A8512 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A8512' PDF : 18 Pages View PDF
A8512
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 14 for a typical application schematic. The
A8512 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
A8512, 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.
• A8512 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.
VOUT 18 LEDs per string
VBAT
8 to 24 V
C1 C2
L1
D1
Q1
RSC ROVP
C3 C4
P
P
P
R1
C5
R2
R3
RFSET
RISET
Rz1
DRIVER SENSE1 SENSE2 OVP
VIN
VBIAS
FAULT
EN
PWM
COMP
FSET
ISET
VREG7V
A8512
LED1
LED2
LED3
LED4
LED5
C6
Cz1
LED6
AGND AGND LGND LGND PGND
P
R2, R3 optional (A8512 has
internal pull-down resistors)
Figure 14. Typical application circuit with single controller; VIN pin tied to VBAT .
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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