ZLED7520 Datasheet, PDF (13/28 Pages) List of Unclassifed Manufacturers – High Current 40V LED Driver with Internal Switch

ZLED7520
High Current 40V LED Driver with Internal Switch
2 Circuit Description
2.1 ZLED7x20 Overview
The ZLED7x20 is a continuous-mode inductive step-down converter LED driver for driving single or multiple
series-connected LEDs from a voltage input higher than the LED voltage (Vin = 6 to 40 VDC; see section 3.2.2 for
important details). The ZLED7x20 provides an adjustable output current (1.2A maximum for ZLED7020; 1.0A
maximum for ZLED7320; 0.75A maximum for ZLED7520; 0.35A maximum for ZLED7720), which is nominally set
via an external sense resistor Rs and controlled by the ZLED7x20’s integrated high-side output current-sensing
circuit and output switch. An external control signal (e.g., DC voltage, PWM waveform, or microprocessor signal)
on the ADJ pin can be used to linearly adjust the output for continuous, variable, or gated-output current. See
page 3 for a block diagram of the ZLED7x20.
The output can be turned off by applying a voltage ≤0.2V (typical) to the ADJ pin, which puts the ZLED7x20 in a
low-current standby state. See section 2.6 for a description of this shutdown mode.
Only a resistor, a diode, an inductor, and three capacitors are needed for a typical basic application. Refer to the
application circuits in section 3 for the location of the components referenced in the following sections.
2.2 Control of Output Current via External Sense Resistor Rs
External sense resistor Rs, which is connected between the V_IN and I_SENSE pins as shown in Figure 3.1, sets
I_OUTnom, the nominal average output current. Equation (1) can be used to calculate the nominal output current,
which is the LX switch output current I_LX if the ADJ pin is floating (V_ADJ = V_REF =1.2V). See section 3.3.1 for
recommended values for Rs in a typical basic application and section 3.4 for layout guidelines for Rs. Note that
the peak I_OUTnom including ripple (see section 3.3.5) must not exceed the maximum current specifications (1.3.10).
I_OUTnom
=
0.1V
Rs
(1)
2.3 Control of Output Current via an External DC Control Voltage on the ADJ Pin
An external DC voltage (V_ADJ) input on the ADJ pin can control brightness by setting the output current to a value
below the nominal average current I_OUTnom determined by R_S. With this method, the output current can be adjusted
from 25% to 100% of I_OUTnom. The DC voltage source must be capable of driving the ADJ pin’s input impedance
R_ADJ (500kΩ ± approximately 25%; internal pull-up resistor to V_REF). See Figure 3.2 for a typical application circuit.
The nominal average output current I_OUTdc resulting from an external DC control voltage V_ADJ can be calculated via
equation (2) where 0.3V≤ V_ADJ ≤1.2V:
I_OUTdc
=
0.083 ∗ V_ADJ
R_S
(2)
Brightness is 100% if V_ADJ = V_REF, the internal reference voltage, which can be measured on the ADJ pin when it is
floating (1.2V, typical). If V_ADJ ≥1.2V, current is automatically clamped at 100% brightness. Note: Absolute
maximum V_ADJ= 6V.
Data Sheet
August 12, 2011
© 2011 Zentrum Mikroelektronik Dresden AG — Rev. 1.2
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.
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