A8514KLPTR-T データシートの表示（PDF） - Allegro MicroSystems
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A8514KLPTR-T Datasheet PDF : 35 Pages
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A8514
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
switching, and the open LED string is removed from operation.
Afterwards VOUT is allowed to fall, and eventually the boost will
resume switching and the A8514 will resume normal operation.
A8514 also has built-in secondary overvoltage protection to
protect the internal switch in the event of an open diode condi-
tion. Open Schottky diode detection is implemented by detecting
overvoltage on the SW pin of the device. If voltage on the SW
pin exceeds the device safe operating voltage rating, the A8514
disables and remains latched. To clear this fault, the IC must be
shut down either by using the PWM/EN signal or by going below
the UVLO threshold on the VIN pin. Figure 24 illustrates this.
As soon as the switch node voltage (SW) exceeds 60 V, the IC
shuts down. Due to small delays in the detection circuit, as well
as there being no load present, the switch node voltage will rise
above the trip point voltage.
Figure 25 illustrates when the A8514 is being enabled during an
open diode condition. The IC goes through all of its initial LED
detection and then tries to enable the boost, at which point the
open diode is detected.
Open diode
condition detected
C1
C2
PWM
SW node
VOUT
IOUT
C3
C4
t
Figure 24. OVP protection in an open Schottky diode event, while the IC is
in normal operation; shows PWM (ch1, 5 V/div.), SW node (ch2, 50 V/div.),
VOUT (ch3, 20 V/div.), and IOUT (ch4, 200 mA/div.), time = 1 μs/div.
PWM
Open diode
condition detected
C1
SW node
C2
VOUT
C3
IOUT
C4
t
Figure 25. OVP protection when the IC is enabled during an open diode
condition; shows PWM (ch1, 5 V/div.), SW node (ch2, 50 V/div.), VOUT
(ch3, 10 V/div.), and IOUT (ch4, 200 mA/div.), time = 500 μs/div.
Allegro MicroSystems, Inc.
20
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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