LM3466 Smart Linear LED Driver for Multi-Channel LED Systems General Description Features The LM3466 integrates a linear LED driver for lighting systems which consist of multiple LED strings powered by a constant current power supply. It equalizes the current provided by the supply in a pre-set ratio for each active LED string, where an active string is a fully turned on LED string, regardless of the number of strings connected to the supply or the forward voltage of each LED string. If any LED string opens during operation, the LM3466 automatically equalizes the supply current through all of the remaining active LED strings. As a result, the overall brightness of the lighting system is maintained even if some LED strings open during operation. The LM3466 lighting system is simple to design owing to a proprietary control scheme. To minimize the component count, the LM3466 integrates a 70V, 1.5A N-channel power MOSFET with a current limit of 2.06A. To add one more LED string to the system, only a single resistor, a capacitor, and a LM3466 are required. Other supervisory features of the LM3466 include under-voltage lock-out, fault reporting, thermal latch off, and thermal shutdown protection. The LM3466 consists of only linear circuitry so that the EMI of the application circuit is not deteriorated. The LM3466 lighting system is EMI friendly if the constant current power supply used is complied to EMI standards. The LM3466 is available in the PSOP-8 exposed DAP package. ■ Easy to design and use for lighting systems consisting of multiple LED strings (support modular design) ■ Automatically equalizes the current of every active LED string, even the forward voltage of each string is different ■ Easy to pre-set and fine-tune current ratio among LED ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ strings (e.g. color temperature adjustment or CRI enhancement) ±1% current accuracy at room temperature and ±1.5% over temperature Maintains constant output power if some strings open (inactive) by automatically equalizing the current of remaining active LED strings Works with a constant current power supply (ac/dc or dc/ dc), and no communication to/from the constant current power supply is required Operates with minimum voltage overhead to maximize power efficiency Wide input voltage range from 6V to 70V Fault status output Thermal shutdown Integrated 70V 1.5A MOSFET with 2.06A current limit Maximum 70V per LED string, 20 LEDs Linear circuitry does not deteriorate EMI PSOP-8 exposed DAP package Applications ■ Street lamps ■ Solid state lighting systems Typical Application 30158901 © 2012 Texas Instruments Incorporated 301589 SNOSB96B www.ti.com LM3466 Smart Linear LED Driver for Multi-Channel LED Systems February 2, 2012 LM3466 Connection Diagram 30158902 Ordering Information Order Number Spec. Package Type NSC Package Drawing LM3466MR NOPB ePSOP-8 MRA08A LM3466MRX Supplied As 95 Units in Anti-Static Rails 2500 units on Tape and Reel Pin Descriptions Pin Name Description Application Information 1 ILED Current Regulator Input Connects to the drain of the integrated power MOSFET. Connects this pin to the cathode of an LED string. Connects a capacitor from this pin to ground to minimize noise if the connecting cable to the LED string is long. 2 COMM Open-drain Status Output Indicates the status of the LM3466 including startup, LED string active/ inactive, TSD. 3 VIN Input Voltage Supply Connects to voltage supply from 6V to 70V. Connects a 10 nF capacitor from this pin to ground for decoupling. 4 VEQ Control Voltage Connects to the VEQ pin of other LM3466 with a 51Ω resistor in series with a 1 µF capacitor to ground. 5 GND Ground Connects to ground. 6 SEN Current Sense Input Senses the voltage of an external current sensing resistor. 7,8 SRC Source of Power MOSFET Connects to the source of the integrated power MOSFET. Connects this pin to an external current sensing resistor. DAP DAP Exposed Pad Thermal connection pad. Connects to a ground plane. www.ti.com 2 If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. VIN, ILED to GND COMM to GND SEN, SRC, VEQ to GND ESD Rating ±2 kV −65°C to + 150°C + 150°C Operating Ratings -0.3V to 75V -0.3V to 7V -0.3V to 5V Supply Voltage Range (VIN) Junction Temperature Range (TJ) 6V to 70V −40°C to + 125°C Thermal Resistance (θJC) 12.8 °C/W Electrical Characteristics Specification with standard type are for TA = TJ = +25°C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum are guaranteed through test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ = +25°C, and are provided for reference purposes only. Unless otherwise stated, the following conditions apply: VIN = 48V. Symbol Parameter Conditions Min Typ Max Units VIN -UVLO-UPPER VIN pin under-voltage lockout (UVLO) upper threshold VIN increasing 4.06 4.78 5.30 V VIN -UVLO-HYS VIN pin UVLO hysteresis VIN decreasing IIN Operating current to the VIN pin VSEN The SEN pin voltage regulation VEQ = 200 mV ISEN SEN pin bias current out VSEN = 0V ILED-OFF ILED pin off current RDS(on) Integrated power MOSFET onresistance VSRC-OPEN SRC pin open circuit threshold VSEN = VSRC, VCOMM = 0V ILIMIT Current Limit VSEN = VSRC = 0V, VILED = 3V COMMILOW COMM pin pull-low current VCOMM = 5V COMMVHIGH COMM pin pull-high voltage COMM pin to ground through a 10 kΩ 6.0 V TSD Thermal Shutdown 150 °C 0.52 V 550 640 µA 200 201.0 mV 195.6 200 201.5 mV 9.77 10.5 11.23 µA VILED = 70V 0.1 0.6 µA IILED = 300 mA 0.5 1.2 Ω 25 31 37 mV 1.75 2.06 2.35 A 34 54 µA 197.1 Note 1: 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 guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Note 3: θJC measurements are performed in general accordance with Mil-Std 883B, Method 1012.1 and utilize the copper heat sink technique. Copper Heat Sink @ 18°C with an ambient temperature @ 22°C. 3 www.ti.com LM3466 Human Body Model Storage Temperature Range Junction Temperature (TJ) Absolute Maximum Ratings (Note 1) Unless otherwise specified the following conditions apply: TJ = 25°C, VIN = 48V with configuration in the additional application circuit for ILED = 0.35A shown in this datasheet. Quiescent Current, IIN vs VIN Current Regulation vs VIN 600 580 I IN (μA) 25°C 560 125°C 540 520 -40°C 500 0 10 20 30 40 V IN (V) 50 60 70 30158926 30158904 Current Regulation (Channel to Channel) vs Temperature Efficiency vs VIN 30158922 30158906 RDS(on) vs Tempearture Current Regulation vs VLED 700 650 R DS(on)(mΩ) LM3466 Typical Performance Characteristics 600 550 500 450 400 -50 0 50 100 TEMPERATURE (°C) 150 30158921 www.ti.com 30158923 4 LED String Disconnect 30158910 30158909 ISEN vs Temperature Current Limit vs Temperature 2.5 10.9 2.4 10.8 2.3 CURRENT LIMIT (A) 11.0 I SEN(μA) 10.7 10.6 10.5 10.4 10.3 10.2 2.2 2.1 2.0 1.9 1.8 1.7 10.1 1.6 10.0 -50 LM3466 Power Up 0 50 100 TEMPERATURE (°C) 1.5 -50 150 0 50 100 TEMPERATURE (°C) 150 30158925 30158924 5 www.ti.com LM3466 Block Diagram 30158929 Overview Current Regulator The LM3466 integrates a linear LED driver for lighting systems which consist of multiple LED strings powered by a constant current power supply. An ideal constant current power supply delivers a constant current (IS) regardless of the output voltage of the connecting load. In the lighting system, each LM3466 regulates the current of an LED string. The current IS provided by the supply is equalized (i.e. shared in a pre-set ratio determined by a single resistor) through each active LED string automatically, regardless of the number of strings connected to the supply or the forward voltage of each string. Here, an active LED string refers to a fully turned on LED string. If any LED string opens during operation, the LED current of all remaining active LED strings will increase to equalize the current provided by the supply automatically. As a result, the total output power remains nearly the same in case of the decrease of active LED strings. This gives an advantage that the overall brightness of the lighting system is maintained even if some LED strings open during operation. A LM3466 lighting system is simple to design owing to a proprietary control scheme. To minimize the component count, the LM3466 integrates a 70V, 1.5A N-channel MOSFET with a current limit of 2.06A. To add one more LED string to the system, only a single resistor, a capacitor, and an LM3466 are required. Other supervisory features of the LM3466 include under-voltage lock-out, fault reporting, thermal latchoff, and thermal shutdown protection. The LM3466 consists of only linear circuitry so that the EMI of the application circuit is not deteriorated. The LM3466 lighting system is EMI friendly if the constant current power supply used is complied to EMI standards. The LM3466 is available in a PSOP-8 exposed DAP package. The LM3466 integrates a current regulator to control the current of a connected LED string. The current is delivered from the supply through the LED string, the ILED pin, the integrated power MOSFET, the SRC pin, and the sensing resistor RSEN connecting from the SRC pin to ground (Figure 1). The voltage of the sensing resistor is fed back to the LM3466 through the SEN pin, either by direct connection or through an extra resistor RSL. The LM3466 regulates the voltage of the SEN pin (VSEN) to a voltage set by its control block. If the sensing resistor of each LM3466 (RSEN,k, k = 1, 2, …, n) is the same, the LED current of each active LED string is the same. If RSEN,k of any LM3466 is different from others, the corresponding LED current (ILED,k) is different, while VSEN of each LM3466 is still the same as others. The LED current of string k is www.ti.com where IS is the current of the supply, and In addition to determining the LED current by means of RSEN,k, an external resistor RSL,k connecting between the SEN pin and RSEN,k can be used to fine tune the LED current for the purpose of color temperature adjustment or CRI enhancement. The SEN pin sources a constant bias current of 10.5 µA such that a constant voltage drop on RSL,k reduces the LED current. Using an external resistor RSL,k affects the current of other LED strings. If RSL,k is added in the k-th LM3466, the corresponding LED current is 6 and the LED current of other strings is where i = 1, 2, …, n except k. The LED current of LED string k is reduced, while the LED current of other channels increases. Figure 2 shows a typical example that the variation of LED current on varying RSL,k. Communication Pin The COMM pin serves as a communication link among all LM3466 in the lighting system. It also indicates the status of the device. The COMM pin is pulled low at startup. After startup, the COMM pin is high/low to indicate that the corresponding LED string is active/inactive. For proper operation of a LM3466 system, the COMM pin of all LM3466 should be either shorted together or connected through a diode in parallel with a resistor. Figure 3 shows an optional circuit for the COMM pin to indicate whether each LED string is active by means of small signal LEDs. The COMM pin of each LM3466 is connected to an external test point COMM_ALL through the optional circuit. The COMM pin is low if the LM3466 is under thermal protection. 30158915 FIGURE 1. A Single LM3466 within a Lighting System 30158917 FIGURE 3. Optional Circuit for the COMM Pin High Voltage Application If the forward voltage of an LED string is higher than 70V, which is the maximum operating voltage of the LM3466, an external MOSFET circuit as shown in Figure 4 is recommended for each channel in order to protect the ILED pin from damaging by a high voltage owing to shorting LEDs (or even the whole LED string). To avoid the ILED pin damage from a high voltage generated by the leakage current, a resistor RLED (1 MΩ is suggested) is placed between the ILED pin and ground. In addition, since VLED is higher than 70V in this case, the VIN pin cannot be directly connected to VLED. External power supplies for VIN and VG (to drive the external MOSFET) are required. Alternatively, Figure 5 shows a circuit for supplying VIN and VG (for all channels in the system). 30158916 FIGURE 2. Variation of ILED vs RSL,k LED String Disconnect and Reconnect One major advantage of the LM3466 lighting system is that the overall brightness is maintained even if some LED strings open during operation. If an active LED string is suddenly disconnected, the LM3466 will automatically equalize the current delivered by the supply IS (i.e. each string increases its LED current in this case) so as to keep IS constant. However, the equalization takes place only after the LED string is confirmed inactive. Once the string is disconnected, VEQ will go to a cycle (goes up and down). If the string is still disconnected for a period of 253 consecutive cycles, the string is confirmed 7 www.ti.com LM3466 inactive. Consequently, the current of other LED strings increases to equalize IS. The output power and the overall brightness of the lighting system are maintained. If a new LED string connects to the system, such as if the disconnected LED string is reconnected again, a power reset is recommended to ensure proper operation. The forward voltage of the new LED string may be higher than the instantaneous VIN, which corresponds to the forward voltage of the highest active LED string. A power reset ensures that VIN goes to the peak voltage (a default characteristic of a constant current power supply) in order to start up the LED string with the highest forward voltage. LM3466 out thermal shutdown against an ambient temperature up to 125°C. 1.6 ILED CURRENT (A) 1.5 1.4 1.3 1.2 1.1 1.0 0 25 50 75 100 AMBIENT TEMPERATURE (°C) 125 30158920 30158927 FIGURE 6. Thermal Derating Curve FIGURE 4. External MOSFET circuit for high voltage applications Application Information Consider a LM3466 lighting system which is powered by a 1.75A constant current power supply and consists of 5 LED strings with 14 LEDs per string. It is expected that the LED current of every LED string is 0.35A. EXTERNAL COMPONENTS RSEN: To set the LED current of all 5 LED strings equal, the sensing resistors corresponding to all 5 LM3466 are equal. It is recommended that the nominal voltage of the SEN pin VSEN should be around 0.3V. Therefore, RSEN is selected to be 1Ω. As a result, VSEN should be 0.35V if the LED current is 0.35A. CLED: If the cable connecting the LED string is long, the parasitic inductance of the cable may generate noise. If this happens, a high quality ceramic capacitor should be connected between the ILED pin and ground. In this example, a 100V, 1 µF ceramic capacitor is used. CIN: A high quality ceramic capacitor for decoupling should be connected from the VIN pin to ground. In this example, a 100V, 0.01 µF ceramic capacitor is used. REQ and CEQ: The VEQ pins of all LM3466 are shorted together and then connected to ground through REQ and CEQ. Only one REQ and one CEQ are required for each LM3466 lighting system. It is recommended that REQ be 51.1Ω and CEQ be 1 µF. 30158928 FIGURE 5. Power supply circuit for the external MOSFET circuit Thermal Protection Thermal protection is implemented by an internal thermal shutdown circuit, which activates at 150°C (typically) to disable the LM3466. In this case, the integrated power MOSFET turns off and the COMM pin is pulled low. Thermal protection helps prevent catastrophic failures from accidental device overheating. When the junction temperature of the LM3466 falls back below 140°C (typical hysteresis = 10°C), the LM3466 resumes normal operation. PC BOARD LAYOUT To minimize the effect of noise, the ground connections of the LM3466 and the sense resistor RSEN,k should be closed. Good heat dissipation helps optimize the performance of the LM3466. The ground plane should be used to connect the exposed pad of the LM3466, which is internally connected to the LM3466 die substrate. The area of the ground plane should be extended as much as possible on the same copper layer above and below the LM3466. Using numerous vias beneath the exposed pad to dissipate heat of the LM3466 to another copper layer is also a good practice. Thermal Latch Off and Derating If thermal protection cycles for 253 times consecutively, the LM3466 is latched off until power reset. When fully turned on, the integrated power MOSFET of the LM3466 is capable of conducting a current of 1.5A below an ambient temperature of 100°C. At 125°C, the LM3466 can conduct a current of 1A without thermal shutdown with a PCB ground plane copper area of 60cm2, 2 oz/Cu. Figure 6 shows a thermal derating curve for the minimum conducting current of a fully turned on LM3466 integrated power MOSFET with- www.ti.com 8 FIGURE 7. Application Circuit of a LM3466 Lighting System 30158918 LM3466 Additional Application Circuit 9 www.ti.com LM3466 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead Plastic ePSOP Package NS Package Number MRA08A www.ti.com 10 LM3466 Notes 11 www.ti.com LM3466 Smart Linear LED Driver for Multi-Channel LED Systems Notes www.ti.com IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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