MP1521 High Efficiency White LED Driver Monolithic Power Systems General Description Features The MP1521 is a constant-current Boost Regulator. This IC has three individual current-sensing feedbacks, which are ideal for driving multiple strings of series connected LEDs. The OLS pin is designed for detecting loose or open LED connections. The IC uses a peak current, constant minimum off-time architecture. The feedback pins measure voltage across sense resistors in series with the LED strings. When supplying a bias current of 20mA, the voltage drop across the sense resistor is only 0.4V to minimize power loss. Either a DC voltage or a PWM signal at the BRT/PWM input can control the LED brightness. The MP1521 has an on board power MOSFET switch that is protected by current limit, open load shutdown, thermal shutdown, and under voltage lockout. Applications Ordering Information Part Number ∗ Package Temperature MP1521EK MSOP10 -20° to +85°C MP1521EQ QFN16 (3x3) -20° to +85°C EV0005 MP1521EK Evaluation Board EV0021 MP1521EQ Evaluation Board On Board Power MOSFET Drive 9 White LEDs from 2.7V Input Drive 15 White LEDs from 5V Input Up to 90% Efficiency Over 80mA Output Current Capacity Open Load Shutdown Low Current Sensing Feedback Voltage Up to 3 String Current Sensing Feedback Analog and Digital PWM Brightness Control UVLO, Thermal Shutdown Soft Start Internal Current Limit Available in Compact MSOP10 and Tiny 3 mm x 3 mm QFN16 Package Evaluation Boards Available Handheld Computers, Cell phones, PDAs, Digital and Video Cameras, Small LCD Displays Li Ion and NiMH Battery Applications ∗ For Tape & Reel, add suffix –Z (i.e., MP1521EK–Z) For Lead Free, add suffix –LF (i.e., MP1521EK–LF–Z) Typical Application Circuit (One String of Six (6) LEDs) IN OFF SW 10 EN BRT/ PWM 2 EN GND 9 OLS 8 3 REF 4 BRT/PWM FB1 7 FB3 FB2 6 5 CIN 100 GND COUT MP1521 White LEDs Efficiency (%) 1 ON Efficiency vs LED current, 1 string of 6 Using Toko D62CB 47µH Inductor VIN L1 D1 90 VIN = 5V 80 VIN = 4V 70 VIN = 3V 60 50 5 10 15 20 25 LED Current (mA) MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 1 MP1521 High Efficiency White LED Driver Monolithic Power Systems Absolute Maximum Ratings Supply Voltage (VIN) Switch Voltage to GND VEN, VREF, VBRT, VFB1, VFB2, VFB3 Storage Temperature Recommended Operating Conditions 28V -0.5V to 28V –0.3V to 6V -55°C to +150°C Supply Voltage (VIN) Operating Temperature Switch Voltage to GND 2.7V to 25V -20°C to +85°C -0.5V to 25V Package Thermal Characteristics Thermal Resistance, ΘJA (MSOP10) Thermal Resistance, ΘJA (QFN16) 150°C/W 60°C/W Electrical Characteristics (VIN = 5.0V, TA = 25°C unless specified otherwise) Parameters Supply Current (shutdown) Supply Current (quiescent) Minimum Off Time, normal operation Minimum Off Time, start-up (Note 1) UVLO Symbol IIN (OFF) IIN (ON) tOFF (NORMAL) tOFF (START) Under Voltage Lockout Enable Threshold Hysterisis Leakage Current Open Load Shutdown Threshold Leakage Current Reference Output Voltage Load Regulation Line Regulation Feedback Comparator Threshold Hysterisis (Note 2) FB Input Bias Current PWM Mode Output-Off Threshold BRT Input Bias BRT Full Scale Threshold (Note 3) Output Switch Switch On Resistance (Note 2) RON Switch Current Limit Leakage Current Thermal Shutdown (Note 2) Condition Min VEN<0.4V VEN >1.5V, VBRT=0V, VFB=0V VEN >1.5V, VBRT =0.6V 400 VFB =0 VEN >1.5V, VBRT =0.6V, 1.5 VFB =0V VIN RISING VIN FALLING Typ 1 550 Max 3 700 Units µA µA 500 700 nS 2.4 µS 2.6 2.4 V V 2.0 1 V mV µA 45 29 1 70 V µA µA 2.1 1.9 0.8 1.0 60 VEN=3V Measured at OLS Pin VOLS=15V VOLS=25V 26 IREF=0A IREF=0 to 100µA VIN =3 to 15V, IREF=0A 1.20 1.235 2.5 2.5 1.27 5 5 V mV mV VBRT =1.2V VBRT =1.2V VFB=0.2V 380 420 -150 400 30 -50 0 mV mV nA VBRT=0.6V 0.18 -100 -30 0.26 0 V nA 1.2 V 0.6 Ω mA µA °C VIN=5.0V 300 0.5 400 VSW=25V 5 160 Notes: 1) First 64 pulses after EN switches high. 2) Guaranteed by design. 3) The output current is off when BRT is driven below the output-off threshold and full-scale when driven above the full-scale threshold. To PWM the output drive BRT above and below these thresholds. MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 2 MP1521 High Efficiency White LED Driver Monolithic Power Systems Pin Description 5 FB3 6 FB1 FB2 SW NC 14 13 GND EN 2 11 GND 10 OLS 9 FB1 NC REF Part Marking: MP1521EK Top View 3 4 8 7 12 FB2 4 BRT OLS 1 7 8 NC FB3 3 REF GND NC 9 15 2 6 EN SW NC 10 5 1 BRT IN IN QFN16 16 MSOP10 Part Marking: A1xx Table 1: MP1521 MSOP10 and QFN16 Pin Assignments MSOP Pin # 1 QFN Pin# 16 Pin Name IN 2 2 EN 3 4 REF 4 5 BRT 5 6 7 8 7 8 9 10 FB3 FB2 FB1 OLS 9 10 - 11, 12 14 1, 3, 6, 13, 15 GND SW N/C MP1521 Rev 2.7 10/06/04 Pin Function Input supply pin. It can be connected to the regulator’s input supply, or to the output for boot-strapped operation (boot-strapped operation is required for VIN of less than 3V). Regulator On/Off control input. Logic high (VEN>1V) turns on IC, logic low puts it into low current shutdown mode. Place a 100KΩ resistor in series with EN if it is connected to a voltage greater than 10V. 1.23V reference used for setting the analog control voltage at BRT input. This reference can supply up to 200µA to an external load. Do not connect any bypass capacitors to this pin. It is internally compensated. Analog or PWM input for controlling LED brightness. When used in analog mode, apply a DC voltage of 0.3 to 1.2V. This input voltage is attenuated by 1/3 to set the voltage across sense resistors at FB1, FB2, and FB3. Maximum brightness (20mA) occurs with 1.2V applied. To control brightness in PWM mode, apply a PWM square wave with a minimum voltage less the 0.18V and a maximum greater than 1.2V. When a voltage less than 0.18V is applied to this pin, the output switch is turned off. The regulator operates at maximum brightness when more than 1.2V is applied. The frequency of the PWM signal must be between 100 to 400 Hz. Feedback input for measuring voltage across current-sense resistor that is in series with LED string. Unused feedback pins must be connected to any used feedback pin. Open Load Shutdown pin senses regulator output voltage to protect IC during open load operation. When this pin’s voltage exceeds 28V, the output switch is shut off. The output switch remains off until the IC is reset by cycling the enable pin (EN) or input supply (IN) pin. Signal and power ground. Connect directly to ground plane. Output switch pin, power DMOS low-side switch. No Connect www.monolithicpower.com 3 MP1521 High Efficiency White LED Driver Monolithic Power Systems Figure 2: MP1521 Functional Block Diagram IN Internal Regulator & Enable Circuit EN UVLO & Thermal Shutdown SW 17V 160K 500nS One-Shot Timer GND 0.25V Feedback Comparator Bandgap Reference 1.23V FB1 FB2 + + BRT Current Limit Comparator + REF 0.5 W Power FET + - Open Load Shutdown Comparator + 20K + 1.23V Control Logic & Output Driv er + OLS FB3 20K 10K 1.2V MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 4 MP1521 High Efficiency White LED Driver Monolithic Power Systems Functional Description Operation PWM/ Brightness Adjust The MP1521 utilizes a constant off-time control scheme (Refer to the Block Diagram). For maximum brightness, the BRT pin is biased at or above 1.2V. Its voltage is routed through the unity gain buffer whose the output of is clamped at 1.2V. A 20K/10K divider from the Buffer to the non-inverting input of the Feedback comparator divides the BRT voltage by three to set the current sense threshold. If any of the feedback pins FB1, FB2, or FB3 is lower than this threshold the Power FET is turned on. The Power MOSFET and inductor current increases until the current limit comparator trips at 0.5A turning off the MOSFET for 500ns. At the end of 500ns if any of the Feedback pins are still lower than the current sense threshold. The Power FET is again turned on. This cycle repeats itself until all three of the feedback pins exceed the threshold. PWM Brightness Adjust is accomplished by driving the BRT pin with a square wave whose low voltage is below 0.2V and whose high voltage is greater than 1.2V. A voltage below 0.2V forces the Power MOSFET off. A voltage greater than 1.2V will cause all three feedback pins to regulate at or above 0.4V Open Load Shut-Off Open Load Shut-Off is implemented by connecting the OLS pin to VOUT. In the fault condition where the connection to the LED’s is open, VOUT will rise up, as all the feedback pins are absent of voltage. Once VOUT exceeds 28V, the part will cease operation until the EN pin is cycled off and on. To disable the open load shut-off feature, connect the OLS pin to GND. Analog Brightness Adjust Analog Brightness Adjust is accomplished by applying a voltage between 0.26V to 1.2V on the BRT pin. The 1.23V REF output can be used to bias a potentiometer whose wiper drives the BRT pin. MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 5 MP1521 High Efficiency White LED Driver Monolithic Power Systems Application Circuits Figure 3: One String of Four (4) LEDs D1, B130 IN 1 SW ON EN 2 90 VIN = 4V 85 4.7µF GND COUT 1µF GND EN CIN 10 MP1521 OFF L 47µH Efficiency vs LED current using 47µH Toko D62CB Inductor Efficiency (%) VIN 80 VIN = 3V 75 9 5 White LEDs BRT OLS REF 4 BRT FB1 5 FB3 FB2 10 15 20 LED Current mA 8 6 20 Line regulation using 47µH Toko D62CB Inductor 22 7 LED Current (mA) 3 21 20 19 18 17 16 15 2.4 3.6 3.0 4.2 VIN (V) Figure 4: One String of Six (6) LEDs (Low inductor height for portables) VIN L1 IN COUT 1µF MP1521 ON OFF SW 10 EN 2 EN 3 REF 4 BRT GND 9 OLS 8 FB1 7 85 CIN 4.7µF GND Efficiency (%) D1, B130 1 Efficiency vs VIN using 1.2mm High Sumida CMD4D11 Inductor 6.8µH 80 10µH 15µH 75 70 BRT White LEDs 2.5 3 3.5 4 4.5 VIN (V) FB3 FB2 6 20 LED Current (mA) 5 Line regulation using 1.2mm High Sumida CMD4D11 Inductor 23.0 21.0 6.8µH 19.0 10µH 17.0 15µH 15.0 2.5 3 3.5 4 4.5 VIN (V) MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 6 MP1521 High Efficiency White LED Driver Monolithic Power Systems Application Circuits Continued Figure 5: Two Strings of Four (4) LEDs or Eight (8) LEDs Total Efficiency vs LED current using 47µH Toko D62CB Inductor L1 47µH D1, B130 1 IN EN OFF 2 GND COUT 1uF MP1521 ON CIN 4.7µF 10 SW Efficiency (%) VIN GND 9 EN BRT 4 80 VIN = 5V 70 VIN = 4V 60 White LEDs 3 90 VIN = 3V OLS 8 REF 50 5 FB1 BRT 15 25 35 45 7 Total LED Current (mA) FB3 6 FB2 LED current (mA) 5 20 20 Line Regulation using 47µH Toko D62CB Inductor 25 20 15 10 2.5 3 3.5 4 4.5 VIN (V) Figure 6: Three Strings of Three (3) LEDs or Nine (9) LEDs Total L1 47µH Efficiency vs LED current using 47µH Toko D62CB Inductor VIN D1, B130 IN SW 10 ON EN 2 OFF EN GND COUT 1µF MP1521 GND 9 White LEDs OLS 8 7 3 REF 4 BRT FB1 5 FB3 FB2 100 Efficiency (%) 1 CIN 4.7µF 90 VIN = 5V 80 VIN = 4V 70 VIN = 3V 60 50 BRT 0 20 60 40 80 LED current (mA) 20 20 20 LED Current (mA) 6 22 Line regulation using 47µH Toko D62CB Inductor 20 18 16 1.4 MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 2.0 2. 6 3.0 3.6 4.2 VIN (V) 7 MP1521 High Efficiency White LED Driver Monolithic Power Systems Package Information MSOP10 0.0197(0.500)TYP 0.004(0.100) 0.008(0.200) PIN 1 IDENT . SEE DETAIL "A" 0.114(2.900) 0.122(3.100) 0.184(4.700) 0.200(5.100) 0.014(0.350)TYP GATE PLANE 0.010(0.250) 0.014(0.350)TYP 0.114(2.900) 0.122(3.100) DETAIL "A" 0o-6o 0.017(0.400) 0.025(0.600) 0.030(0.750) 0.038(0.950) 0.032(0.800) 0.044(1.100) 0.002(0.050) 0.006(0.150) 0.008(0.200)REF NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters. QFN16 (3 x 3) 3.00 (0.118) BSC Pin 1 Identification Pin 1 Identification 1 0.18 (0.007) 0.28 (0.011) 4 16 5 3.00 (0.118) BSC 1.400 (0.055) 1.700 (0.067) exp. pad Bottom View 0.550 (0.0217) 0.450 (0.0177) 8 13 12 0.90 (0.035) 1.00 (0.039) 0.178 (0.007) 0.228 (0.009) 0.450 (0.0177) 0.350 (0.0138) 9 1.500 (0.059) Ref. 0.00 (0.000) 0.05 (0.002) NOTE: 1) Control dimension is in millimeters. Dimension in bracket is inch. NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change without notice. Please contact the factory for current specifications. No responsibility is assumed by MPS for its use or fit to any application, nor for infringement of patent or other rights of third parties. MP1521 Rev 2.7 10/06/04 © 2004 MPS, Inc. Monolithic Power Systems, Inc. 983 University Ave, Building A, Los Gatos, CA 95032 USA Tel: 408-357-6600 ♦ Fax: 408-357-6601 ♦ www.monolithicpower.com 8