ZLED7520ZI1R ZMDI, ZLED7520ZI1R Datasheet - Page 21

• Manufacturer Part Number: ZLED7520ZI1R
• Description: LED Lighting Drivers LED driver
• Manufacturer: ZMDI

Specifications of ZLED7520ZI1R

• Rohs: yes
• Input Voltage: 6 V to 40 V
• Operating Frequency: 1 MHz
• Maximum Supply Current: 600 uA
• Output Current: 0.75 A
• Maximum Operating Temperature: + 105 C
• Mounting Style: SMD/SMT
• Package / Case: DFN-5
• Minimum Operating Temperature: - 40 C
• Power Dissipation: 500 mW

Example: For an application of 3 LEDs driven at 0.33A and supplied with 24VDC, a maximum ripple of 10% is
allowed. The ZLED7x20 is operated at 150kHz with a duty cycle of 0.4 leading to an on time of 2.67µs. As
calculated in equation 12, a capacitor C1 of 470nF may be adequate, again including a safety margin of about
50%.
To achieve maximum stability over temperature and voltage, an X7R, X5R, or better dielectric is recommended
while Y5V must be avoided.
3.3.4
External capacitor C2 minimizes ground bounce during switching of the internal MOSFET output switch. Ground
bounce is typically caused by parasitic inductance and resistance due to the distance between the grounds for the
power supply and the ZLED7x20 GND pin. Use a 0.1µF, X7R ceramic capacitor to ground for C2.
3.3.5
If required, the C3 can be used to reduce peak-to-peak ripple current in the LED string. Low ESR capacitors
should be used because the efficiency of C3 largely depends on its ESR and the dynamic resistance of the LEDs.
For an increased number of LEDs, using the same capacitor will be more effective. Lower ripple can be achieved
with higher capacitor values, but this will increase start-up delay by reducing the slope of the LED voltage as well
as cause increased current during converter start-up. The capacitor will not affect operating frequency or effici-
ency. For a simulation or bench optimization, C3 values of a few µF are an applicable starting point for the given
configuration. Ripple current reduction is approximately proportional to the value of C3.
3.3.6
The flyback diode D1 must have a continuous current rating greater than the maximum output load current and a
peak current rating higher than the peak L1 coil current. Important: Use a low-capacitance, fast Schottky diode
that has low reverse leakage at the maximum operating temperature and maximum operating voltage for the
application to avoid excess power dissipation and optimize performance and efficiency. For silicon diodes, there is
a concern that the higher forward voltage and increased overshoot from reverse recovery time could increase the
peak LX pin voltage (V
3.4
The following guidelines are strongly recommended when laying out application circuits:
Data Sheet
August 12, 2011
C
1
ZLED7520
High Current 40V LED Driver with Internal Switch
MIN
Important: Locate the L1 inductor and the C1 input decoupling capacitor as close as possible to the
ZLED7x20 to minimize parasitic inductance and resistance, which can compromise efficiency. Use low
resistance connections from L1 to the LX and V
All circuit board traces to the LX pin must be as short as possible because it is a high-speed switching
node.
If the ADJ pin floats, all circuit board traces to the ADJ pin must be as short as possible to reduce noise
pickup.
Application Circuit Layout Requirements
De-bouncing Capacitor C2
Capacitor C3 for Reducing Output Ripple
Diode D1
. 0
33
24
A
V
*
*
. 2
© 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.
0
67
1 .
LX
s
). The total voltage V
367
nF
LX
(including ripple voltage) must not be >50V.
IN
pins.
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