A8513 ALLEGRO [Allegro MicroSystems], A8513 Datasheet - Page 10

• Manufacturer Part Number: A8513
• Description: Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A8513
capacitors. After the A8513 senses there is enough voltage on the
LED pin, it increases the LED current to the preset regulation
current. The COMP pin will continue to source 80 uA until the
LEDs are able to run at the full preset current level.
Boost converter frequency
The switching frequency of the boost regulator is preset internally
to one of four frequencies. The frequency options are:
Figure 4. Typical PWM dimming sequence, with PWM dimming frequency
of 1000 Hz and 10% duty cycle; shows COMP (ch1, 1 V/div.), V
10 V/div.), I
time = 500 μs/div.
Figure 5. Typical EN/PWM signal (5 V/div.) to LED current (100 mA/div.)
turn-on delay. The delay measured about 250 ns. V
series LEDs is approximately 36 V, I
C1
C2
C3
C4
C3
C4
LED
A8513KLYTR-1-T
A8513KLYTR-2-T
A8513KLYTR-3-T
A8513KLYTR-4-T
EN/PWM
EN/PWM
(ch3, 100 mA/div.), and EN/PWM (ch4, 5 V/div.),
COMP
Part Number
V
I
I
LED
LED
LED
t
t
LED
Switching Frequency (f
is 150 mA. (time = 500 ns/div.)
(MHz)
0.25
0.5
2
1
IN
is 12 V, V
Wide Input Voltage Range, High Efficiency
SW
OUT
LED
)
(ch2,
for 10
LED current setting and LED dimming
The LED current, I
from 40 to 150 mA. Connect a resistor, R
and GND to set the I
formula :
where I
This formula sets the maximum current through the LEDs, which
is referred to as the 100% current.
PWM dimming
The LED current can be reduced from the 100% current level by
PWM dimming using the EN/PWM pin. When the EN/PWM pin
is pulled high, the A8513 turns on and the LED pin sinks 100%
current (figure 4). When EN/PWM is pulled low, the boost con-
verter and LED sink are turned off. The compensation (COMP)
pin is floated, and critical internal circuits are kept active.
The A8513 has very fast turn-on and turn-off times during PWM
dimming to minimize low PWM duty cycle errors. The typical
PWM signal delay t
t
going low, is shown in figure 6.
Analog dimming
The A8513 can also be dimmed by using an external DAC or
other voltage source applied either directly to the ground side of
the R
Figure 5. Typical EN/PWM signal (5 V/div.) to LED current (100 mA/div.)
turn-off delay. The typical delay is about 250 ns. (time = 500 ns/div.)
dPWM(off)
C3
C4
ISET
LED
resistor or through an external resistive divider to the
time, between the PWM signal and the LED current
is in A and R
EN/PWM
I
Fault Tolerant LED Driver
LED
I
LED
=
=
LED
dPWM(on)
LED
V
R
1.003 V
R
ISET
ISET
, is set using the ISET pin, and can range
ISET
ISET
current, according to the following
× A
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
is 250 ns (figure 5). The typical
is in Ω.
× 1045
ISET
t
ISET
, between this pin
(2)
10