AL8807MP-13 Diodes Inc., AL8807MP-13 Datasheet - Page 10

• Manufacturer Part Number: AL8807MP-13
• Description: LED Lighting Drivers 36V High EFF Low EMI 1A Buck LED Driver
• Manufacturer: Diodes Inc.

Specifications of AL8807MP-13

• Product Category: LED Lighting Drivers
• Rohs: yes
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: MSOP-8EP

Applications Information
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 can be applied to the CTRL pin to change the output current to a
value below the nominal average value set by resistor R
than 500Hz, however higher dimming frequencies can be used, at the expense of dimming dynamic range and accuracy.
Typically, for a PWM frequency of 500Hz the accuracy is better than 1% for PWM ranging from 1% to 100%.
Zooming in at duty cycles below 10% shows:
The accuracy of the low duty cycle dimming is affected by both the PWM frequency and also the switching frequency of the
AL8807. For best accuracy/resolution the switching frequency should be increased while the PWM frequency should be
reduced.
The CTRL pin is designed to be driven by both 3.3V and 5V logic levels directly from a logic output with either an open drain
output or push pull output stage.
AL8807
Document number: DS35281 Rev. 4 - 2
700
600
500
400
300
200
100
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0
0
(cont.)
10
10
20
HIGH EFFICIENCY LOW EMI 36V 1A BUCK LED DRIVER
Fig. 32 Low Duty Cycle PWM Dimming @ 300Hz
30
Fig. 31 PWM Dimming @ 500Hz
300Hz PWM DUTY CYCLE (%)
30
www.diodes.com
SET
PWM DIMMING (%)
40
10 of 21
. To achieve this resolution the PWM frequency has to be lower
50
50
60
70
70
80
90
V
L = 68µH
R = 0.15
T = 25°C
2 LEDs
IN
A
S
90
= 12V
DC
Ω
100
100
AL8807
© Diodes Incorporated
June 2012