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LT3519 LED Driver with Integrated Schottky Diode FEATURES
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DESCRIPTION
The LT(R)3519 are fixed frequency step-up DC/DC converters designed to drive LEDs. They feature an internal 45V, 750mA low side switch and Schottky diode. Combining a traditional voltage feedback and a unique floating current sense feedback allows these converters to operate as a constant-voltage source or constant-current source. Internal compensation simplifies applications. These devices feature floating LED current sense pins that provide the most flexibility in choosing a converter configuration to drive the LEDs. The LED current is externally programmable with a 250mV sense resistor. The external PWM provides up to 3000:1 PWM dimming and the CTRL input provides analog dimming.
L, LT, LTC, LTM, Linear Technology and the Linear logo 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.
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Up to 3000:1 True Color PWMTM Dimming Wide Input Voltage Range Operation from 3V to 30V Transient Protection to 40V Floating LED Current Sense from 0V to 45V 45V, 750mA Internal Switch Internal Schottky Diode Constant-Current and Constant-Voltage Regulation Boost, SEPIC, Buck-Boost Mode or Buck Mode Topology Open LED Protection and Open LED Status Pin Programmable Undervoltage Lockout with Hysteresis Fixed Frequency: 400kHz (LT3519) Internal Compensation CTRL Pin Provides Analog Dimming Low Shutdown Current: <1A 16-Lead MSOP Package
APPLICATIONS
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Automotive Industrial Constant Current Source Current Limited Constant Voltage Source
TYPICAL APPLICATION
4W Boost Automotive LED Driver
VIN 6V TO 30V 68H 1F SW ANODE CATHODE ISP VIN 1M 100k 1M 243k VREF CTRL 137k OPENLED GND SHDN/UVLO LT3519 FB 29.4k ISN 1M 38V LED 100mA 2.5
LED Current vs VIN
VOUT 4.7F 100 LED CURRENT (mA) 80 60 40 20 0 PWM M1 PWM
3519 TA01a
120
VIN = 6V AND ABOVE
0
10 VIN (V)
20
30
3519 TA01b
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LT3519 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW GND OPENLED PWM SHDN/UVLO VIN SW ANODE GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 GND VREF CTRL FB ISN ISP CATHODE GND
VIN, OPENLED (Note 3) .............................................40V SHDN/UVLO (Note 4) ...............................................40V SW, ISP , ISN, ANODE, CATHODE ..............................45V PWM, CTRL ..............................................................10V FB, VREF ......................................................................3V Operating Ambient Temperature Range (Note 2).................................................. -40C to 125C Maximum Junction Temperature........................... 125C Storage Temperature Range................... -65C to 125C
MS PACKAGE 16-LEAD PLASTIC MSOP TJMAX = 125C, JA = 130C/W
ORDER INFORMATION
LEAD FREE FINISH LT3519EMS#PBF LT3519IMS#PBF TAPE AND REEL LT3519EMS#TRPBF LT3519IMS#TRPBF PART MARKING* 3519 3519 PACKAGE DESCRIPTION 16-Lead Plastic MSOP 16-Lead Plastic MSOP TEMPERATURE RANGE -40C to 125C -40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER VIN Operating Voltage Range VIN Supply Current
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, SHDN/UVLO = 12V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS Continuous Operation (Note 3) SHDN/UVLO = 0V (Shutdown) PWM = 0V (Idle) PWM > 1.5V, FB = 1.5V (Active, Not Switching) ISP = 24V, CTRL = 2V ISP = 0V, CTRL = 2V ISP = 24V, CTRL = 100mV 2.5V < ISP < 45V 400kHz (LT3519) 400kHz (LT3519)
l l l
MIN 3
TYP 0.1 2.0 2.5
MAX 30
UNITS V A mA mA
Current Sense Voltage (VISP-VISN) Zero Current Sense Voltage (VISP-VISN) Current Sense Voltage Line Regulation Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT
240 -12 320 94 750
250 250 -6 0.02 400 97 980 300
260 0 440 1150
mV mV mV %/V kHz % mA mV
ISW = 500mA
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LT3519 ELECTRICAL CHARACTERISTICS
PARAMETER Switch Leakage Current CTRL for Full-Scale LED Current CTRL Pin Bias Current PWM Input High Voltage PWM Input Low Voltage PWM Pin Resistance to GND FB Regulation Voltage (VFB) FB Pin Threshold Voltage for OPENLED Falling FB Pin Bias Current ISP , ISN Idle Input Bias Current ISP , ISN Full-Scale Input Bias Current Schottky Forward Drop Schottky Leakage Current SHDN/UVLO Threshold Voltage Falling SHDN/UVLO Input Low Voltage SHDN/UVLO Pin Bias Current Low SHDN/UVLO Pin Bias Current High VREF Output Voltage VREF Output Pin Regulation OPENLED Output Low (VOL) OPENLED Leakage Current IVIN Drops Below 1A SHDN/UVLO = 1.15V SHDN/UVLO = 1.30V -100A IVREF 0A 3V < VIN < 40V IOPENLED = 1mA FB = 0V, OPENLED = 40V
l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 12V, SHDN/UVLO = 12V, CTRL = 2V, PWM = 5V, unless otherwise noted.
CONDITIONS SW = 45V, PWM = 0V 1.2 Current Out of Pin, CTRL = 0.1V 1.5 0.4 70 1.190 1.220 VFB - 60mV Current Out of Pin, FB = 1V PWM = 0V ISP = ISN = 24V ISCHOTTKY = 500mA CATHODE = 24V, ANODE = 0V
l
MIN
TYP
MAX 2
UNITS A V nA V V k V V nA A A V
50
100
1.250 120 1
60 17 0.8
4 1.180 1.8 1.96 1.220 2.2 10 2 1.270 0.4 2.6 100 2.04 0.04 240 1
A V V A nA V %/V mV A
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 LT3519E is guaranteed to meet specified performance from 0C to 125C. Specifications over the -40C to 125C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3519I is guaranteed
to meet performance specifications over the -40C to 125C operating temperature range. Note 3. Absolute maximum voltage at VIN and OPENLED is 40V for nonrepetitive one second transients and 30V for continuous operation. Note 4. For VIN below 6V, the SHDN/UVLO pin must not exceed VIN for proper operation.
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LT3519 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25C unless otherwise noted)
VISP-VISN Threshold vs VCTRL
300 250 VISP-VISN THRESHOLD (mV) 200 150 100 50 0 -50 0 0.5 1.0 VCTRL (V)
3519 G01
Switch Current Limit vs Duty Cycle
1200 1100 1000 900 800 700 600 0 25 50 75 DUTY CYCLE (%) 100
3519 G02
VREF Voltage vs Temperature
2.04 2.03 2.02 VREF (V) 2.01 2.00 1.99 1.98 1.97 1.96 -50 -25 50 75 0 25 TEMPERATURE (C) 100 125 VIN = 12V
VIN = 12V VISP = 24V SWITCH CURRENT LIMIT (mA) 1.5 2.0
3519 G03
VISP-VISN Threshold vs Temperature
260 258 VISP-VISN THREHSOLD (mV) 256 254 252 250 248 246 244 242 240 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 VIN = 12V VISP = 24V VCTRL = 2V 1200 SWITCH CURRENT LIMIT (mA) 1100 1000 900 800 700
Switch Current Limit vs Temperature
VIN = 12V 420 410 FREQUENCY (kHz) -25 75 0 50 25 TEMPERATURE (C) 100 125 400 390 380 370
Oscillator Frequency vs Temperature
600 -50
360 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
3519
3519 G04
3519 G05
VISP-VISN Threshold vs VISP
260 258 VISP-VISN THRESHOLD (mV) 256 VIN = 12V VCTRL = 2V 2.04 2.03 2.02
VREF Voltage vs VIN
3.0 2.5 VIN CURRENT (mA) 2.0 1.5 1.0 0.5 0
Quiescent Current vs VIN
254 VREF (V) 252 250 248 246 244 242 240 0 10 30 20 VISP (V) 40 50
3519 G07
2.01 2.00 1.99 1.98 1.97 1.96 0 5 10 15 20 VIN (V)
3519 G08
VPWM = 5V VFB = 1.5V 0 10 20 VIN (V) 30 40
3519 G09
25
30
35
40
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LT3519 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25C unless otherwise noted)
FB Regulation Voltage vs Temperature
1.25 VIN = 12V 100 90 80 VFB-VFB_OPENLED (mV) 70 60 50 40 30 20 10 1.20 -50 -25 50 25 75 0 TEMPERATURE (C) 100 125 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 1.20 -50 -25 50 25 75 0 TEMPERATURE (C) 100 125
FB OPENLED Threshold vs Temperature
VIN = 12V SHDN/UVLO THRESHLD (V) 1.30
SHDN/UVLO Threshold vs Temperature
VIN = 12V
1.24 1.23 VFB (V)
1.28 SHDN/UVLO RISING 1.26
1.22
1.24
SHDN/UVLO FALLING
1.21
1.22
3519 G10
3519 G11
3519 G12
Switch Saturation Voltage (VCESAT)
500 SCHOTTKY LEAKAGE CURRENT (A) 450 400 SWITCH VOLTAGE (V) 350 300 250 200 150 100 50 0 0 200 600 800 400 SWITCH CURRENT (mA) 1000
3519 G13
Schottky Leakage Current vs Temperature
10 9 8 7 6 5 4 3 2 1 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 VR = 24V SCHOTTKY FORWARD CURRENT (mA) 900 800 700 600 500 400 300 200 100 0
Schottky Forward Voltage Drop
0
1000 800 200 600 400 SCHOTTKY FORWARD VOLTAGE DROP (mV)
3519 15
3519 G14
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LT3519 PIN FUNCTIONS
GND (Pins 1, 8, 9, 16): Power Ground and Signal Ground. Tie to GND plane for best thermal performance. OPENLED (Pin 2): Open LED Status Pin. The OPENLED pin asserts if the FB input is greater than the FB regulation threshold minus 60mV (typical). The pin must have an external pull-up resistor to function. When the PWM input is low and the converter is idle, the OPENLED condition is latched to the last valid state when the PWM input was high. When the PWM input goes high again, the OPENLED pin will be updated. This pin may be used to report an open LED fault. PWM (Pin 3): Pulse Width Modulated Input. A signal low disables the oscillator and turns off the main switch. PWM has an internal pull-down resistor. Tie PWM pin to VREF if not used. SHDN/UVLO (Pin 4): Shutdown and Undervoltage Lockout Pin. An accurate 1.22V falling threshold with externally programmable hysteresis detects when power is okay to enable switching. Rising hysteresis is generated by the external resistor divider and an accurate internal 2A pulldown current. Above the 1.25V (nominal) rising threshold (but below 6V), SHDN/UVLO input bias current is sub-A. Below the falling threshold, a 2A pull-down current is enabled so the user can define the hysteresis with external resistor selection. Tie to 0.4V or less to disable device and reduce VIN quiescent current below 1A. Pin may be tied to VIN, but do not tie it to a voltage higher than VIN if VIN is less than 6V. VIN (Pin 5): Input Supply Pin. This pin must be locally bypassed with a 1F ceramic capacitor (or larger) placed close to it. SW (Pin 6): Switch Pin. Connect the inductor at this pin. Minimize the trace at this pin to reduce EMI. ANODE (Pin 7): Internal Schottky Anode Pin. CATHODE (Pin 10): Internal Schottky Cathode Pin. ISP (Pin 11): Current Sense Resistor Positive Pin. This input is the noninverting input of the internal current sense amplifier. ISN (Pin 12): Current Sense Resistor Negative Pin. This input is the inverting input of the internal current sense amplifier. FB (Pin 13): Voltage Loop Feedback Pin. It is used to connect to output resistor divider for constant voltage regulation or open LED protection. The internal transconductance amplifier will regulate FB to 1.22V (nominal) through the DC/DC converter. If the FB input is regulating the loop, the OPENLED pull-down is asserted. This action may signal an open LED fault. Do not leave the FB pin open. If not used, connect to GND. CTRL (Pin 14): Current Sense Threshold Voltage Adjustment Pin. This pin sets the threshold voltage across the sense resistor between ISP and ISN. Connect directly to the VREF pin or a voltage above 1.2V for full-scale threshold of 250mV, or use a voltage between 0.1V and 1.2V to linearly adjust the threshold. Tie CTRL pin to the VREF pin if not used. VREF (Pin 15): Reference Output Pin. Typically 2V. This pin can supply up to 100A.
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LT3519 BLOCK DIAGRAM
LED ARRAY RSENSE COUT L1 VIN PWM 11 ISP 12 ISN 3 PWM 10 CATHODE D1 VIN 5 7 ANODE 6 SW
+
4
-
100mV
-+
1.2V 14 CTRL
A3 1.22V R1 13 R2 VIN 4 SHDN/UVLO 2A 1.22V Q3 FB
A2
ERROR AMPLIFIER
CC
-
+ -
G4
BANDGAP AND BIAS RAMP GENERATOR FB VIN 100A OSCILLATOR 1.16V
15
VREF
A6 2V
Q2
+
+
+
RC
-
+ + -
A1
CIN
+
A4 PWM COMPARATOR G1 R S Q G2
G3 MAIN SWITCH DRIVER Q1 MAIN SWITCH
+
A5 RS
-
GND 1, 8, 9, 16
+ -
OPENLED Q4
2
+
3519 BD
-
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LT3519 OPERATION
The LT3519 are constant frequency, current mode regulators with an internal power switch and Schottky. Operation can be best understood by referring to the Block Diagram. At the start of each oscillator cycle, the SR latch is set, which turns on the Q1 power switch. 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, A4. When this voltage exceeds the level at the negative input of A4, the SR latch is reset, turning off the power switch. The level at the negative input of A4 is set by the error amplifier A3. A3 has two inputs, one from the voltage feedback loop and the other one from the current loop. Whichever feedback input is lower takes precedence to set the VC node voltage, and forces the converter into either a constant-current or a constant-voltage mode. The LT3519 are designed to transition cleanly between these two modes of operation. The current sense amplifier senses the voltage across RSENSE and provides an x4 pre-gain to amplifier A1. The output of A1 is simply an amplified version of the difference between the voltage across RSENSE and the lower of VCTRL or 1.1V. In this manner, the error amplifier sets the correct peak switch current level to regulate the current through RSENSE. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. The current regulated in RSENSE can be adjusted by changing the input voltage VCTRL. The FB voltage loop is implemented by the amplifier A2. When the voltage loop dominates, The VC node voltage is set by the amplified difference of the internal reference of 1.22V and the FB pin. If FB voltage is lower than the reference voltage, the switch current will increase; if FB voltage is higher than the reference voltage, the switch demand current will decrease. The LED current sense feedback interacts with the FB voltage feedback so that FB will not exceed the internal reference and the voltage between ISP and ISN will not exceed the threshold set by the CTRL pin. For accurate current or voltage regulation, it is necessary to be sure that under normal operating conditions the appropriate loop is dominant. To deactivate the voltage loop entirely, FB can be connected to GND. To deactivate the LED current loop entirely, the ISP and ISN should be tied together and the CTRL input tied to VREF . When the FB input exceeds a voltage about 60mV lower than the FB regulation voltage, the pull-down driver on the OPENLED pin is activated. This function provides a status indicator that the load may be disconnected and the constant-voltage feedback loop is taking control of the switching regulator. Dimming of the LED array is accomplished by pulsing the current using the PWM pin. When the PWM pin is low, switching is disabled and the error amplifier is turned off so that it does not drive the VC node. Also, all internal loads on the VC node are disabled so that the charge state of the VC node will be saved on the internal compensation capacitor. This feature reduces transient recovery time. When the PWM input again transitions high, the demand current for the switch returns to the value just before PWM last transitioned low. To further reduce transient recovery time, an external MOSFET should be used to disconnect the LED array current loop when PWM is low, stopping COUT from discharging.
APPLICATIONS INFORMATION
Dimming Control There are two methods to control the current source for dimming using the LT3519. The first method, PWM Dimming, uses the PWM pin to modulate the current source between zero and full current to achieve a precisely programmed average current. To make this method of current control more accurate, the switch demand current is stored on the internal VC node during the quiescent phase when PWM is low. This feature minimizes recovery time when the PWM signal goes high. To obtain best PWM dimming performance, it is necessary to use an external disconnect switch in the LED current path to prevent the output capacitor from discharging during the PWM signal low phase. For best product of analog and PWM dimming, the minimum PWM low or high time should be at least six switching cycles. Maximum PWM period is
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LT3519 APPLICATIONS INFORMATION
determined by the system. The maximum PWM dimming ratio (PWMRATIO) can be calculated from the maximum PWM period (tMAX) and the minimum PWM pulse width (tMIN) as follows: PWMRATIO = Example: tMAX = 9ms, tMIN = 3s PWMRATIO = 9ms = 3000 : 1 3s tMAX tMIN When VCTRL is more than 1V but less than 1.2V, the LED current is in the nonlinear region of VISP-VISN Threshold vs VCTRL as shown in the Typical Performance Characteristics. The LED current programming feature through the CTRL pin possibly increases the total dimming range by a factor of ten. In order to have the accurate LED current, precision resistors are preferred (1% is recommended). The CTRL pin should not be left open. Tie to VREF if not used. Programming Output Voltage (Constant Voltage Regulation) or Open LED/Overvoltage Threshold For a boost application, the output voltage can be set by selecting the values of R1 and R2 (see Figure 1) according to the following equation: VOUT = R1 +1 * 1.22V R2
The second method of dimming control, Analog Dimming, uses the CTRL pin to linearly adjust the current sense threshold during the PWM high state. When the CTRL pin voltage is less than 1V but more than 100mV, the LED current is: ILED = VCTRL - 100mV 4 * RSENSE
When VCTRL is higher than 1.2V, the LED current is clamped to be: ILED = 250mV RSENSE
For open LED protection of a boost type LED driver, set the resistor from the output to the FB pin such that the expected VFB during normal operation will not exceed 1.1V. For a buck mode or buck-boost mode LED driver, the output voltage is typically level-shifted to a signal with respect to GND as illustrated in Figure 2. The open LED voltage level can be expressed as: VOUT = VBE(Q1) + R1 * 1.22V R2
+
RSENSE(EXT)
OUT
VOUT R1 LT3519 FB R2
3519 F01
R1 V
-
Q1 LT3519 FB R2
3519 F02
100k
LED ARRAY
Figure 1. FB Resistor Divider for Boost LED Driver
Figure 2. Open LED Protection FB Resistor Connector for Buck Mode or Buck-Boost Mode LED Driver
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LT3519 APPLICATIONS INFORMATION
Programming the Turn-On and Turn-Off Thresholds with the SHDN/UVLO Pin The falling SHDN/UVLO value can be accurately set by the resistor divider. A small 2A pull-down current is active when SHDN/UVLO is below the 1.22V threshold. The purpose of this current is to allow the user to program the rising hysteresis. The following equations should be used to determine the values of the resistors: R1+ R2 VIN(FALLING) = * 1.22V R2 VIN(RISING) = 2A * R1+ VIN(FALLING)
VIN R1 LT3519 SHDN/UVLO R2
3519 F03
Table 1. Recommended Inductor Vendors
VENDOR Sumida Toko Cooper Vishay PHONE (408)321-9660 (408)432-8281 (561)998-4100 (402)563-6866 WEB www.sumida.com www.toko.com www.cooperet.com www.vishay.com
Input Capacitor Selection For proper operation, it is necessary to place a bypass capacitor to GND close to the VIN pin of the LT3519. A 1F or greater capacitor with low ESR should be used. A ceramic capacitor is usually the best choice. In the buck mode configuration, the capacitor at the input to the power converter has large pulsed currents. For best reliability, this capacitor should have low ESR and ESL and have an adequate ripple current rating. A 2.2F ceramic type capacitor is usually sufficient for LT3519. Output Capacitor Selection The selection of output capacitor depends on the load and converter configuration, i.e., step-up or step-down and the operating frequency. For LED applications, the equivalent resistance of the LED is typically low, and the output filter capacitor should be sized to attenuate the current ripple. To achieve the same LED ripple current, the required filter capacitor value is larger in the boost and buck-boost mode applications than that in the buck mode applications. Lower operating frequencies will require proportionately higher capacitor values. For LED buck mode applications, a 1F ceramic capacitor is usually sufficient. For the LED boost and buck-boost mode applications, a 2.2F ceramic capacitor is usually sufficient. Very high performance PWM dimming applications may require a larger capacitor value to support the LED voltage during PWM transitions. Use only ceramic capacitors with X7R, X5R or better dielectric as they are best for temperature and DC bias stability of the capacitor value. All ceramic capacitors exhibit loss
Figure 3. SHDN/UVLO Threshold Programming
Inductor Selection The inductor used with the LT3519 should have a saturation current rating of 1A or greater. For buck mode LED drivers, the inductor value should be chosen to give a ripple current 150mA or more. In the buck mode, the inductor value can be estimated using the formula: L (H) = DBUCK = DBUCK * ( VIN - VLED ) H * A * MHz fOSC (MHz) * 0.15A V VLED VIN
VLED is the voltage across the LED string, VIN is the input voltage to the converter, and fOSC is the switching frequency. In the boost configuration, the inductor can be estimated using the formula: L (H) = DBOOST * VIN H * A * MHz fOSC (MHz) * 0.15A V
DBOOST =
( VLED - VIN )
VLED
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LT3519 APPLICATIONS INFORMATION
of capacitance value with increasing DC voltage bias, so it may be necessary to choose a higher value capacitor to get the required capacitance at the operation voltage. Always check that the voltage rating of the capacitor is sufficient.
Table 2. Recommended Ceramic Capacitor Vendors
VENDOR TDK Kemet Murata Taiyo Yuden PHONE (516)535-2600 (408)986-0424 (814)237-1431 (408)573-4150 WEB www.tdk.com www.kemet.com www.murata.com www.t-yuden.com
Schottky diode to charge the output capacitor. The selection of inductor and capacitor value should ensure the peak of the inrush current to below 5A. In addition, the LT3519 turn-on should be delayed until the inrush current is less than the maximum current limit. Board Layout 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 (see Figure 4) is essential. Minimize the length and area of all traces connected to the switching node pin (SW). Keep the sense voltage pins (ISP and ISN) away from the switching node. The bypass capacitor on the VIN supply to the LT3519 should be placed as close as possible to the VIN pin and GND. Likewise, place COUT next to the CATHODE pin. Do not extensively route high impedance signals such as FB and CTRL, as they may pick up switching noise. Figure 5 shows the recommended component placement.
Open LED Detection The LT3519 provide an open-collector status pin, OPENLED, that pulls low when the FB pin is within ~60mV of its 1.22V regulated voltage. If the open LED clamp voltage is programmed correctly using the FB pin, then the FB pin should never exceed 1.1V when LEDs are connected, therefore, the only way for the FB pin to be within 60mV of the 1.22V regulation voltage is for an open LED event to have occurred. Inrush Current The LT3519 have a built-in Schottky diode for a boost converter. When supply voltage is applied to VIN pin, the voltage difference between VIN and VOUT generates inrush current flowing from input through the inductor and the
* * * * * * * * L1 CIN
GND GND VREF OPENLED PWM CTRL SHDN/UVLO FB VIN ISN ISP SW ANODE CATHODE GND GND
* * * * * * * * COUT
RS
L1
SW
D1
VOUT
VIN
GND
VOUT
3519 F05
+
VIN LOAD
Figure 5. Suggested Layout
3519 F04
Figure 4. High Frequency Path
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LT3519 TYPICAL APPLICATIONS
4W Boost Automotive LED Driver
L1 68H C1 1F SW ANODE CATHODE VIN ISP 1M 100k 1M 243k VREF CTRL 137k OPENLED GND SHDN/UVLO LT3519 FB 29.4k ISN 1M 38V LED 100mA RSENSE 2.5 VOUT C2 4.7F
VIN 6V TO 30V
PWM M1 5V
3519 TA02a
C1: TDK C3216X7R1H105K PWM C2: MURATA GRM32ER71H475KA88 L1: COILTRONICS DR74-680-R M1: VISHAY SILICONIX Si2328DS RSENSE: STACKPOLE ELECTRONICS RHC 2512 2.49 NOTE: VIN = 8.2V RISING TURN ON VIN = 6.2V FALLING UVLO VIN > 10V FULL LED CURRENT AND FOLDBACK BELOW VOUT 42.7V OVERVOLTAGE PROTECTION
1000:1 PWM Dimming at 120Hz
94 PWM 5V/DIV ILED 0.1A/DIV IL 0.3A/DIV
Efficiency vs VIN
92 EFFICIENCY (%) VIN = 12V 2s/DIV
3519 TA02b
90
88
86
84
6
10
14
18 VIN (V)
22
26
30
3519 TA02c
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LT3519 TYPICAL APPLICATIONS
Buck-Boost Mode 150mA LED Driver
16V LED 150mA RSENSE 1.67 L1 47H VIN 6V TO 24V C1 1F 1M VOUT C2 1F
VIN SHDN/UVLO
SW ANODE ISN ISP 357k 10k Q1 C3 4.7F
100k 1M 210k
243k
VREF PWM CTRL
LT3519
CATHODE
OPENLED C1: TDK C3216X7R1H105K C2: TDK C3216X7R1H105K C3: TDK C3216X7R1E475K L1: COILTRONICS DR73-470-R Q1: DIODES FMMT 555 PNP GND
FB 24.3k
3519 TA03a
NOTE: VIN = 8.2V RISING TURN ON VIN = 6.2V FALLING UVLO VIN > 7V FULL LED CURRENT AND FOLDBACK BELOW VOUT - VIN 18.5V OVERVOLTAGE PROTECTION
Waveform for Open LED
82 ILED 0.1A/DIV VOUT 10V/DIV OPENLED 10V/DIV VIN = 12V 50s/DIV
3519 TA03b
Efficiency vs VIN
80 78 EFFICIENCY (%) 76 74 72 70 68 66 6 9 12 15 VIN (V) 18 21 24
3519 TA03c
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LT3519 TYPICAL APPLICATIONS
Buck Mode 500mA LED Driver
VIN 12V TO 30V (UP TO 40V TRANSIENT)
C1 4.7F 1M SHDN
1M
VIN CATHODE ISP SHDN/UVLO CTRL LT3519 VREF OPENLED ISN M1 Q2 9V LED 500mA 1k 10k VOUT L1 47H SW ANODE GND PWM PWM FB 14.7k 5V
3519 TA04a
RSENSE 0.5
100k
191k
1.5k C2 10F
130k
C1: MURATA GRM32ER71H475KA88 C2: TDK C3216X7R1C106M Q1: DIODES FMMT 555 PNP Q2: DIODES FMMT 494 NPN L1: COILTRONICS DR73-470-R M1: VISHAY SILICONIX Si2337DS
Q1
Waveforms for Open LED
92 ILED 0.5A/DIV VIN-VOUT 10V/DIV OPENLED 10V/DIV VIN = 15V 25s/DIV
3519 TA04b
Efficiency vs VIN
90 EFFICIENCY (%) 88 86 84 82 80 10 14 18 22 VIN (V) 26 30
3519 TA04C
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LT3519 PACKAGE DESCRIPTION
MS Package 16-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1669 Rev O)
0.889 (.035
0.127 .005)
5.23 (.206) MIN
3.20 - 3.45 (.126 - .136)
0.305 0.038 (.0120 .0015) TYP
0.50 (.0197) BSC
4.039 0.102 (.159 .004) (NOTE 3) 16151413121110 9
RECOMMENDED SOLDER PAD LAYOUT
0.280 0.076 (.011 .003) REF
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP
4.90 0.152 (.193 .006)
3.00 0.102 (.118 .004) (NOTE 4)
0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) SEATING PLANE
12345678 1.10 (.043) MAX
0.86 (.034) REF
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.17 -0.27 (.007 - .011) TYP
0.50 (.0197) BSC
0.1016 (.004
0.0508 .002)
MSOP (MS16) 1107 REV O
3519f
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
LT3519 TYPICAL APPLICATIONS
SEPIC 150mA LED Driver
L1A 68H VIN 4V TO 24V C1 1F C3 2.2F L1B 68H
*
*
SW ANODE CATHODE ISP VIN VOUT C2 4.7F RSENSE 1.67 SHDN/UVLO ISN 1M FB 69.8k OPENLED GND 16V LED 150mA LT3519 C1: TDK C3216X7R1H105K C2: TDK C3216X7R1E475K C3: TDK C3216X7R1E225K L1: COILTRONICS DRQ74-680-R (COUPLED INDUCTOR) M1: VISHAY SILICONIX Si2328DS NOTE: VIN = 6V RISING TURN ON VIN = 4V FALLING UVLO VIN > 9V FULL LED CURRENT AND FOLDBACK BELOW VOUT 18.5V OVERVOLTAGE PROTECTION
1M 100k 1M 432k VREF CTRL 158k
PWM M1 PWM 5V
3519 TA05a
Waveforms for LED Shorted to Ground
88 IL1A+IL1B 0.2A/DIV EFFICIENCY (%) ILED 0.1A/DIV ILED_SHORTED 0.5A/DIV VIN = 12V 50s/DIV
3519 TA05b
Efficiency vs VIN
86 84 82 80 78 76 74 4 8 12 16 20 24
3519 TA05c
VIN (V)
RELATED PARTS
PART NUMBER LT1618 DESCRIPTION Constant-Current, Constant-Voltage 1.24MHz, High Efficiency Boost Regulator LT3466/LT3466-1 Dual Full Function, 2MHz Diodes White LED Step-Up Converter with Built-In Schottkys LT3486 Dual 1.3A White LED Converter with 1000:1 True Color PWM Dimming LT3491 2.3MHz White LED Driver with Integrated Schottky Diode LT3497 LT3517 LT3518 LT3591 Dual Full Function 2.3MHz LED Driver with 250:1 True Color PWM Dimming with Integrated Schottky Diodes Full-Featured LED Driver with 1.5A Switch Current Full-Featured LED Driver with 2.3A Switch Current Constant-Current, 1MHz, High Efficiency White LED Step-Up Converter with Built-in Schottkys COMMENTS Up to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ= 1.8mA, ISD < 1A, MS 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 Drives Up to 6 LEDs. VIN: 2.5V to 12V, VOUT(MAX) = 27V, SC70/DFN Packages Drives Up to 12 LEDs. VIN: 2.5V to 10V, VOUT(MAX) = 32V, 3mm x 2mm DFN Package VIN: 3V to 40V, VOUT(MAX) = 45V, Dimming = 5.000:1 True Color PWM, ISD < 1A, 4mm x 4mm QFN and TSSOP Packages VIN: 3V to 40V, VOUT(MAX) = 45V, Dimming = 3.000:1 True Color PWM, ISD < 1A, 4mm x 4mm QFN and TSSOP Packages Up to 10 White LEDs, VIN: 2.5V to 12V, VOUT(MAX) = 45V, 3mm x 2mm DFN Package
3519f
ThinSOT is a trademark of Linear Technology Corporation.
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0809 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2009

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