AL8806MP8-13 Diodes Zetex, AL8806MP8-13 Datasheet - Page 10

• Manufacturer Part Number: AL8806MP8-13
• Manufacturer: Diodes Zetex

Specifications of AL8806MP8-13

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Applications Information
AL8806 Operation
In normal operation, when voltage is applied at +V
sense resistor R
voltage +V
This rising current produces a voltage ramp across R
and applies a proportional voltage to the input of the internal comparator.
When this voltage reaches an internally set upper threshold, the internal switch is turned off. The inductor current continues to
flow through R
determined by the forward voltage drop of the LEDs and the schottky diode.
This decaying current produces a falling voltage at R
voltage across R
threshold, the internal switch is turned on again. This switch-on-and-off cycle continues to provide the average LED current set
by the sense resistor R
LED Current Control
The LED current is controlled by the resistor R
Connected between V
If the CTRL pin is driven by an external voltage (higher than 0.4V and lower than 2.5V), the average LED current is:
For example for a desired LED current of 1.33A and a default voltage V
DC Dimming
The CTRL pin can be driven by an external DC voltage (V
average value defined by R
shown on page 4 for 4 different current levels.
When the CTRL voltage falls below the threshold, 0.4V, the output switch is turned off which allows PWM dimming.
Note that 100% brightness setting corresponds to V
is higher than V
V
AL8806 (Preliminary)
Document number: DS35144 Rev. 1 - 1
CTRL
= V
REF
IN
.
and the inductor L1.
SET
SET
REF
SET
, L1, the LEDs and the schottky diode D1, and back to the supply rail, but it decays, with the rate of decay
, inductor L1, and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input
, the device will not overdrive the LED current and will still set the current according to the equation
12V
is applied at the input of the internal comparator. When this voltage falls to the internally set lower
IN
SET
and SET the nominal average output current in the LED(s) is defined as:
.
AC
~
SET
D2
D4
. The LED current decreases linearly with the CTRL voltage when 0.5V ≤ V
R
Figure 1: Typical Application Circuit
SET
SET
D3
D5
=
in Figure 1.
V
I
C1
IN
LED
CTRL
THD
, the AL8806 internal switch is turned on. Current starts to flow through
I
LED
1
SET
, which is sensed by the AL8806. A voltage proportional to the sense
www.diodes.com
= V
I
V
LED
. The internal circuit of the AL8806 senses the voltage across R
V
=
HIGH EFFICIENCY 30V 1.5A BUCK LED DRIVER
CTRL
D1
REF
10 of 16
V
REF
V
CTRL
CTRL
=
REF
AL8806
, nominally 2.5V. For any voltage applied on the CTRL pin that
R
V
=
), to adjust the output current to a value below the nominal
THD
SET
R
. 1
0
R
V
SET
33
1 .
THD
SET
CTRL
2
2
5 .
5 .
=2.5V the resulting resistor is:
≈
75
m
(PRELIMINARY)
Ω
L1
C2
AL8806
© Diodes Incorporated
February 2011
CTRL
≤ 2.5V, as
SET