A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 19

• Manufacturer Part Number: A8514KLPTR-T
• Description: IC LED DVR WHT 4X80MA 16-ETSSOP
• Manufacturer: Allegro Microsystems Inc

Specifications of A8514KLPTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A8514
While the IC is being PWM-dimmed, the IC rechecks the dis-
abled LED every time the PWM signal goes high, to prevent false
tripping of an LED short event. This also allows some self-cor-
rection if an intermittent LED pin short to V
Overvoltage protection
The A8514 has overvoltage protection (OVP) and open Schottky
diode (D1 in figure 1) protection. The OVP protection has a
default level of 8.1 V and can be increased up to 53 V by con-
necting resistor R
the current into the OVP pin exceeds 199 μA (typical), the OVP
comparator goes low and the boost stops switching.
The following equation can be used to determine the resistance
for setting the OVP level:
where:
Figure 22. OVP protection in an output disconnect event; shows V
(ch1, 10 V/div.), SW node (ch2, 50 V/div.), PWM (ch3, 5 V/div.), and
I
OUT
C2
C1
C3
C4
V
OUTovp
(ch4, 200 mA/div.), time = 1 ms/div.
Output disconnect
event detected
is the target overvoltage level,
R
OVP
OVP
= ( V
between the OVP pin and V
OUTovp
t
– V
OVP(th)
SW node
V
PWM
) / I
I
OUT
OUT
OUT
OVPH
is present.
OUT
Wide Input Voltage Range, High Efficiency
. When
OUT
(5)
There are several possibilities for why an OVP condition would
be encountered during operation, the two most common being: a
disconnected output, and an open LED string. Examples of these
are provided in figures 22 and 23.
Figure 22 illustrates when the output of the A8514 is discon-
nected from load during normal operation. The output voltage
instantly increases up to OVP voltage level and then the boost
stops switching to prevent damage to the IC. If the output is
drained off, eventually the boost might start switching for a short
duration until the OVP threshold is hit again.
Figure 23 displays a typical OVP event caused by an open LED
string. After the OVP condition is detected, the boost stops
Figure 23. OVP protection in an open LED string event; shows V
(ch1, 10 V/div.), SW node (ch2, 50 V/div.), PWM (ch3, 5 V/div.), and
I
OUT
C2
C1
C3
C4
R
V
teristics table, and
I
OVPH
OVP
OVP(th)
(ch4, 200 mA/div.), time = 500 μs/div.
is the value of the external resistor, in Ω,
is the current into the OVP pin.
is the pin OVP trip point found in the Electrical Charac-
Fault Tolerant LED Driver
SW node
V
PWM
I
OUT
OUT
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
t
condition detected
LED string open
OUT
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