APW7001QAI-TRG datasheet(13/19 Pages) ANPEC

13 / 19 page

Rev. A.4 - Oct., 2009

APW7001

www.anpec.com.tw

Application Information

Figure 2. PWM Dimming Application Circuit

ENS

ENM

APW7001

OFF

PWM

OFF

PWM

Figure 3. PWM Dimming Frequency vs. LED Current

Figure 4. ENM/ENS Timing

100

f=100Hz

LED=20mA

in 2x mode

f=10kHz

Dimming Duty (%)

f=40kHz

f=50kHz

Capacitor Selection

For lower input and output voltage ripples, both input and

output capacitors should be larger values and lower ESR

capacitors. However, the larger output capacitor values

will increase the soft-start time. The lower charge pump

flying capacitors values and ESR improve the efficiency,

but lower capacitor values may limit the LED’s currents at

low input voltage.

It is recommended that the low ESR and low variation

over temperature, such as the ceramic capacitors with

X7R or X5R and the value is 1

µF for the input capacitor,

output capacitor, and the charge pump flying capacitors.

Brightness Control

1. PWM dimming using ENM, or/and EMS

The first method for dimming the LEDs is to apply a PWM

signal into the ENM or/and ENS pins. Figure 2 shows the

application circuit. The average LED current is propor-

tional to the PWM signal duty cycle. Note that the frequency

of PWM signal will affect the minimum dimming duty.

Figure 3 shows the LED current vs. dimming frequency

and dimming duty, the recommend dimming frequency

is below 10kHz. The PWM signal can either be applied to

ENM or ENS, or both inputs can be tied together and the

PWM signal can be applied to both pins. Table 3 shows

the truth table of ENM and ENS dimming control. The

average LED current is calculated by the following

equation:

Where:

LED(max) is programmed LED current by ISET pin

toff is the off time of the PWM signal

ton is the on time of the PWM signal

OUT

ENM

ILED

Bright ness

ENS

ILED

Bright ness

100%

25%

50%

Shutdown

75%

20ms

(main)

(sub)

ENM

ENS

LED Status

PWM

LED1, 2, 3, 4 are turned off

LED5, 6 are PWM dimming

PWM

LED1, 2, 3, 4 are PWM dimming

LED5, 6 are turned off

PWM

LED1, 2, 3, 4 are turned on

LED5, 6 are PWM dimming

PWM

LED1, 2, 3, 4 are PWM dimming

LED5, 6 are turned on

PWM

LED1, 2, 3, 4 are PWM dimming

LED5, 6 are PWM dimming

Table 3. The Truth Table of ENM and

ENS Dimming Control

toff

ton

(max)

LED

)

avg

(

LED

APW7001QAI-TRG Datasheet(PDF) 13 Page - Anpec Electronics Coropration

APW7001QAI-TRG Datasheet(HTML) 13 Page - Anpec Electronics Coropration

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Datasheet Download

Link URL