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| TM MP3204 1.3MHz Fixed Frequency 5 White LED Driver with Open LED Protection The Future of Analog IC Technology TM DESCRIPTION The MP3204 is a step-up converter designed for driving up to 5 series white LEDs from a single cell Lithium Ion battery. The MP3204 uses 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 MP3204 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. The MP3204 is available in a small 6-pin TSOT23 package. FEATURES * * * * * * * * * * * * * * On Board Power MOSFET Drives up to 5 Series White LEDs Up to 87% Efficiency Over 1MHz Fixed Switching Frequency Low 104mV Feedback Voltage Soft-Start/PWM Dimming UVLO, Thermal Shutdown Internal Current Limit Open Load Shutdown Available in a TSOT23-6 Package Cell Phones Handheld Computers and PDAs Digital Still Cameras Small LCD Displays APPLICATIONS EVALUATION BOARD REFERENCE Board Number EV3204DJ-00A Dimensions 1.9"X x 1.8"Y x 0.4"Z "MPS" and "The Future of Analog IC Technology" are Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION VIN 5V LED1 LED2 EFFICIENCY (%) Efficiency vs LED Current 88 87 86 85 84 83 82 81 80 79 78 77 4 LEDs LED3 6 1 SW 5 OV 4 2 IN EN LED4 LED5 EN 5 LEDs MP3204 FB GND 3 3 LEDs VIN=3.6V 5 10 15 LED CURRENT (mA) 20 MP3204-TAC-S01 MP3204-EC01 MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 1 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER PACKAGE REFERENCE TOP VIEW SW GND FB 1 2 3 TSOT23 MP3204-PD01_TSOT23 ABSOLUTE MAXIMUM RATINGS (1) SW Voltage.................................. -0.5V to +28V All Other Pins.............................. -0.3V to +6.5V Storage Temperature .............. -55C to +150C 6 5 4 IN OV EN Recommended Operating Conditions (2) IN Supply Voltage.............................. 2.5V to 6V Output Voltage....................................VIN to 21V Operating Temperature ............. -40C to +85C Thermal Resistance Temperature -40C to +85C (3) 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. JA JC Part Number* MP3204DJ * Package TSOT23-6 For Tape & Reel, add suffix -Z (eg. MP3204DJ-Z) For Lead Free, add suffix -LF (eg. MP3204DJ-LF-Z) ELECTRICAL CHARACTERISTICS VIN = VEN = 5V, TA = +25C, unless otherwise noted. Parameters Operating Input Voltage Supply Current (Shutdown) Supply Current (Quiescent) Switching Frequency Maximum Duty Cycle Under Voltage Lockout IN Under Voltage Lockout Under Voltage Lockout Hysteresis Open Lamp Shutdown Threshold Symbol VIN VEN = 0V VFB = 0.15V fSW VFB = 0V UVLO VIN Rising 1.0 85 Condition Min 2.5 0.1 690 1.3 92 2.25 92 VOV VOV Rising 28 Typ Max 6 1 750 1.5 Units V A A MHz % V mV V 2.45 MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 2 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER ELECTRICAL CHARACTERISTICS (continued) VIN = VEN = 5V, TA = +25C, unless otherwise noted. Parameters Enable EN Threshold EN Threshold EN Hysteresis EN Input Bias Current Feedback FB Voltage FB Input Bias Current Output Switch SW On-Resistance (4) SW Current Limit Thermal Shutdown (4) Notes: 4) Guaranteed by design, not tested. Symbol Condition VEN Rising VEN Rising, VIN = 2.5V VEN = 0V, 5V Min 1.0 0.8 Typ 1.35 90 Max 1.6 Units V V mV A mV nA mA C 1 94 -600 104 -300 0.5 350 160 114 VFB = 0.1V RON Duty Cycle = 60% PIN FUNCTIONS Pin # 1 2 3 Name SW GND FB 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 MP3204 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. This pin must be locally bypassed. 4 5 6 EN OV IN MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 3 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER OPERATION The MP3204 uses constant frequency, peak current mode boost regulator architecture to regulate a series of white LEDs. The operation of the MP3204 can be understood by referring to the block diagram of Figure 1. At the start of each oscillator cycle the FET is turned on through the control circuitry. To prevent subharmonic 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 FB 3 + + AMPLIFIER 104mV PWM COMPARATOR + + CURRENT SENSE AMPLIFIER 1.3MHz OSC MP3204_F01_BD01 output voltage of the error amplifier, the power FET is turned off. 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. This is the manner in which the peak current level keeps the output in regulation. If the feedback voltage begins 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. CONTROL LOGIC M1 1 SW 2 GND Figure 1--Functional Block Diagram MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 4 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER APPLICATION INFORMATION VIN 2.5V to 6V CMDSH-3 LED1 LED2 6 IN EN 1 SW OFF ON 4 2 MP3204 OV FB 5 3 LED3 GND MP3204_F02 Figure 2--Driving 3 White LEDs A typical application circuit can be seen in Figure 2. The 3 white LEDs can be driven from a voltage supply range of 2.5V to 6V at an output current of 20mA. A 0.22F output capacitor is sufficient for most applications but an output capacitor of up to 1F may be used. A 22H inductor with low DCR (inductor resistance) is recommended for improved efficiency. A 1F ceramic capacitor is recommended for the input capacitance in the real system. Schottky diodes have fast recovery times and a low forward voltage and are also recommended. Schottky diodes with ratings of 100mA to 200mA are sufficient for use with the MP3204. The switching characteristics during normal operation can be seen in Figure 3. The MP3204 has internal soft-start to limit the amount of current through VIN at startup and to also limit the amount of overshoot on the output. The current limit is increased by a fourth every 40s, giving a total soft start time of 120s. VSW 5V/div. VOUT RIPPLE (AC COUPLED) 50mV/div. IL 100mA/div. MP3204_F03 Figure 3--Steady-State Operation (VIN=3.6V, 3 LEDs, 20mA) MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 5 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER Table 1--ILED vs. R1 ILED (mA) 1 5 10 15 20 R1 () 104 20.8 10.4 6.93 5.2 Figure 4 shows the startup behavior of the MP3204. The ramped voltage that is 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. VEN 5V/div. VOUT 5V/div. IIN 100mA/div. MP3204_F04 Figure 4--Startup Waveforms (VIN=3.6V, 3 LEDs, 20mA) Figure 5 shows the dependence on current limit versus duty cycle. 500 Analog and Digital Dimming There are three different ways to control dimming for the MP3204 during normal operation. The first way uses a DC voltage to control the feedback voltage, which can be seen 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. VDC LED1 CURRENT LIMIT (mA) 400 LED2 300 200 100 0 LED3 MP3204 FB 3 0 20 40 60 80 DUTY CYCLE (%) 100 MP3204_F05 MP3204_F06 Figure 5--Current Limit vs. Duty Cycle Setting the LED Current The LED current is controlled by the feedback resistor, R1, as shown in Figure 2. The current through the LEDs is equal to 104mV/R1. Table 1 shows the selection of resistors for a given LED current. Figure 6--Dimming Control Using a DC Voltage MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 6 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER Open Load Protection Open Load protection will shutoff the MP3204 if the output voltage goes too high when the OV pin is tied to the output. In some cases an LED may fail, which will result in the feedback voltage always being zero. The part will run at the maximum duty cycle, boosting the output voltage higher and higher. By tying the OV pin to the top of the LED string the MP3204 checks the said condition and if the output ever exceeds 28V the MP3204 will shutdown. The part will not switch on again until the power is recycled. Figure 9 shows the behavior of the MP3204 into an open load. VEN 5V/div. Other applications require the use of a logic signal to execute the dimming. This can be seen in Figure 7. The PWM signal is applied to the EN pin of the MP3204. The LEDs will switch between full load to complete shutoff. The average current through the LEDs will increase proportionally to the duty cycle of the PWM signal. The signal used in Figure 7 should be 1KHz or below due to the soft-start function. LED1 LED2 LED3 PWM 4 MP3204 EN FB 3 VOV 10V/div. MP3204_F07 Figure 7--PWM Dimming Control Using a Logic Signal If the PWM signal is above 1KHz, dimming can be achieved by using the circuit shown in Figure 8. LED1 VSW 10V/div. MP3204_F09 Figure 9--Startup Waveforms into an Open Load (VIN=3.6V) 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 the high frequency switching, the length and area of all the traces connected to the switch node should be minimized. Refer to the evaluation board EV3204DJ-00A for a sample layout of theBMP3204. MP3204 FB 3 LED2 LED3 PWM MP3204_F08 Figure 8--Dimming Control Using a Filtered PWM Signal MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 7 TM MP3204 - 6V, 1.3MHz WHITE LED DRIVER PACKAGE INFORMATION TSOT23-6 2.90 BSC 3 10TYP. (2 plcs) 0.950 TYP. 0.950 TYP. 3 C L 1.60 BSC 2.80 BSC 0 0.25 BSC. Gauge Plane + 4 - 0 0.400 0.10 0.300(Min) 0.500(Max) (6 PLCS) C L 0.870.03 1.00 Max. 0.127 TYP. 10 TYP. (2 plcs) SEATING PLANE 0.00-0.10 NOTE: 1. Dimensions and tolerances are as per ANSI Y14.5M, 1994. 2. Die is facing up for mold. Die is facing down for trim/form, ie. reverse trim/form. 3. Dimensions are exclusive of mold flash and gate burr. 4. The footlength measuring is based on the gauge plane method. 5. All specification comply to Jedec Spec MO193 Issue C. NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. 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. MP3204 Rev. 1.3 9/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved. 8 |
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