LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 350 mA, Constant Current Output Floating Buck Switching Converter for High Power LEDs Check for Samples: LM3407 FEATURES DESCRIPTION • • • • The LM3407 is a constant current output floating buck switching converter designed to provide constant current to high power LEDs. The device is ideal for automotive, industrial and general lighting applications. The LM3407 has an integrated power NMOSFET that makes the application solution compact and simple to implement. An external 1% thick-film resistor allows the converter output voltage to adjust as needed to deliver constant current within 10% accuracy to a serially connected LED string of varying number and type. Converter switching frequency is adjustable from 300 kHz to 1 MHz. The LM3407 features a dimming input to enable LED brightness control by Pulse Width Modulation (PWM). Additionally, a separate enable pin allows for low power shutdown. An exposed pad MSOP-8 PowerPAD package provides excellent heat dissipation and thermal performance. Input UVLO and output open-circuit protection ensure a robust LED driver solution. 1 2 • • • • • • Input operating range 4.5V to 30V Output voltage range: 0.1VIN to 0.9VIN Accurate constant current output Independent device enable (CMOS compatible) and PWM dimming control Converter switching frequency adjustable from 300 kHz to 1 MHz No external control loop compensation required Supports ceramic and low ESR output capacitors Input Under Voltage Lock Out (UVLO) Thermal shutdown protection MSOP-8 PowerPAD Package APPLICATIONS • • • • • LED Driver Constant Current Source Automotive Lighting General Illumination Industrial Lighting TYPICAL APPLICATION 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2008–2013, Texas Instruments Incorporated LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com CONNECTION DIAGRAM Top View 8 1 ISNS LX DIM GND EN VCC 2 7 3 6 EP 4 5 FS VIN Figure 1. 8-Lead Plastic MSOP-8 PowerPAD Package See Package Number DGN0008A PIN DESCRIPTIONS 2 Pin Name Description 1 ISNS LED Current Sense pin Connect resistor RISNS from this pin to ground for LED current sensing. The current sensing resistor should be placed close to this pin. Application Information 2 DIM PWM Dimming Input pin Applying logic level PWM signal to this pin controls the average brightness of the LED string. 3 EN Device Enable pin 4 FS Switching Frequency Setting pin 5 VIN Input Voltage pin 6 VCC Internal Regulator Output pin 7 GND Device Ground pin 8 LX Drain of N-MOSFET Switch EP GND Thermal Pad Applying logic high to this pin or leaving this pin open enables the switcher. When this pin is pulled low, the switcher is disabled and will enter low power shutdown mode. Connect resistor RFS from this pin to ground to set the switching frequency. The input voltage should be in the range of 4.5V to 30V. This output pin should be bypassed by a ceramic capacitor with a minimum value of 1µF. High quality X5R or X7R ceramic capacitor is recommended. This pin should be connected to the system ground. Connect this pin to the output inductor and anode of the Schottky diode. The bottom pad should be connected to ground. For good thermal performance, place 4 to 6 thermal vias from EP to bottom layer PCB ground plane. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. ABSOLUTE MAXIMUM RATINGS (1) If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/Distributors for availability and specifications. VALUE / UNIT VIN to GND -0.3V to 36V VIN to GND (Transient) 42V (500 ms) LX to GND -0.3V to 36V LX to GND (Transient) -3V (2 ns), 42V (500 ms) ISNS, FS, DIM, EN to GND ESD Rating Human Body Model -0.3V to 7V (2) 2kV Junction Temperature 150°C Storage Temperature −65°C to + 125°C Soldering Information (1) (2) Lead Temperature (Soldering, 10sec) 260°C Infrared or Convection (20sec) 235°C Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics. The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. RECOMMENDED OPERATING CONDITIONS VALUE / UNIT VIN 4.5V to 30V −40°C to + 125°C Junction Temperature Range Thermal Resistance (θJA) (1) (1) 50°C/W θJA of 50°C/W with thermal pad, EP soldered to a minimum of 2 square inches of 1 oz. Copper on the top or bottom PCB layer. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 3 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com ELECTRICAL CHARACTERISTICS VIN = 12V unless otherwise indicated. Typical and limits appearing in plain type apply for TA = TJ = 25°C (Note 4). Limits appearing in boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are specified by design, test, or statistical analysis. Parameter Test Conditions Min Typ Max Units 0.58 0.78 0.98 mA 0.20 0.27 0.39 mA µA SYSTEM PARAMETERS IIN Operating Input Current IQ Quiescent Input current 4.5V ≤ VIN ≤ 30V VEN = 5V, VPWM = 5V, LX = open 4.5V ≤ VIN ≤ 30V VEN = 5V, VPWM = 0V ISHUT Shutdown Input Current VEN = 0V 48 60 VUVLO Input Under Voltage Lock-out Threshold VIN Rising 36 3.6 4.5 VUVLO-HYS UVLO Hysteresis VIN Falling 200 VEN_H EN pin HIGH Threshold VEN Rising 1.9 VEN_L EN pin LOW Threshold VEN Falling VDIM_H DIM pin HIGH Threshold VDIM Rising VDIM_L DIM pin LOW Threshold VDIM Falling fSW Switching Frequency 1.3 1.3 2.4 1.75 1.9 V mV V V 2.4 V 1.75 V RT = 80 kΩ 500 kHz RT = 40 kΩ 1000 tON-MIN Minimum On-time 200 ns TSD Thermal Shutdown Threshold 165 °C TSD-HYS Thermal Shutdown Hysteresis 25 °C VIN = 12V 4.5 V Isink = 80mA 0.77 INTERNAL VOLTAGE REGULATOR VCC VCC Regulator Output Voltage (1) N-MOSFET DRIVER RDS(ON) Main Switch ON Resistance 1.45 Ω CONTROL LOOP AEA (1) 4 Error Amp Open Loop Gain 60 dB VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading to the pin. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 TYPICAL PERFORMANCE CHARACTERISTICS Unless otherwise specified, all curves shown are taken in typical application at VIN = 12V, TA = 25°C, and ILED = 350 mA (driving two power LEDs). Output Current vs Input Voltage (TA = -40°C) Output Current vs Input Voltage (TA = 25°C) Figure 2. Figure 3. Output Current vs Input Voltage (TA = 125°C) Efficiency vs Input Voltage (TA = -40°C) Figure 4. Figure 5. Efficiency vs Input Voltage (TA = 25°C) Efficiency vs Input Voltage (TA = 125°C) Figure 6. Figure 7. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 5 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) Unless otherwise specified, all curves shown are taken in typical application at VIN = 12V, TA = 25°C, and ILED = 350 mA (driving two power LEDs). 6 Switch On Time vs Input Voltage Operating Input Current vs Input Voltage Figure 8. Figure 9. VCC Voltage vs Input Voltage Output Current vs RISNS Figure 10. Figure 11. Switching Frequency vs RFS Continuous Mode Operation (VIN = 12V, L = 33µH, fSW = 1MHz) Figure 12. Figure 13. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 TYPICAL PERFORMANCE CHARACTERISTICS (continued) Unless otherwise specified, all curves shown are taken in typical application at VIN = 12V, TA = 25°C, and ILED = 350 mA (driving two power LEDs). Continuous Mode Operation (VIN = 12V, L = 33µH, fSW = 500kHz) Continuous Mode Operation (VIN = 24V, L = 33µH, fSW = 1MHz) Figure 14. Figure 15. Continuous Mode Operation (VIN = 24V, L = 33µH, fSW = 500kHz) DIM Pin Enable Transient (VIN = 12V, L = 33µH, fSW = 1MHz) Figure 16. Figure 17. DIM Pin Disable Transient (VIN = 12V, L = 33µH, fSW = 1MHz) Figure 18. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 7 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com SIMPLIFIED FUNCTIONAL BLOCK DIAGRAM FS VIN VIN VCC regulator Clock Generator + 3.6V - VCC VCC LX SD UVLO 6 DIM Set DIM SWITCH CONTROL Slope Compensation DIM + - 400 k: ISNS Reset PWM Comparator 3.6V EA gm 3.6V 5 PA + EN Q1 Waveform shaping and Average Current Sense SD 198mV + - GND FUNCTIONAL DESCRIPTION OVERVIEW The LM3407 is a constant current output floating buck switching converter with wide input voltage range and low feedback current sense reference voltage. These characteristics make the LM3407 an efficient solution to provide constant current to high power LEDs. The device is ideal for automotive, industrial and general lighting applications where high power LEDs are used as the lighting source. The LM3407 has an integrated power NMOSFET that makes the application solution compact and simple to implement. An external 1% thick-film resistor allows the converter output voltage to adjust as needed to deliver constant current within 10% accuracy to a serially connected LED string of varying number and type. Converter switching frequency is adjustable from 300 kHz to 1 MHz. The LM3407 features a dimming input to enable LED brightness control by Pulse Width Modulation (PWM). Additionally, a separate enable pin allows for low power shutdown. An exposed pad MSOP-8 PowerPAD package provides excellent heat dissipation and thermal performance. Input UVLO and output opencircuit protection ensure a robust LED driver solution. FLOATING BUCK SWITCHING CONVERTER The LM3407 is designed for floating buck configuration. Different from conventional buck converters, a low side power N-MOSFET is used. The floating buck configuration simplifies the driver stage design and reduces the die size of the power MOSFET. Additionally, the connections of the power diode, inductor and output capacitor are switched to ground with a ground referenced power switch, Q1. The extraction of inductor current information can be easily realized by a simple current sensing resistor. These benefits combine to provide a high efficiency, low cost, and reliable solution for LED lighting applications. 8 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 The operation of the LM3407 constant current output floating buck converter is explained below. With the internal switch Q1 turned ON, current flows through the inductor L1 and the LED array. Energy is also stored in the magnetic field of the inductor during the ON cycle. The current flowing through RISNS during the ON cycle is monitored by the Average Current Sensing block. The switch will remain ON until the average inductor current equals 198mV / RISNS. When the switch is turned OFF, the magnetic field starts to collapse and the polarity of the inductor voltage reverses. At the same time, the diode is forward biased and current flows through the LED, releasing the energy stored in the inductor to the output. True average output current is achieved as the switching cycle continuously repeats and the Average Current Sensing block controls the ON duty cycle. A constant current output floating buck converter only works in Continuous Conduction Mode (CCM); if the converter enters Discontinuous Conduction Mode (DCM) operation, the current regulation will deteriorate and the accuracy of LED current cannot be maintained. The operating waveforms for the typical application circuit are shown in Figure 19. VLX time ILX time ID1 time VISNS ILED x RISNS = 198 mV time ILED, IL1 ILED = 198 mV / RISNS time tON tOFF T T = tON + tOFF Figure 19. Operating Waveforms of a Floating Buck Converter PULSE LEVEL MODULATION (PLM) The LM3407 incorporates the innovative Pulse Level Modulation technique. With an external 1% thick film resistor connected to the ISNS pin, the converter output voltage can adjust automatically as needed to deliver constant current within 10% accuracy to a serially connected LED string of different number and type. Pulse Level Modulation is a novel method to provide precise constant current control with high efficiency. It allows the use of low side current sensing and facilitates true average output current regulation regardless of the input voltage and inductor value. Pulse Level Modulation can be treated as a process that transforms a trapezoidal pulse chain into a square pulse chain with an amplitude equal to the center of inductor current ramp. Figure 20 shows the waveform of the converter in steady state. In the figure, IL1 is the inductor current and ILX is the switch current into the LX pin. VISNS is the voltage drop across the current sensing resistor RISNS. VMSL is the center of the inductor current ramp and is a reference pulse that is synchronized and has an identical pulse width to VISNS. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 9 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 IL1 www.ti.com IOUT = IL1(AVG) IOUT time ILX time VISNS VMSL time VRP VREF time tON tOFF T Figure 20. LM3407 Switching Waveforms The switching frequency and duty ratio of the converter equal: tON D= tON + tOFF and fSW = 1 tON + tOFF (1) By comparing the area of VISNS and VRP over the ON period, an error signal is generated. Such a comparison is functionally equivalent to comparing the middle level of ISNS to VRP during the ON-period of a switching cycle. The error signal is fed to a PWM comparator circuit to produce the PWM control pulse to drive the internal power N-MOSFET. Figure 21 shows the implementation of the PWM switching signal. The error signal is fed to a PWM comparator circuit to produce the PWM control pulse to drive the internal power N-MOSFET. Figure 21 shows the implementation of the PWM switching signal. In closed loop operation, the difference between VMSL and VRP is reflected in the changes of the switching duty cycle of the power switch. This behavior is independent of the inductance of the inductor and input voltage because for the same set of IOUT * RISNS, ON time, and switching period, there exists only one VMSL. Figure 22 shows two sets of current sense signals named VISNS1 and VISNS2 that have identical frequencies and duty cycles but different shapes of trapezoidal waveforms, each generating identical PWM signals. 10 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 VISNS1 VMSL 0 VPWM 0 VISNS2 VMSL 0 Figure 21. Pulse-Level Transformation When VMSL is higher than VREF, the peak value of VRP, the switching duty cycle of the power switch will be reduced to lower VMSL. When VMSL is lower than the peak value of VRP, the switching duty cycle of the power switch will be increased to raise VMSL. For example, when IOUT is decreased, VMSL will become lower than VREF. In order to maintain output current regulation, the switching duty cycle of the power switch will be increased and eventually push up VMSL until VMSL equals VREF. Since in typical floating buck regulators VMSL is equal to IOUT * RISNS, true average output current regulation can be achieved by regulating VMSL. Figure 23 shows the waveforms of VISNS and VRP under closed loop operation. 1/fSW VRP VREF D/fSW 0 VPWM D/fSW + 1/fSW Error Amplifier - 0 PWM signal Generator To power switch VISNS VMSL 0 D/fSW 1/fSW PWM sawtooth T Figure 22. Implementation of the PWM Switching Signal Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 11 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com T tON VRP IOUT * RISNS 0 VISNS VMSL < VREF VMSL = VREF Figure 23. Waveforms of VISNS and VRP Under Closed Loop Operation INTERNAL VCC REGULATOR The LM3407 has an internal 4.5V linear regulator. This regulated voltage is used for powering the internal circuitry only and any external loading at the VCC pin is not recommended. The supply input (VIN) can be connected directly to an input voltage up to 30V. The VCC pin provides voltage regulated at 4.5V for VIN ≤ 6V. For 4.5V ≤ VIN ≤ 6V, VIN pin will be connected to VCC pin directly by an internal bypassing switch. For stability reason, an external capacitor CVCC with at least 680 nF (1 µF recommended) must be connected to the VCC pin. CLOCK GENERATOR The LM3407 features an integrated clock generator to control the switching frequency of the converter, fSW. An external resistor RFS, connected to the FS pin and ground, determines the switching frequency. The oscillator frequency can be set in the range of 300 kHz to 1 MHz. The relationship between the frequency setting resistance and the oscillator frequency is described in the Application Information Section. PWM DIMMING OF LED STRING Dimming of LED brightness is achieved by Pulse Width Modulation (PWM) control of the LED current. Pulse Width Modulation control allows LED brightness to be adjusted while still maintaining accurate LED color temperature. The LM3407 accepts an external PWM dimming signal at the DIM pin. The signal is buffered before being applied to the internal switch control block responsible for controlling the ON/OFF of the power switch, Q1. The DIM pin is internally pulled low by a resistor and no LED current will be available when the DIM pin is floating or shorted to ground. Functionally, the DIM pin can also be used as an external device disable control. Device switching will be disabled if the DIM pin is not connected or tied to ground. LOW POWER SHUTDOWN MODE The LM3407 comes with a dedicated device enable pin, EN, for low power shutdown of the device. By putting the device in shutdown mode, most of the internal circuits will be disabled and the input current will reduced to below typically 50µA. The EN pin is internally pulled high by a 5µA current source. Connecting the EN pin to ground will force the device to enter low power shutdown mode. To resume normal operation, leave the EN pin open or drive with a logic high voltage. INPUT UNDER-VOLTAGE LOCK-OUT (UVLO) The LM3407 incorporates an input Under-Voltage Lock-Out (UVLO) circuit with hysteresis to keep the device disabled when the input voltage (VIN) falls below the Lock-Out Low threshold, 3.4V typical. During the device power-up, internal circuits are held inactive and the UVLO comparator monitors the voltage level at the VIN pin continuously. When the VIN pin voltage exceeds the UVLO threshold, 3.6V typical, the internal circuits are then enabled and normal operation begins. 12 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 APPLICATION INFORMATION SWITCHING FREQUENCY SELECTION The selection of switching frequency is based on the consideration of the conversion efficiency, size of the passive components, and the total solution cost. In general, increasing the switching frequency will allow the use of smaller external components but will decrease the conversion efficiency. Thus, the selection of switching frequency is a compromise between the system requirements and may vary from design to design. The LM3407 switching frequency can be set in the range from 300 kHz to 1 MHz by adjusting the value of RFS. The switching frequency is inversely proportional to the value of RFS. In order to ensure good operation stability, a resistor with 1% tolerance between 40 kΩ and 96 kΩ and with good thermal stability is suggested. The switching frequency is estimated by the expression below: fSW = 40 Meg RFS + 40 in kHz (2) In the equation, fSW is the oscillator frequency and RFS is the frequency setting resistance. The above equation is only valid for oscillator frequencies in the range of 300 kHz to 1 MHz, so the frequency setting resistance will be in the range of about 40 kΩ to 150 kΩ. LED CURRENT SETTING The LED current setting is important to the lifetime, reliability, and color temperature of the LED string. The LED current should be properly selected according to the characteristics of the LED used. Over-driving the LED array can cause the color temperature to shift and will shorten the lifetime of the LEDs. The output current of the LM3407 can be set by RISNS, which is calculated from the following equation: 0.198V RISNS = IOUT (3) To ensure the accuracy of the output current, a resistor with 1% tolerance should be used for RISNS. It is also important for the designer to ensure that the rated power of the resistor is not exceeded with reasonable margin. For example, when IOUT is set to 350 mA, the total power dissipation on RISNS in steady state is (0.35A)2 x 0.565Ω, which equals 69 mW, indicating a resistor of 1/8W power rating is appropriate. INPUT AND OUTPUT CAPACITORS The input capacitor supplies instantaneous current to the LM3407 converter when the internal power switch Q1 turns ON. The input capacitor filters the noise and transient voltage from the input power source. Using low ESR capacitors such as ceramic and tantalum capacitors is recommended. Similar to the selection criteria for the output capacitor, ceramic capacitors are the best choice for the input to the LM3407 due to their high ripple current rating, low ESR, and relatively small size compared to other types. A 4.7 µF X7R ceramic capacitor for the input capacitor is recommended The output capacitor COUT is used to reduce LED current ripple, filter noise, and smooth output voltage. This capacitor should have low ESR and adequate capacitance. Excessively large output capacitances create long enable and disable times, which is particularly significant when a high dimming frequency is used. Since the loading and input conditions differ from design to design, a 2.2 µF X7R ceramic capacitor is a good initial selection. A DC voltage rating equal to or higher than twice the forward voltage of the LED string is recommended. COUT is optional and can be omitted for applications where small brightness variation is acceptable. Omitting COUT also helps reduce the cost and board size of the converter. With the absence of COUT, the LED forward current equals the inductor current. In order to ensure proper operation of the converter the peak inductor current must not exceed the rated forward current of the LEDs. Otherwise the LEDs may be damaged. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 13 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com SELECTION OF INDUCTOR In order to achieve accurate constant current output, the LM3407 is required to operate in Continuous Conduction Mode (CCM) under all operating conditions. In general, the magnitude of the inductor ripple current should be kept as small as possible. If the PCB size is not limited, higher inductance values result in better accuracy of the output current. However, in order to minimize the physical size of the circuit, an inductor with minimum physical outline should be selected such that the converter always operates in CCM and the peak inductor current does not exceed the saturation current limit of the inductor. The ripple and peak current of the inductor can be calculated as follows: Inductor Peak to Peak Ripple Current: IL(ripple) = VIN - (n x VF) - 0.198 1 + 1 RISNS x (n x VF) L x VIN x fSW (4) Peak Inductor Current: IL(peak) = 0.198 IL(ripple) + 2 RISNS where • • n is the number of LEDs in a string VF is the forward voltage of one LED. (5) The minimum inductance required for the specific application can be calculated by: Lmin = VIN - (n x VF) - 0.198 x 1 + 1 x (RISNS x n x VF) RISNS 0.197 x VIN x fSW (6) For applications with no output capacitor in place, the magnitude of the inductor ripple current should not be more than 20% of the average inductor current, which is equivalent to the output current, IOUT. However, in some situations the physical size of the required inductor may be too large and thus not allowed. The output capacitor can help absorb this current ripple to significantly reduce the ripple component along the LED string. With an output capacitor COUT in place, the magnitude of the inductor ripple current can be relaxed to 80% of the output current. Figure 24 illustrates the relationship between IOUT, IL(peak), and IL(ripple). IL1 IL (peak) IOUT IL (ripple) time tON tOFF T Figure 24. Relationship between IOUT, IL(peak) and IL(ripple) Table 1 provides the suggested inductance of the inductor for 500 kHz and 1 MHz switching frequency operation with COUT = 4.7µF and IL(ripple) = 0.8 x IOUT 14 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 Table 1. Suggested Inductance Value of the Inductor VIN / V Number of LED 1 2 3 4 5 6 7 Inductor selection table for FSW = 500 kHz, COUT = 4.7µF (1µF for 1 LED) 5 22 µH 10 22 µH 22 µH 15 22 µH 22 µH 22 µH 20 22 µH 33 µH 22 µH 22 µH 22 µH 25 22 µH 33 µH 33 µH 22 µH 22 µH 22 µH 30 22 µH 47 µH 33 µH 33 µH 33 µH 22 µH 22 µH Inductor selection table for FSW = 1 MHz, COUT = 4.7µF (1µF for 1 LED) 5 22 µH 10 22 µH 22 µH 15 22 µH 22 µH 22 µH 20 22 µH 22 µH 22 µH 22 µH 22 µH 25 22 µH 33 µH 22 µH 22 µH 22 µH 22 µH 30 22 µH 33 µH 33 µH 33 µH 22 µH 22 µH 22 µH FREE-WHEELING DIODE The LM3407 is a non-synchronous floating buck converter that requires an external free-wheeling diode to provide a path for recirculating current from the inductor to the LED array when the power switch is turned OFF. Selecting the free-wheeling diode depends on both the output voltage and current. The diode must have a rated reverse voltage higher than the input voltage of the converter and a peak current rating higher than the expected maximum inductor current. Using a schottky diode with a low forward voltage drop can reduce power dissipation and enhance conversion efficiency. PRINTED CIRCUIT BOARD DESIGN Since the copper traces of PCBs carry resistance and parasitic inductance, the longer the copper trace, the higher the resistance and inductance. These factors introduce voltage and current spikes to the switching nodes and may impair circuit performance. To optimize the performance of the LM3407, the rule of thumb is to keep the connections between components as short and direct as possible. Since true average current regulation is achieved by detecting the average switch current, the current setting resistor RISNS must be located as close as possible to the LM3407 to reduce the parasitic inductance of the copper trace and avoid noise pick-up. The connections between the LX pin, rectifier D1, inductor L1, and output capacitor COUT should be kept as short as possible to reduce the voltage spikes at the LX pin. It is recommended that CVCC, the output filter capacitor for the internal linear regulator of the LM3407, be placed close to the VCC pin. The input filter capacitor CIN should be located close to L1 and the cathode of D1. If CIN is connected to the VIN pin by a long trace, a 0.1µF capacitor should be added close to VIN pin for noise filtering. In normal operation, heat will be generated inside the LM3407 and may damage the device if no thermal management is applied. For more details on switching power supply layout considerations see TI Lit NumberSNVA021: Layout Guidelines for Switching Power Supplies. Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 15 LM3407 SNVS553B – JANUARY 2008 – REVISED MAY 2013 www.ti.com Figure 25. Typical Application Schematic for 6 LEDs Figure 26. Typical Application Schematic for 1 LED 16 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 LM3407 www.ti.com SNVS553B – JANUARY 2008 – REVISED MAY 2013 REVISION HISTORY Changes from Revision A (May 2013) to Revision B • Page Changed layout of National Data Sheet to TI format .......................................................................................................... 16 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Product Folder Links: LM3407 17 PACKAGE OPTION ADDENDUM www.ti.com 2-May-2013 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish (2) MSL Peak Temp Op Temp (°C) Top-Side Markings (3) (4) LM3407MY/NOPB ACTIVE MSOPPowerPAD DGN 8 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 STZB LM3407MYX/NOPB ACTIVE MSOPPowerPAD DGN 8 3500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 STZB (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. 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Addendum-Page 1 Samples PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM3407MY/NOPB MSOPPower PAD DGN 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3407MYX/NOPB MSOPPower PAD DGN 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM3407MY/NOPB MSOP-PowerPAD DGN 8 1000 210.0 185.0 35.0 LM3407MYX/NOPB MSOP-PowerPAD DGN 8 3500 367.0 367.0 35.0 Pack Materials-Page 2 MECHANICAL DATA DGN0008A MUY08A (Rev A) BOTTOM VIEW www.ti.com IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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