AIC1647 White LED Step-Up Converter in SOT23 FEATURES DESCRIPTION 1.2MHz Fixed Frequency Current-Mode PWM Operation. AIC1647 is a fixed frequency step-up DC/DC Efficiency Up to 84% at VIN=4.2V, 3LEDs, ILED=20mA Drives Up to 6LEDs in series constant current to provide backlight in hand- converter designed to drive white LEDs with a held devices. Series connection of the LEDs provides identical LED currents resulting in Low Supply Current: 70µA Matches LED Current Require Tiny Inductors and Capacitors Tiny SOT23-5 Package uniform brightness. This configuration eliminates the need for ballast resistors. Low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. AIC1647 is a step-up PWM converter, which APPLICATIONS includes an internal N-channel MOSFET switch for high efficiency. The high switching frequency, Cellular Phones PDAs Digital Still Cameras Handheld Devices White LED Display Backlighting 1.2MHz, allows the use of tiny external components, saves the layout space and cost. AIC1647 is available in a space-saving, 5-lead SOT-23-5 package. TYPICAL APPLICATION CIRCUIT C1 1µF L 90 D1 VIN=4.2V 6.8µH VIN SW BZV55-B12 11.8V~12.2V SHDN GND C2 1µF FB D2 20mA R1 AIC1647 85 Efficiency (%) 3.3~4.2V 80 VIN=3.6V VIN=3.0V 75 70 3 LEDs, 6.8µH L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ105KA, TAIYO YUDEN 1K RFB 4.7Ω L1: 976AS-6R8M, TOKO 65 D1: RB521S-30, ROHM 60 0 5 10 LED Current (mA) 15 20 Fig. 1 Li-Ion Powered Driver with Over Voltage Protection for Three White LEDs Analog Integrations Corporation Si-Soft Research Center DS-1647P-03 010405 3A1, No.1, Li-Hsin Rd. I, Science Park, Hsinchu 300, Taiwan, R.O.C. TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw 1 AIC1647 ORDERING INFORMATION AIC1647XXXX ORDER NUMBER PACKING TYPE TR: TAPE & REEL BG: BAG AIC1647CV&PV (SOT-23-5) PIN CONFIGURATION FRONT VIEW VIN SHDN 5 4 PACKAGE TYPE V: SOT-23-5 C: Commercial P: Lead Free Commercial Example: 1 2 3 SW GND FB AIC1647CVTR in SOT-23-5 Package & Tape & Reel Packing Type MARKING Part No. CV PV AIC1647 1647 1647P ABSOLUTE MAXIMUM RATINGS Input Voltage (VIN) 6V SW Voltage 33V FB Voltage 6V SHDN Voltage 6V –40°C to 85°C Operating Temperature Range 125°C Maximum Junction Temperature –65°C to 150°C Storage Temperature Range Lead Temperature (Soldering, 10 sec) 260°C Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. TEST CIRCUIT L1 VIN C1 1µF D1 10µH VIN C2 SW BZV55-B12 11.8V~12.2V SHDN GND 0.22µF D2 FB AIC1647 L1: 976AS-100M, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ224KG, TAIYO YUDEN ILED R1 1K RFB 4.7Ω 2 AIC1647 ELECTRICAL CHARACTERISTICS (V SHDN =3V, VIN=3V, TA=25°C, unless otherwise specified.) (Note 1) PARAMETER SYMBOL Minimum Operating Voltage VIN Maximum Operating Voltage VIN Supply Current IIN TEST CONDITIONS MIN TYP MAX 2.5 UNIT V 5.5 V mA Switching 1 5 Non switching 70 100 V SHDN = 0V 0.1 1.0 95 105 µA ERROR AMPLIFIER Feedback Voltage VFB FB Input Bias Current IFB 85 VFB=95mV 1 mV nA OSCILLATOR Switching Frequency fOSC 0.8 1.2 Maximum Duty Cycle DC 85 90 1.6 MHz % POWER SWITCH SW ON Resistance RDS(ON) 1.4 5 Ω Switch Leakage Current ISW(OFF) VSW=33V 0.1 1 µA CONTROL INPUT SHDN Voltage High VIH ON SHDN Voltage Low VIL OFF 1.5 V 0.3 V Note 1: Specifications are production tested at TA=25°C. Specifications over the -40°C to 85°C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC). 3 AIC1647 TYPICAL PERFORMANCE CHARACTERISTICS 1.6 Switching Frequency (MHz) Feedback Voltage (mV) 95.0 94.5 94.0 93.5 93.0 92.5 92.0 -50 0 50 100 1.4 1.2 1.0 0.8 0.6 0.4 -50 150 Temperature (°C) Fig. 2 Feedback Voltage vs. Temperature 0 50 100 Temperature (°C) Switching Frequency vs. Temperature Fig. 3 150 1.6 70 Supply Current (mA) Supply Current (µA) FB=GND 60 FB=VIN 50 40 Non-Switching 30 2 3 4 5 Supply Voltage (V) Fig. 4 Supply Current vs. Supply Voltage 1.0 0.8 6 Switching 2 3 Fig. 5 4 5 6 Supply Voltage (V) Supply Current vs. Supply Voltage 100 ILED_DUTY / ILEDMAX (%) 1.3 RDSON (Ω) 1.2 0.6 1.4 1.2 1.1 1.0 0.9 0.8 2.5 1.4 3.0 3.5 4.0 4.5 5.0 5.5 Supply Voltage (V) Fig. 6 RDS-ON vs. Supply Voltage 6.0 VIN=3.6V; L=10µH CIN=1µF, COUT=0.22µF 3LEDs 80 60 100Hz & 200Hz 40 500Hz 20 0 1KHz 2KHz 0 3KHz 20 40 60 80 100 SHDN PIN PWM Duty (%) Fig. 7 Dimming Control by Shutdown PIN 4 AIC1647 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 90 90 VIN=4.2V VIN=4.2V 85 85 Efficiency (%) Efficiency (%) VIN=3.0V 80 VIN=3.6V 75 3 LEDs, 10µH 70 80 VIN=3.6V 75 VIN=3.0V 4 LEDs, 10µH 70 L1: 976AS-100M, TOKO L1: 976AS-100M, TOKO D1: RB521S-30, ROHM 65 65 D1: RB521S-30, ROHM Test circuit refer to Fig.1 Test circuit refer to Fig.1 60 60 0 5 10 15 20 LED Current (mA) Fig. 8 3 LEDs Efficiency vs. LED Current 0 5 Fig. 9 10 VIN=4.2V VIN=4.2V 75 75 Efficiency (%) Efficiency (%) 80 VIN=3.6V VIN=3.0V 70 5 LEDs, 10µH L1: 976AS-100M, TOKO 65 VIN=3.6V 70 VIN=3.0V 6 LEDs, 10µH 65 L1: 976AS-100M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1 0 5 10 15 D1: RB521S-30, ROHM Test circuit refer to Fig.1 60 20 LED Current (mA) Fig. 10 5 LEDs Efficiency vs. LED Current 0 80 Efficiency (%) Efficiency (%) VIN=4.2V D1: RB521S-30, ROHM Test circuit refer to Fig.1 75 80 VIN=3.6V 3 LEDs, 6.8µH 70 15 L1: 976AS-6R8M, TOKO 85 VIN=3.0V 10 LED Current (mA) 6 LEDs Efficiency vs. LED Current 6 LEDs, 6.8µH VIN=4.2V 75 5 Fig. 11 90 L1: 976AS-6R8M, TOKO VIN=3.6V 70 VIN=3.0V 65 D1: RB521S-30, ROHM Test circuit refer to Fig.1 65 60 20 80 85 60 15 LED Current (mA) 4 LEDs Efficiency vs. LED Current 0 5 10 15 20 LED Current (mA) Fig. 12 3 LEDs Efficiency vs. LED Current 60 0 Fig. 13 5 10 15 LED Current (mA) 6 LEDs Efficiency vs. LED Current 5 AIC1647 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) VSHDN, 2V/div VSHDN, 2V/div VOUT, 2V/div IINDUCTOR, 100mA/div IINDUCTOR, 100mA/div VOUT, 20V/div VIN=3.6V; 3 LEDs; L1=10µF; COUT=0.22µF; ILED=20mA Fig. 14 VIN=3.6V; 6 LEDs; L1=10µF; COUT=0.22µF; ILED=10mA Start-Up from Shutdown Fig. 15 Start-Up from Shutdown 11.0 10.5 Output Voltage (V) VOUT, 100mV/div IINDUCTOR, 100mA/div 10.0 9.5 9.0 8.0 6 Samples' Temperature Data 7.5 VSW , 10V/div 7.0 -40 -20 0 20 40 60 80 Temperature (°C) Fig. 17 Output voltage vs. temperature VIN=3.6V; 3 LEDs; L1=10µF; COUT=0.22µF; ILED=10mA Fig. 16 3 LEDs ILED=20mA 8.5 Operation Wave Form 100 LED Current (mA) 25 20 15 VIN=4.2V 10 V =3.6V IN 5 VIN=3.3V VIN=2.5V 0 -80 -60 -40 4 LEDs -20 0 20 40 60 80 Temperature (°C) Fig. 18 LED Current vs. Temperature 100 6 AIC1647 BLOCK DIAGRAM VIN SHDN 95mV VREF PWM/PFM Control + FB SW Error AMP. Control Logic + - - RC Driver M1 PWM Comparator CC Slope Internal Soft Start 1.2MHz Compensation Oscillator Current AMP + RS - GND PIN DESCRIPTIONS PIN 1: SW - Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. PIN 2: GND - Ground Pin. Tie directly to local ground plane. PIN 3: FB - Feedback Pin. Reference voltage is 95mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB = 95mV/ILED PIN 4: SHDN - Shutdown pin. Tie to higher than 1.5V to enable device, 0.3V or less to disable device. PIN 5: VIN - Power input pin. Bypass VIN to GND with a capacitor sitting as close to VIN as possible. 7 AIC1647 APPLICATION INFORMATION Inductor Selection Open-Circuit Protection A 10µH inductor is recommended for most AIC1647 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail, the feedback voltage will be zero. AIC1647 will then switch to a high duty cycle resulting in a high output voltage, which may cause SW pin voltage to exceed its maximum 33V rating. A zener diode can be used at the output to limit the voltage on SW pin (Figure 1). The zener voltage should be larger than the maximum forward voltage of the LED string. The current rating of the zener should be larger than 0.1mA. Capacitor Selection The small size of ceramic capacitors makes them ideal for AIC1647 applications. X5R and X7R types are recommended because they retain their capacitance over wider ranges of voltage and temperature than other types, such as Y5V or Z5U. 1µF input capacitor with 1µF output capacitor are sufficient for most AIC1647 applications. Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AIC1647 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of AIC1647. An Schottky diode rated at 100mA to 200mA is sufficient for most AIC1647 applications. LED Current Control LED current is controlled by feedback resistor (RFB in Fig. 1). The feedback reference voltage is 95mV. The LED current is 95mV/ RFB. In order to have accurate LED current, precision resistors are preferred (1% recommended). The formula for RFB selection is shown below. RFB = 95mV/ILED Dimming Control There are three different ways of dimming control circuits as follows: 1. Using a PWM Signal PWM brightness control provides the widest dimming range by pulsing the LEDs on and off at full and zero current, respectively. The change of average LED current depends on the duty cycle of the PWM signal. Typically, a 0.1kHz to 1kHz PWM signal is used. Two applications of PWM dimming with AIC1647 are shown in Figure 19 and Figure 20. One, as Figure 19, uses PWM signal to drive SHDN pin directly for dimming control. The other, as Figure 20, employs PWM signal going through a resistor to drive FB pin. If the SHDN pin is used, the increase of duty cycle results in LED brightness enhancement. If the FB pin is used, on the contrary, the increase of duty cycle will decrease its brightness. In this application, LEDs are dimmed by FB pin and turned off completely by SHDN . 2. Using a DC Voltage For some applications, the preferred method of a dimming control uses a variable DC voltage to adjust LED current. The dimming control using a DC voltage is shown in Figure 21. Cautiously selecting R1 and R2 is essential so that the current from the variable DC source is much smaller than the LED current and much larger 8 AIC1647 than the FB pin bias current. With a VDC ranging from 0V to 5V, the selection of resistors in Figure 21 results in dimming control of LED current from 20mA to 0mA, respectively. D1 L1 VIN C1 1µF PWM 3. Using a Filtered PWM Signal Filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. The circuit is shown in Figure 22. RB512S-30 10µH VIN C2 SW BZV55-B12 11.8V~12.2V SHDN GND 1µF D2 FB 20mA R1 AIC1647 1K RFB 4.7Ω Fig. 19 Dimming Control Using a PWM Signal with Open-Circuit Protection D1 L1 VIN C1 1µF RB512S-30 10µH VIN C2 SW BZV55-B12 11.8V~12.2V SHDN GND 1µF D2 20mA FB AIC1647 PWM R2 R1 51K 1K RFB 4.7Ω Fig. 20 Dimming Control Using a PWM Signal 9 AIC1647 D1 L1 VIN C1 1µF RB512S-30 10µH VIN C2 SW 1µF D2 BZV55-B12 11.8V~12.2V SHDN GND 20mA FB AIC1647 0~5VDC R2 R1 51K 1K RFB 4.7Ω Fig. 21 Dimming Control Using a DC Voltage D1 L1 VIN C1 1µF RB512S-30 10µH VIN C2 SW 1µF D2 BZV55-B12 11.8V~12.2V SHDN 20mA FB GND AIC1647 R3 PWM 5.1K R2 R1 51K 1K C3 0.1µF RFB 4.7Ω Fig. 22 Dimming Control Using a Filter PWM Signal APPLICATION EXAMPLE D1 L VIN C1 1µF 10µH VIN SW C2 1µF RB521S-30 SHDN 20mA GND FB AIC1647 R2 1K RFB R1 4.7Ω 4.7Ω Fig. 23 Six white LEDs application in Li-Ion Battery 10 AIC1647 PHYSICAL DIMENSIONS (unit: mm) SOT-23-5 D A A E E1 S Y M B O L e e1 SEE VIEW B WITH PLATING MIN. MAX. A 0.95 1.45 A1 0.05 0.15 A2 0.90 1.30 b 0.30 0.50 c 0.08 0.22 3.00 D 2.80 E 2.60 3.00 E1 1.50 1.70 e 0.95 BSC e1 1.90 BSC c A A2 b SOT-25 MILLIMETERS SECTION A-A A1 BASE METAL L 0.60 REF 0° 8° 0.25 θ 0.60 0.30 L1 GAUGE PLANE SEATING PLANE θ L L1 VIEW B Note: Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 11