A8519KETTR-R datasheet(13/35 Pages) ALLEGRO

13 / 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

Table 2: LED Detection Voltage Thresholds

LED Pin Voltage

Level

LED Pin

Action

Less than 70 mV

Indicates a short to

PCB GND

A8519 will not

proceed with power

up.

150 mV

Not used

LED string connected

with the unused LED

pin is removed from

operation

325 mV

LED pin in use

None

Figure 4: LED String Detect Occurs when All LED Strings are

Selected to be Used

LED Detection

Figure 5: Detect Voltage is about 150 mV when LED Pin 2 is not

Used

If an LED pin is shorted to ground, the A8519 will not proceed

with soft-start until the short is removed from the LED pin. This

prevents the A8519 from powering up and putting an uncon-

trolled amount of current through the LEDs.

Figure 6: One LED Pin is Shorted to GND.

The IC will not proceed with power up until LED pin is released, at

which point the LED pin is checked to see if it is used.

Powering Up: Boost Output Undervoltage Protection

During startup, after the input disconnect switch has been

enabled, the output voltage is checked through the OVP pin. If

the sensed voltage does not rise above VUVP(th), the output is

assumed to be at fault and the IC will not proceed with soft-start.

Undervoltage protection may be caused by one of the following

faults:

•

Output capacitor shorted to GND

•

Boost inductor or diode open

•

OVP sense resistor open

After an Output UVP fault has been detected, the A8519 immedi-

ately shuts down but does not latch off. It will retry as soon as the

UVP fault is removed.

In case of output capacitor shorted to GND fault, however, the

high inrush current will also trip the Input OCP fault. This causes

the IC to shut down and latch off. To enable the IC again, the

PWM pin must be pulled low for at least 32,750 clock cycles

(about 16 ms at 2 MHz), then pulled high again.

VLED2

LED current regulation begins

VLED1

VISET

VPWM

VLED2

VLED1

VISET

VPWM

LED2 is not used

VLED2

VLED1

VISET

VPWM

Short is removed

Short is applied

at LED1

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