AIC1648 Built-in OVP White LED Step-Up Converter FEATURES DESCRIPTION Built-In Open Circuit Protection Over Voltage Protection AIC1648 is a fixed frequency step-up DC/DC converter designed to drive white LEDs with a Efficiency Up to 84% at VIN=4.2V, 3LEDs, ILED=20mA 1.2MHz Fixed Switching Frequency Drives Up to 5LEDs in series constant current to provide backlight in handheld devices. Series connection of LEDs provides identical LED currents resulting in uniform brightness. This configuration eliminates Low Supply Current: 70A Matches LED Current Requires Tiny Inductor and Capacitors Tiny SOT-23-6 Package the need of ballast resistors. The built-in open load protection prevents the damage resulting from an open circuit condition. Low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. APPLICATIONS AIC1648 is a step-up PWM converter, which Cellular Phones PDAs DSCs Handheld Devices White LED Display Backlighting includes an internal N-channel MOSFET switch for high efficiency. The high switching frequency, 1.2MHz, allows the use of tiny external components. AIC1648 is available in a space-saving, 6-lead SOT-23-6 package. TYPICAL APPLICATION CIRCUIT C1 1F 90 D1 L VIN=4.2V 6.8H VIN C2 1F SW SHDN OVP GND 20mA FB AIC1648 85 Efficiency (%) 3.3~4.2V 80 VIN=3.6V VIN=3.0V 75 70 3 LEDs, 6.8H L1: 976AS-6R8M/D321F, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ105KA, TAIYO YUDEN RFB 4.7 L1: 976AS-6R8M, TOKO 65 D1: RB521S-30, ROHM 60 0 5 10 LED Current (mA) 15 20 Fig. 1 Li-Ion Powered Driver for Three White LEDs Analog Integrations Corporation Si-Soft Research Center DS-1648P-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 AIC1648 ORDERING INFORMATION AIC1648XXXX ORDER NUMBER PACKING TYPE TR: TAPE & REEL BG: BAG AIC1648CG&PG (SOT-23-6) PIN CONFIGURATION FRONT VIEW VIN OVP SHDN 6 5 4 1 2 3 PACKAGE TYPE G: SOT-23-6 C: COMMERCIAL P: LEAD FREE COMMERCIAL Example: SW GND FB AIC1648CGTR in SOT-23-6 Package & Tape & Reel Packing Type MARKING Part No. CG PG AIC1648 1648 1648P ABSOLUTE MAXIMUM RATINGS Input Voltage (VIN) 6V SW Voltage 33V FB Voltage 6V SHDN Voltage 6V OVP Voltage 34V -40C to 85C Operating Temperature Range Maximum Junction Temperature 125C -65C to 150C Storage Temperature Range 260C Lead Temperature (Soldering, 10 sec) Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. TEST CIRCUIT D1 L1 VIN C1 1F 10H VIN SHDN GND C2 0.22F SW OVP ILED FB AIC1648 L1: 976AS-100M, TOKO D1: RB521S-30, ROHM C1: JMK107BJ105KA, TAIYO YUDEN C2: EMK212BJ224KG, TAIYO YUDEN RFB 4.7 2 AIC1648 ELECTRICAL CHARACTERISTICS (V SHDN =3V, VIN=3V, TA=25C, 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 A 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 Switch Leakage Current ISW(OFF) VSW=33V 0.1 1 A CONTROL INPUT SHDN Voltage High VIH ON SHDN Voltage Low VIL OFF 1.5 V 0.3 V OVER VOLTAGE PROTECTION OVP Input Resistance ROVP OVP Threshold VOVP 1V Hysteresis typical 0.6 1.2 1.8 M 22 27 32 V Note 1: Specifications are production tested at TA=25C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC). 3 AIC1648 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 (A) 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 4 5 Supply Voltage (V) Supply Current vs. Supply Voltage Fig. 5 6 100 ILED_DUTY / ILEDMAX (%) 1.3 RDSON () 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=10H CIN=1F, COUT=0.22F 3LEDs 80 60 100Hz & 200Hz 40 500Hz 20 1KHz 2KHz 0 0 Fig. 7 3KHz 20 40 60 80 SHDN PIN PWM Duty (%) 100 Dimming Control by Shutdown PIN 4 AIC1648 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, 10H 70 80 VIN=3.6V 75 VIN=3.0V 4 LEDs, 10H 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 85 10 20 90 VIN=4.2V VIN=4.2V 85 75 Efficiency (%) 80 Efficiency (%) 15 LED Current (mA) 4 LEDs Efficiency vs. LED Current VIN=3.6V VIN=3.0V 70 5 LEDs, 10H 80 VIN=3.0V 75 3 LEDs, 6.8H 70 L1: 976AS-100M, TOKO 65 L1: 976AS-6R8M, TOKO D1: RB521S-30, ROHM Test circuit refer to Fig.1 60 5 10 15 D1: RB521S-30, ROHM Test circuit refer to Fig.1 65 60 0 VIN=3.6V 20 LED Current (mA) Fig. 10 5 LEDs Efficiency vs. LED Current VSHDN, 2V/div 0 5 10 15 20 LED Current (mA) Fig. 11 3 LEDs Efficiency vs. LED Current VOUT, 100mV/div IINDUCTOR, 100mA/div VOUT, 2V/div IINDUCTOR, 100mA/div VSW , 10V/div VIN=3.6V; 3 LEDs; L1=10F; COUT=0.22F; ILED=20mA Fig. 12 Start-Up from Shutdown VIN=3.6V; 3 LEDs; L1=10F; COUT=0.22F; ILED=10mA Fig. 13 Operation Wave Form 5 AIC1648 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 25 11.0 10.0 9.5 9.0 3 LEDs ILED=20mA 8.5 8.0 15 VIN=4.2V 10 V =3.6V IN VIN=3.3V 5 6 Samples' Temperature Data 7.5 7.0 20 LED Current (mA) Output Voltage (V) 10.5 -40 -20 0 20 40 60 80 Temperature (C) Fig. 14 Output voltage vs. temperature VIN=2.5V 4 LEDs 0 -80 100 -60 -40 -20 0 20 40 60 80 Temperature (C) Fig. 15 LED Current vs. Temperature 100 BLOCK DIAGRAM Over Voltage Comparator 27V SHDN PWM/PFM Control + - OVP SW VIN Control Logic 95mV VREF M1 Driver + * - + FB PWM Comparator Error AMP - RC* Slope Compensation 1.2MHz Oscillator CC + * Internal Soft Start Current AMP. - RS* GND 6 AIC1648 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 to obtain LED current according to the formula: PIN 4: SHDN - Shutdown pin. Tie to higher than 1.5V to enable device, 0.3V or less to disable device. PIN 5: OVP - Overvoltage protection. When VOUT is greater than 27V, the internal MOSFET turns off. PIN 6: VIN - Power input pin. Bypass VIN to GND with a capacitor sitting as close to VIN as possible. RFB = 95mV/ILED APPLICATION INFORMATION Inductor Selection A 10H inductor is recommended for most AIC1648 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). Capacitor Selection The small size of ceramic capacitors makes them ideal for AIC1648 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. 1F input capacitor with 1F output capacitor are sufficient for most AIC1648 applications. Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AIC1648 applications. The forward voltage drop of an 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 AIC1648. An Schottky diode rated at 100mA to 200mA is sufficient for most AIC1648 applications. LED Current Control LED current is controlled by feedback resistor (RFB in Figure 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 Open-Circuit Protection 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. AIC1648 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. Connect builtin OVP (Over Voltage Protection) pin to output terminal to prevent the damage resulting from an open circuit condition. 7 AIC1648 cycle will decrease its brightness. In this application, LEDs are dimmed by FB pin and turned off completely by SHDN . Dimming Control There are three different ways of dimming control circuits as follows: 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 18. With a VDC ranging from 0V to 5V, the selection of resistors in Figure 18 results in dimming control of LED current from 20mA to 0mA, respectively. 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 AIC1648 are shown in Figure 16 and Figure 17. One, as Figure 16, uses PWM signal to drive SHDN pin directly for dimming control. The other, as Figure 17, 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 D1 L VIN C1 1F 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 19. 10H VIN SW C2 RB521S-30 1F SHDN OVP PWM GND FB AIC1648 RFB 4.7 Fig. 16 Dimming Control with a PWM Signal D1 L VIN C1 1F 10H VIN SW C2 1F RB521S-30 SHDN OVP GND FB AIC1648 PWM R2 R1 51K 1K RFB 4.7 Fig. 17 Dimming Control Using a PWM Signal 8 AIC1648 D1 L VIN C1 1F 10H VIN C2 1F RB521S-30 SW SHDN OVP GND FB AIC1648 VDC 0~5V R2 R1 51K 1K RFB 4.7 Fig. 18 Dimming Control Using a DC Voltage D1 L VIN C1 1F 10H C2 1F RB521S-30 VIN SW SHDN OVP GND FB AIC1648 R1 PWM R3 5.1K 1K R2 51K RFB 4.7 C3 0.1F Fig. 19 Dimming Control Using a Filter PWM Signal APPLICATION EXAMPLE D1 L 3.0~4.2V C1 1F 10H VIN SW C2 1F RB521S-30 SHDN OVP 20mA GND FB AIC1648 RFB 4.7 R1 4.7 Fig. 20 Six White LEDs Application in Li-Ion Battery 9 AIC1648 PHYSICAL DIMENSIONS (unit: mm) SOT-23-6 D S Y M B O L A A e e1 SEE VIEW B b WITH PLATING c A A2 MIN. MAX. 0.95 1.45 A1 0.05 0.15 A2 0.90 1.30 b 0.30 0.50 c 0.08 0.22 D 2.80 3.00 E 2.60 3.00 E1 1.50 1.70 E E1 A SOT-26 MILLIMETERS 0.95 BSC 1.90 BSC L 0.60 0.30 L1 0.60 REF 0 8 0.25 A1 BASE METAL SECTION A-A e e1 GAUGE PLANE SEATING PLANE 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. 10