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PDF A8500 Data sheet ( Hoja de datos )
| Número de pieza | A8500 | |
| Descripción | Flexible WLED/RGB Backlight Driver | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de A8500 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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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)
Description
TheA8500 is a multi-output WLED driver for medium display
backlighting. TheA8500 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 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
Approximate Scale 1:1
EN pin dimming:
serial pulse train input
VEN
IOUT
PWM pin dimming:
digital PWM input
VPWM
IOUT
APWM pin dimming:
analog PWM input
VAPWM
Typical Application
VIN
5 V ±10%
CIN
0.1 μF/ 10 V
VBAT
5 to 25 V
L1
10 μH
CBAT
1 μF/ 25 V
D1
ROVP COUT
EN
PWM
VIN
SW SW
OVP
AGND
2.2 μF
50 V
APWM
SKIP
COMP
CC
RFSET
FSET
ISET
A8500
PGND
SEL3
SEL2
VIN
RISET
LED1
LED3 LED5 LED7
LGND
SEL1
LED2
LED8 LED6 LED4
IOUT
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.
8500P-DS
1 page  
A8500
Flexible WLED/RGB Backlight Driver
for Medium Size LCDs
ELECTRICAL CHARACTERISTICS (continued), valid at TA = –40°C to 85°C, typical values at TA = 25°C, VIN = 5 V, unless
otherwise noted
Characteristics
Symbol
Test Conditions
Min. Typ. Max. Units
LED Current Sinks
LEDx Regulation Voltage
ISET to ILEDx Current Gain
Voltage on ISET Pin
ISET Allowable Current Range
LEDx Accuracy
VLEDx
AISET
VISET
ISET
ErrLEDx
ISET = 100 μA
RISET = 12 kΩ; 100% current ratio,
measured as average of LED1 to LED8;
LED1 to LED8 = 0.5 V
– 500 –
– 210 –
– 1.23 –
40 – 120
– ±1.2 –
mV
–
V
μA
%
LEDx Matching
∆LEDx
ISET = 100 μA , 100% current ratio;
LED1 to LED8 = 0.5 V
– ±1.5 –
%
LEDx Switch Leakage Current
LEDx Switch Leakage Current
ILSleak5
ILSleak21
VLEDx= 5 V, EN = PWM = APWM = 0, TA = 25°C
VLEDx= 21 V, EN = PWM = APWM=0
Serial Pulse Timing (see figure 4 for further explanation)
EN Pulse Low Time
EN Pulse High Time
tLO
tHI
Initial EN or APWM Pulse High Time (rela-
tive to switching period)
tHI(init)
First EN or APWM pulse after
shutdown
SKIP = Low
SKIP = High
––1
–1–
μA
μA
0.5 – 100 μs
0.5 – 100 μs
–
256
–
Switching
Pulses
–
64
–
Switching
Pulses
Level Change Delay (relative to switching
period)
tHID
SKIP = Low
SKIP = High
–
256
–
Switching
Pulses
–
64
–
Switching
Pulses
Shutdown Delay (relative to switching
period on EN or APWM)
tSHDN
Falling edge of EN or APWM
pulse
SKIP = Low
SKIP = High
–
256
–
Switching
Pulses
–
64
–
Switching
Pulses
Soft Start
Soft Start Boost Current Limit
Soft Start LEDx Current Limit
Thermal Shutdown Threshold
ISWSS
ILEDSS
TSHDN
Initial soft start current for boost switch
Current through enabled LEDx pins during soft
start, RISET=12 kΩ
40°C hysteresis
-1 -
- 1.25 -
– 165 –
A
mA
°C
Allegro MicroSystems, LLC
5
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5 Page 
A8500
Flexible WLED/RGB Backlight Driver
for Medium Size LCDs
At startup, the output capacitor is discharged and the IC enters
soft start. The boost current is limited to 1 A, and all active LEDx
pins sink 1/16 of the set 100% current until all of the enabled
LEDx pins reach 0.5 V. After the IC comes out of soft start, the
boost current and the LEDx pin currents are set to 100% current.
The output capacitor charges to the voltage level required to sup-
ply full LEDx current within a few cycles. The IC is shut down
immediately when PWM goes low.
Analog Dimming with an External PWM Signal on the APWM
Pin. When the APWM pin is pulled high, with the EN and PWM
pins low, the A8500 turns on in this mode. The first pulse after
shutdown should be greater than tHI(init). The logic level PWM
signal applied to the APWM pin multiplies ISET by the duty cycle
to set the reference current level for the LED pins. The typical
range for the APWM signal frequency is 20 kHz to 2 MHz. The
output current ripple at 20 kHz, 50% duty cycle, is less than 5%
of the set value. The LED current accuaracy at 2 MHz, 50% duty
cycle, is less than 3%. In this mode, the A8500 goes through a
soft start routine similar to serial dimming.
Device Internal Protection
Overcurrent Protection (OCP). The A8500 has a pulse-by-pulse
current limit of 2 A on the boost switch. This current limit is
independent of duty cycle.
Thermal Shutdown Protection (TSD). The IC shuts down when
junction temperature exceeds 165°C and restarts when the junc-
tion temperature falls by 40°C.
Overvoltage Protection (OVP). The A8500 has overvoltage
protection to protect the IC against output overvoltage. The over-
voltage level can be set, from 30 to 45 V typical, with an external
resistor, ROVP, as shown in figure 10. When the current though
the OVP pin exceeds 54.9 μA, the OVP comparator goes high.
When the OVP pin current falls below 47.8 μA, OVP is reset.
180
VIN D1 VOUT
160 fAPWM (kHz)
140 20
120 100
100 500
80
60
40
20
OVP
Disable
SW SW
ROVP
OVP
28.8 V
–
+
1.23 V
22 kΩ
DZ
A
4.4 kΩ
COUT
0
0 20 40 60 80 100
Duty Cycle (%)
Figure 9. APWM pin dimming linearity.
Figure 10. Overvoltage protection circuit. Three alternative
configurations at (A) are available, as follows:
External Component
ROVP only
DZ only
both ROVP and DZ
OVP Rating
up to 45 V
up to 47 V
redundancy
Allegro MicroSystems, LLC
11
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet A8500.PDF ] | |
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