ZLED7320 datasheet(13/28 Pages) ETC2

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ZLED7320

High Current 40V LED Driver with Internal Switch

Data Sheet

August 12, 2011

the prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice.

13 of 27

OUTnom =

ADJ

OUTdc

083

∗

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 VIN and ISENSE pins as shown in Figure 3.1, sets

IOUTnom, the nominal average output current. Equation (1) can be used to calculate the nominal output current,

which is the LX switch output current ILX if the ADJ pin is floating (VADJ = VREF =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 IOUTnom including ripple (see section 3.3.5) must not exceed the maximum current specifications (1.3.10).

(1)

2.3

Control of Output Current via an External DC Control Voltage on the ADJ Pin

An external DC voltage (VADJ) input on the ADJ pin can control brightness by setting the output current to a value

below the nominal average current IOUTnom determined by RS. With this method, the output current can be adjusted

from 25% to 100% of IOUTnom. The DC voltage source must be capable of driving the ADJ pin’s input impedance

RADJ (500k

± approximately 25%; internal pull-up resistor to VREF). See Figure 3.2 for a typical application circuit.

The nominal average output current IOUTdc resulting from an external DC control voltage VADJ can be calculated via

equation (2) where 0.3V

≤ VADJ ≤1.2V:

(2)

Brightness is 100% if VADJ = VREF, the internal reference voltage, which can be measured on the ADJ pin when it is

floating (1.2V, typical). If VADJ ≥1.2V, current is automatically clamped at 100% brightness. Note: Absolute

maximum VADJ= 6V.

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