A8519KETTR-R datasheet(21/35 Pages) ALLEGRO

21 / 35 page

Wide Input Voltage Range, High-Efficiency,

Fault-Tolerant LED Driver

A8519 and

A8519-1

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Figure 30 shows the cycle-by-cycle current limit showing induc-

tor current as a green trace. Note the inductor current is truncated

and as a result the output voltage is reduced as compared to

normal operation shown for the 11×4 LED configuration.

Boost Switch Overcurrent Protection

The boost switch is protected with cycle-by-cycle current limit-

ing set at a minimum of 3 A. Figure 29 illustrates the normal

operation of the switch node (VSW), inductor current, and output

voltage (VOUT) for a 11×4 LED configuration.

Figure 29: Normal Operation of Switch Node (VSW), Inductor

Current, and Output Voltage (VOUT)

Figure 30: Cycle-by-Cycle Current Limit

VOUT

VSW

VPWM

Inductor Current

VOUT

VSW

Inductor Current

VPWM

Current is Truncated Here

The A8519 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’s safe operating voltage rating, the A8519

disables and remains latched. To clear this fault, the IC must be

shut down by either using the PWM signal or by going below the

UVLO threshold on the VIN pin.

Figure 28 illustrates open Schottky diode protection while the

IC is in normal operation. As soon as the switch node voltage

(VSW) exceeds 48 V, the IC will shut down. Due to small delays

in the detection circuit, as well as there being no load present, the

switch node voltage (VSW) will rise above the trip point voltage.

Figure 28: Open Schottky Diode Protection

Open diode detected VOUT

VSW

VPWM

ILED(TOTAL)

When enabling the A8519 into an open-diode condition, the IC

will first go through all of its initial LED detection and will then

check the boost output voltage. At that point, the open diode is

detected.

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