CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator GENERAL DESCRIPTION FEATURES The CM3706A is a high efficiency monolithic synchronous ◆ High Efficiency: Up to 96% buck regulator using a constant frequency, current mode ◆ 1.5Mhz Constant Switching Frequency architecture. The device is available in an adjustable ◆ 600mA Output Current at VIN=3V version. Supply current with no load is 300uA and drops to ◆ Integrated Main switch and synchronous rectifier. No Schottky Diode Required <1uA in shutdown. The 2.5V to 6.5V input voltage range makes the CM3706A ideally suited for single Li-Ion, two to ◆ 2.5V to 6.5V Input Voltage Range four AA battery-powered applications. 100% duty cycle ◆ Output Voltage as Low as 0.6V provides low dropout operation, extending battery life in ◆ 100% Duty Cycle in Dropout portable systems. PWM pulse skipping mode operation ◆ Low Quiescent Current: 300µA provides very low output ripple voltage for noise sensitive ◆ Slope Compensated Current Mode Control for Excellent Line and Load Transient Response applications. Switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors ◆ Short Circuit Protection and capacitors. The internal synchronous switch increases ◆ Thermal Fault Protection efficiency and eliminates the need for an external Schottky ◆ <1uA Shutdown Current diode. Low output voltages are easily supported with the ◆ Space Saving 5-Pin Thin TSOT23 package 0.6V feedback reference voltage. APPLICATIONS Cellular and Smart Phones MP3 / MP4 Player Microprocessors and DSP Core Supplies Portable Instruments Wireless and DSL Modems Digital Still and Video Cameras PDAs TYPICAL APPLICATIONS 4 IN 3 VIN 2.5V TO 5.5V Cin 4.7uF 1 2.2uH OUT SW CM3706A RUN GND VFB 2 634k 5 316K Cout 10uF 22PF Figure 1. Basic Application Circuit with CM3706A adjustable version 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 1 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator PIN CONFIGURATION TSOT23-5 Top View BLOCK DIAGRAM 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 2 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator PIN DESCRIPTION Pin No. Symbol Description 1 RUN Regulator Enable control input. Drive RUN above 1.5V to turn on the part. Drive RUN below 0.3V to turn it off. In shutdown, all functions are disabled drawing <1µA supply current. Do not leave RUN floating. 2 GND Ground Pin. 3 SW Power Switch Output. It is the Switch note connection to Inductor. This pin connects to the drains of the internal P-CH and N-CH MOSFET switches. 4 VIN Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 2.2µF or greater ceramic capacitor. 5 FB VFB (CM3706A): Feedback Input Pin. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V. ORDERING INFORMATION/ MARKING Adjustable Output Version Part Number CM3706AGIM25 2008/03/07 Rev. 1.0 Output Adj Top Mark A1XY Champion Microelectronic Corporation Temp Range -40°C to +85°C Page 3 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator ABSOLUTE MAXIMUM RATINGS(Note 1) Absolute maximum ratings are those values beyond which the device could be permanently damaged. Input Supply Voltage...................................................–0.3V to 7.0V Peak SW Sink and Source Current………...…………….. 1.5A RUN, VFB Voltages ………………………...…– 0.3V to (VIN + 0.3V) Junction Temperature (Note 2) ........... ........................ 125°C SW Voltage....…………........………..……..… – 0.3V to (VIN + 0.3V) Storage Temperature Range ....................... – 65°C to 150°C Operating Temperature Range….…………..…-40°C to +85°C Lead Temperature (Soldering, 10 sec)......................... 300°C OPERATING CONDITIONS Temperature Range .......................... -40°C to 85°C Vin Operating Range .........................2.5V to 5.5V Thermal Resistance (Note 3): Package TSOT23-5 ӨJA ӨJC 250°C/W 110°C/W Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: CM3706A : TJ = TA + (PD)╳(ӨJA) Note 3: Thermal Resistance is specified with approximately 1 square of 1 oz copper. 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 4 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator ELECTRICAL CHARACTERISTICS (Unless otherwise stated, these specifications apply TA=25°C; VIN=+3.6V) maximum ratings are stress ratings only and functional device operation is not implied. Parameter Conditions Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode Regulated Feedback Voltage MAX unit 6.5 V VFB=0.5V 300 400 VFB=0V, VIN=4.2V 0.1 1.0 µA µA TA = +25°C 0.5880 0.6000 0.6120 V TA= 0°C ≤ TA ≤ 85°C 0.5865 0.6000 0.6135 V TA= -40°C ≤ TA ≤ 85°C 0.5820 0.6000 0.6180 V ±30 nA 0.01 0.4 %/V 0.04 0.40 %/V VFB = 0.65V Reference Voltage Line Regulation VIN = 2.5V to 5.5V, Output Voltage Line Regulation VIN = 2.5V to 5.5V,IOUT=10mA Peak Inductor Current TYP 2.5 VFB Input Bias Current Output Voltage Load Regulation MIN IOUT from 10 to 600mA VIN=3V, VFB=0.5V or VOUT=90% Duty Cycle <35% 0.0015 %/mA 0.75 1.00 1.25 A 1.2 1.5 1.8 MHz Oscillator Frequency VFB=0.6V or VOUT=100% RDS(ON) of P-CH MOSFET ISW = 300mA 0.4 0.50 Ω RDS(ON) of N-CH MOSFET ISW = -300mA 0.35 0.45 Ω SW Leakage VRUN = 0V, VSW= 0V or 5V, VIN = 5V ±0.01 ±1 µA RUN Threshold -40°C ≤ TA ≤ 85°C 0.45 1.5 V ±0.1 ±1 µA 0.3 RUN Leakage Current Thermal Shutdown Trip Threshold Output over voltage lockout ΔVOVL = VOVL – VFB 150 ℃ 60 mV Note 4: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization. 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 5 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator FUNCTIONAL DESCRIPTION Operation Idle Mode Operation CM3706A is a monolithic switching mode Step-Down DC-DC At very light loads, the CM3706A automatically enters Idle converter. It utilizes internal MOSFETs to achieve high Mode. In the Idle Mode, the inductor current may reach zero efficiency and can generate very low output voltage by using or reverse on each pulse. internal reference at 0.6V. It operates at a fixed switching automatically skip pulses to frequency, and uses the slope compensated current mode maintain output regulation. The bottom MOSFET is turned architecture. This Step-Down DC-DC Converter supplies off by the current reversal comparator, IZERO, and the switch 600mA output current at VIN = 3V with input voltage range voltage will ring. This is discontinuous mode operation, and from 2.5V to 6.5V. is normal behavior for the switching regulator. Current Mode PWM Control Maximum Load Current The CM3706A will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases. Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of the internal main switch (P-Ch MOSFET) and synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current error voltage. is above the The current comparator, ICOMP, limitsthe peak The PWM control loop will inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either Note 5: The duty cycle D of a step-down converter is defined the inductor current starts to reverse, as indicated by the as: current reversal comparator, IZERO, or the beginning of the D = TON × f OSC × 100% ≈ next clock cycle. The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present. V OUT × 100% VIN where TON is the main switch on time, and fOSC is the oscillator frequency (1.5Mhz). Dropout Operation When the input voltage decreases toward the value of the output voltage, the CM3706A allows the main switch to remain on for more than one switching cycle and increases the duty cycle (Note 5) until it reaches 100%. The output voltage then is the input voltageminus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the IC. 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 6 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator Typical Performance Characteristics (Test Figure 1 above unless otherwise specified) 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 7 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator Output Voltage vs Temperature Pulse Skipping Mode Operation Load step 2008/03/07 Rev. 1.0 Discontinuous Operation Load step Champion Microelectronic Corporation Start-Up from shutdown Load step Page 8 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator APPLICATIONS INFORMATION L1 Setting the Output Voltage Figure 2 above shows the basic application circuit with CM3706A adjustable output version. The external resistor 4 IN Cin 4.7uF ⎛ R2 ⎞ VOUT = 0.6V ⎜1 + ⎟ R1 ⎠ ⎝ 1 SW CM3706A RUN GND VFB OUT VIN 2.5VTO 5.5V sets the output voltage according to the following equation: 2.2uH 3 2 R2 1%634k 5 Cout 10uF R1 316K C1 22PF 1% C3 C2 R1=316KΩ ; R2= 316KΩ ; VOUT =1.2V R1=316KΩ ; R2= 470KΩ ; VOUT =1.5V Figure2 Application Circuit with R1=316KΩ ; R2= 630KΩ ; VOUT =1.8V adjustable output versions R1=316KΩ ; R2= 1MΩ ; VOUT =2.5V R1=316KΩ ; R2= 1.42MΩ ; VOUT =3.3V. For output voltages above 2.0V, when light-load efficiency is Input Capacitor Selection important, the minimum recommended inductor is 2.2µH. The input capacitor reduces the surge current drawn from the For optimum voltage-positioning load transients, choose an input and switching noise from the device. The input capacitor inductor with DC series resistance in the 50mΩ to 150mΩ impedance at the switching frequency shall be less than input range. For higher efficiency at heavy loads, or minimal load source impedance to prevent high frequency switching current regulation (but some transient overshoot), the resistance passing to the input. A low ESR input capacitor sized for should be kept below 100mΩ. The DC current rating of the maximum RMS current must be used Ceramic capacitors with inductor should be at least equal to the maximum load current X5R or X7R dielectrics are highly recommended because of plus half the ripple current to prevent core saturation their low ESR and small temperature coefficients. A 4.7µF (600mA+105mA). ceramic capacitor for most applications is sufficient. Output Capacitor Selection Inductor Selection The output capacitor is required to keep the output voltage For most designs, the CM3706A operates with inductors of ripple small and to ensure regulation loop stability. The output 1µH to 4.7µH. Low inductance values are physically smaller capacitor must have low impedance at the switching frequency. but require faster switching, which results in some efficiency Ceramic loss. The inductor value can be derived from the following recommended due to their low ESR and high ripple current.The equation: output ripple VOUT is determined by: L= Where ΔI L VOUT × (V IN − VOUT ) V IN × ΔI L × f OSC ΔVOUT ≤ is inductor Ripple Current. Large value capacitors with X5R or X7R dielectrics are ⎞ VOUT × (V IN − VOUT ) ⎛ 1 ⎟⎟ × ⎜⎜ ESR + V IN × f OSC × L 8 × f × C 3 osc ⎝ ⎠ inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current Input Zener Selection approximately 35% of the maximum load current In USB device application, we will add zener. The zener 600mA, or ΔI L =210mA. 2008/03/07 Rev. 1.0 can be reduced the surge voltage when device plug in and plug out. Application circuit is show in Figure3. Champion Microelectronic Corporation Page 9 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator PACKAGE DIMENSION D 5 4 b1 With Plating c c1 A A1 E1 E A2 b b Base Metal b1 c Section B-B c1 D E 1 e 2 3 e1 E1 b L L1 e θ1 e1 θ θ1 θ A2 A θ2 θ2 A1 L See Section B-B L1 Note5: Package outline exclusive of mold flash and metal burr. 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 10 CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator IMPORTNT 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 Sales & Marketing 5F, No. 11, Park Avenue II, Science-Based Industrial Park, HsinChu City, Taiwan 300 7F-6, No.32, Sec. 1, Chenggong Rd., Nangang District, Taipei City 115, Taiwan T E L : +886-3-567 9979 F A X : +886-3-567 9909 http://www.champion-micro.com T E L : +886-2-2788 0558 F A X : +886-2-2788 2985 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 11