LDS8711

© 2010 IXYS Corp.

7

Doc. No. 8711DS, Rev. N1.0

Characteristics subject to change without notice

BLOCK DIAGRAM

Figure 3. LDS8711 Functional Block Diagram

BASIC OPERATION

At power-up, EN/PWM pin should be logic LOW. The

LDS8711 starts operating when EN/PWM pin is

asserted logic high. The device becomes enabled

and wait for the first pulse that determines mode, at

LED current sets to factory programmed value and

every next incoming pulse will be rec ognized as

enters Smart OneWire

™ interface mode and wait for

command. Every next of 16 incoming pulses will be

recognized as command. After LDS8711 accepts

command, the current sets in respect to programmed

value, and device changes mode to PWM. If device is

not able to recognize command due some error, it

enters shutdown mode after 10 ms.

If the input voltage is sufficient to regulate all LED

currents, the device remains in operating mode. The

voltage up to 250 mV above summary LED forward

voltage significantly increasing driver’s efficiency.

If the input voltage is insufficient or falls to a level

where the regulated currents cannot be maintained,

the Under-Voltage protection turns device off setting

it in shutdown mode.

The LDS8711 has soft start function that prevent high

input current spike at device’ wake-up.

The EN/PWM pin should be held low for more than

10 ms to completely turn device in low current

shutdown mode.

LED Current Setting

The maximum current value in the LED string may be

factory preset in the range from 10 to 30 mA in 0.125

mA steps, or set by Smart OneWire

™ interface in the

range from 0.125 to 32 mA. The average LED string

current that determines LED brightness may be

controlled applying PWM signal to the EN/PWM pin.

The maximum PWM frequency is 30 kHz, while

frequiencies below 100 Hz are not recommended to

avoid visible LED flikering. Duty cycle that determines

average LED string current may vary in the range

from 5% to 100% at 1 k Hz or from 20% to 100% at

30 kHz with high linearity current regulation.

It gives possibility regulate brightness either in DC

mode with changing color temperature, or in PWM

mode with stable color temperature.

To start LDS8711 in PWM Mode, the first positive

pulse applied to EN/PWM pin after power-up should