A8503
High Efficiency 6-Channel, 2 MHz, WLED/RGB Driver for
Medium Displays, with Integrated 55 V Power Switch
Features and Benefits
▪
Active current sharing between LED strings for ±0.6%
accuracy and matching
▪
Drives up to 12 series × 6 parallel = 72 LEDs (V
f
= 3.2 V,
I
f
= 20 mA) at 5 V
▫
Each individual current sink is capable of 35 mA
▫
Adjustable overvoltage protection (OVP)
▪
600 kHz to 2 MHz adjustable switching frequency
▫
Open or shorted LED string protection
▫
Open Schottky diode protection
▫
Overtemperature, cycle-by-cycle current limit,
undervoltage, and soft start time-out protections
▫
Selectable latched/auto-restart protection modes
▪
No audible MLCC noise during PWM dimming
▪
No pull-up resistors required for LED modules that use
ESD capacitors
Continued on the next page…
Description
The A8503 is a multi-output WLED/RGB LED driver for
medium-size LCD backlighting. It integrates a current-mode
boost converter with internal power switch and six current
sinks. The boost converter can provide output voltages up to
47 V. The boost converter can drive up to 72 LEDs at 20 mA
per LED with a battery voltage down to 5 V. The LED sinks
are capable of sinking up to 35 mA each, and can also be
paralleled together to achieve even higher LED currents. The
A8503 provides protection against overvoltage, open diode,
open or shorted LED string, and overtemperature. A dual
level cycle-by-cycle current limit function provides soft start
and protects against overloads. A soft start timeout monitor is
provided to enhance protection when starting up into a fault
condition.
When the MODE pin is set low, the A8503 latches on a fault,
and can be re-enabled only by cycling the input voltage, V
IN
,
or by toggling the EN pin. Connecting the MODE pin high
provides auto-restart after fault events. The A8503 features
Continued on the next page…
Package: 26 contact MLP/QFN (suffix EC)
Applications
▪
Notebook and sub-notebook displays
▪
LCD monitors
▪
LCD panels
Approximate size
Typical Application
V
BAT
5 to 27 V
V
IN
4.3 to 5.5 V
R
PULLUP
FAULT
C
BAT
4.7
μF
35 V
VIN
L1
10
μH
SW SW
D1
R
OVP
C
OUT
2.2
μF
OVP
C
IN
0.1
μF
FAULT
FSET
COMP
EN
A8503
PAD
LED1
LED2
LED3
LED4
LED5
LED6
R
FSET
C
COMP
1
μF
EN
Shutdown
PWM
LED State
Off Off Off On Off
R
ISET
Enable
MODE
PWM
ISET
AGND PGND PGND DGND LGND
Figure 1. Typical application circuit
8503-DS
A8503
High Efficiency 6
-Channel
, 2 MHz, WLED/RGB Driver for
Medium Displays, with Integrated 55 V Power Switch
Features and Benefits (continued)
▪
Extends battery life
▫
Efficiency optimized for 3-cell notebooks
▫
0.1
μA
shutdown current
▫
Unique architecture eliminates external voltage divider and
associated battery drain
▪
Rugged and small footprint solution
▫
55 V, 2 A DMOS switch in 4 mm × 4 mm package—allows
IPC-2221/2 / IPC-D-275 compliant PCB layout
Description (continued)
EN (enable) and PWM (dimming) pins to comply with popular
notebook backlight control interfaces.
The device is offered in a 26-contact, 4 mm × 4 mm, 0.75 mm
nominal overall height QFN, with exposed pad for enhanced thermal
dissipation. It is lead (Pb) free, with 100% matte tin leadframe
plating.
Selection Guide
Part Number
A8503GECTR-T
Packing
1500 pieces per 7-in. reel
Package
26-contact QFN/MLP with exposed thermal pad
Absolute Maximum Ratings
Characteristic
SW Pins
LED1 through LED6 Pins
OVP Pin
Remaining Pins
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
T
A
T
J
(max)
T
stg
Range G
Symbol
V
SW
V
LEDx
V
OVP
Notes
Rating
–0.3 to 57
–0.3 to 34
–0.3 to 47
–0.3 to 7
–40 to 105
150
–55 to 150
Units
V
V
V
V
ºC
ºC
ºC
Thermal Characteristics
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
EC package, on 4-layer PCB based on JEDEC standard
Value Units
35
ºC/W
*Additional thermal information available on the Allegro website
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A8503
High Efficiency 6
-Channel
, 2 MHz, WLED/RGB Driver for
Medium Displays, with Integrated 55 V Power Switch
Functional Block Diagram
Vbat
5 to 27 V
Cbat
4.7
μF/35
V
V
OUT
L
10
μH
SW
SW
R
OVP
10 kΩ
OVP
C
OUT
2.2
μF
OSC
FSET
R
fset
OCP
Soft Start
Current Mode
Boost Controller
OVP
Comparators
O VP
LED1
+
+
-
Ref
PGND
LED2
-
COMP
C
comp
1
μF
EN
ON/OFF
Feedback
and
Control
Reference
Current
Generator
LED3
PWM
ISET
LED4
LED-select
Logic
Internal
Power
UVLO
Cin
0.1μF
Shut
down
Latch
Reset
R
Flip-flop
S
FAULT
OVP
OCP
Vin
4.3 to 5.5 V
VIN
Open and
Short LED
Detect
TSD
LED5
LED6
Rpullup
MODE
FAULT
LGND
AGND
PGND PGND
DGND
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A8503
High Efficiency 6
-Channel
, 2 MHz, WLED/RGB Driver for
Medium Displays, with Integrated 55 V Power Switch
Pin-out Diagram
25 OVP
24 SW
23 SW
26 NC
22 NC
21 PGND
20 PGND
19 PWM
PAD
18 DGND
17 EN
16 FAULT
15 NC
LED3 10
LED4 12
LED5 13
LGND 11
LED6 14
8
LED1
9
LED2
NC
COMP
VIN
ISET
AGND
FSET
MODE
1
2
3
4
5
6
7
(Top View)
Terminal List Table
Name
AGND
COMP
DGND
EN
¯ ¯ ¯¯ ¯
¯ L¯
¯
FAU¯ T
FSET
ISET
LEDx
LGND
MODE
NC
OVP
PAD
PGND
PWM
SW
VIN
Number
5
2
18
17
16
6
4
8,9,10,11,
12,13,14
11
7
1, 15, 22, 26
25
–
20, 21
19
23, 24
3
Connect to common star ground
Compensation pin; connect 1
μF
capacitor to AGND or common star ground
Digital ground; connect to common star ground
Device enable
During normal operation, this pin is high (high impedance); at a fault event, this pin pulls low
Set switching frequency; connect R
FSET
from FSET to AGND
Sets 100% current through LED string; connect R
ISET
from ISET to AGND
LED current sinks; connect unused LEDx pins to ground
Power ground pin for LEDx current sinks; connect to common star ground
Apply V
IL
for latching faults, apply V
IH
for auto-restart; see Fault Mode table
Not connected internally
Connect this pin to output capacitor +ve node through R
OVP
to enable overvoltage protection; select
R
OVP
> 10 kΩ (V
OVP
is 44 V typical)
Exposed thermal pad, common star ground for PGND, DGND, LGND, and AGND; connect to copper
plane of the application PCB for heat transfer
Power ground; connect both pins to common star ground
PWM LED-current control; apply logic level PWM for dimming
DMOS switch drain node; tie SW pins together on the PCB
Input supply for the IC; decouple with a 0.1
μF
ceramic capacitor
Function
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A8503
High Efficiency 6
-Channel
, 2 MHz, WLED/RGB Driver for
Medium Displays, with Integrated 55 V Power Switch
ELECTRICAL CHARACTERISTICS
1
Valid using circuit shown in figure 1, T
A
= T
J
= 25°C except
indicates specifications
guaranteed from
−40°C
to 105°C, V
IN
= 5.0 V, EN = PWM = V
IH
, R
ISET
= 12.4 kΩ, R
FSET
= 34 kΩ, MODE = AGND , unless otherwise
noted
Characteristics
Input Voltage Range
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis Window
Supply Current
Symbol
V
IN
V
UVLO
V
UVLOHYS
Switching, at no load
I
VIN
Shutdown, EN= V
IL
, T
A
= 25°C
Standby, EN = V
IH
, PWM = V
IL
Boost Controller
Switching Frequency
Minimum Switch Off-Time
Minimum Switch On-Time
Logic Input Levels (EN and PWM pins)
Input Voltage Level Low
Input Voltage Level High
Input Leakage Current
Overvoltage Protection
Output Overvoltage Threshold
Overvoltage Protection Leakage Current
Overvoltage Protection Sense Current
Boost Switch
Switch On-Resistance
Switch Leakage Current
Switch Current Limit
LED Current Sinks
LEDx Pin Regulation Voltage
I
SET
to I
LEDx
Current Gain
ISET Pin Voltage
ISET Allowable Current Range
LEDx Current Accuracy
3
LEDx Current Matching
4
Switch Leakage Current (LEDx)
LED Short-Detect Voltage
V
LEDx
A
ISET
V
ISET
I
SET
Err
ILEDX
∆I
LEDX
I
SWLKG(L)
V
SC
LED1 through LED6 = 0.6 V, at 100% Current
I
SET
= 100
μA,
LED1 though LED6 = 0.6 V, at 100%
Current
V
LEDx
= 12 V, EN = 0
LEDx pin voltage level that forces latched shutdown,
MODE = low
I
SET
= 100
μA
–
–
–
33
–3
–3
–
–
600
320
1.235
–
±0.6
±0.6
0.1
18.7
–
–
–
110
3
3
–
–
mV
A/A
V
μA
%
%
μA
V
R
DS(on)
I
SWLKG(B)
I
SWLIM
I
SW
= 1 A
V
SW
= 22 V
–
–
–
250
0.1
2.7
–
–
–
mΩ
μA
A
V
OVP
I
OVPLKG
I
OVPH
V
OVP
= 22 V, R
OVP
= 0
Ω,
EN = V
IL
–
–
–
44
0.1
240
–
–
–
V
μA
μA
V
IL
V
IH
I
ILKG
EN = PWM = 5 V
–
1.5
–
–
–
100
0.4
–
–
V
V
μA
f
SW
t
off(min)
t
on(min)
1.2
–
–
1.5
72
72
1.9
–
–
MHz
ns
ns
V
IN
falling
Test Conditions
Min.
4.2
–
–
–
–
–
Typ.
2
–
–
0.1
7
0.1
1
Max.
5.5
4.0
–
–
1
2
Unit
V
V
V
mA
μA
mA
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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