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| SS8051 Micro-Power Step-up DC/DC Converter FEATURES Configurable output voltage up to 28V Quiescent current of 20A Shutdown current <1A Shutdown-pin current <1A Supply range from 2.5V to 6.5V Low VDS(on): 250mV (ISW =300mA) Tiny SOT23-5 package With a typical quiescent current of 20A and a supply voltage range of 2.5V to 6.5V, it is suitable for battery powered portable applications, such as PDAs and handheld computers. When the SS8051 goes into shutdown mode, it consumes less than 1A. DESCRIPTION The SS8051 boost converter is designed for small to medium size LCD panels requiring high bias voltages. APPLICATIONS STN/TFT LCD Bias Personal Digital Assistants (PDAs) Handheld Computers Digital Still Cameras Cellular Phones WebPad White LED Driver Local 3V to 5V Conversion Furthermore, with a 350mA current limit, 500ns fixed minimum off-time and tiny SOT23-5 package, the SS8051 can be used with smaller inductors and other surface-mount components to minimize the required PCB footprint in space-conscious applications. To control the SS8051, no other external current is needed for the shutdown pin, which typically consumes less than 1A over the full supply range. TYPICAL APPLICATION CIRCUIT 10uH 20V 12mA SW 1M 2.5V - 4.2V VCC SS8051 SHDN 4.7F GND FB 62k 1F Rev.2.01 6/06/2003 www.SiliconStandard.com 1 of 9 SS8051 ORDERING INFORMATION SS8051TXXXX Packing type TR: Tape and reel TB: Tube Pinout type T11 T12 Example: SS8051T12TR T12 pin configuration shipped in tape and reel packing SOT23-5 TOP VIEW SHDN 1 VCC 2 GND 3 4 SW PIN CONFIGURATION SW 1 GND 2 FB 3 4 SHDN VCC 5 SS8051T11 FB SS8051T12 5 PIN DESCRIPTION NAME SW GND FB SHDN FUNCTION Switch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor. Ground. Feedback Pin. Set the output voltage by selecting values for R1 and R2 (see Block Diagram): VOUT -1 R1 = R2 1. 2 Active-Low Shutdown Pin. Tie this pin to logic-high to enable the device or tie it to logic-low to turn the device off. Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. VCC ABSOLUTE MAXIMUM RATINGS SW to GND.................................................................................-0.3V to +30V FB to GND..................................................................................-0.3V to VCC VCC, SHDN to GND..................................................................................-0.3V to +7V Operating Temperature Range............................................................. -40C to 85C Maximum Operating Junction Temperature.................................................... +125C Storage Temperature Range .............................................................. -65C to 150C Maximum Lead Temperature (Soldering, 10sec)............................................ +300C Rev.2.01 6/06/2003 www.SiliconStandard.com 2 of 4 SS8051 ELECTRICAL CHARACTERISTICS (VCC = 3.6V, V SHDN = 3.6V, TA = 25C) PARAMETER Input Voltage Range Not switching Quiescent Current FB Comparator Trip Point Output Voltage Line Regulation FB Pin Bias Current (Note 2) Switch Off Time 2.5V Switch VDS(ON) Switch Current Limit SHDN SHDN SHDN Pin Current Input Voltage High Input Voltage Low Switch Leakage Current Note 1: The SS8051 is guaranteed to meet performance specifications from 0C to 85C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 2: Bias current flows into the FB pin. Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 4 SS8051 TYPICAL PERFORMANCE CHARACTERISTICS (V CC =+3.6V, V SHDN =+3.6V, L=10H, TA=25C, unless otherwise noted.) Output Voltage vs. Input Voltage 21 21 Output Voltage vs. Load Current Output Voltage (V) Output Voltage (V) 20.5 IOUT =1mA 20 IOUT=10mA 20.5 V IN=2.7V 20 V IN=4.2V 19.5 19.5 19 2.5 3 3.5 4 4.5 5 5.5 19 1 2 3 4 5 6 7 8 9 10 Input Voltage (V) Load Current (mA) Efficiency vs. Load Current 90 85 80 V IN=4.2V 50 Quiescent Current vs. Temperature Quiescent Current (A) 40 Efficiency (%) 75 70 V IN=3.6V 30 V IN=4.2V V IN=2.7V 65 60 55 50 0.1 1 10 100 20 V IN=2.7V 10 -20 0 20 40 60 80 100 Load Current (mA) Temperature (C) Vds(on) vs. Temperature 500 1.22 Feedback Voltage vs. Temperature Feedback Voltage (V) Switch Vds_on (mV) 400 VIN=2.7V 300 1.21 V IN=2.7V 1.2 200 V IN=4.2V 1.19 V IN=4.2V 100 -20 0 20 40 60 80 100 1.18 -20 0 20 40 60 80 100 Temperature (C) Temperature (C) Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 4 SS8051 TYPICAL PERFORMANCE CHARACTERISTICS (cont.) FB Bias Current vs. Temperature 30 Switch Current Limit vs. Temperature 450 Feedback Bias Current (nA) V IN =2.7V Peak Current (mA) 400 V IN =4.2V 25 350 V IN =2.7V 20 V IN =4.2V 300 15 -20 0 20 40 60 80 100 250 -20 0 20 40 60 80 100 Temperature (C ) Temperature (C ) Line Transient Load Transient Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 4 SS8051 BLOCK DIAGRAM L1 V IN C1 VCC SHDN SW C2 VOUT BIAS VOUT SHUTDOWN LOGIC PUMP CONTROL OC DRIVER COMP en_sw + T OFF P U L S E CONTROL R1 + ERROR COMP FB R2 1.2 V VREF GND APPLICATIONS INFORMATION The SS8051 is a boost converter with an integrated N-channel MOSFET (refer to the block diagram above). The boost cycle is initiated when the FB pin voltage drops below 1.2V and the MOSFET turns on. During the period that the MOSFET is on, the inductor current ramps up until the 350mA current limit is reached. Then the MOSFET turns off and the inductor current flows through the external schottky diode, ramping down to zero. During the MOSFET off period, the inductor current charges the output capacitor and the output voltage climbs. This pumping mechanism continues cycle by cycle until the FB pin voltage exceeds 1.2V and the non-switching mode starts. In this mode, the SS8051 consumes as little as 20uA typically, saving on battery power. The appropriate inductance value for the boost regulator application may be calculated from the following equation. Select a standard inductor close to this value. Inductor Selection - Boost Regulator PART LQH3C4R7 LQH3C100 LQH3C220 CD43-4R7 CD43-100 CDRH4D18-4R7 CDRH4D18-100 DO1608-472 DO1608-103 DO1608-223 TABLE 1. RECOMMENDED INDUCTORS VALUE?H) 4.7 10 22 4.7 10 4.7 10 4.7 10 22 MAX DCR ? ) W 0.26 0.30 0.92 0.11 0.18 0.16 0.20 0.09 0.16 0.37 Coilcraft www.coilcraft.com VENDOR Murata www.murata.com Sumida www.sumida.com Choosing an Inductor There are several recommended inductors that work well with the SS8051 in Table 1. Use the equations and recommendations in the next few sections to find the proper inductance value for your design. L= VOUT-VIN(MIN)+VD ILIM x tOFF Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 4 SS8051 Here, VD = 0.4V (Schottky diode voltage), ILIM = 350mA and tOFF = 500ns. A larger value can be used to slightly increase the available output current, but limit it to about twice the calculated value. When too large an inductor is used, the output voltage ripple will increase without providing much additional output current. In conditions of varying VIN, such as battery power applications, use the minimum VIN value in the above equation. A smaller value can be used to give smaller physical size, but overshoot of the inductor current will occur (see Current Limit Overshoot section). without any problem, but the total efficiency will suffer. For best performance, the IPEAK is best kept below 500mA. Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output to minimize the output ripple voltage and the peak-to-peak transient voltage. Multilayer ceramic capacitors (MLCC) are the best choice, as they have a very low ESR and are available in very small packages. Their small size makes them a good match with the SS8051's SOT-23 package. If solid tantalum capacitors (like the AVX TPS, Sprague 593D families) or OS-CON capacitors are used, they will occupy more volume than ceramic ones and the higher ESR increases the output ripple voltage. It is important to use a capacitor with a sufficient voltage rating. Inductor Selection - SEPIC Regulator For a SEPIC regulator using the SS8051, the approximate inductance value can be calculated using the formula below. As for the boost inductor selection, a larger or smaller value can be used. L=2 VOUT + VD ILIM x tOFF A low ESR surface-mount ceramic capacitor also makes a good selection for the input bypass capacitor, which should be placed as close as possible to the SS8051. A 4.7F input capacitor is sufficient for most applications. Diode Selection Current Limit Overshoot The SS8051 uses a constant off-time control scheme; the MOSFET is turned off after the 350mA current limit is reached. When the current limit is reached and the MOSFET actually turns off, there is a 100ns delay time. During this time, the inductor current exceeds the current limit by a small amount. The formula below can calculate the peak inductor current. For most SS8051 applications, the high switching frequency requires high-speed Schottky diodes, such as the Motorola MBR0530 (0.5A, 30V) with their low IPEAK = ILIM + VIN(MAX) - VSAT L x 100ns forward voltage drop and fast switching speed. Many different manufacturers make equivalent parts, but make sure that the component is rated for at least 0.35A. To achieve high efficiency, the average current rating of the Schottky diodes should be greater than the peak switching current. Choose a reverse breakdown voltage greater than the output voltage. Lowering Output Ripple Voltage Here, VSAT = 0.25V (switch saturation voltage). For systems with high input voltages and smaller inductance values, the current overshoot will be most apparent. This overshoot can be useful as it helps increase the amount of available output current. By using a small inductance value, the current limit overshoot can be quite high. Even though it is internally current limited to 350mA, the internal MOSFET of the SS8051 can handle larger currents The SS8051 supplies energy to the load in bursts by ramping up the inductor current, then delivering that current to the load. Using low ESR capacitors will help Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 4 SS8051 minimize the output ripple voltage, but proper selection of the inductor and the output capacitor also plays a big role. If a larger inductance value or a smaller capacitance value is used, the output ripple voltage will increase because the capacitor will be slightly overcharged each burst cycle. To reduce the output ripple, increase the output capacitance value, or add a 10pF feed-forward capacitor in the feedback network of the SS8051 (see the circuits in the Typical Applications section). To add this small inexpensive 10pF capacitor will greatly reduce the output voltage ripple. TYPICAL APPLICATION CIRCUITS Boost Converter L1 4.7uH V L1:MURATA LQH3C4R7M24 D1:MOTOROLA MBR0520 D1 5V 50mA 390k R1 C2 22F 120k R2 C1 4.7F V IN 2.5V to 4.2V SEPIC Converter L1 10uH C3 1uF 1 L1,L2:MURATA LQH3C100K24 D1:MOTOROLA MBR0520 D1 3.3V 60mA VCC SW L2 10H SHDN FB 270k R2 470k R1 C2 22F IN VCC 2.5V to 4.2V VCC SW SW SHDN SHDN C1 4.7F GND FB FB GND L1 10uh/0.5A VBAT 2.5V~5.5V C1 4.7F VCC SW D1 MBR0530 C2 1F D2(Optional) 27V SS8051 ON/OFF Control SHDN FB GND White LED Driver R3 308k 1% VBIAS(+3.3V) R2 120k_1% R4 660k 1% R1 30_1% PWM Dim PWM Dimming Control VH=3.3V VL=0V Freq=160~240Hz Dimming Ratio>50:1 Drive 2~8 White LEDs Rev.2.01 6/06/2003 www.SiliconStandard.com 3 of 4 SS8051 PACKAGE DIMENSIONS SOT-23-5 (unit: mm) DIMENSIONS IN MILLIMETERS D C L SYMBOLS MIN A 1.00 0.00 0.70 0.35 0.10 2.70 1.40 --------2.60 0.37 1 A1 A2 b 1 NOM 1.10 ----0.80 0.40 0.15 2.90 1.60 1.90(TYP) 0.95 2.80 -----5 MAX 1.30 0.10 0.90 0.50 0.25 3.10 1.80 --------3.00 ----9 E H e1 e C D E e A A2 A1 e1 H L ?1 b 1. Package body sizes exclude mold flash protrusions or gate burrs 2. Tolerance 0.1000 mm (4mil) unless otherwise specified 3. Coplanarity: 0.1000mm 4. Dimension L is measured in gage plane Feed direction SOT-23-5 package orientation Information 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 4 of 4 |
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