A8514KLPTR-T データシートの表示（PDF） - Allegro MicroSystems

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A8514KLPTR-T

Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver

Allegro MicroSystems 

A8514

Wide Input Voltage Range, High Efficiency

Fault Tolerant LED Driver

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 VOUT is present.

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 ROVP between the OVP pin and VOUT . When

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:

ROVP = ( VOUTovp – VOVP(th) ) / IOVPH

(5)

where:

VOUTovp is the target overvoltage level,

ROVP is the value of the external resistor, in Ω,

VOVP(th) is the pin OVP trip point found in the Electrical Charac-

teristics table, and

IOVPH is the current into the OVP pin.

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

Output disconnect

event detected

C2

VOUT

SW node

C1

C3

PWM

IOUT

C4

t

Figure 22. OVP protection in an output disconnect event; shows VOUT

(ch1, 10 V/div.), SW node (ch2, 50 V/div.), PWM (ch3, 5 V/div.), and

IOUT (ch4, 200 mA/div.), time = 1 ms/div.

VOUT

LED string open

condition detected

C2

SW node

PWM

C1

C3

IOUT

C4

t

Figure 23. OVP protection in an open LED string event; shows VOUT

(ch1, 10 V/div.), SW node (ch2, 50 V/div.), PWM (ch3, 5 V/div.), and

IOUT (ch4, 200 mA/div.), time = 500 μs/div.

Allegro MicroSystems, Inc.

19

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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