A8512 Datasheet, PDF (1/18 Pages) Allegro MicroSystems – LED Backlight Driver for Medium/Large Displays

A8512
LED Backlight Driver for LCD Monitors and Televisions
Features and Benefits
▪ Six integrated high current sinks
▪ Fixed frequency current mode control with integrated gate driver
▪ 300 kHz to 1 MHz adjustable switching frequency
▪ Controlled startup using options of Enable, PWM signal, or
battery voltage ramp
▪ Parallel operation with one boost controller (master) and up to
five slave controllers
▪ Active current sharing between LED strings for ±0.6% accuracy
and matching
▪ No audible MLCC noise during PWM dimming
▪ Adjustable overvoltage protection (OVP)
▪ Open or shorted LED string protection
▪ Overtemperature, cycle-by-cycle current limit, and
undervoltage protection
▪ SOIC 24-pin package for easy single-side PCB manufacturing,
or TSSOP 24-pin and QFN 28-contact packages with exposed
thermal pad for better thermal performance
Packages:
24-pin SOICW
with internally fused pins
(LB package)
28-contact QFN
with exposed thermal pad
(ET Package)
24-pin TSSOP
with exposed thermal pad
(LP package)
Not to scale
Description
The A8512 is a multi-output WLED/RGB driver for
backlighting LCD monitors and televisions. It integrates a boost
controller to drive external MOSFET, and six internal current-
sinks. The boost converter operates in constant frequency
(programmable) current mode control.
PWM dimming allows LED currents to be controlled in 500:1
ratio. The LED sink current is set by an external R_ISET resistor
(see chart below). More than one LED sinks can be combined
together to achieve even higher current per LED string. Multiple
A8512s can be connected in parallel, with one master controller
controlling the boost stage, and up to five slave controllers,
which act as LED sinks. This allows up to 36 LED strings to
be powered by just one boost converter.
TheA8512 operates from a single supply of 8 to24V. It provides
protection against overvoltage, open or shorted LED string,
and overtemperature. A dual level cycle-by-cycle current limit
function provides soft start and protects against overloads.
The device is provided in a 24-pin SOICW package (LB), with
internally fused pins for enhanced thermal dissipation, and a
28-contact 5 mm × 5 mm QFN package (ET) and a 24-pin
TSSOP package (LP), both with an exposed thermal pad for
enhanced thermal dissipation. All packages are lead (Pb) free,
with 100% matte tin leadframe plating.
Typical Application Circuit
VBAT
8 to 24 V
C1 C2
L1
D1
Q1
RSC ROVP1
C3 C4
Fault
Enable
PWM
P
P
P
R1
C5
RFSET
RISET
Rz1
DRIVER SENSE1 SENSE2 OVP
VIN
VBIAS
FAULT
EN
PWM
COMP
FSET
ISET
VREG7V
A8512
Master
LED1
LED2
LED3
LED4
LED5
C6
Cz1
LED6
AGND AGND LGND LGND PGND
18 LEDs per string
P
Control Bus
VOUT
ROVP2
VBAT
P
DRIVER SENSE1 SENSE2
VIN
VBIAS
OVP
C7
RFSET
RISET
Rz2
FAULT
EN
PWM
COMP
FSET
ISET
VREG7V
A8512
Slave A
LED1
LED2
LED3
LED4
LED5
C8
Cz2
LED6
AGND AGND LGND LGND PGND
P
18 LEDs per string
To additional slaves
130
120
110
100
90
80
70
60
50
40
30
20
6
LED Current versus ISET Resistor Value
V_REF = 1.24 V, Gain = 640
8 10 12 14 16 18 20 22 24 26 28 30
R_ISET (kΩ)
Figure 1. Typical application circuit for single IC operation, and (in dotted box) master/slave multiple IC operation.
A8512L-DS, Rev. 6