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LT3496 Triple Output LED Driver FEATURES
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DESCRIPTION
The LT(R)3496 is a triple output DC/DC converter designed to operate as a constant-current source and is ideal for driving LEDs. The LT3496 works in buck, boost or buckboost mode. The LT3496 uses a fixed frequency, current mode architecture resulting in stable operation over a wide range of supply and output voltages. A frequency adjust pin allows the user to program switching frequency between 330kHz and 2.1MHz to optimize efficiency and external component size. The LT3496 supports 3000:1 dimming control on each channel. Each of the three regulators is independently operated by that channel's PWM signal. The PWM feature allows precise adjustment of the color mixing or dimming ratio of the LED source. Each of the three channels has a built-in gate driver to drive an external LED-disconnect P-channel MOSFET, allowing high dimming range. The output current range of each channel of the LT3496 is programmed with an external sense resistor. The CTRL pin is used to adjust the LED current either for analog dimming or overtemperature protection.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 7199560, 7321203, and others pending.
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True Color PWMTM Dimming Delivers Up to 3000:1 Dimming Ratio Built-In Gate Driver for PMOS LED Disconnect Three Independent Driver Channels with 750mA, 45V Internal Switches Operates in Buck, Boost, Buck-Boost Modes CTRL Pin Accurately Sets LED Current Sense Threshold Over a Range of 10mV to 100mV Adjustable Frequency: 330kHz to 2.1MHz Open LED Protection Wide Input Voltage Range: Operation from 3V to 30V Transient Protection to 40V Surface Mount Components 28-Lead (4mm x 5mm) QFN and TSSOP Packages
APPLICATIONS
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RGB Lighting Billboards and Large Displays Automotive and Avionic Lighting Constant-Current Sources
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TYPICAL APPLICATION
High Dimming Ratio Triple Output LED Power Supply
PVIN 42V CAP1 200m LED1 TG1 TG2 CAP2 200m LED2 CAP3 200m LED3 TG3 PWM 5V/DIV 7 LEDs 0.5A 0.47F 0.47F 0.5A 0.5A 0.47F IL 0.5A/DIV 1F 3
3000:1 PWM Dimming at 120Hz
18H
18H
18H
ILED 0.5A/DIV
3496 TA01b
0.5s/DIV SW1 CAP1-3 LED1-3 VIN PWM1-3 SHDN SW2 LT3496 GND SW3 TG1-3 VC1-3 VREF CTRL1-3 FADJ OVP1-3
VIN 3V TO 24V 1F
22k 470pF
PWM1-3 SHDN
3496 TA01a
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LT3496 ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN (Note 4) ...............................................................40V SW1-SW3, LED1-LED3, CAP1-CAP3 ........................45V TG1-TG3 ............................................ CAP - 10V to CAP PWM1-PWM3 ...........................................................20V VREF, CTRL1-CTRL3, FADJ, VC1-VC3, OVP1-OVP3 .2.5V
SHDN (Note 4) ...........................................................VIN Operating Junction Temperature Range (Note 2).................................................. -40C to 125C Max Junction Temperature.................................... 125C Storage Temperature Range................... -65C to 150C
PIN CONFIGURATION
TOP VIEW SHDN PWM3 PWM2 PWM1 VREF CTRL3 CTRL2 CTRL1 FADJ 1 2 3 4 5 6 7 8 9 29 28 VIN PWM2 27 TG3 26 LED3 25 CAP3 24 SW3 23 SW2 22 CAP2 21 LED2 20 TG2 19 SW1 18 CAP1 17 LED1 16 TG1 15 OVP1 PWM1 1 VREF 2 CTRL3 3 CTRL2 4 CTRL1 5 FADJ 6 VC3 7 VC2 8 9 10 11 12 13 14 TG1 OVP3 OVP2 OVP1 LED1 VC1 29 TOP VIEW PWM3 SHDN LED3 22 CAP3 21 SW3 20 SW2 19 CAP2 18 LED2 17 TG2 16 SW1 15 CAP1 TG3 VIN
28 27 26 25 24 23
VC3 10 VC2 11 VC1 12 OVP3 13 OVP2 14
FE PACKAGE 28-LEAD PLASTIC TSSOP TJMAX = 125C, JA = 25C/W, JC = 10C/W EXPOSED www..com PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
UFD PACKAGE 28-LEAD (4mm 5mm) PLASTIC QFN TJMAX = 125C, JA = 43C/W, JC = 2.7C/W EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT3496EFE#PBF LT3496IFE#PBF LT3496EUFD#PBF LT3496IUFD#PBF TAPE AND REEL LT3496EFE#TRPBF LT3496IFE#TRPBF LT3496EUFD#TRPBF LT3496IUFD#TRPBF PART MARKING* 3496FE 3496FE 3496 3496 PACKAGE DESCRIPTION 28-Lead Plastic TSSOP 28-Lead Plastic TSSOP 28-Lead (4mm x 5mm) Plastic QFN 28-Lead (4mm x 5mm) Plastic QFN TEMPERATURE RANGE -40C to 125C -40C to 125C -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/
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LT3496 ELECTRICAL CHARACTERISTICS
PARAMETER VIN Operation Voltage VIN Undervoltage Lockout Full-Scale LED Current Sense Voltage One-Tenth Scale LED Current Sense Voltage CAPn/LEDn Operating Voltage VREF Output Voltage VREF Line Regulation Quiescent Current in Shutdown Quiescent Current Idle Quiescent Current Active (Not Switching) Switching Frequency IREF = 200A, Current Out of Pin 3V VIN 40V, IREF = 10A SHDN = 0V PWM1-PWM3 = 0V VC1-VC3 = 0V FADJ = 1.5V FADJ = 0.5V FADJ = 0.1V FADJ = 1.5V (2.1MHz) FADJ = 0.5V (1.3MHz) FADJ = 0.1V (330kHz) Current Out of Pin, CTRL1-3 = 0.1V Current Out of Pin, FADJ = 0.1V Current Out of Pin, OVP1-3 = 0.1V 0.95 PWM1-3 = 0V CAP1-3 = 24V CAP1-3 = 24V (Note 3) ISW = 500mA (Note 3) SHDN = 0V, SW = 5V 180 PWM1-3 = 0V SHDN = 0V 750 -20
l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 5V, VSHDN = 5V, CAP1-3 = 5V, PWM1-3 = 5V, FADJ = 0.5V, CTRL1-3 = 1.5V, OVP1-3 = 0V, unless otherwise noted.
CONDITIONS (Note 4) CAP1-3 = 24V CTRL1-3 = 100mV, CAP1-3 = 24V MIN 3 2.1
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TYP
MAX 30 2.4 103 104 12.5 45 2.04 0.03 10 7.5 14 2300
UNITS V V mV mV mV V V %/V A mA mA kHz kHz kHz % % %
98 97 7.5 2.5 1.96
100 10 2 0.1 6 11
1900
2100 1300 330 78 87 97 20 20 10 1 0 4.5 200 1000 260
Maximum Duty Cycle
70
CTRL1-3 Input Bias Current FADJ Input Bias Current OVP1-3 Input Bias Current OVP1-3 Threshold VC1-3 Idle Input Bias Current VC1-3 Output Impedance EAMP gm (IVC/VCAP-LED)
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100 100 100 1.05 20
nA nA nA V nA M S
SW1-3 Current Limit SW1-3 VCESAT
1250 2 250 1 1
mA mV A A A A
SW1-3 Leakage Current CAP1-3 Input Bias Current CAP1-3, LED1-3 Idle Input Bias Current CAP1-3, LED1-3 Input Bias Current in Shutdown
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LT3496 ELECTRICAL CHARACTERISTICS
PARAMETER SHDN Input Low Voltage SHDN Input High Voltage SHDN Pin Current PWM1-3 Input Low Voltage PWM1-3 Input High Voltage PWM1-3 Pin Current Gate Off Voltage (CAP1-3-TG1-3) Gate On Voltage (CAP1-3-TG1-3) Gate Turn-On Delay Gate Turn-Off Delay Current Into Pin CAP1-3 = 40V, PWM1-3 = 0V CAP1-3 = 40V , CLOAD = 300pF CAP1-3 = 40V (Note 5) , CLOAD = 300pF CAP1-3 = 40V (Note 5) 5.5 1.2 160 0.1 6.5 110 110 210 0.3 7.5 VSHDN = 5V, Current Into Pin 1.5 65 100 0.4
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 5V, VSHDN = 5V, CAP1-3 = 5V, PWM1-3 = 5V, FADJ = 0.5V, CTRL1-3 = 1.5V, OVP1-3 = 0V, unless otherwise noted.
CONDITIONS MIN TYP MAX 0.4 UNITS V V A V V A V V ns ns
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 LT3496E is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3496I is guaranteed over the full -40C to 125C operating junction temperature range.
Note 3: Current flows into pin. Current limit and switch VCESAT is guaranteed by design and/or correlation to static test. Note 4: Absolute maximum voltage at the VIN and SHDN pins is 40V for nonrepetitive 1 second transients, and 30V for continuous operation. Note 5: Gate turn-on/turn-off delay is measured from 50% level of PWM voltage to 90% level of gate on/off voltage.
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LT3496 TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
14 12 INPUT CURRENT (mA) 10 8 6 4 2 0 0 10 VC = GND, NOT SWITCHING 20 VIN (V)
3496 G01
(TA = 25C unless otherwise noted) Switch Current Limit vs Duty Cycle
1000
Switch On Voltage
500 PWM1-3 = 5V SWITCH CURRENT LIMIT (mA) 400 SWITCH VOLTAGE (mV) 800
300
600
PWM1-3 = 0V
200
400
100
200
30
40
0
0 0 200 600 800 400 SWITCH CURRENT (mA) 1000
3496 G02
0
20
60 40 DUTY CYCLE (%)
80
100
3496 G03
Switch Current Limit vs Temperature
1200 1000 CURRENT LIMIT (mA) 800 VREF (V) 600 400 200 2.04 2.03 2.02 2.01 2.00 1.99 1.98 1.97 50 25 75 0 TEMPERATURE (C) 100 125
Reference Voltage vs Temperature
2250 2000 SWITCH FREQUENCY (kHz) 1750
Switch Frequency vs FADJ
1500
1250 1000 750 500 250
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0 -50 -25
1.96 -50 -25
0
75 50 25 TEMPERATURE (C)
100
150
0 0 0.2 0.4 0.6 0.8 FADJ (V) 1.0 1.2
3496 G06
3496 G04
3496 G05
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LT3496 TYPICAL PERFORMANCE CHARACTERISTICS
Switch Frequency vs Temperature
2.4 FADJ = 1.2V 2.3 SWITCH FREQUENCY (MHz) 2.2 2.1 2.0 1.9 1.8 -50 -25 VCAP-LED THRESHOLD (mV) 100 80 60 40 20 0 50 25 75 0 TEMPERATURE (C) 100 125 VCAP-LED TRHESHOLD (mV) 120 VCAP = 24V 102 101 100 99 98 97 0 0.2 0.4 0.6 0.8 CTRL (V) 1 1.2
3496 G08
(TA = 25C unless otherwise noted)
VCAP-LED Threshold vs CTRL
103
VCAP-LED Threshold vs VCAP
CTRL = 1.2V
0
10
20 30 VCAP (V)
40
50
3496 G09
3496 G07
VCAP-LED Threshold vs Temperature
103 102 101 100 40V 99 98 TG 30V CTRL = 1.2V VCAP = 24V 5V PWM 0V
PMOS Turn On Waveforms
PMOS Turn Off Waveforms
VCAP-LED THRESHOLD (mV)
5V PWM 0V
40V TG 30V
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97 -50 -25 50 25 75 0 TEMPERATURE (C) 100 125 VCAP = 40V 200ns/DIV
3496 G11
VCAP = 40V
200ns/DIV
3496 G12
3496 G10
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LT3496 PIN FUNCTIONS
PWM1, PWM2, PWM3: Pulse Width Modulated Input. Signal low turns off the respective converter, reduces quiescent supply current and causes the VC pin for that converter to become high impedance. PWM pin must not be left floating; tie to VREF if not used. VREF: Reference Output Pin. Can supply up to 200A. The nominal Output Voltage is 2V. CTRL1, CTRL2, CTRL3: LED Current Adjustment Pins. Sets voltage across external sense resistor between CAP and LED pins of the respective converter. Setting CTRL voltage to be less than 1V will control the current sense voltage to be one-tenth of CTRL voltage. If CTRL voltage is higher than 1V, the default current sense voltage is 100mV. The CTRL pin must not be left floating. FADJ: Switching Frequency Adjustment Pin. Setting FADJ voltage to be less than 1V will adjust switching frequency up to 2.1MHz. If FADJ voltage is higher than 1V, the default switching frequency is 2.1MHz. The FADJ pin must not be left floating. VC1, VC2, VC3: Error Amplifier Compensation Pins. Connect a series RC from these pins to GND. OVP1, OVP2, OVP3: Open LED Protection Pins. A voltage higher than 1V on OVP turns off the internal main switch of the respective converter. Tie to ground if not used.
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PWM pin is low, the TG pin pulls up to CAP to turn off the external MOSFET. When the PWM pin is high, the external MOSFET turns on. CAPn-TGn is limited to 6.5V to protect the MOSFET. Leave open if the external MOSFET is not used. LED1, LED2, LED3: Noninverting Input of Current Sense Error Amplifier. Connect directly to LED current sense resistor terminal for current sensing of the respective converter CAP1, CAP2, CAP3: Inverting Input of Current Sense Error Amplifier. Connect directly to other terminal of LED current sense resistor terminal of the respective converter. SW1, SW2, SW3: Switch Pins. Collector of the internal NPN power switch of the respective converter. Connect to external inductor and anode of external Schottky rectifier of the respective converter. Minimize the metal trace area connected to this pin to minimize electromagnetic interference. VIN: Input Supply Pin. Must be locally bypassed. Powers the internal control circuitry. SHDN: Shutdown Pin. Used to shut down the switching regulator and the internal bias circuits for all three converters. Tie to 1.5V or greater to enable the device. Tie below 0.4V to turn off the device. Exposed Pad: Signal Ground and Power Ground. Solder paddle directly to ground plane.
TG1, TG2, TG3: The Gate Driver Output Pin for Disconnnect P-Channel MOSFET. One for each converter. When the
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LT3496 BLOCK DIAGRAM
D1 C2 VIN C1
+
VSENSE
-
ILED
M1
LED1
L1
RSENSE 0.2
CAP1 R3 OVP1 R4 RC CC PWM1 VC1
LED1
TG1 A7 MOSFET DRIVER
PWM1
SW1
+ +
V1 R1 2k A1
EAMP 1V
-
- -
VC SR LATCH A3 A2 SLOPE R S Q
1V CTRL1
CTRL BUFFER R2 20k
VIN C3
VIN SHDN VREF
INTERNAL REGULATOR AND UVLO
VIN ISRC 200A RAMP GENERATOR
R5
C4
R6
Figure 1. LT3496 Block Diagram Working in Boost Configuration
8
+
2V REFERENCE
-
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A9
Q2
OSCILLATOR
FADJ SHARED COMPONENTS
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+
+ + -
A8
Q3
+
A4 PWM COMPARATOR ISENS2 A10
-
A6 NPN DRIVER A5 Q1
+ -
GND
REPLICATED FOR EACH CHANNEL
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LT3496 APPLICATIONS INFORMATION
Operation The LT3496 uses a fixed 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. The oscillator, ramp generator, reference, internal regulator and UVLO are shared among the three converters. The control circuitry, power switch etc., are replicated for each of the three converters. Figure 1 shows the shared circuits and only converter 1 circuits. If the SHDN pin is tied to ground, the LT3496 is shut down and draws minimal current from VIN. If the SHDN pin exceeds 1.5V, the internal bias circuits turn on. The switching regulators start to operate when their respective PWM signal goes high. The main control loop can be understood by following the operation of converter 1. The start of each oscillator cycle sets the SR latch, A3, and turns on power switch Q1. The signal at the noninverting input (SLOPE node) of the PWM comparator A2 is proportional to the sum of the switch current and oscillator ramp. When SLOPE exceeds VC (the output of the error amplifier A1), A2 resets the latch and turns off the power switch Q1 through A4 and A5. In this manner, A10 and A2 set the correct peak current level to keep the output in regulation. Amplifier A8 has two noninverting inputs, one from the 1V internal www..com and the other one from the CTRL1 pin. voltage reference Whichever input is lower takes precedence. A8, Q3 and R1 force V1, the voltage across R1, to be one tenth of either 1V or the voltage of CTRL1 pin, whichever is lower. VSENSE is the voltage across the sensing resistor, RSENSE, which is connected in series with the LEDs. VSENSE is compared to V1 by A1. If VSENSE is higher than V1, the output of A1 will decrease, thus reducing the amount of current delivered to LEDs. In this manner the current sensing voltage VSENSE is regulated to V1. Converters 2 and 3 are identical to converter 1. PWM Dimming Control LED1 can be dimmed with pulse width modulation using the PWM1 pin and an external P-channel MOSFET, M1. If the PWM1 pin is pulled high, M1 is turned on by internal driver A7 and converter 1 operates nominally. A7 limits CAP1-TG1 to 6.5V to protect the gate of M1. If the PWM1 pin is pulled low, Q1 is turned off. Converter 1 stops operating, M1 is turned off, disconnects LED1 and stops current draw from output capacitor C2. The VC1 pin is also disconnected from the internal circuitry and draws minimal current from the compensation capacitor CC. The VC1 pin and the output capacitor store the state of the LED1 current until PWM1 is pulled up again. This leads to a highly linear relationship between pulse width and output light, and allows for a large and accurate dimming range. A P-channel MOSFET with smaller total gate charge (QG) improves the dimming performance, since it can be turned on and off faster. Use a MOSFET with a QG lower than 10nC, and a minimum VTH of -1V to -2V. Don't use a Low VTH PMOS. To optimize the PWM control of all the three channels, the rising edge of all the three PWM signals should be synchronized. In the applications where high dimming ratio is not required, M1 can be omitted to reduce cost. In these conditions, TG1 should be left open. The PWM dimming range can be further increased by using CTRL1 pin to linearly adjust the current sense threshold during the PWM1 high state. Loop Compensation Loop compensation determines the stability and transient performance. The LT3496 uses current mode control to regulate the output, which simplifies loop compensation. To compensate the feedback loop of the LT3496, a series resistor-capacitor network should be connected from the VC pin to GND. For most applications, the compensation capacitor should be in the range of 100pF to 1nF The com. pensation resistor is usually in the range of 5k to 50k. To obtain the best performance, tradeoffs should be made in the compensation network design. A higher value of compensation capacitor improves the stability and dimming range (a larger capacitance helps hold the VC voltage when the PWM signal is low). However, a large compensation capacitor also increases the start-up time and the time to recover from a fault condition. Similarly, a larger compensation resistor improves the transient response but may reduce the phase margin. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance. The stability, PWM
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LT3496 APPLICATIONS INFORMATION
dimming waveforms and the start-up time should be checked across all operating conditions. Open-LED Protection The LT3496 has open-LED protection for all the three converters. As shown in Figure 1, the OVP1 pin receives the output voltage (the voltage across the output capacitor) feedback signal from an external resistor divider. OVP1 voltage is compared with a 1V internal voltage reference by comparator A6. In the event the LED string is disconnected or fails open, converter 1 output voltage will increase, causing OVP1 voltage to increase. When OVP1 voltage exceeds 1V, the power switch Q1 will turn off, and cause the output voltage to decrease. Eventually, OVP1 will be regulated to 1V and the output voltage will be limited. In the event one of the converters has an open-LED protection, the other converters will continue functioning properly. Switching Frequency and Soft-Start The LT3496 switching frequency is controlled by FADJ pin voltage. Setting FADJ voltage to be less than 1V will reduce switching frequency. If FADJ voltage is higher than 1V, the default switching frequency is 2.1MHz. In general, a lower switching frequency should be used where either very high or very low switch duty www..com cycle is required or higher efficiency is desired. Selection of a higher switching frequency will allow use of low value external components and yield a smaller solution size and profile. Connecting FADJ pin to a lowpass filter (R5 and C4 in Figure 1) from the REF pin provides a soft-start function. During start-up, FADJ voltage increases slowly from 0V to the setting voltage. As a result, the switching frequency increases slowly to the setting frequency. This function limits the inrush current during start-up. Undervoltage Lockout The LT3496 has an undervoltage lockout circuit that shuts down all the three converters when the input voltage drops below 2.4V. This prevents the converter from switching in an erratic mode when powered from a low supply voltage. Input Capacitor Selection For proper operation, it is necessary to place a bypass capacitor to GND close to the VIN pin of the LT3496. 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 PVIN has large pulsed currents due to the current returned though the Schottky diode when the switch is off. For the best reliability, this capacitor should have low ESR and ESL and have an adequate ripple current rating. The RMS input current is: IIN(RMS) =ILED *
(1- D) * D
where D is the switch duty cycle. A 1F ceramic type capacitor placed close to the Schottky diode and the ground plane is usually sufficient for each channel. Output Capacitor Selection The selection of output filter capacitor depends on the load and converter configuration, i.e., step-up or step-down. For LED applications, the equivalent resistance of the LED is typically low, and the output filter capacitor should be large enough 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. For the LED buck mode applications, a 0.22F ceramic capacitor is usually sufficient for each channel. For the LED boost and buck-boost applications, a 1F ceramic capacitor is usually sufficient for each channel. If higher LED current ripple can be tolerated, a lower output capacitance can be selected to reduce the capacitor's cost and size. Use only ceramic capacitors with X7R or X5R dielectric, as they are good for temperature and DC bias stability of the capacitor value. All ceramic capacitors exhibit loss 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 1 shows some recommended capacitor vendors.
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LT3496 APPLICATIONS INFORMATION
Table 1. Ceramic Capacitor Manufacturers
VENDOR Taiyo Yuden AVX Murata Kemet TYPE Ceramic Ceramic Ceramic Ceramic SERIES X5R, X7R X5R, X7R X5R, X7R X5R, X7R CDRH3D16 PART NUMBER Sumida CMD4D06 2.2 3.3 2.2 3.3 4.7 CDRH4D28 CDRH5D28 CooperET SD3112 2.2 3.3 4.7 SD14 SD20 SD25 Tayio Yuden NR3015 NP04SZB 2.2 4.7 4.7 10 15 22 0.06 0.12 0.075 0.100 0.180 0.210 1.48 1.02 1.6 1.2 0.95 0.77 4.0 x 4.0 x 1.8 3.0 x 3.0 x 1.5 10 15 22 33 0.140 0.165 0.246 0.2058 0.1655 0.2053 0.2149 0.97 0.90 0.74 1.1 1.25 1.12 1.11 5.0 x 5.0 x 2.5 5.0 x 5.0 x 1.4 5.0 x 5.0 x 2.0 3.1 x 3.1 x 1.2 10 15 22 33 0.116 0.174 0.072 0.085 0.105 0.128 0.149 0.122 0.189 0.95 0.77 1.20 1.10 0.90 1.00 0.76 0.9 0.75 6.0 x 6.0 x 3.0 5.0 x 5.0 x 3.0 3.8 x 3.8 x 1.8 3.5 x 4.3 x 0.8
Table 2. Surface Mount Inductors
VALUE (H) DCR ( MAX) IRMS (A) SIZE W x L x H (mm3)
Inductor Selection Several inductors that work well with the LT3496 are listed in Table 2. However, there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and their entire range of parts. Ferrite core inductors should be used to obtain the best efficiency. Choose an inductor that can handle the necessary peak current without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to minimize I2R power losses. An inductor with a magnetic shield should be used to prevent noise radiation and cross coupling among the three channels. Diode Selection The Schottky diode conducts current during the interval when the switch is turned off. Select a diode VR rated for the maximum SW voltage. It is not necessary that the forward current rating of the diode equal the switch current limit. The www..com average current, IF , through the diode is a function of the switch duty cycle. Select a diode with forward current rating of: IF = IL * (1 - D) where IL is the inductor current. If using the PWM feature for dimming, it is important to consider diode leakage, which increases with the temperature from the output during the PWM low interval. Therefore, choose the Schottky diode with sufficient low leakage current. Table 3 shows several Schottky diodes that work well with the LT3496.
Table 3. Schottky Diodes
PART NUMBER ZETEX ZLLS350 ZLLS400 40 40 0.38 0.52 SOD523 SOD323 VR (V) IF (A) PACKAGE
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LT3496 APPLICATIONS INFORMATION
Programming the LED Current The LED current of each channel is programmed by connecting an external sense resistor RSENSE in series with the LED load, and setting the voltage regulation threshold across that sense resistor using CTRL input. If the CTRL voltage, VCTRL, is less than 1V, the LED current is: ILED = VCTRL 10 * RSENSE voltages to ensure that a junction temperature of 125C is not exceeded. This is especially important when operating at high ambient temperatures. The Exposed Pad on the bottom of the package must be soldered to a ground plane. This ground should then be connected to an internal copper ground plane with thermal vias placed directly under the package to spread out the heat dissipated by the LT3496. Board Layout The high speed operation of the LT3496 demands careful attention to board layout and component placement. The Exposed Pad of the package is the only GND terminal of the IC and is important for thermal management of the IC. Therefore, it is crucial to achieve a good electrical and thermal contact between the Exposed Pad and the ground plane of the board. Also, in boost configuration, the Schottky rectifier and the capacitor between GND and the cathode of the Schottky are in the high frequency switching path where current flow is discontinuous. These elements should be placed so as to minimize the path between SW and the GND of the IC. To reduce electromagnetic interference (EMI), it is important to minimize the area of the SW node. Use the GND plane under SW to minimize interplane coupling to sensitive signals. To obtain good current regulation accuracy and eliminate sources of channel to channel coupling, the CAP and LED inputs of each channel of the LT3496 should be run as separate lines back to the terminals of the sense resistor. Any resistance in series with CAP and LED inputs should be minimized. Finally, the bypass capacitor on the VIN supply to the LT3496 should be placed as close as possible to the VIN terminal of the device.
If VCTRL is higher than 1V, the LED current is: ILED = 100mV RSENSE
The CTRL pins should not be left open. The CTRL pin can also be used in conjunction with a PTC thermistor to provide overtemperature protection for the LED load as shown in Figure 2.
VREF 45k 2V 50k CTRL1-3
5k PTC
3496 F02
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Figure 2
Thermal Considerations The LT3496 is rated to a maximum input voltage of 30V for continuous operation, and 40V for nonrepetitive one second transients. Careful attention must be paid to the internal power dissipation of the LT3496 at higher input
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LT3496 TYPICAL APPLICATIONS
Minimum BOM Buck Mode LED Driver
PVIN 42V CAP1 330m LED1 CAP2 330m LED2 CAP3 330m LED3 C1-C3 1F 3
7 LEDs
0.3A C4 C5 0.22F 0.22F
0.3A
0.3A C6 0.22F
L1 15H
D1
D2
L2 15H
L3 15H
D3
VIN 3V C7 1F
PWM1-3 SHDN
SW1 CAP1-3 LED1-3 VIN PWM1-3 SHDN
SW2 LT3496 GND
SW3
TG1-3 VC1-3 VREF CTRL1-3 FADJ OVP1-3
OPEN 22k 470pF
3496 TA07a
C1-C3, C7: MURATA GRM31MR71H105KA88 C4-C6: MURATA GRM21BR71H224KA01 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 150M
300:1 PWM Dimming at 120Hz
100 PWM 5V/DIV
Efficiency
PWM = 3V CTRL = 0V TO 1.2V 95 EFFICIENCY (%)
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IL 0.5A/DIV ILED 0.5A/DIV 5s/DIV
3496 TA07b
90
85
80
75
0
50
100
150 200 ILED (mA)
250
300
3496 TA07c
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13
LT3496 TYPICAL APPLICATIONS
Triple Boost 100mA x 10 LED Driver
PVIN 12V L1 10H C1 2.2F
L2 10H
L3 10H
D1 C2 1F CAP1 1 LED1 TG1 M1 TG2 C3 1F
D2 CAP2 1 LED2 M2 TG3 C4 1F
D3 CAP3 1 LED3 M3
825k 10 LEDs 100mA OVP1 20k 10 LEDs 100mA
825k OVP2 20k 10 LEDs 100mA
825k OVP3 20k
VIN 3V C5 1F
PWM1-3 SHDN
SW1 CAP1-3 LED1-3 VIN PWM1-3 SHDN C1: MURATA GRM31MR71C225KA35 C2-C5: MURATA GRM31MR71H105KA88 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1-M3: ZETEX ZXMP6A13F
SW2 LT3496 GND
SW3
TG1-3 OVP1-3 VC1-3 VREF FADJ CTRL1-3
10k 470pF
3496 TA03a
3000:1 PWM Dimming at 120Hz
95 PWM 5V/DIV 90 85 EFFICIENCY (%) 80 75 70 65 60 55 0.5s/DIV
3496 TA03b
Efficiency vs PWM Duty Cycle
CTRL = 2V
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IL 0.5A/DIV ILED 0.1A/DIV
50 0 20 80 60 40 PWM DUTY CYCLE (%) 100
3496 TA03d
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14
LT3496 TYPICAL APPLICATIONS
Dual Boost LED Driver
PVIN 12V L1 10H C1 2.2F
L2 10H
L3 10H
D1 C2 1F CAP1 1 LED1 C3 1F
D2 CAP2 1 LED2 C4 1F
D3 CAP3 1 LED3
M1
M2
825k 10 LEDs 100mA OVP1 20k 10 LEDs 200mA
825k OVP2-3 20k
SW1 TG1 CAP1-3 LED1-3 VIN PWM1-3 SHDN C1: MURATA GRM31MR71C225KA35 C2-C5: MURATA GRM31MR71H105KA88 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1, M2: ZETEX ZXMP6A13F
SW2 LT3496 GND
SW3 TG2
VIN 3V TO 12V C5 1F
PWM SHDN
OVP1-3 TG3 VC1-3 VREF FADJ CTRL1-3
OPEN 10k 470pF
3496 TA04
Triple Boost 20mA x 8 LED Driver
PVIN 5V C1 2.2F
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L1 22H
L2 22H
L3 22H
D1 C2 1F CAP1 5 LED1 TG1 M1 TG2 C3 1F
D2 CAP2 5 LED2 M2 TG3 C4 1F
D3 CAP3 5 LED3 M3
825k 8 LEDs 20mA OVP1 20k 8 LEDs 20mA
825k OVP2 20k 8 LEDs 20mA
825k OVP3 20k
VIN 5V C5 1F
PWM1-3 SHDN
SW1 CAP1-3 LED1-3 VIN PWM1-3 SHDN C1: MURATA GRM31MR71C225KA35 C2-C5: MURATA GRM31MR71H105KA88 D1-D3: ZETEX ZLLS350 L1-L3: TAIYO YUDEN NP04SZB 220M M1-M3: ZETEX ZXMP6A13F
SW2 LT3496
SW3
TG1-3 OVP1-3 VC1-3 VREF CTRL1-3 FADJ
82k
10k 470pF
GND
20k
3496 TA08a
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15
LT3496 TYPICAL APPLICATIONS
Buck-Boost Mode 300mA x 6 LED Driver
PVIN 10V TO 16V C1 2.2F 300mA L1 10H L2 10H L3 10H M1 LED1 1 CAP1 D1 LED2 1 CAP2 D2 D3 LED3 1 CAP3 825k OVP1-3 20k 6 LEDs
C2 0.1F PVIN SW1 VIN 3V TO 16V C8 1F CAP1-3 LED1-3 VIN PWM1-3 SHDN
C3 1F
C4 0.1F PVIN SW2 LT3496 GND
C5 1F
C6 0.1F PVIN SW3 TG1 OVP1-3 TG2-3 VC1-3 VREF FADJ CTRL1-3
C7 1F
OPEN 10k 470pF
3496 TA05
PWM SHDN
C1: MURATA GRM31MR71E225KA93 C2, C4, C6: MURATA GRM21BR71H104KA01B C3, C5, C7: MURATA GRM31MR71H105KA88 C8: MURATA GRM31MR71E105KA93 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1: ZETEX ZXMP6A13F
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16
LT3496 TYPICAL APPLICATIONS
Triple Buck Mode LED Driver with Open LED Protection
PVIN 12V TO 40V CAP1 200m LED1 TG1 M1 TG2 M2 CAP2 200m LED2 M3 CAP3 200m LED3 TG3 C1-C3 1F 3
20k 0.5A C4 0.47F C5 0.47F 0.5A
20k
20k 0.5A C6 0.47F
5.6k M4 OVP1 2k L1 10H
5.6k M5 M6 OVP2 OVP1 2k 2k L2 10H
5.6k L3 10H
D1
D2
D3
VIN 3V TO 24V C7 1F
PWM1-3 SHDN
SW1 CAP1-3 LED1-3 VIN PWM1-3 SHDN
SW2 LT3496 GND
SW3
TG1-3 OVP1-3 VC1-3 VREF FADJ CTRL1-3
22k 470pF
3496 TA02
C1-C3, C7: MURATA GRM31MR71H105KA88 C4-C6: MURATA GRM188R71C474KA88 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1-M3: ZETEX ZXMP6A13F M4-M6: PHILIPS BC858B
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17
LT3496 PACKAGE DESCRIPTION
FE Package 28-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation EB
4.75 (.187) 9.60 - 9.80* (.378 - .386) 4.75 (.187) 28 2726 25 24 23 22 21 20 19 18 1716 15 6.60 0.10 4.50 0.10
SEE NOTE 4
2.74 (.108) 0.45 0.05 1.05 0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 0.10
6.40 2.74 (.252 (.108) BSC
1 2 3 4 5 6 7 8 9 10 11 12 13 14 1.20 (.047) MAX
0 -8
4.30 - 4.50* (.169 - .177)
0.25 REF
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
0.65 (.0256) BSC
0.195 - 0.30 (.0077 - .0118) TYP
0.05 - 0.15 (.002 - .006)
FE28 (EB) TSSOP 0204
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE
4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE
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18
LT3496 PACKAGE DESCRIPTION
UFD Package 28-Lead Plastic QFN (4mm x 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70
0.05
4.50
0.05 3.10
0.05 2.50 REF 2.65 0.05 3.65 0.05
PACKAGE OUTLINE
0.25 0.05 0.50 BSC 3.50 REF 4.10 0.05 5.50 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) 0.75 0.05 R = 0.05 TYP
2.50 REF R = 0.115 TYP 27 28
PIN 1 NOTCH R = 0.20 OR 0.35 45 CHAMFER
0.40 1 2
0.10
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5.00 0.10 (2 SIDES)
3.50 REF 3.65 0.10 2.65 0.10
(UFD28) QFN 0506 REV B
0.200 REF 0.00 - 0.05
0.25
0.05
0.50 BSC BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X). 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
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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.
19
LT3496 TYPICAL APPLICATION
Triple Buck-Boost Mode 100mA x 6 LED Driver
PVIN 10V TO 16V C1 2.2F 100mA L1 10H 6 LEDs L2 10H 100mA 6 LEDs L3 10H 100mA 6 LEDs
3000:1 PWM Dimming at 120Hz
TG3 M3 3.9M OVP3 100k IL 0.5A/DIV C7 1F PVIN ILED 0.1A/DIV PWM 5V/DIV
TG1
M1 3.9M OVP1 100k
TG2
M2 3.9M OVP2 100k
LED1 1 CAP1 D1 C2 0.1F
LED2 1 CAP2 D2 C4 0.1F
LED3 1 CAP3 D3 C6 0.1F
C3 1F PVIN
C5 1F PVIN
VIN 3V TO 16V C8 1F
PWM SHDN
SW1 CAP1-3 LED1-3 VIN PWM1-3 SHDN
SW2 LT3496 GND
SW3
TG1-3 OVP1-3 VC1-3 VREF FADJ CTRL1-3
0.5s/DIV
3496 TA06b
10k 470pF
3496 TA06
C1: MURATA GRM31MR71E225KA93 C2, C4, C6: MURATA GRM21BR71H104KA01B C3, C5, C7: MURATA GRM31MR71H105KA88 C8: MURATA GRM31MR71E105KA93 D1-D3: DIODES DFLS160 L1-L3: TAIYO YUDEN NP04SZB 100M M1-M3: ZETEX ZXMP6A13F
RELATED PARTS
PART NUMBER LT1618
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DESCRIPTION Constant Current, 1.4MHz, 1.5A Boost Converter 1MHz, 800mA Synchronous Buck-Boost High Power LED Driver Dual Constant Current, 2MHz, High Efficiency White LED Boost Regulator with Integrated Schottky Diode 1.1A (ISW), 1.3MHz/2.1MHz, High Efficiency Step-Up DC/DC Converters with Integrated Soft-Start Step-Down 1A 2MHz LED Driver Dual Step-Down 1.5A, 2mV LED Driver High Current 2MHz Quad 1.5A Output LED Driver 3A, 42V, 3MHz Step-Up Regulator with Dual Rail-to-Rail Current Sense
COMMENTS VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1A, 10-Pin MS Package VIN: 2.7V to 5.5V, VOUT(MAX) = 5.5V, IQ = 2.5mA, ISD < 6A, QFN Package VIN: 2.7V to 24V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 16A, DFN Package VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1A, ThinSOTTM Package VIN: 4V to 36V, VOUT(MAX) = 15V, IQ = 2.6mA, ISD < 1A, TSSOP Package VIN: 4V to 36V, IQ = 6mA, ISD < 1A, 20-Lead TSSOPE Package VIN: 2.8V to 16V, VOUT(MAX) = 33.5V, IQ = 5.5mA, ISD < 1A, 38-Lead 5mm x 7mm QFN Package VIN: 2.5V to 2.5V, VOUT(MAX) = 40V, IQ = 5mA, ISD < 1A, QFN, 16-Pin TSSOPE Packages
LT3453 LT3466 LT3467/LT3467A LT3474 LT3475 LT3476 LT3477 LT3478/LT3478-1 LT3479
4.5A, 2.25MHz LED Driver with 3000:1 Ture Color PWMTM VIN: 2.8V to 36V, VOUT(MAX) = 40V, IQ = 6.1mA, ISD < 3A, 16-Pin TSSOPE Package Dimming 3A, Full-Featured DC/DC Converter with Soft-Start and Inrush Current Protection VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 6.5mA, ISD < 1A, DFN, TSSOP Packages
ThinSOT and True Color PWM are trademarks of Linear Technology Corporation.
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20 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 1208 REV E * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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