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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 1A shutdown current and 20A 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.
APPLICATION
* Cellular Telephones * PDAs * Wireless Equipment * MP3 player * Digital Camera * Portable Instruments
FEATURES
* High efficiency up to 95% * Automatic Power Saving Mode at light loads, only 20A quiescent current. * Wide input voltage range: +2. 5V~+5.5V * Output voltage range: 0.6V~VIN * High output current 600mA * Low dropout operation: 100% * Shutdown current<1A * 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
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SC46208
ORDERING INFORMATION
Device no SC46208 SC4620810 SC4620812 SC46208XX SC4620815 SC4620818 SC4620825 SC4620833 Seal name 6208 20810 20812 20815 20818 20825 20833 Package SOT-23-5 SOT-23-5 SOT-23-5 SOT-23-5 SOT-23-5 SOT-23-5 SOT-23-5 voltage: Default: adjustable 10 :1.0V 12 :1.2V 15 :1.5V 18 :1.8V 25 :2.5V 33 :3.3V Remark Note: "xx" indicates the output
BLOCK DIAGRAM
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SC46208
ABSOLUTE MAXIMUM RATING
Characteristics Input Supply Voltage VIN Enable Voltage EN SW Voltage Output Feedback Voltage Operating Temperature Storage Temperature ESD Characteristic(HBM) Symbol VIN VEN VSW VFB Tamb TSTG ESD Rating -0.3 ~ +6 -0.3 ~ VIN -0.3 ~ VIN+0.3 -0.3 ~ +6 -40 ~ + 85 -65 ~ +125 4.0 Unit V V V V C C KV
ELECTRICAL CHARACTERISTICS(unless otherwise noted, Tamb =25C, VIN=3.6V, L=2.2H, COUT=10F,
load current ILOAD=0) Characteristics Input Voltage Range Feedback Voltage Quiescent Current (Switch Off) Quiescent Current (Shutdown Mode) Quiescent Current (PWM Mode) Output Voltage Regulation Output Voltage Load Regulation Feedback Current PMOS On Resistor NMOS On Resistor PMOS Limit Current Switch Frequency Max. Duty Switch Leakage Current SW EN Input High Level EN Input Low Level EN Leakage Current Thermal Shutdown Temperature Thermal Shutdown Hysteresis Temperature Symbol VIN VFB Only for adjustable version Iswitch off FB=0.62V,or VOUT=103% ISHDN Iq VOUT VLOAD 0mA IL 600mA IFB RPMOS RNMOS ILIMIT FS DMAX ILSW VH VL ILEN Tj(sd) Thyst --Only for adjustable version ISW=100mA ISW=-100mA 2.5VVIN 5.5V FB=0.6V,or VOUT=100 FB=0 V,or VOUT=0 FB=0.5V EN=0V,SW=0V or 5V,VIN =5V -----0.01 150 20 1.5 0.3 1 --100 0.01 1 1.25 1. -50 0.45 0.35 1.5 1.25 600 EN=0V FB=0.5V , Or VOUT=90% Test conditions Min. 2.5 0.585 0.6 20 0.1 200 0.5 0.1 50 0.5 0.4 1.75 1.5 Typ. Max. 5.5 0.615 30 1 300 Unit. V V A A A % mV/mA nA A MHz KHz % A V V A C C
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SC46208
PIN CONFIGURATION
FB/VOUT 5 VIN 4
SC46208
1 EN
2 GND
3 SW
PIN DESCRIPTION
Pin no. 1 2 3 4 5 Pin name EN GND SW VIN FB/VOUT I/O I -I/O -I Descriptions Enable input port, this pin should not float. Ground. 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 20A, 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
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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 150C 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 20C.
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 1H to 4.7H. 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 x x 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, 10-22F 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 4.7F 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.
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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.
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SC46208
TYPICAL APPLICATION CIRCUIT
Fig. 1Output voltage adjustable regulator, single battery to 2.5V converter
Fig.2Output 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.
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SC46208
TYPICAL ELECTRICAL CHARACTERISTICS CURVES (Tamb=25C, unless otherwise specified)
Efficiency VS Input Voltage of SC46208 100 95 90 85 80 75 70 65 60 55 50 2 3 4 Input Voltage(V) 5 6 VOUT=1.8V IOUT=0.1mA IOUT=1mA IOUT=600mA IOUT=100mA IOUT=10mA
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Frequency(MHz)
Efficiency (%)
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SC46208
TYPICAL ELECTRICAL CHARACTERISTICS CURVES (Tamb=25C, unless otherwise specified)
Output Voltage VS Load Current 1.844 1.834 1.824 1.814 1.804 1.794 1.784 1.774 0 VIN3.6V TA=25 C
100 200 300 400 500 600 700 800 900 Load Current(mA)
SC46208 Load Step VOUT 100mV/DIV AC COUPLED
Output Ripple Voltage
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
Time(500ns/DIV) VIN=3.6V VOUT=1.2V ILOAD=600mA
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SC46208
PACKAGE OUTLINE
SOT-23-5
2.920.10 08 0.35 0.2 0.450.15
Unit: mm
2.800.15
1.600.10
0.950 1.900.10
0.70
0.150.05
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: The operator must put on wrist strap which should be earthed to against electrostatic. Equipment cases should be earthed. All tools used during assembly, including soldering tools and solder baths, must be earthed. MOS devices should be packed in antistatic/conductive containers for transportation.
NoteSilan 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.
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00.100
1.100.05
1.150.10
REV:1.1
2008.09.10 Page 10 of 11

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