ZLED7000 Datasheet

© 2016 Integrated Device Technology, Inc.

13

April 20, 2016

(

)

s

73

.

2

9

.

0

48

.

0

3

.

0

A

333

.

0

V

4

.

3

V

12

A

333

.

0

3

.

0

H

220

T

ON

µ

Ω

Ω

Ω

µ

=

+

+

∗

−

−

∗

∗

=

(

)

s

47

.

5

3

.

0

48

.

0

A

333

.

0

V

36

.

0

V

4

.

3

A

333

.

0

3

.

0

H

220

T

OFF

µ

Ω

Ω

µ

=

+

∗

+

+

∗

∗

=

MAX

ON

F

MIN

V

T

I

C

∆

∗

=

The following calculation example yields an operating frequency of 122kHz and a duty cycle of 0.33:

Input data: VIN

=12V, L=220μH, r

L

=0.48Ω, V

LED=3.4V, IAVG =333mA and VD =0.36V

(5)

And

(6)

3.2

External Component – Capacitor C1

To improve system efficiency, use a low-equivalent-series-resistance (ESR) capacitor for input decoupling

because this capacitor must pass the input current AC component. The capacitor value is defined by the target

maximum ripple of the supply voltage; the value is given by equation (7).

(7)

Where

IF

Value of output current

ΔV

MAX

Maximum ripple of power supply

TON

Maximum ON time of MOSFET

In the case of an AC supply with a rectifier, the capacitor value must be chosen high enough to make sure that

the DC voltage does not drop below the maximum forward voltage of the LED string plus some margin for the

voltage drops across the coil resistance, shunt resistor, and ON resistance of the switching transistor.

Recommendation: Use capacitors with X5R, X7R, or better dielectric for maximum stability over temperature and

voltage. Do not use Y5V capacitors for decoupling in this application. For higher capacitance values, aluminum

electrolytic caps with high

switching capability should be used. In this case, improved performance can be

reached by an additional X7R/X5R bypass capacitor of at least 100nF.

3.3

External Component – Diode D1

For the rectifier D1, select a high-speed, low-capacitance Schottky diode with low reverse leakage at the

maximum operating voltage and temperature to ensure maximum efficiency and performance.

Important: Choose diodes with a continuous current rating higher than the maximum output load current and a

peak current rating above the peak coil current. When operating above 85°C, the reverse leakage of the diode

must be addressed because it can cause excessive power dissipation in the ZLED7000.