A8500 Datasheet, PDF (1/16 Pages) Allegro MicroSystems – Flexible WLED/RGB Backlight Driver for Medium Size LCDs

A8500
Flexible WLED/RGB Backlight Driver for Medium Size LCDs
Features and Benefits
▪ Active current sharing between LED strings for ±1.5%
typical current matching and ±1.2% typical accuracy
▪ Drive up to 12 series × 8 parallel = 96 LEDs
(V_f = 3.2 V, I_f = 20 mA)
▪ Flexible dimming, using alternative methods:
▫ LED duty cycle control (PWM pin)
▫ DC current using serial programming (EN pin)
▫ DC current using external PWM signal (APWM pin)
▫ An external resistor
▪ Boost converter with integrated 50 V, 2 A DMOS
▪ LED sinks rated for 30 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 A8500 is a multi-output WLED driver for medium display
backlighting. The A8500 integrates a boost converter and eight
current-sinks to provide a flexible 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 A8500 can support any application requiring 4 to 96
WLEDs. The boost converter is a constant frequency current-
mode converter.
Each LED channel can sink 30 mA, and channels can be
paralleled for higher currents. Flexible dimming allows output
channels to either run at an adjustable DC value or with
externally controlled PWM duty cycles.
The A8500 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
EN pin dimming:
serial pulse train input
V_EN
I_OUT
PWM pin dimming:
digital PWM input
V_PWM
I_OUT
APWM pin dimming:
analog PWM input
V_APWM
Typical Application
V_S
5 V ±10%
C_IN
0.1 µF/ 10 V
V_BAT
5 to 25 V
L1
10 µH
C_BAT
1 µF/ 25 V
D1
ROVP COUT
EN ^VIN
PWM
SW SW
OVP
AGND
2.2 µF
50 V
APWM
SKIP
COMP
C_C
RFSET
FSET
ISET
A8500
PGND
SEL3 ^VIN
SEL2
RISET
LED1
LED3 LED5 LED7
LGND
SEL1
LED2
LED8 LED6 LED4
I_OUT
8500-DS
Figure 1. LCD monitor backlight, driving 96 LEDs. LED V_f = 3.2 V, 20 mA per LED string. Overvoltage
protection set to 45 V nominal (40.5 V minimum). Alternative dimming control pulse trains illustrated
for EN, PWM, and APWM control. See also: Recommended Components table, page 14.