSC
0.80 – 1.00
0.00 – 0.10
REF
1.00 MAX
GAUGE PLANE
0.15 BSC
0.26 – 0.46
SC8 SC70 0905 REV Ø
0.10 – 0.18
(NOTE 3)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. DETAILS OF THE PIN 1 IDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE INDEX AREA
7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70 AND JEDEC MO-203 VARIATION BA
DC Package
6-Lead DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115
TYP
0.56 ± 0.05
(2 SIDES)
0.675 ±0.05
2.50 ±0.05
1.15 ±0.05 0.61 ±0.05
(2 SIDES)
PACKAGE
OUTLINE
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.38 ± 0.05
4
2.00 ±0.10
(4 SIDES)
PIN 1
CHAMFER OF
EXPOSED PAD
3
0.25 ± 0.05
0.50 BSC
1.42 ±0.05
(2 SIDES)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
6
0.75 ±0.05
1
(DC6) DFN 1103
0.25 ± 0.05
0.50 BSC
1.37 ±0.05
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2)
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
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
3491fa
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT3491
U
TYPICAL APPLICATIO
Li-Ion Driver for Six White LEDs
Efficiency
80
SHUTDOWN AND
DIMMING CONTROL
VIN = 3.6V
6 LEDs
75
CTRL
VIN
L1
10µH
RSENSE
10Ω
LT3491
SW
C1
1µF
70
CAP
EFFICIENCY (%)
VIN
3V TO 5V
LED
GND
C2
1µF
65
60
55
50
45
40
0
5
10
15
20
LED CURRENT (mA)
3491 TA06b
3491 TA06a
C1: TAIYO YUDEN LMK212BJ105MD
C2: TAIYO YUDEN GMK316BJ105ML
L1: MURATA LQH32CN100
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ThinSOT is a trademark of Linear Technology Corporation.
3491fa
16
Linear Technology Corporation
LT 0406 • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2006