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A708
www.addmtek.com DESCRIPTION The A708 is a 3 channels 20mA advanced current regulator for driving LEDs. Only bypass capacitor is required and the noise is very low. The special circuit design provides over 90% efficiency because of the very low dropout voltage. Target end applications are LED backlights for color LCD display, such as mobile phone, smart phone, PDA, notebook, and monitor, etc.
3 CHANNELS 20mA ADVANCED CURRENT REGULATOR
FEATURES Fixed 20mA DC constant sink current. Individual current sink circuit for each LED string to prevent short / open circuit on LEDs. TSOT-26 package available. High efficiency. Supply voltage range 2.7V ~ 12V. Output sustaining voltage up to 17V. 0.1uA standby current. 2KV HBM ESD protection. Advanced Bi-CMOS process.
TYPICAL APPLICATION CIRCUIT
APPLICATIONS Small Size Color LCD Backlights.
V LED+
Mobile Phone, Smart Phone.
C BP
LED Backlight for Portable DVD, NB, Monitors, and UMPC. PACKAGE PIN OUT
VDD 1
LED1 LED2 LED3
6 LED1 5 LED2 4 LED3
A708
GND 2 EN 3
V DD C IN Enable
VDD
A708
EN GND
A708 TSOT-26
ORDER INFORMATION TA (C) -40 ~ 85
Y
Plastic TSOT-26 6-pin A708YFT
Note: The letter "F" is marked for Lead Free process, and letter "T" is marked for Tape & Reel.
Copyright (c) 2007 ADDtek Corp.
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ABSOLUTE MAXIMUM RATINGS Input Voltage, VDD Output Sustaining Voltage, VLEDn Voltage at all other pins Maximum Junction Temperature, TJ Storage Temperature Range Lead Temperature (soldering, 10 seconds)
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal. (Note)
-0.3V to 13.2V -0.3V to 17V -0.3V to 12V 150OC -40OC to 150C 260OC
POWER DISSIPATION TABLE Package Y TA=70 C TA= 85C JA Derating factor ( mW/C ) TA25C Power rating (mW) Power rating (mW) Power rating (mW) (C / W ) TA25 OC 220 4.5 568 363 295
Note : Junction Temperature Calculation: TJ = TA + (PD x JA). PD: Power Dissipation, TA: Ambient temperature, JA: Thermal Resistance-Junction to Ambient The JA numbers are guidelines for the thermal performance of the device/PC-board system. All of the above assume no ambient airflow.
BLOCK DIAGRAM
VDD EN
VDDI
A708
Control Logic
Driving Stage Driving Stage Driving Stage
LED1 LED2 LED3 GND
Reference Current
Copyright (c) 2007 ADDtek Corp.
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PIN DESCRIPTION Pin Name LED1 ~ LED3 EN VDD GND PGND Pin Function Output pins; connect to LED's cathode. Enable control pin. Pulling this pin high will enable the device. Pulling this pin to GND will disable the device. Power supply Ground Power ground
RECOMMENDED OPERATING CONDITIONS Parameter Symbol Min Typ Supply Voltage VDD 2.7 Output Sink current ILED Operating free-air temperature range TA -40
Max 12 25 +85
Unit V mA C
ELECTRICAL CHARACTERISTICS VDD=3.7V, VIH=3.3V, VIL=GND, No Load, TA=25C, (Unless otherwise noted) Parameter "Low" Input Voltage "High" Input Voltage "Low" Input Current "High" Input Current LED Dropout Voltage LED Sink Current LED Sink Current Deviation Load Regulation Line Regulation Supply Current Standby Supply Current IDD IDDSTBY Symbol VIL VIH IIL IIH VLEDL ILED ILEDn Note 1 Rank A Note 2 VLEDn=0.15~3V VDD=2.7~12V, VLEDn=0.15V 300 0.1 19 18 Condition Min 0 1.7 -5.0 -5.0 75 20 20 Typ Max 0.4 VDD +5.0 +5.0 90 21 22 3 3 3 600 Unit V V A A mV mA % % % uA uA VDD LEDn EN Apply Pin
Note 1: LED Dropout Voltage: 90% x ILEDn @ VLEDn=150mV Note 2: ILEDn(max)-ILEDn(average) and ILEDn(average)-ILEDn(min)
Copyright (c) 2007 ADDtek Corp.
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CHARACTERISTIC CURVES
Output Current vs. Supply Voltage
21.00 Output Current (mA) Output Current (mA) 21.0 V DD=3.7V V EN=3.3V V DROP =0.2V
Output Current vs. Temperature
20.50
20.5 20.0
20.00 19.50 V EN=3.3V V DROP =0.2V TA =25 0.0 5.0 10.0 Supply Voltage (V) 15.0
19.5 19.0 -50
19.00
0
50 Temperature ( )
100
150
Output Current vs. Dropout Voltage
25.00 Output Current (mA) 20.00 15.00 10.00 5.00 0.00 10 V DD=3.7V V EN=3.3V TA=25 100 1,000 Dropout Voltage (mV) 10,000
Max. Allowable Dropout (mV) 10 8 6 4 2
Max. Allowable VDrop vs. Ambient Temp.
V DD=3.7V V EN=3.3V TJ,MAX =125 ILED,T otal =60mA
0 10
30
50 70 90 Ambient Temperature (C)
110
Copyright (c) 2007 ADDtek Corp.
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APPLICATION INFORMATION
Enable
Pulling the EN pin to high will enable the device sinking constant current on LED pins. Pulling the EN pin to ground will shutdown the device. This pin should not be left floating and need to be terminated.
LED Number in the String Driven by Each Channel
The breakdown voltage of LEDn pin is 17V so that each channel can drive up to 9 pcs of LEDs in series. When the chip is disabled, the forward voltage of the LED may drop to half of the rated value because of the extremely small leakage current.
LED Brightness Control
The LED sink current was fixed at 20mA. Apply PWM signal to EN pin and control the duty that could control the LED brightness from 0% to maximum.
V IN
C BP
LED1
LED2
LED3
V DD
C IN
VDD
A708
EN GND
Enable
Efficiency
The ACR (Advanced Current Regulator) architecture offers ultra low output dropout that significantly improves the efficiency compared to Inductive Boost type or Capacitor Charge Pump type LED driver. The system efficiency, defined as the ratio between the LEDs power and the input supplied power, is: Efficiency = (VF1 x ILED1 + VF2 x ILED2 + VF3 x ILED3 ) / ( VDD x IDD ) Where, VF is the forward voltage of LED.
Copyright (c) 2007 ADDtek Corp.
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Li-ion Battery Voltage Supply
The A708 can work with Li-ion battery. The supply voltage of Li-ion battery ranges from 4.5V down to lower than 3V while the white/blue LED forward voltage (VF) is in the range of 2.9V to 3.5V at 20mA current. The supply voltage range and LED forward voltage can be set to fully utilize Li-ion battery energy. For example, if the forward voltage of white LED is 3.2V at 20mA, the Li-ion battery can discharge until output voltage reaches 3.275V (normally around 1% ~ 3% power left in the battery). When Li-ion battery voltage is lower than the 3.275V, the LED current (brightness) will start to decrease.
V DD
LED1
LED2
LED3
Li-ion Battery Enable
VDD
A708
EN GND
Copyright (c) 2007 ADDtek Corp.
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PACKAGE
Surface Mount TSOT-26
D b L L1 C
SYMBOLS A A1
MILLIMETERS MIN --0.00 0.84 0.35 0.10 2.70 2.60 1.40 ----0.30 0.5 0 4 TYP --0.05 0.87 0.40 0.125 2.90 2.80 1.60 0.95 1.90 0.40 0.6 4 10 MAX 1.00 0.10 0.90 0.50 0.15 3.10 3.00 1.80 ----0.60 0.7 8 12
E
E1
A2 b C D
e e1 4x1
E E1 e e1 L L1 1
A
A2
A1
4x1
Copyright (c) 2007 ADDtek Corp.
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IMPORTANT NOTICE
ADDtek reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. ADDtek integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of ADDtek products in such applications is understood to be fully at the risk of the customer. In order to minimize risks associated with the customer's applications, the customer should provide adequate design and operating safeguards. ADDtek assumes to no liability to customer product design or application support. ADDtek warrants the performance of its products to the specifications applicable at the time of sale.
ADDtek Corp. 9F, No. 20, Sec. 3, Bade Rd., Taipei, Taiwan, 105 TEL: 2-25700299 FAX: 2-25700196
Copyright (c) 2007 ADDtek Corp. 8 DD076_A -AUGUST 2007

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