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PDF A8600 Data sheet ( Hoja de datos )
| Número de pieza | A8600 | |
| Descripción | WHITE LED BACKLIGHT DRIVER SIX-STRING | |
| Fabricantes | AiT Semiconductor | |
| Logotipo |  |
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AiT Semiconductor Inc.
www.ait-ic.com
A8600
WHITE LED BACKLIGHT DRIVER
SIX-STRING WITH ACTIVE CURRENT
DESCRIPTION
The A8600 is a high-efficiency driver for white
light-emitting diodes (LED(s)). It is designed for large
liquid-crystal displays (LCD(s)) that employ an array of
LED(s) as the light source. A current-mode step-up
controller drives up to six parallel strings of multiple
series-connected LED(s). Each string is terminated with
ballast that achieves ±1.5% current regulation accuracy,
ensuring even bright-ness for all LED(s).
The A8600 has a wide input-voltage range from 4.5V to
26V, and provides a fixed 20mA or adjustable 15mA to
25mA full-scale LED current. The A8600 has two
dimming control modes to enable a wide variety of
applications. In direct DPWM mode, the LED current is
directly turned on and off by a PWM signal. In analog
dimming mode, an internal phase-locked loop (PLL)
circuit translates the PWM signal into an analog signal
and linearly controls the LED current down to 12.5%.
Below 12.5%, digital dimming is added to allow lower
average LED current down to 1%. Both control methods
provide 100:1 dimming range. The A8600 has multiple
features to protect the controller from fault conditions.
Separate feedback loops limit the output voltage if one
or more LED(s) fail open or short. The controller features
cycle-by cycle current limit to provide consistent
operation and soft-start capability. A thermal shutdown
circuit provides another level of protection. The step-up
controller uses an external MOSFET, which provides
good efficiency and allows for scalable output power and
maximum operating voltage. Low feedback voltage at
each LED string (450mV) helps reduce power loss. The
A8600 features selectable switching frequency (500kHz,
750kHz, or 1MHz), which allows trade-offs between
external component size and operating efficiency.
The A8600 is available in QFN20 (4x4) Package.
FEATURES
Drives Six Parallel Strings with Multiple
Series-connected LED(s) per String
±1.5% Current Regulation Accuracy
Between Strings
Low 450mV Feedback Voltage at Full
Current Improves Efficiency
Step-Up Controller Regulates the Output
Just Above the Highest LED String Voltage
Full-Scale LED Current Adjustable from
15mA to 25mA, or Preset 20mA
Wide 100:1 Dimming Range
Programmable Dimming Control: Direct
DPWM or Analog Dimming
Built-In PLL for Synchronized Dimming
Control Open and Short LED Protections
Output Over voltage Protection
Wide Input Voltage Range from 4.5V to 26V
External MOSFET Allows a Large Number of
LED(s) per String
500kHz/750kHz/1MHz Switching Frequency
Available in QFN20 (4x4) Package
APPLICATIONS
Notebook, Sub notebook, and Tablet
Computer Displays
Automotive Systems
Handy terminals
TYPICAL APPLICATION
ORDERING INFORMATION
Package Type
Part Number
QFN20
Q20
A8600Q20R
A8600Q20VR
Note
R: Tape & Reel
V: Green Package
AiT provides all Pb free products, suffix “ V “ means
Green Package
REV1.0
-FEB 2010 RELEASED -
-1-
1 page  
AiT Semiconductor Inc.
www.ait-ic.com
ELECTRICAL CHARACTERISTICS
A8600
WHITE LED BACKLIGHT DRIVER
SIX-STRING WITH ACTIVE CURRENT
VIN=12V, V/SHDN=VIN, CCV=0.1μF, TA=0℃ to +85℃, unless otherwise specified. Typical values are at TA=25℃.)
Parameter
Conditions
Min Typ. Max Units
VIN=VCC
4.5 -
5.5
IN Input Voltage Range
VCC=bypassed to GND
through 1uF capacitor
V
5.5 - 26.0
IN Quiescent Current
V/SHDN=high VIN=26V
BRT=GND VIN=VCC=5V
-
-
1
1
2
2
mA
VCC Output voltage
V/SHDN=5V,6V＜VIN＜26V,
0＜IVCC＜10mA
4.7
5
5.3
V
VCC Short Circuit Current
- 15 56 130 mA
VCC UVLO Threshold
Rising edge,
hysteresis=20mV
4
4.25
4.45
V
EXT High Level
10mA from EXT to GND
VCC-0.1
VCC
-
V
EXT Low Level
-10mA from EXT to VCC
- 0 0.1 V
EXT On-Resistance
EXT high or low
-2 5Ω
EXT Sink/Source Current
EXT forced to 2V
-1 -A
OSC High-Level Threshold
-
VCC-0.4
-
-V
OSC Midlevel Threshold
-
1.5
-
VCC-2.0
V
OSC Low-Level Threshold
- - - 0.4 V
VOSC=VCC
0.9 1
1.1 MHz
Operating Frequency
VOSC=open
VOSC=GND
675 750
450 500
825
550
kHz
Minimum Duty Cycle
PWM mode
Pulse skipping, no load
- 10
-0
-
-
％
Maximum Duty Cycle
- 94 95 - ％
CS Trip Voltage
Duty cycle=75％
85 100 115 mV
/SHDN Logic-Input High Level
-
2.1 -
-V
/SHDN Logic-Input Low Level
-
- - 0.8 V
BRT, ENA Logic-Input High Level
-
2.1 -
-V
BRT, ENA Logic-Input Low Level
-
- - 0.8 V
/SHDN Leakage Current
/SHDN=26V
- - +42 μA
CS Leakage Current
VCS=GND
- +40 +50 μA
OSC Leakage Current
- -3 - +3 μA
BRT,ENA Leakage Current
- -1 - +1 μA
FSET,ISET Leakage Current FSET=ISET=VCC
-1 - +1 μA
OV Leakage Current
-
-0.1
-
+0.1
μA
ISET Voltage
-
1.12
1.19
1.26
V
ISET High-Level Threshold
Default setting for 20mA
full-scale LED current
VCC-0.4
-
-V
REV1.0
-FEB 2010 RELEASED -
-5-
5 Page 
AiT Semiconductor Inc.
www.ait-ic.com
A8600
WHITE LED BACKLIGHT DRIVER
SIX-STRING WITH ACTIVE CURRENT
cannot be disabled by grounding any of the FB_ pins after the IC is powered up.
All FB_ pins in use are measured and the highest signal (HVC) and the lowest signal (LVC) are extracted for
two feedback loops. HVC is used to identify excessive dissipation across the current-source inputs. When
HVC is greater than VCC + 0.6V (typ) for greater than 65ms (see the Current-Source Fault Protection section),
a fault latch is set and the A8600 is shut down. The LDO output is not affected by the fault latch. LVC is fed
into the step-up converter’s error amplifier to regulate the step-up converter’s output voltage.
Current-Source Fault Protection
The LED current sources are protected against string open, short, and gross mismatch faults, using over
voltage detection circuitry on each FB_ pin. If any of these three fault conditions persists for a preset duration,
the fault strings are disabled. The duration of the fault time depends on the dimming mode and the duty cycle
of the BRT input (DBRT). In the DPWM mode, the timeout interval is:
tTIMEOUT_DPWM = 65ms/DBRT
In analog dimming mode, the fault time is fixed at 65ms for DBRT greater than 12.5%. When DBRT is less than
12.5%, the timeout interval is:
tTIMEOUT_ANALOG = 8.125ms/DBRT
The fault latch can be cleared by cycling the power or toggling the shutdown pin/SHDN.
Open-Current Source Protection
The A8600 step-up converter output voltage is regulated according to the minimum value of the enable FB_
voltages. If an individual LED string is open, the respective FB_ is pulled down to near ground. In this
situation, the step-up converter output voltage increases but is clamped to a level set with the OV feedback
input. When this elevated output voltage is applied to the undamaged strings, excessive voltage drop
develops across the FB_ pins. If the resulting HVC signal exceeds VCC + 0.6V for greater than 65ms, the fault
strings are disabled to protect the circuit.
LED-Short and String Mismatch Protection
Normally, white LED(s) have variations in forward-voltage drop of 3.1V to 3.6V. The A8600 can tolerate
slight mismatches between LED strings. When the sum of the LED forward voltages creates a mismatch in
the strings so the HVC signal exceeds VCC + 0.6V for greater than 65ms, the fault condition circuit is
triggered in much the same way as the circuit responds to open string faults. Similar protection is activated
when an LED is shorted. The larger the number of series-connected LED(s) (N), the smaller the tolerable
mismatch between LED(s):
REV1.0
-FEB 2010 RELEASED -
- 11 -
11 Page | ||
| Páginas | Total 25 Páginas | |
| PDF Descargar | [ Datasheet A8600.PDF ] | |
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