NCP5008, NCP5009
http://onsemi.com
12
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 V
bat
,
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
(V
bat
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
I
ref
PHOTO
L2
CS
CLK
1
2
Q1
NPN−PHOTO
GND
4
V
bat
3
5 6
LOCAL
GND
7
4 8
GND
L1
9
V
bat
10
R1
30 k
GND
MICROCONTROLLER
Vcc
GND
NCP5009
L1
22 mH
V
bat
C1
10 mF/6.3 V
GND
D5 MBR0520
LED
D1
LED
D2
LED
D3
LED
D4
2.2 mF/16 V
C2
GND
U1
VBIAS
