AL8808WT-7 Diodes Inc., AL8808WT-7 Datasheet - Page 10

• Manufacturer Part Number: AL8808WT-7
• Description: LED Lighting Drivers LED MV Int Switch TS Switch TSOT25 T&R 3K
• Manufacturer: Diodes Inc.

Specifications of AL8808WT-7

• Rohs: yes
• Input Voltage: 6 V to 30 V
• Operating Frequency: 1 MHz
• Maximum Supply Current: 450 uA
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: TSOT-25
• Minimum Operating Temperature: - 40 C

Application Information
Analog Dimming
The CTRL pin can be driven by an external analog voltage (V
defined by R1. The LED current decreases linearly with the CTRL voltage when 0.5V ≤ V
Note that 100% brightness is achieved when either the CTRL pin is left floating or pulled above 2.5V by an external voltage source.
For 2.6V ≤ V
reference voltage). See Figure 33 below.
PWM Dimming
LED current can be adjusted digitally, by applying a low frequency Pulse Width Modulated (PWM) logic signal to the CTRL pin to turn the device
on and off. This will produce an average output current proportional to the duty cycle of the control signal. In particular, a PWM signal with a
max resolution of 10bit (~0.1% duty cycle) can be applied to the CTRL pin to change the output current to a value below the nominal average
value set by resistor R
be used, at the expense of dimming dynamic range and accuracy.
Typically, for a PWM frequency of 500Hz the accuracy is better than 2% for PWM ranging from 5% to 100%.
AL8808
Document number: DS35648 Rev. 2 - 2
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
CTRL
0
0
V
T = +25°C
L = 68µH
R
1 LED
≤ 5.5V the LED current will not get overdriven and will be set the current according to the equation V
A
10 20 30 40
IN
SET
= 12V
Figure 34. PWM Dimming at 500Hz
= 150m
SET
. To achieve this resolution the PWM frequency has to be lower than 500Hz, however higher dimming frequencies can
PWM DUTY CYCLE (%)
Ω
50 60
(cont.)
100
110
90
80
70
60
50
40
30
20
10
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
70 80
T = 25°C
V
L = 68µH
Figure 33. LED Current Dimming Ration and
A
IN
= 12V
90 100
Typical Error vs. Control Voltage
www.diodes.com
CTRL
LED Current Error
), to adjust the output current to a value below the nominal average value
V
10 of 20
CTRL
(V)
Dimmed LED Current Ratio
10
10
9
8
7
6
5
4
3
2
1
Figure 35. Low Duty Cycle PWM Dimming at 500Hz
0.0
CTRL
≤ 2.5V.
2.5
V
T = +25°C
L = 68µH
R
1 LED
A
IN
SET
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
= 12V
PWM DUTY CYCLE (%)
= 150m
5.0
Ω
7.5
10.0
CTRL
12.5
= 2.5V (the internal
© Diodes Incorporated
AL8808
January 2013
15.0