Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver ■OVERVIEW 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 µA 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 1 SP 2 7 CLK VCC 3 6 GND CTL 4 5 P0 8 ER ■APPLICATIONS • LCD Bias Supplies • White LED Backlighting • Handheld Devices • Digital Cameras • Portable Applications ©Copyright Agamem Microelectronics Inc. 1 www.agamem.com.tw 2007/1/22 Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver ■PIN DESCRIPTIONS Pin No. Symbol I/O Description 1 IN I 2 SP — Soft start and short circuit protection setting 3 VCC — Power supply pin 4 CTL I ON/OFF control pin 5 P0 O Output driver pin 6 GND — Ground pin 7 CLK — Internal PWM frequency setting pin 8 ER O Error amplifier output pin Output voltage feedback pin ■BLOCK DIAGRAM Vcc CLK 3 7 Regulator Oscillator 0.5V 0.1V IN 1 ER 8 Error Amp. + 5 + PWM COMP. + + P0 Output driver 0.6V Soft start short circuit protection 6 2 4 GND SP CTL ©Copyright Agamem Microelectronics Inc. 2 www.agamem.com.tw 2007/1/22 Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver ■ABSOLUTE MAXIMUM RATINGS (Ta = +25°C) Parameter Symbol Rating Condition Unit Min Max — 16 V — –50 mA — 50 mA Power supply voltage VCC Output source current IO+ Output sink current IO – Allowable dissipation PD Ta ≤ +25° C — 430* mW Operating temperature Top — –30 +85 。 C +125 。 C Storage temperature — Tstg –55 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 Value Symbol Unit Min Typ Max VCC 1.8 — 15 V VI –0.2 — 1.0 V CTL pin input voltage VCTL –0.2 — VCC V Output source current IO+ –40 — — mA Output sink current IO – — — 40 mA SP pin capacitance CPE — 0.1 — µ F Phase compensation capacitance CP — 0.1 — µ F Output current setting resistance RB 150 390 5000 Ω Timing resistance RT 1.0 3.0 10.0 kΩ Timing capacitance CT 100 270 10000 pF Oscillation frequency fCLK 10 500 1000 kHz Operating temperature TOP –30 +25 +85 Power supply voltage Error amplifier input voltage ©Copyright Agamem Microelectronics Inc. 3 www.agamem.com.tw 。 C 2007/1/22 AA1700 Agamem Microelectronics Inc. PRELIMINARY Constant Current White LED driver ■ELECTRICAL CHARACTERISTICS 。 (VCC = +2 V, Ta = +25 C) Parameter Circuit to prevent malfunction at low input voltage (U.V.L.O.) Symbol Reset voltage VR Threshold voltage VTH Value Condition — Typ Max — — 0.9 V 1.1 1.3 1.5 V –1.5 –1.0 –0.7 µ A 0.7 0.8 0.9 V –1.5 –1.0 –0.7 µ A Charging current ICS Soft start Voltage at soft start completion VtS Short circuit detection (S.C.P.) Charging current ICPC Threshold voltage Oscillation frequency Frequency input stability VtPC — 0.7 0.8 0.9 V fCLK RT = 3.0 kΩ , CT = 270 pF 400 500 600 kHz fdV VCC = 2 V to 15 V — 2 10 % Frequency variation with temperature fdT Ta = –30°C to +85°C — 5 — % Input threshold voltage VT VER = 450 mV 480 500 520 mV VT input stability VTdV VCC = 2 V to 15 V — 5 20 mV VT variation with temperature VTdT Ta = –30°C to +85°C — 1 — % Input bias current IB –1.0 –0.2 1.0 µ A Voltage gain Frequency bandwidth AV 70 100 145 V/V — 6 — MHz 0.78 0.87 — V — 0.05 0.2 V — –40 –24 µ A 24 40 — µ A 65 75 85 % Sawtooth wave oscillator (CLK) Error amplifier Idle period adjustment section Maximum output voltage range BW — VSP = 0 V VIN = 0 V — AV = 0 dB VOM+ — VOM – Output source current Output sink current IOM – Maximum duty cycle tDUTY ©Copyright Agamem Microelectronics Inc. VSP = 0 V Unit Min IOM+ VER = 0.45 V RT = 3.0 kΩ , CT = 270 pF VER = 0.8 V 4 www.agamem.com.tw 2007/1/22 AA1700 Agamem Microelectronics Inc. PRELIMINARY Constant Current White LED driver (Continued) Parameter Symbol Output voltage Output section Output current setting section/ Control section Entire device Value Condition Unit Min Typ Max VOH1 RB = 390 Ω , IO = –15 mA 1.0 1.2 — V VOH2 RB = 750 Ω , VCC = 1.8 V IO = –10 mA 0.8 1.0 — V VOL1 RB = 390 Ω , IO = 15 mA — 0.1 0.2 V VOL2 RB = 750 Ω , VCC = 1.8 V IO = 10 mA — 0.1 0.2 V Output source current Output sink current IO+ RB = 390 Ω , VO = 0.9 V — –30 –20 mA IO – RB = 390 Ω , VO = 0.3 V 30 60 — mA Pull down resistance RO 20 30 40 kΩ 0.2 0.3 0.4 V –20 — 0 µ A — — –45 µ A –1.8 — –0.1 mA — Pin voltage VCTL RB = 390 Ω Input off condition IOFF Input on condition ION Pin current range ICTL Stand-by current ICCS CTL pin open or VCC — — 1 µ A Average supply current ICC RB = 390 Ω — 5.5 9.3 mA — ■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 × 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 × CPE [uF] ©Copyright Agamem Microelectronics Inc. 5 www.agamem.com.tw 2007/1/22 Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver ■FUNCTIONAL DESCRIPTION 1. Switching Regulator Function (1) Sawtooth wave oscillator 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 = -1 VCLKL CT × RT × ln VCLKH 1 CT × RT = 0.48× [HZ] (2) Error amplifier 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 µA or less) can be set by connecting the CTL pin (pin 4) to VCC or by making the pin open circuit. SW Mode OFF Stand-by mode ON Operating mode ©Copyright Agamem Microelectronics Inc. 6 www.agamem.com.tw 2007/1/22 Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver ■ TYPICAL APPLICATION EXAMPLE 22uH Vout D1 1N5821 QA 1 SP 2 Vcc Vin 33uF 3 CTL 8 4 7 6 5 ER other LED series IN AA1700 L1 56uH QB CLK 12KΩ GND P0 Q1 FZT489 0.1uF 10uF 0.1uF 390O (*adjustable) Q2 270pF 3KΩ CTL-IN C1815 RLED RLED 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 = 25Ω) 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. ©Copyright Agamem Microelectronics Inc. 7 www.agamem.com.tw 2007/1/22 Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver CDS Control for IR LED Vcc SP Vcc CTL 1 2 3 4 8 AA1700 IN 7 6 5 ER CLK GND VR1 50K P0 D3 R2 R7 300Ω 390Ω Q2 C1815 CdS Light Sensitive Resistor Q3 C1815 C8 10uF R8 4.7KΩ 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. ©Copyright Agamem Microelectronics Inc. 8 www.agamem.com.tw 2007/1/22 Agamem Microelectronics Inc. PRELIMINARY AA1700 Constant Current White LED driver ■PACKAGE DIMENSIONS AA1700AP - 8-pin Plastic TSSOP E1 E L C AA1700AP theta D SYMBOLS A A1 A2 b C D E E1 e L y theta 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° A2 A1 A 12°(4X) e b 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 ©Copyright Agamem Microelectronics Inc. 9 www.agamem.com.tw 2007/1/22 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. ©Copyright Agamem Microelectronics Inc. 10 www.agamem.com.tw 2007/1/22