A8519KETTR-R datasheet(19/35 Pages) ALLEGRO

19 / 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

The LED current can be adjusted using the following formula:

where VISET is the ISET pin voltage and VDAC is the DAC output

voltage.

When VDAC is equal to 1 V, the output is strictly controlled by

the RISET resistor. When VDAC is higher than 1 V, the LED cur-

rent is reduced. When VDAC is lower that 1 V, the LED current is

increased.

LED String Short Detect

All LEDx pins are capable of handling the maximum VOUT that

the converter can deliver, thus allowing for LEDx pin to VOUT

protection in case of a connector short.

In case some of the LEDs in an LED string are shorted, the volt-

age at the corresponding LEDx pin will increase. Any LEDx pin

that has a voltage exceeding VLEDx(SC) will be removed from

operation. This will prevent the IC from dissipating too much

power by having a large voltage present on an LEDx pin.

I =

ISET

–

V – V

ISET

DAC

Figure 25: Disabling of LED1 String when the LED1 Pin Voltage is

Increased Above 4.6 V

ILED(TOTAL)

VLED1

VPWM

VDAC

ISET

A8519

DAC

Voltage Source

AGND

GND

Simpliﬁed Diagram of

Voltage LED Current

Control

Figure 23: Typical Application Circuit Using a DAC to Control the

LED Current in the A8519

The ISET current is controlled by the following formula:

where VISET is the ISET pin voltage and VDAC is the DAC output

voltage.

When the DAC voltage is 0 V, the LED current will be at its max-

imum. To keep the internal gain amplifier stable, do not decrease

the current through the RISET resistor to less than 20 µA.

Below is a typical application circuit using a DAC to control the

LED current using a two-resistor configuration. The advantage of

this circuit is that the DAC voltage can be higher or lower, thus

adjusting the LED current to a higher or lower value of the preset

LED current set by the RISET resistor.

I =

ISET

V – V

ISET

DAC

VDAC

R ISET

ISET

A8519

DAC

AGND

GND

Simpliﬁed Diagram of

Voltage LED Current

Control

Figure 24: Typical Application Circuit Using a DAC and RISET

Resistor to Control the LED Current in the A8519

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