ZLED7001

Universal LED Driver with Temperature Compensation

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.

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2.4.

Current Sensing

equation (3):

LED

CSTH

CS

I

15

.

1

V

R





(3)

Where

The current sense input of the ZLED7001 is connected to the non-inverting inputs of two comparators. The

inverting terminal of one comparator is tied to an internal 240mV reference and the inverting terminal of the

other comparator is connected to the LD pin. The outputs of both comparators are fed into an OR gate, and

the output of the OR gate is connected to the reset pin of the flip-flop. Thus, the comparator that has the lower

voltage at the inverting input determines when the GATE output is turned off.

The comparator outputs also include a typical 480ns blanking time that prevents spurious turn-offs of the

external MOSFET due to the turn-on spike normally present as a result of transistor gate-source capacitance.

In rare cases, this internal blanking time might not be enough to filter out the turn-on spike. If so, an external

Note that the comparators are relatively fast: 80ns typical response time. Invalid triggering by these com-

parators could result if the layout fails to minimize external inductances.

2.5.

Timing Circuit



















pF

10

C

1

ns

510

T

OFF

TIME

_

OFF

(4)

2.6.

PWM Dimming Application Circuit

For PWM dimming applications, the ZLED7001’s PWMD pin is driven with a low-frequency square-wave

control signal. The GATE pin’s driver is enabled when the control signal is high and disabled when the control

signal is low. The LED current’s rise and fall rate is controlled only by the inductance value, the supply

voltage, and LED forward voltage.

If the PWMD pin is allowed to float, the PWM dimming function is disabled.

2.7.

Linear Dimming Application Circuit

For linear dimming applications, an external voltage ranging from 50mV (typical) to 240mV (typical) is applied

to the LD (linear dimming) pin to control the LED current during operation. Linear dimming can be used to

adjust the LED current level to reduce the LED’s brightness. In this case, connect a resistor between the

VREF pin and the LD pin and connect a negative-temperature-coefficient (NTC) thermistor between the LD

pin and ground. The ZLED7001 can also provide temperature compensation, (see the application circuit on

page 2 and section 2.8).