SS6896

SS6896 1.4MHz Current-Mode Step-Up DC/DC Converter Features l Description The SS6896 is a current-mode pulse-width modulation (PWM), step-up DC/DC converter. The built-in high-voltage N-channel MOSFET allows the SS6896 to support applications with up to 30V output voltage, as well as Single-Ended Primary Inductance Converters (SEPIC) and other low-side switching DC/DC converters. The h igh switching frequency (1.4MHz) permits the use of small external components. The soft -start function is programmable with an external capacitor, which sets the input current ramp rate. The SS6896 is available in a space-saving SOT-23-6 package. Fixed-frequency 1.4MHz Current-Mode PWM operation. Adjustable output voltage up to 30V. Guaranteed 13V/ 200mA output with 5V Input. Input Range 2.5V to 10V. Maximum 0.1µA shutdown current. Programmable soft-start. W orks with tiny inductors and capacitors Space-s aving SOT-23-6 package. l l l l l l l Applications l l White LED Backlight. OLED Driver. Typical Application Circuits V IN 3.3V or 4.2V C1 4 .7µF SS6896 6 L D1 CH521S -30 86 84 C3 82 E fficiency (%) ZD1 BZV55 -B12 11.8V~12.2V 1µF 80 78 76 74 72 70 68 2 4 6 8 10 12 14 16 18 20 VIN=4.2V VIN=3.3V IN LX 1 3 OFF ON 4 SHDN FB SS GND 5 2 R2 1K Ω R1 I LED L: GTSK-51-150M (15 µH) L: GTSK-51-100M (10 µH) C2 0.033µ F LED Current (mA) Fig. 1 Li-Ion Powered Driver for three white LEDs VIN 3.6V or 4.2V C1 4.7 µF SS6896 6 O FF O N 4 L D1 CH521S-30 80 C3 1µF 78 76 Z D1 BZV55 -B24 23.5V~24.5V E fficiency (%) 74 72 70 68 66 64 62 60 2 4 6 8 IN LX 1 3 VIN=4.2V VIN=3.6V SHDN FB SS GND 5 2 R2 1KΩ R1 ILED C2 0.033µF L: GTSK-51-150M (15 µH) L: GTSK-51-100M (10 µH) 10 12 14 16 18 20 LED Current (mA) Fig. 2 Li-Ion Powered Driver for six white LEDs Rev.2.01 6/06/2003 www.SiliconStandard.com 1 of 12 SS6896 Ordering Information SS6896CX XX PACKING TYPE TR: TAPE & REEL BG: BAG PACKAGE TYPE G: SOT -23-6 Pin Configuration SOT- 23 -6 (CG) FRONT VIEW 1: LX 2: GND 3: FB 4: SHDN 5: SS 6: IN 6 5 4 1 2 3 Example: SS6896CGTR à i n SOT-23- 6 p ackage in tape and reel. l SOT -23-6 Marking Part No. S S6896CG Marking 1896 Absolute Maximum Ratings LX to GND FB to GND IN, SHDN SS to GND LX Pin RMS Current Continuous Power Dissipation (TA = +70°C) (Note 1) 6-Pin SOT23 (derate 9.1mW/°C above +70°C) Operating Temperature Range Junction Temperature Storage Temperature Range Lead Temperature (soldering, 10s) 727mW -40°C to +85°C +150°C -65°C to +150°C +300°C -0.3V to +33V -0.3V to +6V -0.3V to +11V -0.3V to +6V 0.6A Note 1: Thermal properties are specified with product mounted on PC board with one square-inch of copper area and still air. Test Circuit VIN 2.5V to 10V + C1 10µF/16V L1 D1 VOUT SS14 + R1 C4 10µF C5 1µF SS6896 C3 LX FB 1 3 6 4 IN SHDN SS 5 SHDN GND 2 R2 C2 0.033µF Rev.2.01 6/06/2003 www.SiliconStandard.com 2 of 12 SS6896 Electrical Characteristics PARAMETER Input Supply Range Output Voltage Adjust Range VIN Undervoltage Lockout Quiescent Current Shutdown Supply Current ERROR AMPLIFIER Feedback Regulation Set Point FB Input Bias Current Line Regulation OSCILLATOR Frequency Maximum Duty Cycle POWER SWITCH Steady State Output Current On- Resistance Leakage Current SOFT-START Reset Switch Resistance Charge Current CONTROL INPUT Input Low Voltage Input High Voltage VIL VIH I SHDN V SHDN , VIN = 2. 5V to 10V V SHDN , VIN = 2. 5V to 10V V SHDN = 3V V SHDN = 0 1.0 25 0.01 50 0.1 0.3 V V µA VSS = 1.2V 1.5 4 100 7.0 Ω µA Io RDS(ON) ILX(OFF) VLX = 12V, TA = +25°C VLX = 12V Refer to Fig. 18 1 0.1 1.4 1 10 A Ω µA fOSC DC 1000 82 1400 86 1800 KHz % VFB IFB VFB = 1.24V 2.6V < VIN < 5.5V 1.205 1.23 21 0.05 1.255 80 0.20 V nA %/V (V IN=V SHDN =3V, FB=GND, SS=Open, T A= -40° C to 85° C, unless otherwise specified) CONDITIONS MIN 2.5 2.2 0.1 1 0.01 0.01 0. 2 5 0.5 10 TYP MAX 10 30 VFB = 1.3V, not switching VFB = 1.0V, switching V SHDN = 0, TA = +25°C V SHDN = 0 UNITS V V V mA µA µA SYMBOL VIN VOUT UVLO VIN rising, 50mV hysteresis IIN SHDN Input Current Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 12 SS6896 Typical Performance Characteristics 1.50 1.50 S witching Frequency (MHz) 1.45 TA=25° C Frequency (MHz) VI N=3.6V 1.45 1.40 1.35 1.40 1.30 1.35 1.25 1.20 -40 -20 0 20 40 60 80 100 1.30 2 3 4 5 6 7 8 9 10 11 Temperature (° C) Fig. 3 Switching Frequency vs. Temperature 1.7 1.6 Supply Voltage (V) Fig. 4 Frequency vs. Supply Voltage 5.50 VI N=3.6V Output Voltage (V) 2 3 4 5 6 7 8 9 10 11 1.5 5.25 RDS(ON) (Ω) 1.4 1.3 1.2 1.1 1.0 0.9 0.8 5.00 4.75 4.50 1 10 100 Supply Voltage (V) F ig. 5 R DSON vs. Supply Voltage 12.5 2.4 Output Current (mA) Fig. 6 Load Regulation (L1=10uH) VIN =3.6V Output Voltage (V) Supply Current (mA) 12.0 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 FB=1.0V SHDN=1.0V 11.5 11.0 10.5 1 10 1 00 2 3 4 5 6 7 8 9 10 11 Output Current (mA) Fig. 7 Load Regulation (L1=22uH) Supply Voltage (V) Fig. 8 Switching Current Rev.2.01 6/06/2003 www.SiliconStandard.com 4 of 12 SS6896 Typical Performance Characteristics (Continued) 90 90 85 V IN=4.2V VIN =2.7V VIN=3.6V VIN =3.3V Supply Current (£ g ) A 85 Efficiency (%) 80 FB=1.3V SHDN=1.0V 80 75 70 65 60 V IN =2.5V 75 70 VOUT=5.0V 65 2 3 4 5 6 7 8 9 10 11 0 100 200 300 400 500 600 Supply Voltage (V) Fig. 9 Non-Switching Current Output Current (mA) Fig. 10 Efficiency vs. Output Current (L1=10µH) 90 V OUT=12V 85 VLX Efficiency (%) 80 75 70 VIN=4.2V VIN =3.6V V IN=3.3V ILX VIN=5.0V VOUT 65 60 0 50 100 150 200 Output Current (mA) Fig. 11 Efficiency vs. output current (L1=22µH) Fig. 12 Operation Wave Form (VIN=3V;VOUT=5V;L1=10µH;R1=36K;R2=12K; C3=39pF;IOUT=200mA) Rev.2.01 6/06/2003 www.SiliconStandard.com 5 of 12 SS6896 Typical Performance Characteristics (Continued) SHDN VSW VOUT VOUT ILX ILX Fig. 13 Operation Wave Form (VIN =5V; V OUT =12V, L1=22 µH; R1=105K; R2=12K;C3=1nF;IOUT =200mA) Fig. 14 Start-Up from Shutdown (V IN =3.3V ;V OUT =13V ;RLOAD=300Ω ) V OUT VOUT ILX ILX Fig. 15 Load Step Response (V IN =3.3V; V OUT =5V;L1=10uH; I OUT=5mA to 200mA) Fig. 16 Load Step Response (V IN =5V ; V OUT=12V ;L1=22uH; IOUT=5mA to 150mA) Rev.2.01 6/06/2003 www.SiliconStandard.com 6 of 12 SS6896 Typical Performance Characteristics 1.25 (Continued) 800 Maximum Output Current (mA) V OUT=13V 700 600 500 VOUT=5V 400 300 200 100 Feedback Voltage (V) 1.24 VOUT=9V VOUT=15V 1.23 1.22 1.21 V IN=3.6V 1.20 -50 - 25 0 25 50 75 100 Temperature (° C) 2 3 4 5 6 7 8 9 10 Supply Voltage (V) Fig. 17 Feedback Pin Voltage Fig. 18 Maximum Output current vs. Supply Voltage (L1:10µH Vo=5V,9V ; L1=22 µH Vo=13V,15V) Block Diagram VIN P WM/PFM C o ntrol S oft - Start R4 R3 E rror Amp + FB Q1 1 Q2 8 R1 RC CC 1 .4MHz O s cillator x1 + x20 LX + - I9 SS 4 µA PWM Comparator C o ntrol L ogic D r iver S HDN R2 S l ope Compensation C u rrent A m p x 5 RS GND Rev.2.01 6/06/2003 www.SiliconStandard.com 7 of 12 SS6896 Pin Descriptions PIN 1: LX Power Connect rectifier. between to LX as Ground. Feedback Input. Connect a resistive voltage -divider from the output to FB to set the output voltage. Switching Connection. LX to inductor and output Keep the distance the components as close possible. SHDN with a slew rate of 0.1V/µs or greater. Do not leave SHDN unconnected. SHDN draws up to 50µA. PIN 5: SS Soft -Start Input. Connect a soft -start capacitor from SS to GND in order to soft -start the converter. Leave SS open to disable the soft -start function. Internal Bias Voltage Input. Connect IN to the input voltage source. Bypass IN to GND with a capacitor sitting as close to IN as possible. PIN 2: GND PIN 3: FB - PIN 6: IN - PIN 4: SHDN - Shutdown Input. Drive SHDN low to turn off the converter. To automatically start the converter, connect SHDN to IN. Drive Rev.2.01 6/06/2003 www.SiliconStandard.com 8 of 12 SS6896 Application Information Inductor Selection A 15µ H inductor is recommended for most SS6896 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.4MHz and low DCR (copper wire resistance). R1 = 1.23V/ILED (1) 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 SS6896 will then switch to a high duty cycle resulting in a high output voltage, which may cause the SW pin voltage to exceed its maximum 30V rating. A zener diode can be used at the output to limit the voltage on the SW pin (Fig. 20). 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 SS6896 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. A 4.7µF input capacitor and a 1 µF output capacitor are sufficient for most SS6896 applications. Dimming Control Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for SS6896 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 1.4MHz switching frequency of the SS6896. A Schottky diode rated at 100mA to 200mA is sufficient for most SS6896 applications. There are three different types 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 using the control signal. The LEDs operate at either zero or full current, The average LED current changes with the duty cycle of the PWM signal. Typically, a 1kHz to 10kHz PWM signal is used. PWM dimming with the SS6896 can be accomplished two different ways (see Fig. 21). The SHDN pin can be driven directly or a resistor can be added to drive the FB pin. If the SHDN pin is used, increasing the duty cycle will increase the LED brightness. If the FB pin is used, increasing the duty cycle will decrease the brightness. Using this method, the LEDs are dimmed using FB and turned off completely using SHDN . LED Current Control LED current is controlled by a feedback resistor (R1 in Fig. 1). The feedback reference is 1.23V. The LED current is 1.23V/R1. In order to have accurate LED current, precision resistors are preferred (1% recommended). The formula for R1 selection is shown below. Rev.2.01 6/06/2003 2. Using a DC Voltage For some applications, the preferred method of brightness control uses a variable DC voltage to adjust the LED current. The dimming control using a www.SiliconStandard.com 9 of 12 SS6896 DC voltage is shown in Fig. 22. 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 should 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 5V, the selection of resistors in Fig. 22 gives dimming control of LED current from 20mA to 0mA. VIN 3V to 4.2V C1 4.7µF SS6896 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 Fig. 23. L1 10µH D1 CH521S-30 ZD1 BZV55-B20 19.6V~20.4V C3 1µF 6 4 IN SHDN SS 5 LX FB GND 2 1 3 OFF ON R2 1K£ [ IOUT=ILED=20mA R1 62£ [ C2 0.033µF Fig. 20 White LED driver with open -circuit protection SS6896 IN PWM SHDN SS FB GND LX Z D1 SS6896 IN LX ZD1 R2 R2 O FF SHDN ON R1 62 £ [ FB 1 KΩ GND R3 3.3KΩ R1 8 2Ω 1K £ [ SS C2 0.033µF C2 0.033µ F P WM (a) Fig. 21 Dimming-control using a PWM signal (b) Rev.2.01 6/06/2003 www.SiliconStandard.com 10 of 12 SS6896 SS6896 SS6896 IN SHDN OFF ON SS GND R3 C2 0.033µ F 3.3K£ [ LX R2 FB 1K £ [ R1 82 £ [ 20mA~0mA Z D1 ZD1 IN SHDN OFF ON SS LX R2 FB 1K £ [ GND R3 3.3K£ [ R4 4K £ [ C1 R1 8 2£ [ C2 0.033µ F VDC 0V~5V 0.1 µF P WM Fig. 22 Dimming-control us ing a DC voltage Fig. 23 Dimming-control using a filtered PWM signal Application Example VIN 3V t o 4.2V C1 4.7µF L1 10µH CH521S-30 D1 C3 1µF ZD1 SS6896 BZV55-B24 23.5V~24.5V 6 4 IN SHDN SS 5 LX FB GND 2 1 3 OFF ON R2 1K£ [ IOUT=ILED=20mA C2 0.033µF R1 R3 62£ [ 62£ [ Fig. 24 Li- Ion powered driver for eight white LEDs with open -circuit protection Rev.2.01 6/06/2003 www.SiliconStandard.com 11 of 12 SS6896 Physical Dimensions l SOT-23-6 (unit: mm) D C L HE SYMBOL A A1 A2 b C MIN 1.00 — 0.70 0.35 0.10 2.70 1.60 MAX 1.30 0.10 0.90 0.50 0.25 3.10 2.00 e θ1 D E e A2 A 1.90 (TYP) 2.60 0.37 1° 3.00 — 9° A1 b H L θ1 In formation furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties. Rev.2.01 6/06/2003 www.SiliconStandard.com 12 of 12