A8502 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A8502' PDF : 35 Pages View PDF
A8502
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
LED current setting and LED dimming
The maximum LED current can be up to 120 mA per channel,
and is set through the ISET pin. To set the ILED current, connect
a resistor, RISET, between this pin and ground, according to the
following formula:
RISET = (1.003 × 980) / ILED
(2)
where ILED is in A and RISET is in Ω. This sets the maximum cur-
rent through the LEDs, referred to as the 100% current. Standard
RISET values, at gain equals 980, are as follows:
Standard Closest RISET
Resistor Value
(kΩ)
8.25
9.76
12.1
15.0
LED current per LED, ILED
(mA)
120
100
80
65
VOUT
COMP
C2
C1
C3
PWM
C4
ILED
t
Figure 11B. Typical PWM diagram showing VOUT, ILED, and COMP pin as
well as the PWM signal. PWM dimming frequency is 500 Hz at 1% duty
cycle ; shows VOUT (ch1, 10 V/div.), COMP (ch2, 2 V/div.), PWM (ch3,
5 V/div.), and ILED (ch4, 50 mA/div.), time = 500 μs/div.
PWM
PWM dimming
The LED current can be reduced from the 100% current level
by PWM dimming using the PWM/EN pin. When the PWM/EN
pin is pulled high, the A8502 turns on and all enabled LEDs sink
100% current. When PWM/EN is pulled low, the boost converter
and LED sinks are turned off. The compensation (COMP) pin is
floated, and critical internal circuits are kept active. The typical
PWM dimming frequencies fall between 200 Hz and 1 kHz. Fig-
ures 11A to 11D provide examples of PWM switching behavior.
C1
ILED
C2
t
Figure 11C. Delay from rising edge of PWM signal to LED current; shows
PWM (ch1, 2 V/div.), and ILED (ch2, 50 mA/div.), time = 200 ns/div.
VOUT
COMP
C2
PWM
C1
C3
PWM
C1
ILED
C4
ILED
t
Figure 11A. Typical PWM diagram showing VOUT, ILED, and COMP pin as
well as the PWM signal. PWM dimming frequency is 500 Hz at 50% duty
cycle; shows VOUT (ch1, 10 V/div.), COMP (ch2, 2 V/div.), PWM (ch3,
5 V/div.), and ILED (ch4, 50 mA/div.), time = 500 μs/div.
C2
t
Figure 11D. Delay from falling edge of PWM signal to LED current turn off;
shows PWM (ch1, 2 V/div.), and ILED (ch2, 50 mA/div.), time = 200 ns/div.
Allegro MicroSystems, Inc.
15
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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