MP2128DT-LF-P

MP1488 800mA Fixed Frequency White LED Driver DESCRIPTION FEATURES The MP1488 is a step-up converter designed for driving up to 27 WLEDs (9 strings of 3 WLEDs each) from a 5V system rail. The MP1488 uses a current mode, fixed frequency architecture to regulate the LED current, which is measured through an external current sense resistor. Its low 104mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an over-voltage condition is present due to an open circuit condition.            The MP1488 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. The MP1488 is available in a small 6-pin TSOT23 package. 2.5V to 6V Input Voltage Range On Board Power MOSFET Drives up to 27 White LEDs at 5V Input Up to 92% Efficiency Over 1MHz Fixed Switching Frequency Open Load Shutdown Low 104mV Feedback Voltage Soft-Start/PWM Dimming UVLO, Thermal Shutdown Internal 800mA Current Limit Available in a TSOT23-6 Package APPLICATIONS     Cell Phones Handheld Computers and PDAs Digital Still Cameras Small LCD Displays All MPS parts are lead-free, halogen free, and adhere to the RoHS directive. For MPS green status, please visit MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION MP1488 Rev. 1.0 3/24/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 1 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER ORDERING INFORMATION Part Number* MP1488DJ Package TSOT23-6 Top Marking See Below * For Tape & Reel, add suffix –Z (e.g. MP1488DJ–Z). For RoHS compliant packaging, add suffix –LF (e.g. MP1488DJ–LF–Z) TOP MARKING Z9: product code of MP1488DJ; Y: year code; W: week code: PACKAGE REFERENCE TSOT23-6 MP1488 Rev. 1.0 3/24/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 2 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER ABSOLUTE MAXIMUM RATINGS (1) SW Pin .................................... –0.5V to +28.5V All Other Pins ............................. –0.3V to +6.5V Storage Temperature .............. –55C to +150C Recommended Operating Conditions (2) IN Supply Voltage ............................. 2.5V to 6V Output Voltage ................................... VIN to 25V Operating Temperature............. –40C to +85C MP1488 Rev. 1.0 3/24/2017 Thermal Resistance (3) θJA θJC TSOT23-6 ............................. 220 .... 110 .. C/W Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 1” square of 1 oz copper. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 3 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER ELECTRICAL CHARACTERISTICS VIN = VEN = 5V, TA = +25C, unless otherwise noted. Parameters Symbol Condition Operating Input Voltage Supply Current (Shutdown) Supply Current (Quiescent) Switching Frequency VIN fSW VFB = 0V UVLO VOV VEN = 0V, 5V V µA µA MHz 85 92 2.25 1.0 0.8 % 2.45 mV 28 V 1.35 1.6 VFB = 0.1V RON Duty Cycle = 60% 1 94 –600 V 92 90 FB Voltage FB Input Bias Current Output Switch Thermal Shutdown 1.0 0.1 690 1.3 6 1 750 1.5 VOV Rising EN Hysteresis EN Input Bias Current Feedback (4) Units VIN Rising VEN Rising, VIN = 5V VEN Rising, VIN = 2.5V (4) Max 2.5 EN Threshold EN Threshold SW On-Resistance (4) SW Current Limit Typ VEN = 0V VFB = 0.15V Maximum Duty Cycle Under Voltage Lockout IN Under Voltage Lockout Under Voltage Lockout Hysteresis Open Lamp Shutdown Threshold Enable Min 104 –300 114 V V mV µA mV nA 0.5 800 Ω mA 160 C Notes: 4) Guaranteed by design. MP1488 Rev. 1.0 3/24/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 4 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER PIN FUNCTIONS TSOT23-6 Pin # Name 1 SW 2 GND 3 FB 4 EN 5 OV 6 IN MP1488 Rev. 1.0 3/24/2017 Description Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to SW. SW can swing between GND and 25V. Ground. Feedback Input. The MP1488 regulates the voltage across the current sense resistor between FB and GND. Connect a current sense resistor from the bottom of the LED string to GND. Connect the bottom of the LED string to FB. The regulation voltage is 104mV. Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns it off. When not used, connect EN to the input source for automatic startup. The EN pin cannot be left floating. Over Voltage Input. OV measures the output voltage for open circuit protection. Connect OV to the output at the top of the LED string. Input Supply Pin. Must be locally bypassed. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 5 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER Figure 1—Functional Block Diagram MP1488 Rev. 1.0 3/24/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 6 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER OPERATION The MP1488 uses a constant frequency, peak current mode boost regulator architecture to regulate the strings of white LEDs. Refer to the block diagram in Figure 1 for details. At the start of each oscillator cycle the FET is turned on through the control circuitry. To prevent sub-harmonic oscillations at duty cycles greater than 50%, a stabilizing ramp is added to the output of the current sense amplifier and the result is fed into the positive input of the PWM comparator. When this voltage equals the output voltage of the error amplifier the power FET is turned off. MP1488 Rev. 1.0 3/24/2017 The voltage at the output of the error amplifier is an amplified version of the difference between the 104mV reference voltage and the feedback voltage. In this way the peak current level keeps the output in regulation. If the feedback voltage starts to drop, the output of the error amplifier increases. This results in more current flowing through the power FET, thus increasing the power delivered to the output. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 7 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER APPLICATION INFORMATION Figure 2—Circuit for Driving 27 WLEDs A typical application circuit is provided in Figure 2. The 27 white LEDs can be driven from a voltage supply range of 4V to 6V at a total output current of 180mA. A 2.2µF output capacitor is sufficient for most applications but up to 1µF may be used. A 10µH inductor with low DCR (inductor resistance) is recommended to improve efficiency. A 4.7µF ceramic capacitor is recommended for the input capacitance in the real system. Schottky diodes with fast recovery and a low forward voltage are recommended. Schottky diodes with a 500mA rating are sufficient for the MP1488. The switching characteristics during normal operation can be seen in Figure 3. The MP1488 has internal soft-start to limit the amount of current through the IN pin at startup and to also limit the amount of overshoot on the output. The current limit is increased by a fourth every 40µs giving a total soft-start time of 120µs. MP1488 Rev. 1.0 3/24/2017 Figure 3—Steady State Operation Figure 4 shows the startup behavior of the MP1488. The ramped voltage added to the current sense amplifier reduces the current output as the duty cycle increases. As more LEDs are added, the output voltage rises but the current that can be delivered to the load is reduced as well. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 8 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER Figure 4—Startup Waveforms Analog and Digital Dimming There are three methods to control dimming for the MP1488 during normal operation. The first method uses DC voltage to control the feedback voltage. This is shown in Figure 6. As the DC voltage increases, current starts flowing down R1, R2 and R3. The loop will continue to regulate the feedback voltage to 104mV. Thus the current has to decrease through the LEDs by the same amount of current as is being injected from the DC voltage source. With a VDC from 0V to 2V, the resistor values shown for R2 and R3 can control the LED current from 0mA to 20mA. Setting the LED Current The LED current is controlled by the feedback resistors R1 and R2, as shown in Figure 2. The current through the LEDs is given by the equation: ILED  104mV  R1  R2 R1 R2 Table 1 shows the selection of resistors for a given LED current. Table 1—ILED vs. R1 ILED (mA) 10 50 100 150 180 MP1488 Rev. 1.0 3/24/2017 R1 (Ω) 10.4 2.08 1.04 1.5 1.2 R2 (Ω) N/A N/A N/A 1.3 1.1 Figure 6—Dimming Control Using a DC Voltage www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 9 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER Other applications require a logic signal to control dimming. This is shown in Figure 7. The PWM signal is applied to the EN pin of the MP1488. The LEDs will switch between full load to completely shut off. The average current through the LEDs will increase proportionally to the duty cycle of the PWM signal. The PWM signal used in Figure 7 should be 1KHz or below due to the soft-start function. Open Load Protection Open Load protection will shut off the MP1488 if the output voltage rises too high when the OV pin is tied to the output. In some cases an LED may fail. This will result in the feedback voltage always remaining at zero. The part will run at maximum duty cycle boosting the output voltage higher and higher. By tying the OV pin to the top of the LED string the MP1488 can check for this condition. If the output exceeds 28V, the MP1488 will shut down. The part will not switch again until the power is recycled. Figure 9 shows the behavior of the MP1488 into an open load. Figure 7—PWM Dimming Control Using a Logic Signal If the PWM signal is above 1KHz, dimming can be achieved using the circuit shown in Figure 8. Figure 9—Startup Waveforms into an Open Load Figure 8— Dimming Control Using a Filtered PWM Signal MP1488 Rev. 1.0 3/24/2017 Layout Considerations Careful attention must be paid to the PCB board layout and component placement. Proper layout of the high frequency switching path is critical to prevent noise and electromagnetic interference problems. Due to high frequency switching, the length and area of all the traces connected to the switch node should be minimized. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 10 MP1488 – 800mA, FIXED FREQUENCY WHITE LED DRIVER PACKAGE INFORMATION TSOT23-6 NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP1488 Rev. 1.0 3/24/2017 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 11