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ZLED7000 Datasheet(PDF) 10 Page - List of Unclassifed Manufacturers |
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ZLED7000 Datasheet(HTML) 10 Page - List of Unclassifed Manufacturers |
10 / 20 page ZLED7000 40V LED Driver with Internal Switch Data Sheet August 12, 2010 © 2010 Zentrum Mikroelektronik Dresden AG — Rev. 1.1 All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice. 10 of 19 2 Circuit Description The ZLED7000 is an inductive step-down converter for driving LEDs. It operates in continuous mode, enabling proper LED current control. The ZLED7000 supports linear or PWM control of the LED current. Only a few external components are needed for typical applications. 2.1 Voltage Supply The ZLED7000 has an internal regulator that disables the LX output until the voltage supply rises above a start-up threshold voltage set internally as needed to ensure that the power MOSFET on-resistance is low enough for proper operation. When the supply voltage exceeds the threshold, the ZLED7000 begins normal operation. Important: The ZLED7000 must be operated within the operating voltage range specified in Table 1.2 to avoid conditions that could result in thermal damage to the ZLED7000. Operating with the supply voltage below the minimum can result in a high switch duty cycle and excessive ZLED7000 power dissipation, risking over- temperature conditions (also see section 4.1 regarding thermal restrictions) that could result in activation of the ZLED7000’s thermal shut-down circuitry. With multiple LEDs, the forward drop is typically adequate to prevent the chip from switching below the minimum voltage supply specification (6V), so there is less risk of thermal shut-down. 2.2 ZLED7000 Standby Mode Whenever the ADJ pin voltage falls below 0.2V, the ZLED7000 turns the output off and the supply current drops to approximately 60μA. This standby mode minimizes current consumption. 2.3 Output Current Control The LED control current output on the LX pin is determined by the value of external components and the control voltage input at the ADJ pin. Selection of the external component RS is discussed below, and other external components are discussed in section 2.3.4. The subsequent sections describe the two options for control voltage input at the ADJ pin: a pulse width modulation (PWM) control signal or a DC control voltage. The ADJ pin has an input impedance † of 500kΩ ±25%. 2.3.1 Output Current and RS The current sense threshold voltage and the value of the external current sense resistor (RS) between VIN and ISENSE set the output current through the LEDs (IOUT). Equation (1) below shows this basic relationship. Unless the ADJ pin is driven from an external voltage (see section 2.3.3), the minimum value for RS is 0.13 Ω to prevent exceeding the maximum switch current (see Table 1.1). S OUT R mV 95 I (1) Where IOUT = Nominal average output current through the LED(s) RS ≥0.13Ω † At room temperature. |
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