ZLED-PCB1 datasheet(11/20 Pages) ETC2

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ZLED7000

40V LED Driver with Internal Switch

Data Sheet

August 12, 2010

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

11 of 19

2.3.2

PWM Control

The output current on LX can be set to a value below the nominal average value determined by resistor RS by

using an external PWM signal as the control signal applied to the ADJ pin. This control signal must be capable

of driving the ZLED7000’s internal 500kΩ pull-up resistor. See Figure 2.1 for an illustration. The minimum

signal voltage range is 0V to 1.8V; the maximum voltage range is 0V to 5V. See Table 1.3 for the

specifications for the signal’s duty cycle DPWM. Any negative spikes on the control signal could interfere with

current control or proper operation of the ZLED7000.

Figure 2.1

Directly Driving ADJ Input with a PWM Control Signal

7000

ZLED

GND

ADJ

1.8V to 5V

PWM

2.3.3

External DC Voltage Control of Output Current

The output current on LX can be set to a value below the nominal average value determined by resistor RS by

using an external DC voltage VADJ (0.3 V ≤ VADJ ≤ 1.2V) to drive the voltage at the ADJ pin. This allows

adjusting the output current from 25% to 100% of IOUTnom. See Figure 2.2 for an illustration. The output current

can be calculated using equation (2). If VADJ matches or exceeds VREF (1.2V), the brightness setting is

clamped at its maximum (100%).

Figure 2.2

External DC Control Voltage at ADJ Pin

ADJ

GND

ZLED7000

ADJ

OUT

079





(2)

Where

IOUT_DC = Nominal average output current through the LED(s) with a DC control voltage

VADJ = External DC control voltage: 0.3 V ≤ VADJ ≤ 1.2V

RS ≥0.13Ω

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