ALLEGRO A8500 User Manual
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
(Vf = 3.2 V, If = 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 25 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)
Approximate Scale 1:1
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 currentmode converter.
Each LED channel can sink 25 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
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
I
OUT
Figure 1. LCD monitor backlight, driving 96 LEDs. LED Vf = 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.
8500-DS, Rev. 2
T ypical Application
V
IN
5 V ±10%
C
0.1 μF/ 10 V
EN
PWM
APWM
SKIP
COMP
C
C
RFSET
FSET
ISET
RISET
LED1
LED3 LED5 LED7 LGND
V
BAT
5 to 25 V
IN
VIN SW SW OVP
L1
10 μH
C
BAT
1 μF/ 25 V
A8500
D1
ROVP
AGND
PGND
SEL3
SEL2
SEL1
LED2
LED8 LED6 LED4
COUT
2.2 μF
50 V
V
IN
Flexible WLED/RGB Backlight Driver
A8500
for Medium Size LCDs
Selection Guide
Part Number Package Packing*
A8500EECTR-T 4 mm × 4 mm QFN/MLP 1500 pieces / 7-in. reel
*Contact Allegro for additional packing options
Device package is lead (Pb) free, with 100% matte tin leadframe plating.
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
SW and OVP Pins –0.3 to 50 V
LED1 through LED8 Pins –0.3 to 23 V
VIN Pin V
IN
Remaining Pins –0.3 to V
Operating Ambient Temperature T
Maximum Junction Temperature T
(max) 150 ºC
J
Storage Temperature T
A
stg
Range E –40 to 85 ºC
–0.3 to 6 V
+ 0.3 V
IN
–55 to 150 ºC
Package Thermal Characteristics*
Characteristic
Package Thermal Resistance
*Additional information is available on the Allegro website
Symbol
R
JA
Note Rating Units
Measured on 3 in. × 3 in., 2-layer PCB 48.5 °C/W
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
A8500
Flexible WLED/RGB Backlight Driver
for Medium Size LCDs
Functional Block Diagram
V
IN
5 V ±10%
C
IN
R
R
FSET
ISET
COMP
C
C
AGND
APWM
SKIP
FSET
EN
SEL1
SEL2
SEL3
PWM
ISET
Reference
100 kΩ
100 kΩ
100 kΩ
Amp
VIN
and
Soft Start
On/Off
Serial Interface
PWM Generator
I
OUT_SET
100 kΩ
+
–
Feedback
Loop
L1
10 μH
SW
SW
D1
V
OUT
COUT
C
BAT
V
BAT
5 to 25 V
+
–
QSR
ROVP
+
∑
OSC
Current Sinks
–
PGND
OVP
LED1
LED2
LED3
LED4
LED5
LED6
LED7
LED8
LGND PGND
LGND
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
A8500
Flexible WLED/RGB Backlight Driver
for Medium Size LCDs
ELECTRICAL CHARACTERISTICS, valid at T
= –40°C to 85°C, typical values at TA = 25°C, VIN = 5 V, unless otherwise noted
A
Characteristics Symbol Test Conditions Min. Typ. Max. Units
Input Voltage Range V
Undervoltage Lockout Threshold V
UVLO Hysteresis Window V
Supply Current I
APWM Frequency Range f
IN
UVLO
UVLOhys
SUP
APWM
VIN falling – – 4 V
Switching at no load, TA = 25°C – 5 – mA
Shutdown EN = PWM = APWM = V
IL
Error Amplifier
Error Amplifier Open Loop Gain A
Error Amplifier Unity Gain Bandwidth UGB
Error Amplifier Transconductance Gm
Error Amplifier Output Sink Current I
Error Amplifier Output Source Current I
VEA
EA
EA
EAsink
EAsource
I
= ±10 A – 850 – A/V
COMP
V
= 1 V – 280 – A
LED1-8
V
= 0 V – –280 – A
LED1-8
Boost Controller
R
= 13 k, SKIP = VIL 1.8 2 2.2 MHz
FSET
Switching Frequency f
Minimum Switch Off-Time t
SW
OFFmin
R
= 26.1 k, SKIP = VIL –1–MHz
FSET
R
= 32.4 k, SKIP = V
FSET
IH
Logic Input Levels (APWM , EN, MODE, PWM, SELx, and SKIP pins unless otherwise specified)
Input Voltage Level Low V
Input Voltage Level High V
Input Leakage Current (APWM, EN,
PWM, and SKIP pins)
Input Leakage Current (SELx pins) I
IL
IH
I
Ileak
SELleak
V
= 5 V, TA = 25°C – – 100 A
I(pin)
Over Voltage Protection (OVP)
Output Overvoltage Rising Limit V
OVP Sense Current I
OVP Release Current I
OVP Leakage Current I
OVP
OVPH
OVPL
OVPleak
V
= 21 V – 0.1 – A
VOP
Boost Switch
Switch On Resistance R
Switch Leakage Current I
Switch Current Limit I
ds(on)
SWleak
SWlim
I
= 1.5 A – 225 – m
SW
V
= 5 V, TA = 25°C – – 1 A
SW
V
= 21 V – 1 – A
SW
4.2 – 5.5 V
– 0.2 – V
– 0.1 1 A
20 – 2000 kHz
–60– dB
–3–MHz
– 200 – kHz
–70– ns
– – 0.4 V
1.5 – – V
––1 A
28 – 32 V
– 54.9 – A
– 47.8 – A
1.8 2 – A
Continued on the next page…
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
A8500
Flexible WLED/RGB Backlight Driver
for Medium Size LCDs
ELECTRICAL CHARACTERISTICS (continued), valid at T
otherwise noted
Characteristics Symbol Test Conditions Min. Typ. Max. Units
LED Current Sinks
LEDx Regulation Voltage V
I
to I
SET
Current Gain A
LEDx
Voltage on ISET Pin V
I
Allowable Current Range I
SET
LEDx Accuracy Err
LEDx Matching
LEDx Switch Leakage Current I
LEDx Switch Leakage Current I
Serial Pulse Timing (see figure 4 for further explanation)
EN Pulse Low Time t
EN Pulse High Time t
Initial EN or APWM Pulse High Time (relative to switching period)
Level Change Delay (relative to switching
period)
Shutdown Delay (relative to switching
period on EN or APWM)
Soft Start
Soft Start Boost Current Limit I
Soft Start LEDx Current Limit I
Thermal Shutdown Threshold T
LEDx
I
ISET
ISET
SET
LEDx
LEDx
LSleak5
LSleak21
LO
HI
t
HI(init)
t
HID
t
SHDN
SWSS
LEDSS
40°C hysteresis – 165 – °C
SHDN
= 100 A – 210 – –
SET
R
= 12 k; 100% current ratio,
ISET
measured as average of LED1 to LED8;
LED1 to LED8 = 0.5 V
I
= 100 A , 100% current ratio;
SET
LED1 to LED8 = 0.5 V
V
= 5 V, EN = PWM = APWM = 0, TA = 25°C – – 1 A
LEDx
V
= 21 V, EN = PWM = APWM=0 – 1 – A
LEDx
First EN or APWM pulse after
shutdown
Falling edge of EN or APWM
pulse
Initial soft start current for boost switch - 1 - A
Current through enabled LEDx pins during soft
start, R
= –40°C to 85°C, typical values at TA = 25°C, VIN = 5 V, unless
A
– 500 – mV
– 1.23 – V
40 – 120 A
– ±1.2 – %
– ±1.5 – %
0.5 – 100 s
0.5 – 100 s
SKIP = Low – 256 –
SKIP = High – 64 –
SKIP = Low – 256 –
SKIP = High – 64 –
SKIP = Low – 256 –
SKIP = High – 64 –
ISET
=12 k
- 1.25 - mA
Switching
Pulses
Switching
Pulses
Switching
Pulses
Switching
Pulses
Switching
Pulses
Switching
Pulses
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5
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