A8513 ALLEGRO [Allegro MicroSystems], A8513 Datasheet - Page 9

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

A8513
The A8513 incorporates a current-mode boost controller with
internal DMOS switch, and a single LED current sink. It can be
used to drive an LED string of up to 14 white LEDs in series,
with current up to 150 mA. For optimal efficiency, the output of
the boost stage is adaptively adjusted to the minimum voltage
required to power the LED string. This is expressed by the fol-
lowing equation:
where
Enabling the IC
The IC turns on when a logic high signal is applied to the
EN/PWM pin (figure 1), and turns off when this pin is pulled to
a logic low. For the device to be enabled, the voltage on the VIN
pin must be greater than V
out (UVLO) threshold (figure 2). Before startup, the A8513 goes
through a system check to determine if there are any fault condi-
tions that would prevent the system from functioning correctly.
Powering up: LED pin short to GND check
After the VIN pin goes above V
pin is shorted to GND by pre-charging the LED pin (figure 3).
When the voltage on the LED pin exceeds 260 mV, the A8513
proceeds with soft start. If a short is present on the LED pin, the
Figure 1. Start-up by slowly ramping up EN/PWM with V
V
EN/PWM (ch4, 2 V/div.), time = 2 ms/div.
C1
C2
C3
C4
V
V
0.88 V at the maximum LED current).
OUT
LED
REG
(ch1, 10 V/div.), I
EN/PWM
COMP
is the voltage drop across the LED string, and
is the regulation voltage of the LED current sink (typically
I
V
LED
OUT
LED
V
(ch2, 50 mA/div.), COMP (ch3, 1 V/div.), and
OUT
UVLOrise
= V
t
LED
UVLOrise
to clear the undervoltage lock-
+ V
REG
, the IC checks if the LED
IN
Functional Description
Wide Input Voltage Range, High Efficiency
at 16 V; shows
(1)
IC will not power up until the short is removed. At this time the
output is also checked for a V
OVP pin does not rise above
Soft start function
During soft start, the COMP pin delivers a steady 80 uA current,
the LED pin current gain is set to A
help limit the inrush current generated by charging the output
Figure 2. Start-up by slowly ramping up V
V
EN/PWM (ch4, 2 V/div.), time = 2 ms/div.
Figure 3. LED detection period; shows ¯ F ¯ ¯ A ¯ ¯ ¯ U ¯ ¯ L ¯ ¯ T ¯ (ch1, 5 V/div.), V
1 V/div.), I
time = 500 μs/div.
C1
C2
C3
C4
C1
C2
C3
C4
OUT
(ch1, 10 V/div.), I
EN/PWM
FAULT
V
EN/PWM
I
LED
LED
COMP
I
V
LED
LED
OUT
(ch3, 100 mA/div.), and EN/PWM (ch4, 5 V/div.),
Fault Tolerant LED Driver
LED detection
UVLO threshold
exceeded
LED
(ch2, 50 mA/div.), COMP (ch3, 1 V/div.), and
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
V
OUT
OVPLO(th)
t
t
short, using the OVP pin. If the
ILEDSS
IN
the IC will not power up.
with EN/PWM at 2 V; shows
. The lower gain will
LED
(ch2,
9