A8519KETTR-R datasheet(23/35 Pages) ALLEGRO

23 / 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

VDD

The VDD pin provides regulated bias supply for internal circuits.

Connect a capacitor with a value of 1 μF or greater to this pin.

The internal LDO can deliver no more than 2 mA of current with

a typical VDD voltage of about 3.5 V, enabling this pin to serve

as the pull-up voltage for the fault pin.

Shutdown

If PWM pin is pulled low for more than tPWML (32,750 clock

cycles), the device enters shutdown mode and clears all internal

fault registers. As an example, at 2 MHz clock frequency, it will

take approximately 16.3 ms to shut down the IC into the low

power mode. When shut down, the IC will disable all current

sources and wait until the PWM goes high to re-enable the IC.

Figure 35 depicts the shutdown using the PWM enable, showing

the 16.3 ms delay between PWM signal and when the VDD and

GATE of disconnect switch turn off.

Figure 35: Shutdown Using the PWM Enable

VVDD

VGATE

VPWM

ILED(TOTAL)

Setting the Current Sense Resistor

As shown in Figure 32:

VIN – VSENSE = VSC + Iadj × Radj

ISC = ((VIN – VSENSE) – Iadj × Radj)/RSC

where VSC = the voltage drop across RSC. The typical threshold

for the current sense is VIN – VSENSE = 110 mV when Radj is 0 W.

The A8519 can have this voltage trimmed using the Radj resistor.

It is recommended to set trip point to be above 3.65 A to avoid

conflicts with the cycle-by-cycle current limit typical threshold.

A sample calculation is done below for 4.25 A of input current.

Calculated max value of sense resistor RSC = 0.11 V / 4.25 A =

0.0259 Ω.

The RSC chosen is 0.024 Ω, a standard value. Therefore, the volt-

age drop across RSC is:

adj

V= 4.25 A×0.024 = 0.102 V

V– V

VSENSE(trip)

adj

= 372

adj

0.11 V – 0.102 V

21.5 µA

Input UVLO

When VIN and VSENSE rise above VUVLOrise threshold, the A8519

is enabled. The A8519 is disabled when VIN falls below VUVLOfall

threshold for more than 50 μs. This small delay is used to avoid

shutting down because of momentary glitches in the input power

supply.

Figure 34 illustrates a shutdown due to a falling input voltage

(VIN). When VIN falls below 3.90 V, the IC will shut down.

Figure 34: Shutdown with Falling Input Voltage

VOUT

VIN

VVDD

ILED(TOTAL)

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