AP1521 White LED Step-Up Converter Features General Description - Inherently Matched LED Current - Drives Up to Four LEDs from a 3.2V Supply - Drives Up to Six LEDs from a 5V Supply - High Efficiency: 84% Typical - Fast 1MHz Switching Frequency - 36V Rugged Bipolar Switch - Low Profile SOT23-5 Pb-Free Packaging The AP1521 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or four LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminates the need for ballast resistors. The AP1521 switches at 1MHz that allows the use of tiny external components. A low 300mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. Applications - Cellular Phones - PDAs, Hand-held Computers - Digital Cameras - MP3 Players - GPS Receivers Pin Descriptions Pin Assignments Top View VIN SHDN SW VSS FB Name Description SW Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. VSS GND pin FB Feedback Pin. Reference voltage is 310mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula： RFB = 310mV / ILED SHDN Shutdown Pin. Tie to 1.5V or higher to enable the device；0.4V or less to disable the device. VIN Input Supply Pin. Must be locally bypassed. SOT23-5L Ordering Information AP1521 X X Package Packing W: SOT23-5L Blank : Tube A : Taping This datasheet contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of this product. No rights under any patent accompany the sale of the product. Rev. 0.1 Apr. 27, 2004 1/8 AP1521 White LED Step-Up Converter Block Diagram 1 SW Comparator Driver A2 + - A1 R S Q1 Q RC + CC FB 3 310mV + VREF 1.25V Σ - VIN 5 RAMP Generator 2 GND Shutdown SHDN 4 1MHz Oscillator Absolute Maximum Ratings Symbol Parameter Rating Unit VIN VIN Pin Voltage 10 V VSW SW Voltage 36 V VFB Feedback Pin Voltage 10 V VSHDN TJ TLEAD TOPR SHDN Pin Voltage 10 Maximum Junction Temperature 125 o C 300 o C -40 to +85 o C Lead Temperature Operating Temperature Range V o TSTG Storage Temperature Range -40 to +125 C Caution The absolute maximum ratings are rated values exceeding which the product could suffer physical damage. These values must therefore not be exceeded under any condition. Anachip Corp. www.anachip.com.tw Rev. 0.1 2/8 Apr. 27, 2004 AP1521 White LED Step-Up Converter Electrical Characteristics (Ta=25°C, VIN = 3V, VSHDN = 3V, unless otherwise noted.) Symbol VIN VIN VFB IFB Parameter Minimum Operation Voltage Maximum Operation Voltage Feedback Pin Voltage Feedback Pin Bias Current Conditions - Supply Current VSHDN = 0V Min. 2.5 -280 10 -- Typ. --310 45 1.9 Max. -10 340 100 2.5 Unit V V mV nA mA -- 0.1 1.0 µA FSW Switching frequency 0.75 1.0 1.25 MHz Duty ISW VSAT PWM Maximum Duty Cycle Switch Current Limit Switch VSAT Switch Leakage Current SHDN Pin Voltage High SHDN Pin Voltage Low SHDN Pin Bias Current 85 ---1.5 --- 90 320 350 0.01 --65 ---5 -0.4 -- % mA mV µA V V µA VSHDN VSHDN ISHDN ISW = 250mA VSW = 5V Enable Disable Typical Application Circuit L1 22uH D1 C2 0.22uF C1 1uF LED1 15mA LED2 SW Vin LED3 Vss R1 20ohm FB SHDN ON OFF C1, C2: X5R or X7R Dielectric D1: Central Semiconductor CMDSH-3 L1: MURATA LQH3C-220 or Equivalent Figure 1. Anachip Corp. www.anachip.com.tw Rev. 0.1 3/8 Apr. 27, 2004 AP1521 White LED Step-Up Converter Applications Information Capacitor Selection The small size of ceramic capacitors makes them ideal for AP1521 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1µF input capacitor and a 0.22µF output capacitor are sufficient for most AP1521 applications. 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. The AP1521 will then switch at a high duty cycle resulting in a high output voltage, which may cause the SW pin voltage to exceed its maximum 36V rating. A zener diode can be used at the output to limit the voltage on the SW pin (Figure 2). 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. Inductor Selection A 22µH inductor is recommended for most AP1521 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1MHz and low DCR (copper wire resistance). L 22uH V IN D COUT 0.22uF C IN 1uF Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AP1521 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 1MHz switching frequency of the AP1521. A Schottky diode rated at 100mA to 200mA is sufficient for most AP1521 applications. VIN SW AP1521 SHDN FB R2 1k R1 15Ω GND Figure 2. LED Driver with Open-Circuit Protection Dimming Control There are four different types of dimming control circuits: 1. Using a PWM Signal to SHDN Pin With the PWM signal applied to the SHDN pin, the AP1521 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle will turn off the AP1521 and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal is 1kHz to 10kHz. The magnitude of the PWM signal should be higher than the minimum LED Current Control The LED current is controlled by the feedback resistor (R1 in Figure 1). The feedback reference is 310mV. The LED current is 310mV/R1. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for R1 selection are shown below. R1 = 310mV/ILED (See Table 1) SHDN voltage. Table 1. R1 Resistor Value Selection ILED (mA) R1 (Ω) 5 62 10 31 12 25.8 15 20.7 20 15.5 AP1521 SHDN PWM Anachip Corp. www.anachip.com.tw Rev. 0.1 4/8 Apr. 27, 2004 AP1521 White LED Step-Up Converter Applications Information (Continued) 2. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases. The selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current. For VDC range from 0V to 2V, the selection of resistors in Figure 3 gives dimming control of LED current from 0mA to 15mA. 4. Using a Logic Signal For applications that need to adjust the LED current in discrete steps, a logic signal can be used as shown in Figure 5. R1 sets the minimum LED current (when the NMOS is off). RSET sets how much the LED current increases when the NMOS is turned on. Start-up and Inrush Current To achieve minimum start-up delay, no internal soft-start circuit is included in AP1521. When first turned on without an external soft-start circuit, inrush current is about 200mA. If soft-start is desired, the recommended circuit and the waveforms are shown in Figure 6. If both soft-start and dimming are used, a 10kHz PWM signal on SHDN is not recommended. Use a lower frequency or implement dimming through the FB pin as shown in Figures 3, 4 or 5. 3. Using a Filtered PWM Signal The 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 4. VDC AP1521 AP1521 FB FB R3 90k R2 5k RSET Logic Signal R1 15Ω Figure 3. Dimming Control Using a DC Voltage Figure 5. Dimming Control Using a Logic Signal D1 2.2nF AP1521 FB PWM 10k R3 90k 0.1uF R1 AP1521 FB R2 5k D2 R2 1k 5k R1 15Ω COUT R1 15Ω D2:MMBT Figure 6. Recommended Soft-Startup Circuit Figure 4. Dimming Control Using a Filtered PWM Signal Anachip Corp. www.anachip.com.tw Rev. 0.1 5/8 Apr. 27, 2004 AP1521 White LED Step-Up Converter Typical Performance Characteristics Li-lon to Two White LEDs D CIN 1uF COUT 1uF VDC Dimming VIN Efficiency (%) VIN 3V To 5V L 22uH SW 90k 5k AP1521 SHDN FB R1 4Ω GND CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603ZD105 D: CENTRAL CMDSH2-3 L: MURATA LQH3C220 85 83 81 79 77 75 73 71 69 67 AP1521 Efficiency(%) v.s. LED Current (mA) Vin=4.2V Vin=3.6V Vin=5V 0 10 20 30 LED Current (mA) 40 50 Li-lon to Three White LEDs D CIN 1uF COUT 0.22uF VDC Dimming VIN Efficiency (%) VIN 3V To 5V L 22uH SW 90k 5k AP1521 SHDN FB R1 4Ω GND CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 D: CENTRAL CMDSH-3 L: MURATA LQH3C220 85 83 81 79 77 75 73 71 69 67 AP1521 Efficiency(%) v.s. LED Current (mA) Vin=4.2V Vin=5V Vin=3.6V 0 10 20 30 40 LED Current (mA) 50 60 Li-lon to Four White LEDs D CIN 1uF COUT 0.22uF VDC Dimming VIN SW AP1521 SHDN FB GND AP1521 Efficiency(%) v.s. LED Current (mA) Efficiency (%) VIN 3V To 5V L 22uH 90k 5k R1 4Ω CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 D: CENTRAL CMDSH-3 L: MURATA LQH3C220 85 83 81 79 77 75 73 71 69 67 Vin=5V Vin=4.2V Vin=3.6V 0 10 20 30 40 50 LED Current (mA) Anachip Corp. www.anachip.com.tw Rev. 0.1 6/8 Apr. 27, 2004 AP1521 White LED Step-Up Converter Typical Performance Characteristics (Continued) Li-lon to Five White LEDs D CIN 1uF COUT 0.22uF VDC Dimming VIN SW 90k 5k AP1521 SHDN FB R1 6.8Ω GND AP1521 Efficiency(%) v.s. LED Current (mA) Efficiency (%) VIN 3.3V To 5V L 22uH 84 81 78 75 72 69 66 63 60 57 CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 D: CENTRAL CMDSH-3 L: MURATA LQH3C220 Vin=5V Vin=3.6V 0 10 20 Vin=4.2V 30 LED Current (mA) 40 50 Li-lon to Six White LEDs D CIN 1uF COUT 0.22uF VDC Dimming VIN SW 90k 5k AP1521 SHDN FB R1 6.8Ω GND AP1521 Efficiency(%) v.s. LED Current (mA) Efficiency (%) VIN 3.6V To 5V L 22uH 84 81 78 75 72 69 66 63 60 57 CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 D: CENTRAL CMDSH-3 L: MURATA LQH3C220 Vin=5V Vin=4.2V Vin=3.6V 0 10 20 30 LED Current (mA) 40 50 Step up DC-DC Regulator VOUT 4.8V D CIN 1uF COUT 0.22uF 15K VIN SW AP1521 FB SHDN GND 1K 90 Efficiency (%) VIN 2.5V~3.3V L 22uH AP1521 Efficiency(%) v.s. Load Current (mA)@Vout=4.8V 85 Vin=3.3V Vin=2.5V 80 75 70 65 60 0 CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603YD224 D: CENTRAL CMDSH-3 L: MURATA LQH3C220 Anachip Corp. www.anachip.com.tw 10 20 30 Load Current (mA) Rev. 0.1 7/8 40 50 Apr. 27, 2004 AP1521 White LED Step-Up Converter Marking Information 4 7 5 XX Y M Identification code (See Appendix) 1 2 Appendix Part Number AP1521 Month: A~L Package SOT23-5 Identification Code FZ Year: 0-9 3 Package Information Package Type: SOT23-5L D e1 θ 1(4x) 5 4 E1 E A 0.10 C 5x A2 Seating Plane A1 1 2 θ 2(4x) 3 b e With Plating b1 C C1 Gauge Plane 0.25 mm θ Base Metal L b Symbol A A1 A2 b b1 c c1 D E E1 L L1 e e1 θ θ1 θ2 L1 Dimensions In Millimeters Min. Nom. Max. 1.05 1.20 1.35 0.05 0.10 0.15 1.00 1.10 1.20 0.25 0.55 0.25 0.40 0.45 0.08 0.20 0.08 0.11 0.15 2.70 2.85 3.00 2.60 2.80 3.00 1.50 1.60 1.70 0.35 0.45 0.55 0.60 Ref. 0.95 Bsc. 1.90 Bsc. o o o 5 10 0 o o o 3 5 7 8o 10o 6o Anachip Corp. www.anachip.com.tw Dimensions In Inches Min. Nom. Max. 0.041 0.047 0.053 0.002 0.004 0.006 0.039 0.043 0.047 0.010 0.022 0.010 0.016 0.018 0.003 0.008 0.003 0.004 0.006 0.106 0.112 0.118 0.102 0.110 0.118 0.059 0.063 0.067 0.014 0.018 0.022 0.024 Ref. 0.037 Bsc. 0.075 Bsc. o o o 0 5 10 o o o 3 5 7 6o 8o 10o Rev. 0.1 8/8 Apr. 27, 2004