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LT3491 White LED Driver with Integrated Schottky in SC70 and 2mm x 2mm DFN DESCRIPTIO
The LT(R)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. 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 x 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.
FEATURES

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 1F Output Capacitor Wide 300:1 True Color PWMTM Dimming Range 8-Lead SC70 Package Low Profile 6-Lead DFN Package (2mm x 2mm x 0.75mm)
APPLICATIO S

Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers
TYPICAL APPLICATIO
Li-Ion Driver for Four White LEDs
SHUTDOWN AND DIMMING CONTROL CTRL EFFICIENCY (%) VIN 3V TO 5V L1 10H SW GND C1 1F VIN LT3491 LED C2 1F CAP RSENSE 10
80 75 70 65 60 55 50 45 40 0
3491 TA01a
VIN = 3.6V 4 LEDs
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100
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Efficiency
10 LED CURRENT (mA)
15
20
3491 TA01b
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LT3491
ABSOLUTE
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RATI GS (Note 1)
12V 32V 32V 12V LED Voltage ............................................................ 32V Operating Temperature Range (Note 2) .. - 40C to 85C Maximum Junction Temperature ......................... 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10sec, SC-70) ......... 300C
Input Voltage (VIN) ................................................. SW Voltage ............................................................. CAP Voltage ............................................................ CTRL Voltage ..........................................................
PACKAGE/ORDER I FOR ATIO
TOP VIEW VIN 1 GND 2 SW 3 7 6 CTRL 5 LED 4 CAP
DC PACKAGE 6-LEAD (2mm x 2mm) PLASTIC DFN
TJMAX = 125C, JA = 102C/W, JC = 20C/ W EXPOSED PAD (PIN 7) SHOULD BE CONNECTED TO PCB GROUND
ORDER PART NUMBER LT3491EDC
DC PART MARKING LCHJ
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 = 25C. VIN = 3V, VCTRL = 3V, unless otherwise specified.
PARAMETER Minimum Operating Voltage LED Current Sense Voltage (VCAP - VLED) CAP, LED Pin Bias Current VCAP, VLED Common Mode Minimum Voltage Supply Current Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current VCTRL for Full LED Current VCTRL to Shut Down IC VCTRL to Turn On IC CTRL Pin Bias Current CAP Pin Overvoltage Protection Schottky Forward Drop Schottky Leakage Current ISCHOTTKY = 100mA VR = 20V

CONDITIONS VCAP = 30V VCAP = 16V, VLED = 16V VCAP = 16V, VLED = 15V, CTRL = 3V CTRL = 0V
ISW = 200mA VSW = 16V VCAP = 30V
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TOP VIEW SW 1 GND 2 GND 3 GND 4 8 CAP 7 LED 6 CTRL 5 VIN
SC8 PACKAGE 8-LEAD PLASTIC SC70
TJMAX = 125C, JA = 270C/ W
ORDER PART NUMBER
DC PART MARKING
LT3491ESC8
LBXQ
MIN 2.5 190
TYP 200 20 2.6 8
MAX 210 40 2.5 4 10 2.8
UNITS V mV A V mA A MHz % mA mV
1.8 88 260
2.3 92 350 200 0.1
5 50
A V mV mV nA
1.5 100 100 26 27 0.8 4 28
V V A
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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 0C to 85C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25C unless otherwise specified)
Switch Saturation Voltage (VCESAT)
350
SWITCH SATURATION VOLTAGE (mV)
SCHOTTKY FORWARD CURRET (mA)
300 250 200 150 100 50 0 0 50 100 150 200 250 300 350 400 SWITCH CURRENT (mA)
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300 250 200 150 100 50 0
SHUTDOWN CURRENT (A)
Sense Voltage (VCAP - VLED) vs VCTRL
240 200
SENSE VOLTAGE (mV)
OUTPUT CLAMP VOLTAGE (V)
INPUT CURRENT (mA)
160 120 80 40 0
0
500
1000 VCTRL (mV)
1500
Switching Waveform
VSW 10V/DIV VCAP 50mV/DIV IL 100mA/DIV VIN = 3.6V 200ns/DIV FRONT PAGE APPLICATION CIRCUIT
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UW
3491 G04
Schottky Forward Voltage Drop
400 350
12 15
Shutdown Current (VCTRL = 0V)
9
6
3
0
0
200
800 1000 600 SCHOTTKY FORWARD DROP (mV)
400
1200
0
3
6 VIN (V)
9
12
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Open-Circuit Output Clamp Voltage
30
6 5 4 3 2 1 0
Input Current in Output Open Circuit
29
28
27
26
25 2000
0
3
6 VIN (V)
9
12
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0
3
6 VIN (V)
9
12
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Transient Response
VCAP 5V/DIV VCTRL 5V/DIV IL 200mA/DIV VIN = 3.6V 1ms/DIV FRONT PAGE APPLICATION CIRCUIT
3491 G08
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LT3491 TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25C unless otherwise specified)
Quiescent Current (VCTRL = 3V)
3.0 2.5
450 400
SCHOTTKY LEAKAGE CURRENT (A)
QUIESCENT CURRENT (mA)
CURRENT LIMIT (mA)
2.0 1.5 1.0 0.5
0 0 3 6 VIN (V) 9 12
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Open-Circuit Output Clamp Voltage vs Temperature
30
OUTPUT CLAMP VOLTAGE (V)
4 3 2 1 0 -50 -25
SWITCH FREQUENCY (MHz)
29
INPUT CURRENT (mA)
28
27
26
25 -50
-25
50 25 0 75 TEMPERATURE (C)
Sense Voltage (VCAP - VLED) vs VCTRL
240 200 SENSE VOLTAGE (mV) 160 120 80 40 0 0 500 1000 VCTRL (mV) 1500 -50C 25C 85C 2000
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SENSE VOLTAGE (mV)
SENSE VOLTAGE (mV)
4
UW
100 125
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Switching Current Limt vs Duty Cycle
15
25C
Schottky Leakage Current vs Temperature
VR = 10V VR = 16V VR = 20V
350 300 250 200 150 100 50 0 30 40 50 60 70 DUTY CYCLE (%) 80 90
12
9
6
3
0 -50
-25
0 25 50 TEMPERATURE (C)
75
100
3491 G11
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Input Current in Output Open Circuit vs Temperature
6 5
2.20
Switching Frequency vs Temperature
VIN = 3V
2.15
2.10
2.05
2.00
50 25 75 0 TEMPERATURE (C)
100
125
1.95 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
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Sense Voltage (VCAP - VLED) vs VCAP
212
212
Sense Voltage (VCAP - VLED) vs Temperature
208
208
204
204
200
200
196
196
192
5
10
15 VCAP (V)
20
25
3491 G16
192 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
3491 G17
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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 :
BLOCK DIAGRA
RAMP GENERATOR VREF 1.25V
SHDN
OSCILLATOR
A1 RC START-UP CONTROL CC
PIN NUMBERS CORRESPOND TO THE 8-PIN SC70 PACKAGE
Figure 1. Block Diagram
+ + -
+
-
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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.
5 VIN PWM COMP DRIVER A2 R S Q
1 SW CAP Q1 OVERVOLTAGE PROTECTION R 8
+
A3
-
+
A = 6.25
-
LED
7
CTRL 6
GND PINS 2, 3, 4
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LT3491
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.
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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
APPLICATIO S I FOR ATIO
INDUCTOR SELECTION A 10H 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 1. Recommended Inductors
L (H) 10 10 10 10 10 10
80 75 70
EFFICIENCY (%)
PART LQH32CN100K53 LQH2MCN100K02 SD3112-100 1001AS-100M (TYPE D312C) CDRH2D11 CDRH2D14
DCR () 0.3 1.2 0.446 0.48 0.5375 0.294
CURRENT RATING (mA) 450 225 550 460 280 700
VENDOR Murata www.murata.com Cooper www.cooperet.com Toko www.toko.com Sumida www.sumida.com
65 60 55 50 45 40 35 30 0 5 VIN = 3.6V 4 LEDs FRONT PAGE APPLICATION CIRCUIT MURATA LQH2MCN100K02 MURATA LQH32CN100K53 TOKO 10001AS-100M SUMIDA CDRH2D11 SUMIDA CDRH2D14 10 15 LED CURRENT (mA) 20
3491 F03
Figure 3. Efficiency Comparison of Different Inductors
CAPACITOR SELECTION 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 1F input capacitor and a 1F output capacitor are sufficient for most applications.
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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 AVX Murata (800) 368-2496 www.t-yuden.com (803) 448-9411 www.avxcorp.com (714) 852-2001 www.murata.com
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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.
IL 200mA/DIV
VCAP 10V/DIV
VIN = 3.6V CIRCUIT OF FRONT PAGE APPLICATION
500s/DIV LEDs DISCONNECTED AT THIS INSTANT
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Figure 4. Output Open-Circuit Waveform
INRUSH CURRENT 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
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 = = = VIN - 0.6 * exp - * 2 L*
r 2 *L 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) 4.2 4.2 4.2 4.2 r () 0.3 1.2 0.58 1.6 L (H) 10 10 15 15 COUT (F) 1.0 1.0 1.0 1.0 IP (A) 1.06 0.86 0.83 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 = 200mV ILED
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Table 4. RSENSE Value Selection for 200mV Sense
ILED (mA) 5 10 15 20 RSENSE () 40 20 13.3 10
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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. 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 ILED
200mV , when VCTRL > 1.5V RSENSE VCTRL , when VCTRL < 1.25V 6.25 * RSENSE 2
Feedback voltage variation versus control voltage is given in the Typical Performance Characteristics.
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LT3491
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 10M (typ).
PWM 10kHz TYP
R1 100k C1 0.1F
LT3491 CTRL
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Figure 5. Dimming Control Using a Filtered PWM Signal
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
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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.
VIN 3V TO 5V L1 10H SW C1 1F GND CTRL LT3491 LED C2 1F VIN CAP RSENSE 10 2.5V 0V PWM FREQ Q1 Si2302 100k
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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
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Figure 7. Direct PWM Dimming Waveforms
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LT3491
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 30s for a 3V input voltage. The achievable dimming range for this application and 100Hz PWM frequency can be determined using the following method. Example: = 100Hz, t SETTLE = 30s tPERIOD = 1 1 = = 0.01s 100
1kHz 10kHz 100Hz
t 0.01s Dim Range = PERIOD = = 300 : 1 t SETTLE 30s Min Duty Cycle = t SETTLE 30s * 100 = * 100 = 0.3% 0 tPERIOD 0.01s
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 30s. 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
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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 20A. 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.
1 10 100 1000
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PWM DIMMING RANGE
Figure 8. Dimming Range Comparison of Three PWM Frequencies
VIN 3V TO 5V L1 10H SW C1 1F GND CTRL PWM FREQ LT3491 LED C2 1F VIN CAP RSENSE 10
2.5V 0V
Q1 Si2302 100k
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Figure 9. Li-Ion to Four White LEDs with Both PWM Dimming and Analog Dimming
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APPLICATIO S I FOR ATIO
LOW INPUT VOLTAGE APPLICATIONS 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. 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.
3.3V C1 0.1F L1 10H SW VIN
2 AA CELLS 2V TO 3.2V
Figure 10. 2 AA Cells to Three White LEDs
CIN CTRL VIN 5 6 LED RSENSE 7 8 COUT CAP GND 4 3 2 1 SW L1 SW RSENSE L1 VIN 1 2 3 GND 7 6 5 4 CAP LED CIN CTRL
GND
(A) SC70 PACKAGE
Figure 11. Recommended Component Placement
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BOARD LAYOUT CONSIDERATIONS 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.
SHUTDOWN AND DIMMING CONTROL CTRL CAP LT3491 LED GND C1 1F RSENSE 10 C2 2.2F
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C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK325BJ225ML L1: MURATA LQH32CN100
COUT
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(B) DFN PACKAGE
11
LT3491
TYPICAL APPLICATIO S
Li-Ion Driver for One White LED
C2 1F RSENSE 10
EFFICIENCY (%)
LED VIN 3V TO 5V L1 10H SW C1 1F GND
3491 TA07a
VIN LT3491
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100
Li-Ion Driver for Two White LEDs
C2 1F RSENSE 10
EFFICIENCY (%)
70 65 60 55 50 45 40 35 30 25 0 5 VIN = 3.6V
LED VIN 3V TO 5V L1 10H SW C1 1F GND
3491 TA08a
VIN LT3491
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100
2-Cell Li-Ion Driver for Torch and Flash Mode LED Control
C2 4.7F VIN 6V TO 9V RSENSE 1 D1 CAP FLASH MODE ILED = 200mA V CTRL 1.5V VCTRL 680mV TORCH MODE ILED = 100mA VIN C1 1F CTRL GND
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EFFICIENCY (%)
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN LMK212BJ475MG D1: AOT-2015 HPW1751B L1: MURATA LQH32CN100
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Efficiency
60 55 50 45 40 35 30 25 VIN = 3.6V
CAP SHUTDOWN AND DIMMING CONTROL
20 15 10 0 5 10 15 LED CURRENT (mA) 20
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CTRL
Efficiency
CAP SHUTDOWN AND DIMMING CONTROL
CTRL
10 LED CURRENT (mA)
15
20
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Efficiency
80 75 70 65 60 55 50 6 6.5 7 7.5 VIN (V) 8 8.5 9 ILED = 100mA
LED L1 10H
LT3491 SW
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LT3491
TYPICAL APPLICATIO S
12V to One White LED at 200mA
C2 4.7F PVIN 12V C3 1F RSENSE 1 D1 CAP VIN 3V SHUTDOWN AND DIMMING CONTROL VIN C1 1F CTRL GND
3491 TA02a
LED L1 15H
EFFICIENCY (%)
LT3491 SW
C1, C3: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN LMK316BJ475ML D1: LUXEON EMITTER LXHL-BWO2 L1: MURATA LQH32CN150
12V to Two White LEDs at 200mA
C2 4.7F PVIN 12V C3 1F RSENSE 1 D1 CAP VIN 3V SHUTDOWN AND DIMMING CONTROL VIN C1 1F CTRL GND
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LED L1 15H
EFFICIENCY (%)
LT3491 SW
C1, C3: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN LMK316BJ475ML D1: LUXEON EMITTER LXHL-BWO2 L1: MURATA LQH32CN150
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Efficiency
80 75 70 65 60 55 50
0 20 40 60 80 100 120 140 160 180 200 LED CURRENT (mA)
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Efficiency
90 85 80 75 70 65 60
0 20 40 60 80 100 120 140 160 180 200 LED CURRENT (mA)
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LT3491
TYPICAL APPLICATIO S
Li-Ion Driver for Three White LEDs
SHUTDOWN AND DIMMING CONTROL CTRL
EFFICIENCY (%)
VIN 3V TO 5V L1 10H C1 1F
VIN LT3491 SW GND
CAP RSENSE 10 LED C2 1F
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100
Li-Ion Driver for Five White LEDs
SHUTDOWN AND DIMMING CONTROL CTRL
L1 10H C1 1F SW
LT3491 LED GND
RSENSE 10 C2 1F
EFFICIENCY (%)
VIN 3V TO 5V
VIN
CAP
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100
14
U
Efficiency
80 75 70 65 60 55 50 45 40
3491 TA04a
VIN = 3.6V 3 LEDs
35 0 2 4 6 8 10 12 14 16 18 20 LED CURRENT (mA)
3491 TA04b
Efficiency
80 75 70 65 60 55 50 45 40 35 0 2 4 6 8 10 12 14 16 18 20 LED CURRENT (mA)
3491 TA05b
VIN = 3.6V 5 LEDs
3491 TA05a
3491fa
LT3491
PACKAGE DESCRIPTIO
0.30 MAX
2.8 BSC 1.8 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.10 - 0.40
GAUGE PLANE 0.15 BSC 0.26 - 0.46
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
2.50 0.05 1.15 0.05 0.61 0.05 (2 SIDES) PACKAGE OUTLINE
0.25 0.05 0.50 BSC 1.42 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
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
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.
U
SC8 Package 8-Lead Plastic SC70
(Reference LTC DWG # 05-08-1639 Rev O)
0.50 REF PIN 8 1.80 - 2.20 (NOTE 4) 1.00 REF 1.80 - 2.40 1.15 - 1.35 (NOTE 4) INDEX AREA (NOTE 6) PIN 1 0.50 BSC 0.15 - 0.27 8 PLCS (NOTE 3) 0.80 - 1.00 0.00 - 0.10 REF 1.00 MAX 0.10 - 0.18 (NOTE 3)
SC8 SC70 0905 REV O
DC Package 6-Lead DFN (2mm x 2mm)
(Reference LTC DWG # 05-08-1703)
R = 0.115 TYP 0.56 0.05 (2 SIDES) 2.00 0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.200 REF 0.75 0.05 1
(DC6) DFN 1103
0.38 0.05 4 6
0.675 0.05
PIN 1 BAR TOP MARK (SEE NOTE 6)
0.25 0.05 0.50 BSC
1.37 0.05 (2 SIDES) 0.00 - 0.05 BOTTOM VIEW--EXPOSED PAD
3491fa
15
LT3491
TYPICAL APPLICATIO
Li-Ion Driver for Six White LEDs
SHUTDOWN AND DIMMING CONTROL CTRL EFFICIENCY (%) VIN 3V TO 5V L1 10H SW C1 1F GND VIN LT3491 LED C2 1F CAP RSENSE 10 80 75 70 65 60 55 50 45 40 0 5 10 LED CURRENT (mA)
3491 TA06b 3491 TA06a
C1: TAIYO YUDEN LMK212BJ105MD C2: TAIYO YUDEN GMK316BJ105ML L1: MURATA LQH32CN100
RELATED PARTS
PART NUMBER LT1618 LT1932 LT1937 LTC(R)3200 LTC3200-5 LTC3201 LTC3202 LTC3205 LT3465/LT3465A LT3466/LT3466-1 LT3486 DESCRIPTION Constant Current, Constant Voltage 1.24MHz, High Efficiency Boost Regulator Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator Low Noise, 2MHz Regulated Charge Pump White LED Driver Low Noise, 2MHz Regulated Charge Pump White LED Driver Low Noise, 1.7MHz Regulated Charge Pump White LED Driver Low Noise, 1.5MHz Regulated Charge Pump White LED Driver High Efficiency, Multidisplay LED Controller Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode Dual Full Function, 2MHz Diodes White LED Step-Up Converter with Built-In Schottkys Dual 1.3A White LED Converter with 1000:1 True Color PWM Dimming COMMENTS Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ = 1.8mA, ISD < 1A, MS Package Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX) = 34V, IQ = 1.2mA, ISD < 1A, ThinSOTTM Package Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1A, ThinSOT/SC70 Packages Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1A, MS Package Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1A, ThinSOT Package Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 6.5mA, ISD < 1A, MS Package Up to 8 White LEDs, VIN: 2.7V to 4.5V, IQ = 5mA, ISD < 1A, MS Package Up to 4 (Main), 2 (Sub) and RGB, VIN: 2.8V to 4.5V, IQ = 50A, ISD < 1A, 24-Lead QFN Package Up to 6 White LEDs, VIN: 2.7V to 16V, VOUT(MAX) = 34V, IQ = 1.9mA, ISD < 1A, ThinSOT Package Up to 20 White LEDs, VIN: 2.7V to 24V, VOUT(MAX) = 39V, DFN, TSSOP-16 Packages Drives Up to 16 100mA White LEDs. VIN: 2.5V to 24V, VOUT(MAX) = 36V, DFN, TSSOP Packages
ThinSOT is a trademark of Linear Technology Corporation.
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
U
Efficiency
VIN = 3.6V 6 LEDs 15 20
3491fa LT 0406 * PRINTED IN THE USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2006

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