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| MP1523 Precision 6-Lamp White LED Driver Monolithic Power Systems INITIAL RELEASE DESCRIPTION The MP1523 is a 5-pin SOT23 step-up converter designed for driving up to six (6) series white LEDs from a single-cell Lithium Ion battery. The MP1523 uses a current limited, variable frequency architecture to regulate the LED current, which is measured through an external current sense resistor. Its low 0.4V feedback threshold reduces power loss and improves efficiency. To prevent damage due to an open circuit condition, the BIAS pin can measure the output voltage and turn off the converter if an over-voltage condition is present. The MP1523 includes under-voltage lockout, current limiting, and thermal overload protection to prevent damage in the event of an output overload. The MP1523 is available in a small 5-pin SOT23 package. FEATURES * * * * * * * * * * * * * * * On Board Power MOSFET Drives up to 6 White LEDs Up to 90% Efficiency Over 80mA Output Current Capacity Open Load Shutdown Low 0.4V Feedback Threshold UVLO, Thermal Shutdown Soft-Start Internal Current Limiter Available in SOT23-5 Package Evaluation Board Available Cell Phones Handheld Computers and PDAs Digital Still and Video Cameras Small LCD Displays APPLICATIONS , "MPS", "Monolithic Power Systems", and "The Future of Analog IC Technology" are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION VIN 2.7V to 5.5V A B 100 90 5 BIAS 4 2 1 SW Up To 6 LEDs EFFICIENCY (%) 80 70 60 50 VIN = 5V VIN = 4V VIN = 3V EN EN MP1523 FB 3 GND MP1523-TAC-S01 5 10 15 20 LED CURRENT (mA) 25 MP1523-EC01 07/04, Rev. 1.6 www.MonolithicPower.com 1 MP1523 - PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE PACKAGE REFERENCE TOP VIEW SW GND FB 1 5 BIAS ABSOLUTE MAXIMUM RATINGS (1) BIAS ............................................... -0.3V to 28V SW .................................................. -0.5V to 28V All Other Pins.................................... -0.3V to 6V Storage Temperature ...............-55C to +150C A3XX 4 EN MP1523_PD01-SOT23-5 2 3 Recommended Operating Conditions (2) BIAS Supply Voltage ....................... 2.7V to 25V Output Voltage....................................VIN to 25V Operating Temperature ..............-40C to +85C Thermal Resistance (3) Part Number* MP1523DT EV0035 * Package SOT23-5 Temperature -40C to +85C Evaluation Board JA (SOT23-5) ..................................... 220C/W JC (SOT23-5) ..................................... 110C/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. For Tape & Reel, add suffix -Z (eg. MP1523DT-Z) For Lead Free, add suffix -LF (eg. MP1523DT-LF-Z) ELECTRICAL CHARACTERISTICS (4) VBIAS = VEN = 5.0V, TA = 25C, unless otherwise noted. Parameter Supply Current (shutdown) Supply Current (quiescent) Minimum Off Time, Normal Operation Minimum Off Time, Start-Up Undervoltage Lockout BIAS Under Voltage Lockout Open Lamp Shutdown Threshold Enable EN Threshold EN Hysteresis EN Input Bias Current Feedback Comparator FB Regulation Threshold FB Hysteresis (5) FB Input Bias Current Output Switch SW On-Resistance (5) SW Current Limit SW Voltage Thermal Shutdown (5) Thermal Shutdown Hysterisis (5) Notes: 4) First 64 pulses after EN switches high. 5) Guaranteed by design. Symbol IBIAS (OFF) IBIAS (ON) TOFF TOFF UVLO Condition VEN = 0V VFB = 0.45V VFB = 0V VFB = 0V (4) Min Typ 1 650 550 1.6 2.3 28 1.1 60 Max 3 750 700 Units A A ns s 300 1.25 2.1 VBIAS Rising, 100mV Hysteresis VBIAS Rising VEN Rising VEN = 0V, 5V VFB Falling VFB = 0.2V 2.65 V V V mV A mV mV nA mA V C C 0.8 1.5 1 380 -150 400 10 -80 0.5 450 160 15 420 RON BV ISW = 10A 300 25 0.6 650 07/04, Rev. 1.6 www.MonolithicPower.com 2 MP1523 - PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs VIN of Figure 2 85 23 Line Regulation of Figure 2 and Figure 3 LED CURRENT (mA) 3.0 3.5 VIN (V) 4.0 4.5 MP1523_TPC01 EFFICIENCY (%) 21 80 19 75 17 70 2.5 15 2.5 3.0 3.5 VIN (V) 4.0 4.5 MP1523_TPC02 PIN FUNCTIONS Pin # Name Description 1 2 3 SW GND FB 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 MP1523 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 threshold is 0.4V. 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. If EN is driven over 6V, place a resistor in series with EN to limit current to 10A or less. Do not leave EN floating! Internal Power Input. BIAS powers the internal circuitry and measures the output voltage for open circuit protection. Connect BIAS to the output at the top of the LED string to enable open load shutdown feature (see Figure 3). Connect BIAS to the input to eliminate open load shutdown feature (see Figure 2). 4 EN 5 BIAS 07/04, Rev. 1.6 www.MonolithicPower.com 3 MP1523 - PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE OPERATION The MP1523 is a step-up converter that operates from an input voltage as low as 2.7V and generates an output voltage up to 25V. The 0.5 internal N-Channel power MOSFET is driven with a variable frequency, constant-peakcurrent architecture for low operating current. The 550ns minimum off time is extended to 1.6s during start-up to yield a smooth glitch free turn-on. Variable Frequency Constant-Peak-Current Operation When the power MOSFET is turned on the inductor current increases until the 0.45A current limit is reached. The internal power MOSFET is then turned off for a minimum of 550ns. At the end of this 550ns transition if the FB pin is still lower than the 400mV threshold the MOSFET will again be turned on, otherwise the MP1523 waits until the voltage drops below the threshold before turning on the MOSFET again. This process allows for optimal use of the inductor, while minimizing the output ripple and size of the output capacitor and maintaining low operating current. Open Load Shutdown Open load shutdown is implemented by connecting the BIAS pin to the output. In the fault condition where the connection to the LED string is open, the output voltage will rise up, as the FB pin has no voltage. Once the output voltage exceeds 28V, the MP1523 will cease operation until the EN pin is cycled off and on. Connecting the BIAS pin to VIN disables open load shutdown but reduces the chip power consumption due to the quiescent current. BIAS (5) 17V 160K 1.23V 20K + Open Load Shutdown Comparator REGULATOR INTERNAL POWER EN (4) SW (1) CONTROL LOGIC CURRENT _ 7V + ERROR AMP. 450mA _ + 400mV + - FB (3) GND (2) Figure 1--Functional Block Diagram 07/04, Rev. 1.6 www.MonolithicPower.com 4 MP1523 - PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE APPLICATIONS INFORMATION Setting the LED current The LED current is set by the sense resistor (R2) at FB. The LED current can be calculated as: ILED V = FB R2 saturation, use an inductor with a saturation current rating that matches the device current limit. Diode selection The MP1523's high switching frequency demands a high-speed rectifier (D1) for optimum efficiency. A schottky diode is recommended due to its fast recovery time and low forward voltage drop. Ensure the diode's average and peak current ratings exceed the average output current and peak inductor current. In addition, the diode's reverse breakdown voltage must exceed the output voltage. Layout Careful PC board layout is required due to fastswitching. All components must be placed as close to the IC as possible. Keep the path between inductor L1, diode D1, and output capacitor C2 extremely short for minimal noise and ringing. The feedback components such as sense resistor R2 must be kept close to the FB pin to prevent noise injection on the FB pin trace. The ground return of C1 and C2 should be tied close to the GND pin. See the MP1523 demo board layout for reference. Where VFB is 400mV. The LED current is set to 20mA if R2 = 20. Capacitor Selection A 1F to 10F ceramic input capacitor (C1) and a 0.47F to 1F ceramic output capacitor (C2) are recommended for most applications. A capacitor (typically 1nF) in parallel with the LED string improves stability, input and output ripple especially when large inductance values (10H or above) are used. For best stability over a wide temperature range, use capacitors with an X5R or X7R dielectric. Inductor selection The MP1523 has a 450mA inductor current limit and can drive up to 6 LEDs at 20mA. Inductance values (L1) from 4.7H to 47H work satisfactorily. Larger values provide the best efficiency while small inductor values allow the smallest inductor size. To prevent 07/04, Rev. 1.6 www.MonolithicPower.com 5 MP1523 - PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE TYPICAL APPLICATIONS / TEST CIRCUITS L1 15H CDM4D11 VIN = 2.7 to 25V C1 1F C2 4.7F D1, B130 Point A 5 BIAS 4 2 1 SW Up to 6 LEDs EN EN GND MP1523 FB 3 R2 20 Note: Pin 5 connects to Point A to eliminate Open Load Shutdown Option Figure 2--One String of up to Six (6) LEDs "without" Open Load Shutdown Option L1 15H CDM4D11 V IN = 2.7 to 25V C1 1F Point B D1, B130 C2 4.7F 5 BIAS 4 2 1 SW Up to 6 LEDs EN E N GND MP1523 F B 3 R2 20 Note: Pin 5 connects to Point B to enable Open Load Shutdown Option Figure 3--One String of up to Six (6) LEDs "with" Open Load Shutdown Option 07/04, Rev. 1.6 www.MonolithicPower.com 6 MP1523 - PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE PACKAGE INFORMATION SOT23-5 2.900.100 5 0.950 TYP. 0.950 TYP. 10 TYP. (2 plcs) 0 5 C L 2.800.200 1.600.100 0~3 0.20 BSC. Gauge Plane 0.45 0.10 0.350(MIN) 0.500(MAX) (5 PLCS) C L 10 TYP. (2 plcs) 10 TYP. (2 plcs) 0 0 0.127 TYP 1.150.150 SEATING PLANE 10 TYP. (2 plcs) 0 0.05(MIN) 0.15(MAX) NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change without notice. Contact MPS for current specifications. MPS encourages users of its products to ensure that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS cannot assume any legal responsibility for any said applications. MP1523 Rev. 1.6 7/14/04 (c) 2004 MPS, Inc. Monolithic Power Systems, Inc. 983 University Avenue, Building A, Los Gatos, CA 95032 USA Tel: 408-357-6600 Fax: 408-357-6601 www.MonolithicPower.com 7 |
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