SC46208 1.25MHz, 600mA, HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN DC-DC CONVERTER DESCRIPTION SC46208 is a synchronous step-down DC-DC converter with high efficiency. It adopts small flat package. The device features 2.5~5.5V input voltage, 600mA output current, peak current mode PWM and integrated compensation net, which is ideal for powering portable equipment that runs from a single cell Li+ battery without external components. The device integrates an internal switch which eliminates the Schottky diode, 1.25MHz high frequency allows the periphery to adopt SMT inductor and capacitor, thus reduce the size of total solution. It can also run at 100% duty cycle for low dropout operation, that is lower than 1μA shutdown current and 20μA quiescent current in power saving mode. It extends battery life in portable system through increasing the efficiency under light loads. SC46208 is available in an adjustable version and fixed version. FEATURES * High efficiency up to 95% * Automatic Power Saving Mode at light loads, only 20μA quiescent current. * Wide input voltage range: +2. 5V~+5.5V * Output voltage range: 0.6V~VIN APPLICATION * Cellular Telephones * PDAs * Wireless Equipment * MP3 player * Digital Camera * Portable Instruments * High output current 600mA * Low dropout operation: 100% * Shutdown current<1μA * 1.25MHz fixed frequency * No Schottky diode required * Thermal shutdown protection * 4KV HBM ESD protection * Small 5-pin SOT-23package HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 1 of 11 SC46208 ORDERING INFORMATION Device no SC46208XX Seal name Package Remark SC46208 6208 SOT-23-5 SC4620810 20810 SOT-23-5 SC4620812 20812 SOT-23-5 SC4620815 20815 SOT-23-5 12 :1.2V SC4620818 20818 SOT-23-5 15 :1.5V SC4620825 20825 SOT-23-5 SC4620833 20833 SOT-23-5 Note: “××” indicates the output voltage: Default: adjustable 10 :1.0V 18 :1.8V 25 :2.5V 33 :3.3V BLOCK DIAGRAM HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 2 of 11 SC46208 ABSOLUTE MAXIMUM RATING Characteristics Symbol Rating Unit Input Supply Voltage VIN VIN -0.3 ~ +6 V Enable Voltage EN VEN -0.3 ~ VIN V SW Voltage VSW -0.3 ~ VIN+0.3 V Output Feedback Voltage VFB -0.3 ~ +6 V Operating Temperature Tamb -40 ~ + 85 °C Storage Temperature TSTG -65 ~ +125 °C ESD Characteristic(HBM) ESD 4.0 KV ELECTRICAL CHARACTERISTICS(unless otherwise noted, Tamb =25°C, VIN=3.6V, L=2.2μH, COUT=10μF, load current ILOAD=0) Characteristics Symbol Input Voltage Range VIN Feedback Voltage VFB Quiescent Current (Switch Off) Quiescent Current (Shutdown Mode) Quiescent Current (PWM Mode) Test conditions Min. Iq Max. Unit. 5.5 V 0.6 0.615 V 20 30 μA 0.1 1 μA 200 300 μA 2.5 Only for adjustable version 0.585 Iswitch off FB=0.62V,or VOUT=103% ISHDN Typ. EN=0V FB=0.5V , Or VOUT=90% Output Voltage Regulation △VOUT 0.5 % Output Voltage Load Regulation △VLOAD 0mA≤ IL ≤600mA 0.1 mV/mA Feedback Current IFB PMOS On Resistor RPMOS ISW=100mA NMOS On Resistor RNMOS ISW=-100mA PMOS Limit Current ILIMIT Switch Frequency FS Only for adjustable version 2.5V≤VIN ≤5.5V FB=0.6V,or VOUT=100％ DMAX FB=0.5V Switch Leakage Current SW ILSW EN=0V,SW=0V or 5V,VIN =5V EN Input High Level VH -- EN Input Low Level VL -- EN Leakage Current ILEN Thermal Shutdown Temperature Tj(sd) Thyst Temperature nA 0.45 0.5 Ω 0.35 0.4 Ω 1.25 1.5 1.75 A 1. 1.25 1.5 MHz 600 KHz 100 % ±0.01 ±1 1.5 μA V 0.3 V -- ±0.01 ±1 μA -- -- 150 -- °C -- -- 20 -- °C HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn 50 FB=0 V,or VOUT=0 Max. Duty Thermal Shutdown Hysteresis -50 REV:1.1 2008.09.10 Page 3 of 11 SC46208 PIN CONFIGURATION FB/VOUT VIN 5 4 SC46208 1 2 3 EN GND SW PIN DESCRIPTION Pin no. Pin name I/O Descriptions 1 EN I Enable input port, this pin should not float. 2 GND -- Ground. 3 SW I/O 4 VIN -- 5 FB/VOUT I Power switch which connect to inductor and output voltage. Supply input pin. Output voltage feedback pin. In the adjustable version, this pin used for connecting external resistive divider. FUNCTION DESCRIPTIONS SC46208 is a 1.25MHz constant frequency, current mode PWM step-down converter. The device integrates PMOS switch and a NMOS synchronous rectifier. It also includes a voltage reference, error amplifier, oscillator, PWM comparator, current comparator, slope compensation, current sense, logic driver, etc... In normal PWM mode, in one cycle, when the oscillator sets RS trigger, internal PMOS conduct, while PWM comparator resets the RS trigger, PMOS is cut off, the peak current of inductor is controlled by error amplifier output. When PMOS is off, the synchronous NMOS will be turned on and stay on until the inductor current reverses (controlled by current comparator ICOMP) or the next clock cycle begins. SC46208 detects the load current automatically, when the load current decreases to a threshold(relate to the input/output voltage and inductance), the system starts power saving mode. In this mode, the dissipation current is only 20μA, thus to improve the conversion efficiency under light loads. Pay attention to the ripple of output voltage, you can add a phase-lead capacitor (pF grade) between the VOUT and FB to reduce the ripple in power saving mode. Dropout Operation When the input voltage decreases toward the value of output voltage, the duty increases, and the input voltage decrease more, PMOS switch on in one cycle and the duty reaches 100%. The output voltage then is the input voltage minus the voltage drop across the PMOS switch and the inductor. Short Circuit Protection When the output is short to ground, the frequency of internal oscillator decreases to 600KHz in order to remain HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 4 of 11 SC46208 enough attenuation time for inductor, thus prevent it from running away. When the output voltage increases, the frequency increases to 1.25MHz gradually. Over Voltage Detection When the over-voltage detect circuit detects the output voltage is more than 6% of the set value, it will shutdown the PMOS switch to prevent the output voltage from over-shoot until the voltage drops to set value. Current Limit and Thermal Shutdown Current limit is implemented through internal comparator, it limits the PMOS current in the 1.5A in one cycle, thus to protect the SC46208 in over load condition. When the die temperature is over 150°C due to the long time over load operation, SC46208 is shutdown automatically until the temperature lower to normal state, the hysteresis temperature during this period is about 20°C. APPLICATION NOTES Refering to typical application circuit of fig 1, the components selection begins with inductor L, then CIN and COUT: Inductor Selection The SC46208 can utilize small surface mount and chip inductors due to its fast 1.25MHz switching frequency. For most applications the SC46208 operates with inductors of 1μH to 4.7μH. The large inductance will decrease the ripple current, but high inductance values will also increase the PCB size, and the low inductance value result in high ripple currents. The ripple also relative with the VIN and VOUT: Iripple = 1 VIN − VOUT VOUT × × fs L VIN The rating current of inductor is equal to half of the max. load current adds half the max. ripple current ,to handle the peak inductor current without saturating. Choose inductor ripple current Iripple approximately 40% of the maximum load current ILOAD(max) , so the rating current Isat satisfied with following formula: 1 Isat > ILOAD(max) + Iripple = (1+ 20%)ILOAD(max) 2 The max. load current is 600mA, for most applications, the inductor of 720mA rating value is enough; for higher efficiency, please choose an inductor with low DC series resistance (DCR). To reduce the noise, use a shielded bobbin inductor. Capacitor Selection The low ESR capacitor is required to keep the output voltage ripple small. There, the multilayer ceramic capacitor is recommended due to their low ESR and small size. In the most applications, 10-22μF output capacitors are enough, higher capacitor can be used to reduce the output ripple and improve transient response. The low ESR input capacitor reduces the surge current drawn from the input and switching noise from the device. Ceramic capacitor is the best selection for input capacitor, and the capacitor should be as near as possible to chip. A 4.7μF ceramic capacitor is sufficient for most applications. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 5 of 11 SC46208 Setting The Output Voltage For voltage adjustable version, SC46208 adjusts the output voltage through two serial resistors, refer to fig. below. We can calculate the output voltage through the following equation: VOUT = (1+ R1)X0.6V R2 The selection of resistor R1, R2 should give attention to the quiescent power and external interfere. Higher impedance reduces the quiescent current (I=0.6V/R2), and lower resistance gives better noise immunity, and is less sensitive to interference, layout parasitics and FB node leakage current. A proper value of feed-forward capacitor C1 can improve the noise immunity of the feedback loops, especially in an improper layout. HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 6 of 11 SC46208 TYPICAL APPLICATION CIRCUIT Fig. 1：Output voltage adjustable regulator, single battery to 2.5V converter Fig.2：Output voltage fixed regulator Note: The circuit and parameters are reference only, please set the parameters of the real application circuit based on the real test. HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 7 of 11 SC46208 TYPICAL ELECTRICAL CHARACTERISTICS CURVES (Tamb=25°C, unless otherwise specified) Efficiency VS Input Voltage of SC46208 100 IOUT=100mA 95 IOUT=10mA 90 IOUT=1mA 85 IOUT=600mA 80 75 70 65 IOUT=0.1mA 60 VOUT=1.8V 55 50 2 3 4 5 6 Frequency(MHz) Efficiency (%) Input Voltage(V) HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 8 of 11 SC46208 TYPICAL ELECTRICAL CHARACTERISTICS CURVES (Tamb=25°C, unless otherwise specified) Output Voltage VS Load Current 1.844 1.834 VIN＝3.6V TA=25 C 1.824 1.814 1.804 1.794 1.784 1.774 0 100 200 300 400 500 600 700 800 900 Load Current(mA) Output Ripple Voltage SC46208 Load Step VOUT 100mV/DIV AC COUPLED VOUT (5mV/DIV) SW (5V/DIV) IL 500mA/DIV IL (500mA/DIV) ILOAD 500mA/DIV 20mS/DIV VIN=3.6V VOUT=1.8V ILOAD=50mA to 600mA HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn Time(500ns/DIV) VIN=3.6V VOUT=1.2V ILOAD=600mA REV:1.1 2008.09.10 Page 9 of 11 SC46208 PACKAGE OUTLINE SOT-23-5 Unit: mm 2.92±0.10 0～8° 0.35 0.70 2.80±0.15 1.60±0.10 0.45±0.15 0.2 0.950 0.15±0.05 1.15±0.10 1.10±0.05 0～0.100 1.90±0.10 MOS DEVICES OPERATE NOTES: Electrostatic charges may exist in many things. Please take following preventive measures to prevent effectively the MOS electric circuit as a result of the damage which is caused by discharge: z The operator must put on wrist strap which should be earthed to against electrostatic. z Equipment cases should be earthed. z All tools used during assembly, including soldering tools and solder baths, must be earthed. z MOS devices should be packed in antistatic/conductive containers for transportation. Note：Silan reserves the right to make changes without notice in this specification for the improvement of the design and performance. Silan will supply the best possible product for customers. HANGZHOU SILAN MICROELECTRONICS CO.,LTD Http://www.silan.com.cn REV:1.1 2008.09.10 Page 10 of 11