UC3656

UNISONIC TECHNOLOGIES CO., LTD UC3656 Preliminary CMOS IC 1MHz,800mA SYNCHRONOUS BUCK CONTROLLER DESCRIPTION The UTC UC3656 is a synchronous buck controller for a DC/DC converter optimized for high-performance microprocessor applications. It is configured with current mode for excellent line and load transient response. At 1MHz operation frequency, the use of small surface mount inductor and capacitor is enabled. The built-in synchronous switch saves the use of an external Schottky diode and increases efficiency. The UTC UC3656 is a low-noise synchronous step-down DC/DC converter that is ideally suited for systems requiring supplies from a 1-cell Li-ion battery or from a 3-cell to 4-cell NiCd, NiMH, or alkaline battery. The UTC UC3656 is generally applied in power supply for portable devices and USB-based power system. FEATURES * High Efficiency (95%) Possible * Input Voltage Range: 2.5V ~ 5.5V * Schottky Diode is Saved * Output Current: 800mA (@5V Input 3.3V Output) * 1.0MHz Oscillation Frequency * Internal ON/OFF * 100% Duty Cycle Allows Low Dropout Operation * Stand-by Current: 1μA (Max.) ORDERING INFORMATION Ordering Number UC3656G-AF5-R Package SOT-25 Packing Tape Reel MARKING www.unisonic.com.tw Copyright © 2010 Unisonic Technologies Co., Ltd 1 of 7 QW-R502-469.A UC3656 PIN CONFIGURATION Preliminary CMOS IC PIN DESCRIPTION PIN NO. 1 2 3 4 5 PIN NAME Run GND SW VIN FB DESCRIPTION ON/OFF Control Power Ground Switch Node Connection to Inductor Power Supply Output Feedback UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 2 of 7 QW-R502-469.A UC3656 BLOCK DIAGRAM Preliminary CMOS IC UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 3 of 7 QW-R502-469.A UC3656 ABSOLUTE MAXIMUM RATING PARAMETER Power Supply Voltage Preliminary CMOS IC RATINGS UNIT -0.3 ~ +6.0 V RUN,FB -0.3 ~ VIN V Input Pin Voltage SW -0.3 ~ VIN +0.3 V P-Channel Switch Source Current (DC) 1000 mA N-Channel Switch Sink Current (DC) 1000 mA Peak SW Sink and Source Current 1.5 A Ambient Operating Temperature TOPR -35 ~ +85 °C Storage Temperature TSTG -55 ~ +150 °C Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. SYMBOL VSS VIN VIN RECOMMENDED OPERATING CONDITIONS PARAMETER Power Supply Voltage Junction Temperature Operating Junction Temperature SYMBOL VIN TJ TJ SYMBOL θJA RATINGS 2.5 ~ 5.5 +150 -20 ~ +85 UNIT V °C °C THERMAL DATA PARAMETER Junction to Ambient RATINGS 165 MIN 2.5 TYP 300 0.5 0.6 0.1 0.5 1.25 1.0 200 0.4 0.35 ±0.1 1.0 ±0.1 UNIT °C/W MAX UNIT 5.5 V µA 1 µA 0.612 V 0.5 % 1.0 % ±200 nA 1.50 A 800 mA 1.2 MHZ KHZ 0.5 Ω 0.45 Ω ±1 µA 1.5 V ±1 µA ELECTRICAL CHARACTERISTICS (VIN=3.6V, TA=25°C, unless otherwise specified.) PARAMETER SYMBOL TEST CONDITIONS Input Supply Range VIN Quiescent Current (Note) IS FB=0.8V, ILOAD=0A, Active Mode Current In Standby Mode IST RUN=0V, VIN=5.5V Feedback Voltage VFB TA=-20°C ~ +85°C Feedback Voltage Line-Regulation VFB-LINE VCC=2.5V ~ 5.5V Feedback Variation with Temperature TA=-20°C ~ +85°C Feedback Current IFB Peak Inductor Current (Note) IPK VIN=5V, VOUT=3.3V Maximum Output Current (Note) IO VIN=5V±5%, VOUT=3.3V, L=4.7µH fOSC1 FB=0.8V Oscillator Frequency fOSC2 FB=0V RDS(ON) of P-Channel MOSFET RPFET ISW =600mA RDS(ON) of N-Channel MOSFET RNFET ISW =-600mA SW Leakage Current ILSW RUN=0V,SW=0Vor 5V,VIN=5V RUN Threshold VRUN RUN Leakage Current IRUN ΔI ( VIN − VOUT ) × t ON Note: IPK = IO + = IO + 2 2×L 0.588 1.10 0.8 0.3 UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 4 of 7 QW-R502-469.A UC3656 Preliminary CMOS IC TYPICAL APPLICATION CIRCUIT L1 4.7μF VIN SW VIN 5.0V 4.7μF SW VOUT 1.8V/800mA 10μF 47pF UC3656 RUN R2 FB R1 1M GND Figure 1 VIN 5.0V 4.7μF SW L1 4.7μF VIN SW VOUT 3.3V/800mA 10μF 47pF UC3656 RUN R2 FB R1 1M GND Figure 2 UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 5 of 7 QW-R502-469.A UC3656 APPLICATION INFORMATION Preliminary CMOS IC Capacitor Selection Proper selection of capacitors using the UTC UC3656 plays a critical role for system performance. The source current of the top MOSFET is square wave of duty cycle in a continuous mode. The input capacitor is generally used to provide a low impedance loop for the edges of pulsed current drawn by the UTC UC3656. A load step at the output can induce ringing at the input VIN. This ringing can couple to the output and be mistaken as loop instability. Increasing the capacitance of the input capacitor can great improve the oscillation. A typical value is 4.7~ 22μF ceramic (X5R or X7R), POSCAP or Aluminum Polymer. With these capacitors, better high frequency bypassing is achieved; resistive losses are thus reduced by their low ESR for higher efficiency. Moreover, the input capacitor RMS current changes with the input voltage and the output voltage. The maximum RMS current in the input capacitor can be expressed in the following formula: IRMS = IOMAX V VO (1 − O ) VIN VIN The output capacitor depends upon the suitable ripple voltage. Low ripple voltage corresponds to lower effective series resistance (ESR). 1 ) The output ripple voltage can be calculated by: ΔVOUT ≅ ΔIL (ESR + 8fCOUT The formula as follows shows the output capacitor RMS ripple current: IRMS = 1 23 VOUT × ( VIN − VOUT ) L × f × VIN For the UTC UC3656, X5R or X7R dielectric formulations have the priority in choosing the input and output ceramic capacitors. This is because these dielectrics provide the best temperature and voltage characteristics of all the ceramics for a given value and size. Inductor Selection Selecting an optimum inductor is dependent upon the expected ripple current and large value inductors lower ripple current and small value inductors result in higher ripple current. In addition, the losses associated with the DCR and its effect on the total converter efficiency should be taken consideration. The inductor is also chosen to limit the ripple current to some pre-fixed value, approx. 20 ~ 40% (TYP.) of the full load current at the maximum input voltage. The inductance value can be calculated in the following equation: ΔIL = 0.2 ~ 0.4 × IOUT(MAX) L= VOUT V (1 − OUT ) f × ΔIL VIN Adjustable Output Voltage A resistive divider adjusts the output voltage of the UTC UC3656, which divides a 0.6V reference voltage at FB pin. The output voltage can be obtained by the equation as follows: VOUT = 0.6V × (1 + R1 ) R2 UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 6 of 7 QW-R502-469.A UC3656 Preliminary CMOS IC UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 7 of 7 QW-R502-469.A