al8400 Diodes, Inc., al8400 Datasheet - Page 10

• Manufacturer Part Number: al8400
• Description: Linear Led Driver-controller With 200mv Current Sense Voltage
• Manufacturer: Diodes, Inc.

AL8400
LINEAR LED DRIVER-CONTROLLER with
200mV CURRENT SENSE VOLTAGE
Application Information
(Continued)
High voltage operation
The AL8400 also provides the capability to drive longer LED chains as the voltage across the LED chain is determined by the
external switch. The lower supply voltage for the AL8400 can be derived from the supply to the LED chain either by putting a
series resistor to the AL8400’s V
pin and putting a suitable zener diode from its V
to GND Figure 5 or by tapping its V
CC
CC
CC
from the LED chain Figure 6.
Figure 5. High voltage operation with zener diode from VIN
Figure 6. High voltage operation tapping V
from the LED string
CC
When the supply voltage for the AL8400 is derived using a zener diode, care has to be taken in dimensioning the resistor R1.
The current spilled from V
has to be enough to polarize the zener and to supply the LED driver. On the other hand, when
IN
the supply voltage for the AL8400 is derived from the LED string, care has to be taken in dimensioning the resistor R
. The
B
current spilled from the LED chain can reduce the accuracy of the system and brightness matching between the LED.
AL8400
10 of 12
March 2011
www.diodes.com
© Diodes Incorporated
Document number: DS35115 Rev. 2 - 2