A8516 View Datasheet(PDF) - Allegro MicroSystems

Part Name

Description

MFG CO.

A8516

LED Backlight Driver for LCD Monitors and Televisions

Allegro MicroSystems 

A8516

LED Backlight Driver for LCD Monitors and Televisions

Application Information

PCB Layout Guidelines As with any switching power supply,

care should be taken in laying out the board. A switching power

supply has sources of high dv/dt and high di/dt which can cause

malfunction. All general norms should be followed for board

layout. Refer to figure 1 for a typical application schematic. The

A8516 evaluation board provides a useful model for designing

application circuit layouts.

The following guidelines should be observed:

• Place bypass capacitors physically close to their respective pins

(VIN, VBIAS, and VREG7V).

• Route analog ground, digital signal ground, LED ground

(LGND pin), and power ground (PGND pin) separately. Con-

nect all these grounds at the common ground plane under the

A8516, serving as a star ground.

• Place the input capacitors (C1, C2), inductor (L1), boost diode

(D1), MOSFET (Q1), and output capacitors (C3, C4) so that

they form the smallest loop practical. Avoid long traces for

these paths.

• Place the resistors RFSET and RISET, and the compensation com-

ponents (Rz and Cz) close to the FSET, ISET, and COMP pins,

respectively. Connect the other ends to the common star ground.

• A8516 has 50 kΩ internal pull-down resistors on the EN and

PWM pins to keep these pins low while driving through tri-state

state (for example, shutdown). Add external resistors R2 and

R3 between the EN and PWM pins and ground, for added noise

immunity. Connect these resistors close to the pins and return to

the common star ground.

• Sense voltage across RSC with smaller length traces. Place the

SENSE1 and SENSE2 traces as close to each other as pos-

sible to minimize noise pickup. Connect the SENSE2 trace to

the negative end of the resistor and do not connect it to power

ground plane.

• Provide a substantial copper plane near MOSFET Q1 and the

IC, to provide good thermal conduction. When using multi-layer

PCB, make sure there are sufficient numbers of thermal vias

underneath and around the IC's exposed pads.

Allegro MicroSystems, Inc.

14

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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