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Agamem Microelectronics Inc. PRELIMINARY
OVERVIEW
AA1700
Constant Current White LED driver
The AA1700 is a high frequency boost DC/DC converter with constant current output that drives white LEDs or similar. The LED current is set with the external resistor. Soft start circuitry prevents excessive current drawn from the supply during power on. Any number of LEDs can be connected in series as long as the summed forward voltages do not lead to exceed the specified operating output voltage range. This IC works with a wide operating supply range (1.8V to 15V) and low current consumption, is optimal for use in high-efficiency white LED driver.
FEATURES
* Drives Up to 8 LEDs in Series. * Second or more string of LEDs can be added. * Low current consumption: Typically 5.5 mA in operation, 1 A or less in stand-by. * PWM mode operation of the boost circuit (frequency range: 10 kHz to 1 MHz). * Incorporates a soft start circuit and adjustable soft start time. * Timer latch LED short-circuit protection circuit (SP). * On/off control function. * Available in an 8-pin TSSOP or SOP package.
PIN Configuration (TOP VIEW) IN SP VCC CTL 1 2 3 4 8 ER 7 CLK 6 GND 5 P0
APPLICATIONS
* LCD Bias Supplies * White LED Backlighting * Handheld Devices * Digital Cameras * Portable Applications
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Agamem Microelectronics Inc. PRELIMINARY
PIN DESCRIPTIONS
Pin No. 1 2 3 4 5 6 7 8 Symbol IN SP VCC CTL P0 GND CLK ER I/O I -- -- I O -- -- O Output voltage feedback pin
AA1700
Constant Current White LED driver
Description
Soft start and short circuit protection setting Power supply pin ON/OFF control pin Output driver pin Ground pin Internal PWM frequency setting pin Error amplifier output pin
BLOCK DIAGRAM
Vcc 3 CLK 7
Regulator
0.5V 0.1V Error Amp. +
Oscillator
5 + PWM COMP. + +
P0
IN
1
Output driver
ER
8
0.6V
Soft start short circuit protection 6 GND 2 SP 4 CTL
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ABSOLUTE MAXIMUM RATINGS
AA1700
Constant Current White LED driver
(Ta = +25C)
Parameter Power supply voltage Output source current Output sink current Allowable dissipation Operating temperature Storage temperature
Symbol VCC IO+ IO - PD Top Tstg
Condition Min -- -- Ta +25 C -- -- -- -- -30 -55
Rating Max 16 -50 50 430* +85 +125
Unit V mA mA mW
C C
WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current, temperature, etc.) in excess of absolute maximum ratings. Do not exceed these ratings.
RECOMMENDED OPERATING RANGE
(Ta = +25 C) Parameter Power supply voltage Error amplifier input voltage CTL pin input voltage Output source current Output sink current SP pin capacitance Phase compensation capacitance Output current setting resistance Timing resistance Timing capacitance Oscillation frequency Operating temperature Symbol Min VCC VI VCTL IO+ IO - CPE CP RB RT CT fCLK TOP 1.8 -0.2 -0.2 -40 -- -- -- 150 1.0 100 10 -30 Value Typ -- -- -- -- -- 0.1 0.1 390 3.0 270 500 +25 Max 15 1.0 VCC -- 40 -- -- 5000 10.0 10000 1000 +85 k pF kHz V V V mA mA F F Unit
C
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Agamem Microelectronics Inc. PRELIMINARY
ELECTRICAL CHARACTERISTICS
AA1700
Constant Current White LED driver
(VCC = +2 V, Ta = +25 C)
Parameter Circuit to prevent malfunction at low input voltage (U.V.L.O.) Soft start Short circuit detection (S.C.P.) Reset voltage Threshold voltage Charging current Voltage at soft start completion Charging current Threshold voltage Oscillation frequency Frequency input stability Frequency variation with temperature Input threshold voltage VT input stability VT variation with temperature Input bias current Voltage gain Frequency bandwidth Error amplifier Maximum output voltage range Output source current Output sink current Idle period adjustment section Maximum duty cycle
Symbol VR VTH ICS VtS ICPC VtPC fCLK fdV fdT VT VTdV VTdT IB AV BW VOM+ VOM - IOM+ IOM - tDUTY
Condition Min -- -- VSP = 0 V -- VSP = 0 V -- RT = 3.0 k , CT = 270 pF VCC = 2 V to 15 V Ta = -30C to +85C VER = 450 mV VCC = 2 V to 15 V Ta = -30C to +85C VIN = 0 V -- AV = 0 dB -- 1.1 -1.5 0.7 -1.5 0.7 400 -- -- 480 -- -- -1.0 70 -- 0.78 -- VER = 0.45 V RT = 3.0 k , CT = 270 pF VER = 0.8 V -- 24 65
Value Typ -- 1.3 -1.0 0.8 -1.0 0.8 500 2 5 500 5 1 -0.2 100 6 0.87 0.05 -40 40 75 Max 0.9 1.5 -0.7 0.9 -0.7 0.9 600 10 -- 520 20 -- 1.0 145 -- -- 0.2 -24 -- 85
Unit V V A V A V kHz % % mV mV % A V/V MHz V V A A %
Sawtooth wave oscillator (CLK)
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Agamem Microelectronics Inc. PRELIMINARY
(Continued) Parameter Symbol VOH1 VOH2 Output voltage Output section Output source current Output sink current Pull down resistance Pin voltage Output current setting section/ Control section Input off condition Input on condition Pin current range Stand-by current Entire device Average supply current VOL1 VOL2 IO+ IO - RO VCTL IOFF ION ICTL ICCS ICC -- RB = 390
AA1700
Constant Current White LED driver
Value Min Typ 1.2 1.0 0.1 0.1 -30 60 30 0.3 -- -- -- -- 5.5 Max -- -- 0.2 0.2 -20 -- 40 0.4 0 -45 -0.1 1 9.3 V V V V mA mA k V A A mA A mA 1.0 0.8 -- -- -- 30 20 0.2 -20 -- -1.8 -- -- Unit
Condition RB = 390 , IO = -15 mA RB = 750 , VCC = 1.8 V IO = -10 mA RB = 390 , IO = 15 mA RB = 750 , VCC = 1.8 V IO = 10 mA RB = 390 , VO = 0.9 V RB = 390 , VO = 0.3 V --
CTL pin open or VCC RB = 390
HOW TO SET THE TIME CONSTANT FOR SOFT START AND SHORT CIRCUIT DETECTION
1. Soft Start
A soft start function, which gradually increases the width of the output pulses at power on, will be applied if a capacitor is connected to the SP pin. This can prevent rush currents and overshoot when the power supply is turned on. Soft start time can be measured by the following equation. (The time until the output ON duty reaches approximately 50%) tS [s] = 0.35 x CPE [uF]
2. Timer Latch Short Circuit Protection
When the load conditions suddenly change due to load effect, the short-circuit protection comparator outputs the + high-level signal (VOM ) and the capacitor CPE connected to the SP terminal starts charging. When the external capacitor CPE has been charged to approximately 0.8V, the latch circuit is set, the output terminal is fixed to low level, and the dead-time is set to 100%. However, the latch circuit is not reset unless the power for the latch circuit is turned off or restarted by the on/off control. * Short circuit detection time tPE [s] = 0.8 x CPE [uF]
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FUNCTIONAL DESCRIPTION
1. Switching Regulator Function
(1) Sawtooth wave oscillator
AA1700
Constant Current White LED driver
This circuit generates a triangular wave like sawtooth with a peak of 0.8V (VCLKH) and a trough of 0.1V (VCLKL) using a capacitor (for the time constant) and resistor connected to the CLK pin (pin 7). The oscillator frequency can be set to any value by selecting appropriate values for the external capacitor and resistor, CT and RT. This oscillator can provide a frequency in the range 10 kHz to 1 MHz.
fCLK
(2) Error amplifier
-1 VCLKL CT x RT x ln VCLKH
0.48x
1 CT x RT
[HZ]
This error amplifier detects and amplifies the DC-DC converter output voltage, and inputs that signal to a PWM comparator. The 0.5 V internal reference voltage is applied to the non-inverting input. Arbitrary gain and phase compensation can be connected by inserting a resistor and capacitor in series between the error amplifier output pin (pin 8) and the inverting input pin (pin 1). (3) PWM comparator The voltage comparator has one inverting and three non-inverting inputs. The comparator is a voltage/pulse width converter that controls the on-period of the output pulse according to its input voltage. The output transistors are turned on during periods when the CLK pin (pin 7) triangular waveform is lower than the error amplifier output voltage, soft start setting voltage, and idle period setting voltage. (4) Output driver The output circuit has a totem pole structure. A constant-current source output with line regulation can be set up at an arbitrary voltage by connecting a current setting resistor to the CTL pin (pin 4).
2. Power Supply On/Off Function
Stand-by mode (supply current 1 A or less) can be set by connecting the CTL pin (pin 4) to VCC or by making the pin open circuit. SW OFF Mode Stand-by mode
ON
Operating mode
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Agamem Microelectronics Inc. PRELIMINARY
TYPICAL APPLICATION EXAMPLE
22uH
AA1700
Constant Current White LED driver
Vout D1 1N5821 QA QB
SP Vcc Vin 33uF CTL 0.1uF
2 3 4
7 6 5
CLK GND P0 12K 10uF
Q1 FZT489 0.1uF
390O (*adjustable) 270pF 3K
Q2 C1815
RLED
RLED
CTL-IN
Note: 1.RLED=0.5V / ILED, ILED : LED Current, for LED brightness control where 0.5V is the feedback reference voltage and ILED = 20mA (RLED = 25 ) for typical application 2.Output voltage Vout is given by Vout=n * Vf + 0.5V where Vf : LED forward voltage drop n : Number of LEDs in series connection 3. The sample described above is an inductive-boost driver, so it should follow the following equation.
VIN < VOUT + VD1, where VD1 is forward voltage drop of diode D1.
4.To avoid some LEDs are damaged and conduce to high current of damaged LED series, the constant current control should be Included by QA, QB, etc. . 5. The chock Inductor (L1) Is for noise filter.
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other LED series
2007/1/22
L1 56uH
IN
1
8
ER
AA1700
Agamem Microelectronics Inc. PRELIMINARY
AA1700
Constant Current White LED driver
CDS Control for IR LED
Vcc IN SP Vcc CTL 390 Q2 C1815 Q3 C1815 C8 10uF R8 4.7K 1 8 ER CLK GND P0 VR1 50K R7 300 D3
2 3 4
AA1700
7 6 5
R2
CdS Light Sensitive Resistor
Note: 1.Light striking the surface of the Cds causes a decrease in resistance, while darkness produces a higher resistance. When the light is bright, Q3 is on and Q2 is off, AA1700 will enter stand-by mode and there is no output current provided. When the light is dark, Q3 is off and Q2 is on, AA1700 will output current and driver the IR LEDs. If the light Is gray, the Q2 and Q3 will enter active mode, the impedance of Cds will decide the collector current of Q3 and also Impact on the Internal impedance of Q2, so the driving current can be controlled. 2.VR1 is for light sensitive control, the value will decide how darkness of the light source the IR LEDs will brighten.
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Agamem Microelectronics Inc. PRELIMINARY
PACKAGE DIMENSIONS
AA1700
Constant Current White LED driver
AA1700AP - 8-pin Plastic TSSOP
C
L
E1
AA1700AP
E
theta
12(4X)
A1
A2
A
D
DIMENSIONS IN MILLIMETERS MIN NOM MAX ----1.20 0.05 --0.15 1.05 0.80 1.00 0.30 0.19 --0.20 --0.09 3.00 3.10 2.90 6.60 6.40 6.20 4.40 4.50 4.30 0.65 ----0.60 0.75 0.45 --0.10 ----8 0
e
b
SYMBOLS A A1 A2 b C D E E1 e L y theta
DIMENSIONS IN INCHES MIN NOM MAX ----0.048 0.002 --0.006 0.031 0.041 0.039 0.007 0.012 --0.008 0.004 --0.118 0.122 0.114 0.252 0.260 0.244 0.173 0.177 0.169 0.026 ----0.024 0.030 0.018 --0.004 ----8 0
NOTE 1. PACKAGE BODY SIZES EXCLUDE MOLD FLASH PROTRUSIONS OR GATE BURRS 2. TOLERANCE +/-0.1 mm UNLESS OTHERWISE SPECIFIED 3. COPLANARITY : 0.1 mm 4. CONTROLLING DIMENSION IS MILLIMETER. CONVERTED INCH DIMENSIONS ARE NOT NECESSARILY EXACT. 5. FOLLOWED FROM JEDEC MO-153
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Agamem Microelectronics Inc. PRELIMINARY
AA1700
Constant Current White LED driver
NOTES ON USE
* The information described herein is subject to change without notice. * The specifications for the product described in this document are for reference only. Upon actual use, therefore, please request that specifications to be separately delivered. *The application circuit examples explain typical applications of the products, and do not guarantee the success of any specific mass-production design. * Application circuit diagrams and circuit constants contained herein are shown as examples of standard use and operation. Please pay careful attention to the peripheral conditions when designing circuits and deciding upon circuit constants in the set. * Take account of common impedance when designing the earth line on a printed wiring board.
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