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| CM3708A 3A LOW-NOISE PWM STEP-DOWN REGULATOR GENERAL DESCRIPTION The CM3708A is a low-noise, pulse-width-modulated (PWM), DC-DC step-down converter. It powers logic and transmitters in small wireless systems such as cellular phones, communicating PDAs, and handy-terminals. The device features an internal synchronous rectifier for high efficiency; it requires no external Schottky diode. Excellent noise characteristics and fixed-frequency operation provide easy post-filtering. The CM3708A is ideally suited for Li-lon battery applications. It is also useful for +3V or +5V fixed input applications. The device operates in one of four modes. Forced PWM mode operates at a fixed frequency regardless of the load. Shutdown mode places the device in standby, reducing quiescent supply current to under 0.1A. The CM3708A can deliver over 3.0A. The output voltage can be adjusted from VREF to VIN. The input range is from 2.0V to 5.0V. Other features of the CM3708A include high efficiency, low dropout voltage. It is available in a space-saving 16-pin SOP & TSSOP package. FEATURES Patent Filed #6,452,366 600KHz switching and synchronization Dynamic output-voltage adjustment from VREF to VIN 3A Guaranteed Output Current 95% Efficiency No Schottky Diode Required 16-pin PSOP/PTSSOP power packages 6A Low Noise Current Limit Protection External Soft Start Rail to Rail output Buck Converter APPLICATIONS Cellular Phone Cordless Phone PDAs and Handy-Terminals AGP Chipset Supplies CPU I/O Supplies Notebook Chipset Supplies Battery Operated Devices PIN CONFIGURATION PSOP-16 (PS16) / PTSSOP-16 (PT16) Top View 1 2 3 4 5 6 7 8 VIN2 PVIN2 LX2 PGND2 AGND VFB NC AGND 16 15 14 13 12 11 10 9 VIN1 PVIN1 LX1 PGND1 AGND SD VREF AGSEN 2004/12/13 Champion Microelectronic Corporation Page 1 CM3708A 3A LOW-NOISE PWM STEP-DOWN REGULATOR PIN DESCRIPTION Pin No. 1,16 2,15 3,14 4,13 5,9,12 8 6 Symbol VIN1, VIN2 PVIN1, PVIN2 LX1, LX2 PGND1, PGND2 AGND Description Voltage supply for internal circuits Voltage supply for output power transistors Inductor connection to the Drains of the internal power MOSFETs Ground for output power transistors Ground for internal reference voltage divider Ground for remote sensing Shutdown active high. CMOS input level 0.75 x VIN 7 10 11 VREF NC VFB VOUT Set Voltage No Connection Feedback node for the VOUT 5 V 0 VIN + 0.3V VIN V V Min. 2 2 Operating Rating Typ. Max. 2.5 2.5 5 5 5 Unit V V V AGSEN SD BLOCK DIAGRAM NC 10 VIN1 1 VIN2 16 SD 6 PVIN1 2 PVIN2 15 AGND AGND AGND 5 9 Oscillator Ramp Generator 12 PW M Controller Therm al Protection MOS 3 14 LX1 LX2 VREF 7 Error Amp 8 AGSEN 11 VFB 4 PGND1 13 PGND2 2004/12/13 Champion Microelectronic Corporation Page 2 CM3708A 3A LOW-NOISE PWM STEP-DOWN REGULATOR ORDERING INFORMATION Part Number CM3708AIT CM3708AGIT* CM3708AIS CM3708AGIS* Temperature Range -40 to 85 -40 to 85 -40 to 85 -40 to 85 Package 16-Pin PTSSOP (PT16) 16-Pin PTSSOP (PT16) 16-Pin PSOP (PS16) 16-Pin PSOP (PS16) *Note: G : Suffix for Pb Free Product ABSOLUTE MAXIMUM RATINGS Absolute maximum ratings are those values beyond which the device could be permanently damaged. PVIN/VIN ............................................................-0.3V to 6.0V Voltage on Any Other Pin ............ GND - 0.3V to VIN + 0.3V Output Current, Source or Sink ......................................3.0A Junction Temperature ........................... ............150C Storage Temperature ............................. -65C to 125C Lead Temperature (Soldering, 5 sec).................... 260C Thermal Dissipation(JC )..... ....................... .50C/W OPERATING CONDITIONS Temperature Range ............................. -40C to 85C PVIN Operating Range .........................2.0V to 5.0V (Unless otherwise stated, these specifications apply TA=25C; VIN=+3.3V and PVIN=+3.3V) maximum ratings are stress ratings only and functional device operation is not implied. (Note 1) CM3708A Min. 0 CM3708A CM3708A CM3708A CM3708A PVIN=5V VFB = 1.4V LC unconnected VFB = 1.4V LC unconnected 6 150 180 480 Typ. Max. VIN 660 3.0 6.0 ELECTRICAL CHARACTERISTICS Symbol SWITCHING REGULATOR VREF fsw IOUT(RMS) IOUT(PEAK) Ilimit MOSFETs RDS(ON) SUPPLY IVIN IPVIN Parameter Test Conditions Unit Adjustable Output Voltage Switching Frequency Maximum Output RMS Current Maximum Output Peak Current Current limit Drain to Source on-State Resistance V KHz A A A m Quiescent Current Quiescent Current 200 500 A A Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions Note 2: VIN, PVIN = 3.3V 10% Note 3: It's not 100% test 2004/12/13 Champion Microelectronic Corporation Page 3 CM3708A 3A LOW-NOISE PWM STEP-DOWN REGULATOR FUNCTIONAL DESCRIPTION The CM3708A step-down, pulse-width-modulated (PWM), DC-DC converter has an adjustable output range from VREF to the input voltage (VIN). An internal synchronous rectifier Fixed-frequency operation enables easy post-filtering, thereby providing excellent noise characteristics. As a result, the CM3708A is an ideal choice for many small wireless systems. VREF The reference voltage could be ranged from 0V to VIN. INPUTS The input voltage reference pin, VREF determine the output voltages (LX1, LX2). If a specific voltage is forced at the VREF improves efficiency and eliminates an external Schottky diode. pin, the output voltage follows the voltage at the VREF pin. OTHER SUPPLY VOLTAGES Several inputs are provided for the supply voltages: PVIN and VIN. The PVIN provide the power supply to the power MOSFETs. VIN provides the voltage supply to the logic section and internal error amplifiers. OUPUTS The output voltage pins (LX1, LX2) are tied to the RF power amp, via an external inductor. Output voltage is determined by the VREF inputs so it can be from 0V to VIN. Internal Power Switches: CM3708A has been integrated 2 Power MOSFETs whose RDS(ON) is around 100m Ohm each. Low Noise Current Limit: CM3708A's current limit is a low noise current limit. It increase the system loop noise immunity while it is doing the current limit protection for the system. The current limit is around 6A for the normal 3A operation. FEEDBACK The VFB pin is an input that can be used for closed loop compensation. This input is derived from the voltage output. AGND pin is a contact node of internal resistor divider for remote sense. APPLICATION CIRCUIT L1 3.3uH Vout J1 1 2 C2 104 C1 220uf/6.3V 10uf/6.3V C4 104 VIN C3 PVIN 1 U1 CM3708A VIN1 PVIN1 LX1 VIN2 PVIN2 LX2 VIN 16 R1 5R1 PVIN J2 DC-INPUT 1 2 C5 2 C7 104 15 PVIN C8 104 C6 100uf/6.3V 3 4 5 14 PGND1 PGND2 AGND SD VREF AGSEN AGND VFB NC AGND 13 12 C9 104 C10 100uf/6.3V 470uf/6.3V VREF 6 7 8 11 10 9 C11 104 R2 200k 2 1 1 2 R3 1k C12 102 2004/12/13 Champion Microelectronic Corporation Page 4 CM3708A 3A LOW-NOISE PWM STEP-DOWN REGULATOR PACKAGE DIMENSION 16-PIN PTSSOP (PT16) 16-PIN PSOP (PS16) 2004/12/13 Champion Microelectronic Corporation Page 5 CM3708A 3A LOW-NOISE PWM STEP-DOWN REGULATOR IMPORTANT NOTICE Champion Microelectronic Corporation (CMC) reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. CMC integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of CMC products in such applications is understood to be fully at the risk of the customer. In order to minimize risks associated with the customer's applications, the customer should provide adequate design and operating safeguards. HsinChu Headquarter 5F, No. 11, Park Avenue II, Science-Based Industrial Park, HsinChu City, Taiwan 300 T E L : +886-3-567 9979 F A X : +886-3-567 9909 http://www.champion-micro.com Sales & Marketing 11F, No. 306-3, Sec. 1, Ta Tung Rd., Hsichih, Taipei Hsien Taiwan 221 T E L : +886-2-8692 1591 F A X : +886-2-8692 1596 2004/12/13 Champion Microelectronic Corporation Page 6 |
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