ZLED7020

High Current 40V LED Driver with Internal Switch

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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Figure 3.4

Basic ZLED7x20 Application Circuit with Output Current Controlled by External Microcontroller Signal

3.2

Thermal Considerations for Application Design

3.2.1

Temperature Effects of Load, Layout, and Component Selection

Do not exceed the package power dissipation limits by driving high load currents or by operating the chip at high

ambient temperatures. Power dissipation also increases if the efficiency of the circuit is low as could result from

selecting the wrong coil or from excessive parasitic output capacitance on the switch output. See the layout

guidelines in section 3.4.

3.2.2

internal regulator disables the drive to the internal power MOSFET output switch. Above this threshold, the

MOSFET on-resistance is low enough for the chip to start to operate; however, if the supply voltage remains

below the specified minimum (6V), the duty cycle of the output switch will be high and the ZLED7x20 power

dissipation will be at a maximum. Avoid operating the ZLED7x20 under such conditions to reduce the risk of

damage due to exceeding the maximum die temperature. When driving multiple LEDs, their combined forward

of thermal damage.

3.3

External Component Selection

Note: Also see section 3.4 for layout guidelines for the following external components.

3.3.1

Sense Resistor Rs

Table 3.1 gives values for Rs under normal operating conditions in the typical application shown in Figure 3.1.

Note: Under the conditions given in Table 3.1, in order to maintain the switch current below the maximum value

specified in section 1, 0.082

is the minimum value for Rs for the ZLED7020, 0.1

for the ZLED7320, 0.13

for

the ZLED7520 and 0.27

for the ZLED7720. It is possible to use different values of Rs if the ADJ pin is driven

from an external voltage.