A8504 Datasheet, PDF (1/18 Pages) Allegro MicroSystems – WLED/RGB Backlight Driver for Medium Size LCDs

A8504
WLED/RGB Backlight Driver for Medium Size LCDs
Features and Benefits
▪ Active current sharing between 6 LED strings for ±1.3%
typical current matching
▪ ±1.2% typical current accuracy
▪ Drive up to 11 series × 8 parallel = 88 LEDs
(V_f = 3.5 V, I_f = 40 mA)
▪ External PWM control for LED dimming
▪ An external resistor for LED current setting
▪ Boost converter with integrated 50 V, 2 A DMOS
▪ LED sinks rated for 45 mA
▪ 200 kHz to 2 MHz switching frequency
▪ Open LED disconnect
▪ Boost current limit, thermal shutdown, and soft start
▪ No audible ceramic capacitor noise during PWM dimming
▪ Adjustable overvoltage protection (OVP)
▪ No pull-up resistors required for LED modules that use
ESD capacitors
Package: 26 pin QFN/MLP (suffix EC)
Description
The A8504 is a multi-output WLED driver for medium display
backlighting. The A8504 integrates a boost converter and eight
current-sinks to provide a WLED/RGB backlight driver. The
boost converter can provide output voltage up to 47 V. The
flexible channel selection control and high voltage capability
allow a wide range of LED backlight applications. The boost
converter is a constant frequency current-mode converter. Each
LED channel can sink 45 mA, and channels can be paralleled
for higher currents. LED current can be controlled with external
PWM duty cycle.
The A8504 is available in a 26 pin, 4 mm × 4 mm QFN/MLP
package that is only 0.75 mm nominal in height. Applications
include:
▪ Thin notebook displays
▪ LCD TV
▪ RGB backlight
▪ GPS systems
▪ Portable DVD players
Approximate Scale 1:1
PWM pin dimming:
digital PWM input
V_PWM
I_OUT
C_C
Typical Application
V_IN
5 V ±10%
C_IN
0.1 μF/ 10 V
V_BAT
5 to 24 V
L1
10 μH
C_BAT
2.2 μF/ 50 V
D1
ROVP
V_OUT
COUT
VIN
SW SW OVP
PWM
SKIP
RFSET
COMP
FSET
ISET
RISET
LED1
LED3 LED5 LED7
A8504
LGND
GND
AGND
PGND
SEL3
SEL2
SEL1
LED2
LED8 LED6 LED4
2.2 μF
50 V
V_IN
Figure 1. LCD monitor backlight, driving 11 green, blue, or white LEDs with V_f= 3.5 V, or 18 red LEDs with V_f = 2.2 V,
per LED string. Overvoltage protection set to 45 V nominal (40.5 V minimum). See also: Recommended Components
table, page 16.
8504-DS, Rev. 1