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MT7603 Datasheet(PDF) 4 Page - Maxic Technology Corporation |
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MT7603 Datasheet(HTML) 4 Page - Maxic Technology Corporation |
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4 / 6 page  MT7603 Maximizing IC Performance Linear Constant – Current LED Driver Rev. 1.00 Page 4 APPLICATION INFORMATION MT7603 is a linear constant-current LED driver. It can achieve accurate constant-current at specific operating voltage range with less peripheral components. Start Up During start-up, VDD is charged through a start-up resistor. As VDD reaches 12V, the control logic starts to work. As the VDD continues rising up to 15V, it will be clamped. When the VDD voltage drops to below 9V, the system shuts down, and the UVLO function is triggered. As shown in Fig.1. VDD EN 12V 9V 15V Fig.1 Start up and close sequence Output Current and Voltage Determination It is important to determine the LED voltage and current, As MT7603 is a linear buck LED driver IC, the peak value of the rectified input voltage must be greater than the output LED voltage. Refer to Fig.2, MT7603 automatically turns on the LED string following the input sine wave. When the input voltage rises and reaches to the LED conducting voltage VLED, The LED string is turned on. Since then, the input voltage continues rising, the LED string voltage keeps stable, the external MOSFET bears the superfluous voltage drop. If the input voltage drops, the procedure is reversed. So high LED voltage makes the LED availability to be low, and low LED voltage will reduce the system efficiency. It is recommended to choose about 120V high-voltage LED string in 120VAC applications; And to choose about 250V high-voltage LED string in 220VAC applications. It can be adjusted according to actual application. Fig.2 LED conduction procedure Sense Resistor Settings The output current be set by the sense resistor RCS. MT7603 generates a control signal by comparing the voltage on sense resistor RCS and internal reference voltage VREF (500mV) to achieve LED constant current output. The peak current of LED light string: Rcs mV Rcs V I REF PAEK 500 (1) Fig.2 shows the LED conduction procedure, MT7603 actually controls the LED peak current during the conduction-time. There are two cases in real application: 1) No large electrolytic capacitor is needed after the rectifier bridge, as shown in Fig.2. At the valley, the input voltage is lower than LED string forward voltage, the output current is zero. When the input voltage is higher than the LED string forward voltage, the output current is IPEAK. So, in the real application, the LED string current is discontinuous, and the ILED is the average LED string current. D × PEAK LED I I (2) Where, D is the LED string conduction ratio. For buy, please contact: info@chimicron.com Skype:info@chimicron.com www.chimicron.com For buy, please contact: info@chimicron.com Skype:info@chimicron.com www.chimicron.com |
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