EV0021

EV0021 Monolithic Power Systems General Description The EV0021 evaluation board uses the MP1521 to drive up to three strings of 5 White LEDs. This MP1521 uses a peak current, constant minimum off-time architecture and has three individual current-sensing feedbacks. The OLS pin is designed for detecting loose or open LED connections. 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. MP1521 High Efficiency White LED Driver EVALUATION BOARD Absolute Maximum Ratings Supply Voltage (VIN) 28V Switch Voltage to GND -0.5V to 28V VEN,VREF, VBRT, VFB1, VFB2, VFB3 –0.3V to 6V Storage Temperature -55°C to +150°C Recommended Operating Conditions Supply Voltage (VIN) 2.7 V to 25V Ordering Information Board Number EV0021 MPS IC Number MP1521EQ Figure 1: EV0021 Evaluation Board EV0021 Rev 1.1_01/21/03 www.monolithicpower.com 1 EV0021 Monolithic Power Systems Figure 2: EV0021 Schematic MP1521 High Efficiency White LED Driver EVALUATION BOARD EV0021 Rev 1.1_01/21/03 www.monolithicpower.com 2 EV0021 Monolithic Power Systems Table 1: EV0021 Bill of Materials Parts ICs MP1521EQ Capacitors 4.7µF 1µF, 25V Resistors 10KΩ 20 Ω Inductors 15µH Diodes B130, 1A, 30V, Schottky LEDS (Not Provided) Package QFN16 1206 1210 0603 0603 CDRH3D16 SMA Vendor MPS Any Any Any Any Sumida Any QTY 1 1 1 3 3 1 1 Components U1 C1 C2 R1, R2, R3 R4, R5, R6 L1 D1 MP1521 High Efficiency White LED Driver EVALUATION BOARD Operating Instructions 1. Connect VCC to the power source’s positive output. 2. Connect GND to supply ground. 3. Applying a logic signal to EN pin will enable the MP1521. 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 the input is greater than 10V. For automatic start up connect EN to VCC. 4. Applying a PWM signal to the BRT will adjust the 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. 5. The FB1, FB2 and FB3 pins can be used to measure the voltage across the current-sense resistor that is in series with the LED strings. Unused feedback pins must be connected to any used feedback pin. 6. OLS senses the 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 (VIN) EV0021 Rev 1.1_01/21/03 www.monolithicpower.com 3 EV0021 Monolithic Power Systems Figure 3: EV0021 Top Silk Layer MP1521 High Efficiency White LED Driver EVALUATION BOARD Figure 4: EV0021 Top Layer Figure 5: EV0021 Bottom Layer 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. EV0021 Rev 1.1 01/21/03 © 2003 MPS, Inc. Monolithic Power Systems, Inc. 3777 Stevens Creek Blvd, Suite 400, Santa Clara, CA 95051-7364 USA Tel: (408) 243-0088, Fax: (408) 243-0099, Web: www.monolithicpower.com 4