A8513 ALLEGRO [Allegro MicroSystems], A8513 Datasheet - Page 13

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

C1
C2
C3
A8513
Secondary Overvoltage Protection
overvoltage protection for the internal boost switch in the event
of an open diode condition. If the voltage on the SW pin exceeds
the device safe operating voltage rating, the A8513 is disabled
and remains latched off (figure 14). The EN/PWM pin must be
brought low longer than t
Boost switch overcurrent protection
The boost switch is protected with cycle-by-cycle current limit-
ing set to I
limit that is sensed on the boost switch. When this current limit
is exceeded, the A8513 immediately shuts down (figure 16). The
secondary current limit is above the cycle-by-cycle current limit
and protects the switch from destructive currents if the boost
inductor is shorted.
Figure 14. Secondary Overvoltage protection tripped when the switching
diode is opened during operation. (A) High voltage is detected on SW
node (ch1, 20 V/div.) and the A8513 is shut down. (B) Fault flag is set
(ch2, 5 V/div.). Shows LED current (ch3, 100 mA/div.), time = 500 ns/div.
FAULT
V
I
LED
SW
SW(LIM)
(figure 15). There is also a secondary current
PWML
to clear this fault.
t
The A8513 has secondary
B
A
Wide Input Voltage Range, High Efficiency
C1
C2
C3
Figure 15. Cycle-by-cycle current limit, inductor current is C3 (1 A/div.).
(A) Fault flag (ch1, 5 V/div.) is not set during cycle-by-cycle current limit,
(B) COMP pin signal (C2, 2 V/div.) is close to 3.6 V. (time = 1 ms/div.)
Figure 16. Secondary current limit during an inductor short condition.
(A) limit is reached, (B) the IC shuts down and the fault flag is set. Shows
fault flag (c1, 5 V/div.), switch node voltage (C2, 20 V/div.), and current
through the inductor (C3, 2 A/div.); time = 1 μs/div.
C1
C2
C3
FAULT
V
I
SW
L
Normal operation
Fault Tolerant LED Driver
A
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Cycle-by-cycle inductor current limit
A
t
t
B
B
A
Inductor Short
C
B
COMP
FAULT
I
L
13