NCP5008 datasheet(14/20 Pages) ONSEMI

14 / 20 page

NCP5008, NCP5009

http://onsemi.com

Output Load Drive

In order to make profit of the built−in Boost capabilities,

one shall operate the NCP5008/NCP5009 in the continuous

output current mode. Such a mode is achieved by using and

external reservoir capacitor (preferably a low ESR ceramic

type) across the LED as depicted in Figures 22, 23, 24, 25,

and 26.

Using an extra photo sensor is not mandatory and the

related pin 2 can be either left open or connected to Vbat,

but must not be grounded on the NCP5009 version only.

At this point, the designer must carefully analyze two

parameters:

1. The output voltage must be limited to 15 V

maximum. It’s the designer responsibility to

make sure that spike voltages beyond the

maximum rating will not exist across pin 8 and

ground. Depending upon a specific application

(Vbat voltage, PCB layout…), using an external

voltage clamp could be necessary.

2. The peak current flowing into the LED diodes

shall be within the maximum ratings specified for

these devices.

The Schottky diode D5, associated with capacitor C2,

provides a rectification and filtering function.

When a pulse−operating mode is acceptable:

• The LEDs brightness can be controlled in LOCAL

mode with a PWM on CS pin as depicted in Figure 24.

• Or the Schottky can be removed and replaced by at

least one LED diode as depicted in Figure 23.

TYPICAL APPLICATION CIRCUIT

Figure 22. Basic DC Current Mode Operation in REMOTE Control

Iref

PHOTO

CLK

NPN−PHOTO

GND

Vbat

LOCAL

GND

Vbat

30 k

GND

Vcc

GND

NCP5009

Vbat

mF/6.3 V

GND

MBR0520

LED

2.2

mF/16 V

GND

VBIAS

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