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Final Electrical Specifications
LT3465 White LED Step-Up Converter with Built-In Schottky in ThinSOT
May 2003
FEATURES
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DESCRIPTIO
Inherently Matched LED Current Drives Up to Six LEDs from a 3.6V Supply No External Schottky Diode Required Automatic Soft-Start Open LED Protection High Efficiency: 81% Typical Requires Only 0.22F Output Capacitor Low Profile (1mm) SOT-23 Packaging
The LT(R)3465 is a step-up DC/DC converter designed to drive up to six LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents and eliminates the need for ballast resistors. This device integrates the Schottky diode required externally on competing devices. Additional features include output voltage limiting when LEDs are disconnected, one-pin shutdown and dimming control, and internal soft-start. The LT3465 switches at 1.2MHz, allowing the use of tiny external components. Constant frequency switching results in low input noise and a small output capacitor. Just 0.22F is required for 3-, 4-, 5- or 6-LED applications. The LT3465 is available in a low profile (1mm) 6-lead SOT-23 (ThinSOTTM) package.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
APPLICATIO S
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Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers
TYPICAL APPLICATIO
L1 22H 3V TO 5V
Conversion Efficiency
82 80
SHUTDOWN AND DIMMING CONTROL
C1 1F
VIN LT3465 CTRL GND FB 10
3465 F01a
C2 0.22F
EFFICIENCY (%)
SW
VOUT
78 76 74 72 70
C1, C2: X5R OR X7R DIELECTRIC L1: MURATA LQH32CN220
Figure 1. Li-Ion Powered Driver for Four White LEDs
0
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.
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5 10 LED CURRENT (mA)
3465 F01b
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15
20
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LT3465
ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW VOUT 1 GND 2 FB 3 6 SW 5 VIN 4 CTRL
Input Voltage (VIN) ................................................. 16V SW Voltage ............................................................. 36V FB Voltage ................................................................ 2V CTRL Voltage .......................................................... 10V Operating Temperature Range (Note 2) .. - 40C to 85C Maximum Junction Temperature ......................... 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT3465ES6 S6 PART MARKING LTH2
S6 PACKAGE 6-LEAD PLASTIC TSOT-23
TJMAX = 125C, JA = 256C/W IN FREE AIR JA = 120C ON BOARD OVER GROUND PLANE
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage FB Pin Bias Current Supply Current Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current VCTRL for Full LED Current VCTRL to Shut Down Chip CTRL Pin Bias Current
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3V, VCTRL = 3V, unless otherwise noted.
CONDITIONS MIN 2.7 16 0C TA 85C Not Switching CTRL = 0V
q q
TYP
MAX
UNITS V V mV nA mA A MHz % mA mV
188 10 1.9 2.0 0.8 90 225
200 35 2.6 3.2 1.2 93 340 300 0.01
212 100 3.3 5.0 1.6
ISW = 250mA VSW = 5V 1.8
5 50
TA = 85C TA = -40C Soft-Start Time Schottky Forword Drop Schottky Leakage Current ID = 150mA VR = 30V
48 40 60
60 50 75 600 0.7
72 60 90
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Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3465E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
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A V mV A A A s V A
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LT3465 TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage (VCESAT)
450
SWITCH SATURATION VOLTAGE (mV)
TA = 25C
SCHOTTKY FORWARD CURRENT (mA)
400 350 300 250 200 150 100 50 0 0 50 100 150 200 250 SWITCH CURRENT (mA) 300 350
150 100 50 0
IQ (A)
VFB vs VCTRL
250 TA = 25C
OUTPUT CLAMP VOLTAGE (V)
FEEDBACK VOLTAGE (mV)
200
25 20 15 10 5
INPUT CURRENT (mA)
150
100
50
0
0
1 0.5 1.5 CONTROL VOLTAGE (V)
Switching Waveforms
1.4
SWITCHING FREQUENCY (MHz)
VSW 10V/DIV IL 100mA/DIV VOUT 100mV/DIV
1.0 0.8 0.6 0.4 0.2 0 -50
FEEDBACK VOLTAGE (mV)
VIN = 3.6V 4 LEDs 20mA
0.2s/DIV
UW
3465 G01
Schottky Forward Voltage Drop
300 250 200 TA = 25C
Shutdown Quiescent Current (CTRL = 0V)
30 27 24 21 18 15 12 9 6 3 TA = 25C
0
1000 400 600 800 200 SCHOTTKY FORWARD DROP (mV)
1200
0
2
4
6
10 8 VIN (V)
12
14
16
3465 G03
3465 G02
Open-Circuit Output Clamp Voltage
35 30
Input Current in Output Open Circuit
5 TA = 25C
TA = 25C
4
3
2
1
0
0
2 4 10 8 12 6 INPUT VOLTAGE (V) 14 16
2
3465 G04
2
2.5
4 3.5 3 INPUT VOLTAGE (V)
4.5
5
3465 G06
3465 G05
Switching Frequency
210 208
Feedback Voltage
1.2
206 204 202 200 198 196 194 192
3465 G07
50 0 TEMPERATURE (C)
100
4365 G08
190 -50 -30 -10 10 30 50 TEMPERATURE (C)
70
90
3465 G09
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LT3465 TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current (CTRL = 3V)
3.0 2.5 2.0 CURRENT LIMIT (mA) -50C 25C 100C 0 5 10 VIN (V) 15 20
3465 G10
IQ (mA)
1.5 1.0 0.5 0
VIN = 3.6V, 4 LEDs
85 8
SCHOTTKY LEAKAGE CURRENT (A)
80
EFFICIENCY (%)
75
70
65
60 -50
50 0 TEMPERATURE (C)
PI FU CTIO S
VOUT (Pin 1): Output Pin. Connect to output capacitor and LEDs. Minimize trace between this pin and output capacitor to reduce EMI. GND (Pin 2): Ground Pin. Connect directly to local ground plane. FB (Pin 3): Feedback Pin. Reference voltage is 200mV. Connect LEDs and a resistor at this pin. LED current is determined by the resistance and CTRL pin voltage:
200mV When VCTRL > 1.5V RFB V ILED CTRL When VCTRL < 1V 5 * RFB ILED
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UW
20mA 15mA
Switching Current Limit
400 350 300 250 200 150 100 50 0 0 20 40 60 DUTY CYCLE (%) 80 -50C 25C 100C 100
3465 G11
Schottky Leakage Current
7 VR = 25 6 5 4 3 2 1 0 -50 0 50 100
3465 G13
10mA
VR = 16 VR = 10
100
3465 G12
TEMPERATURE (C)
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CTRL (Pin 4): Dimming Control and Shutdown Pin. Ground this pin to shut down the device. When VCTRL is greater than about 1.5V, full-scale LED current is generated. When VCTRL is less than 1V, LED current is reduced. VIN (Pin 5): Input Supply Pin. Must be locally bypassed with a 1F X5R or X7R type ceramic capacitor. SW (Pin 6): Switch Pin. Connect inductor here.
LT3465
BLOCK DIAGRA
VIN 5
A1 RC CC
10k RAMP GENERATOR 40k
CTRL 4
1.2MHz OSCILLATOR
Figure 2. LT3465 Block Diagram
APPLICATIO S I FOR ATIO
Operation
The LT3465 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 2. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. 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 SR latch is reset turning 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 feedback voltage and the reference voltage of 200mV. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. The CTRL pin voltage is used to adjust the reference voltage.
+
-
VREF 1.25V
200mV
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W
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FB 3 6 SW COMPARATOR DRIVER A2 R S Q Q1
- + +
VOUT 1
+
0.2
-
2 GND
3465 F02
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Minimum Output Current The LT3465 can drive a 3-LED string at 1.5mA LED current without pulse skipping. As current is further reduced, the device will begin skipping pulses. This will result in some low frequency ripple, although the LED current remains regulated on an average basis down to zero. The photo in Figure 3 details circuit operation driving three white LEDs at a 1.5mA load. Peak inductor current is less than 40mA and the regulator operates in
VSW 5V/DIV
IL 20mA/DIV VOUT 10mV/DIV VIN = 4.2V ILED = 1.5mA 3 LEDs 0.2s/DIV
3465 F03
Figure 3. Switching Waveforms
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LT3465
APPLICATIO S I FOR ATIO
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 switch and diode capacitance. This ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. The ringing can be damped by application of a 300 resistor across the inductor, although this will degrade efficiency. Inductor Selection A 22H inductor is recommended for most LT3465 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). Some inductors in this category with small size are listed in Table 1. The efficiency comparison of different inductors is shown in Figure 4.
Table 1. Recommended Inductors
PART NUMBER LQH32CN220 DCR () 0.71 CURRENT RATING (mA) 250 MANUFACTURER Murata 814-237-1431 www.murata.com Panasonic 714-373-7334 www.panasonic.com Sumida 847-956-0666 www.sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.com Taiyo Yuden 408-573-4150 www.t-yuden.com
IIN 50mA/DIV VOUT 5V/DIV VFB 100mV/DIV
EFFICIENCY (%)
ELJPC220KF
4.0
160
CDRH3D16-220
0.53
350
LB2012B220M
1.7
75
LEM2520-220
5.5
125
Capacitor Selection The small size of ceramic capacitors makes them ideal for LT3465 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as
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85 80 75 70 65 60 55 50 0 5 10 LED CURRENT (mA)
3465 F04
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VIN = 3.6V 4 LEDS
MURATA LQH32CN220 TAIYO YUDEN LB2012B220M TAIYO YUDEN CB2012B220 15 20
Figure 4. Efficiency Comparison of Different Inductors
Y5V or Z5U. A 1F input capacitor and a 0.22F output capacitor are sufficient for most LT3465 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER Taiyo Yuden Murata Kemet PHONE 408-573-4150 814-237-1431 408-986-0424 URL www.t-yuden.com www.murata.com www.kemet.com
Soft-Start The LT3465 has an internal soft-start circuit to limit the input current during circuit start-up. The circuit start-up waveforms are shown in Figure 5.
CTRL 5V/DIV VIN = 3.6V 4 LEDs, 20mA L = 22H C = 0.22F 200s/DIV
3465 F05
Figure 5. Start-Up Waveforms
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LT3465
APPLICATIO S I FOR ATIO
Inrush Current The LT3465 has a built-in Schottky diode. When supply voltage is applied to the VIN pin, the voltage difference between VIN and VOUT generates inrush current flowing from input through the inductor and the Schottky diode to charge the output capacitor to VIN. The maximum current the Schottky diode in the LT3465 can sustain is 1A. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1A. The peak inrush current can be calculated as follows:
IP = = = VIN - 0.6 * exp - * tg-1 * sin tg-1 * L*
r + 1.5 2 *L
(r + 1.5) 1 - L *C 4 * L2
2
where L is the inductance, r is the resistance of the inductor and C is the output capacitance. For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: IP = VIN - 0.6 * exp - * 2 L*
Table 3 gives inrush peak currents for some component selections.
Table 3. Inrush Peak Current
VIN (V) 5 5 3.6 5 r () 0.5 0.5 0.5 0.5 L (H) 22 22 22 33 C (F) 0.22 1 0.22 1 IP (A) 0.38 0.70 0.26 0.60
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LED Current and Dimming Control The LED current is controlled by the feedback resistor (R1 in Figure 1) and the feedback reference voltage. ILED = VFB/RFB The CTRL pin controls the feedback reference voltage as shown in the Typical Performance Characteristics. For CTRL higher than 1.8V, the feedback reference is 200mV, which results in full LED current. CTRL pin can be used as dimming control when CTRL voltage is between 200mV to 1.5V. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RFB selection are shown below. RFB = 200mV/ILED-Full
Table 4. RFB Resistor Value Selection
FULL ILED (mA) 5 10 15 20 R1 () 40.0 20.0 13.3 10.0
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(1)
The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to adjust the CTRL voltage source in dimming control. The circuit is shown in Figure 6. The corner frequency of R1 C1 should be lower than the freqency of the PWM signal. R1 needs to be much smaller than the internal impedance in the CTRL pin, which is 50k.
R1 5k PWM C1 100nF LT3465 CTRL
3465 F06
Figure 6. Dimming Control Using a Filtered PWM Signal
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LT3465
APPLICATIO S I FOR ATIO
Open-Circuit Protection The LT3465 has internal open-circuit protection circuit. In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail, the VOUT is clamped at 30V. The LT3465 will then switch at a very low frequency to minimize the input current. VOUT and input current during output open circuit are shown in the Typical Performance Characteristics. Board Layout Consideration
1 6 5 4 VIN CTRL
3465 F07
As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. Place COUT next to the VOUT pin.
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Always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise-free connection. Recommended component placement is shown in Figure 7.
GND COUT L CIN 2 RFB 3
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Figure 7. Recommended Component Placement
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LT3465
TYPICAL APPLICATIO S
Li-Ion to Two White LEDs
L1 22H 3V TO 5V
80 85 VIN = 3.6V 2 LEDS
EFFICIENCY (%)
SW CIN 1F VIN
VOUT COUT 1F FB R1 4
3465 TA01a
LT3465 CTRL GND
CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603ZD105 L: MURATA LQH3C220
L1 22H 3V TO 5V
CIN 1F
VIN LT3465 CTRL GND FB R1 10
COUT 0.22F
EFFICIENCY (%)
SW
VOUT
CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 L: MURATA LQH3C220
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75
70
65
60
0
10
30 20 LED CURRENT (mA)
40
50
3465 TA01b
Li-Ion to Three White LEDs
85 80 75 70 65 60 55 0 5 10 15 LED CURRENT (mA) 20
3465 TA02b
VIN = 3.6V 3 LEDS
3465 TA02a
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LT3465
TYPICAL APPLICATIO S
Li-Ion to Five White LEDs
L1 22H 3V TO 5V
EFFICIENCY (%)
10
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SW CIN 1F VIN
VOUT COUT 0.22F FB R1 10
3465 TA03a
LT3465 CTRL GND
CIN: TAIYO YUDEN JMK107BJ105 COUT: TAIYO YUDEN GMK212BJ224 L: MURATA LQH3C220
85
VIN = 3.6V 5 LEDS
80
75
70
65
60 0 5 10 15 LED CURRENT (mA) 20
3465 TA03b
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LT3465
PACKAGE DESCRIPTIO
0.62 MAX
0.95 REF
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.20 BSC 1.00 MAX DATUM `A'
0.30 - 0.50 REF 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. JEDEC PACKAGE REFERENCE IS MO-193 0.09 - 0.20 (NOTE 3)
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S6 Package 6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID 0.95 BSC 0.30 - 0.45 6 PLCS (NOTE 3) 0.80 - 0.90 0.01 - 0.10 1.90 BSC
S6 TSOT-23 0302
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LT3465
TYPICAL APPLICATIO
L1 47H 3V TO 5V
EFFICIENCY (%)
SW CIN 1F VIN
VOUT COUT 0.47F FB R1 10
3465 TA04a
LT3465 CTRL GND
CIN: TAIYO YUDEN JMK107BJ105 COUT: TDK 2012X7R1E474K L: MURATA LQH32CN470
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
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Li-Ion to Six White LEDs
85 VIN = 3.6V 6 LEDS 80 75 70 65 60 0 5 10 15 LED CURRENT (mA) 20
3465 TA04b
sn3465 3465is LT/TP 0503 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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