ZLED7015 Datasheet

© 2016 Integrated Device Technology, Inc.

14

April 20, 2016

(

)

S

FB

DC

FB

OUT

R

R

V

V

R

V

I













−

×

−

=

4

3

EN

LX

AGND

ZLED7015

LED

String

VIN = 6 to 30 VDC

COUT

R1

L1

CIN

D1

FB

PGND

OVP

R2

RS

VP

VDD

C1

CVDD

CVP

C2

RVDD

REN

COVP

R4

R3

R5

C3

Microcontroller PMW Signal

5V

0V

The output current controlled by the DC voltage on FB can be calculated using equation (2):

(2)

Where

IOUT = Output current through the LED(s) with a DC control voltage

VFB = Internal feedback reference voltage (Table 1.3, parameter 1.3.7)

VDC = External DC control voltage

2.2.3

Dimming via PWM Control

An external pulse-width modulated (PWM) signal input can be used to control the LED output current by driving

the output current to a value below the nominal average value defined in section 2.2.1. A microcontroller can be

used to generate the PWM signal. See Figure 2.3 for an example circuit. The PWM signal is superimposed on the

feedback voltage from RS at the FB pin via the input filter R5/C3 and R4, which produces a DC voltage with a

ripple. This method of controlling dimming is similar to the external DC voltage control described in section 2.2.2.

The duty cycle of the PWM signal regulates the filtered DC voltage level, which inversely controls the LED output

current level. When the duty cycle is at 100%, the output current is at the minimum. With a 0% duty cycle, the

output current is at the maximum.

Recommendation: With a PWM signal of 0 to 5V, use an R3 value of 10k

Ω and a PWM frequency of >2kHz to

minimize the filtered PWM voltage ripple.

Note: It is important to ensure that the LED output voltage VOUT remains higher than the input voltage VIN in

dimming applications.

Figure 2.3

Example Circuit for Controlling Output Current via a PWM Control Signal