Advanced Analog Technology, Inc. October 2007 AAT7301 Product information presented is for internal use within AAT Inc. only. Details are subject to change without notice. 2A 15V STEP-DOWN DC-DC CONVERTER FEATURES GENERAL DESCRIPTION Buck PWM with Internal PMOS The AAT7301 is a 2A 15V step-down converter, which 4V to 15V Input Voltage Range provides an integrated one-channel PWM solution for Max. 2A Output Current the power supply of DC-DC system. It offers system Under-Voltage Lockout (UVLO) Protection engineers the flexibility to tailor-make the power supply Internal Short Circuit and Thermal Protection circuitry for specific applications. Internal Soft-Start Fixed Switching Frequency (380kHz / 47kHz) 2 µA Shutdown Current SOP-8 Package The buck PWM contains enable control signal, error amplifier, PWM under-voltage comparator, protection, output oscillator, short driver, circuit protection and voltage reference circuit. The AAT7301 contains one buck current mode PWM with internal PMOS. In addition, a digital soft-start is PIN CONFIGURATION also included to prevent inrush current at startup. AAT7301 comes with a fixed 380kHz oscillator, however, when the feedback voltage is lower than 0.7V, the switching frequency changes to 47kHz and returns to 380kHz after the short-circuit is released. TYPICAL APPLICATION – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 1 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 ORDERING INFORMATION DEVICE TYPE PART NUMBER PACKAGE PACKING AAT7301 AAT7301 -S-T S:SOP8 T: Tape and Reel TEMP. RANGE MARKING –40 C to +85 C AAT7301 XXXXXX MARKING DESCRIPTION Device Type Lot no. (6~9 Digits) NOTE: All AAT products are lead free and halogen free. ABSOLUTE MAXIMUM RATINGS PARAMETER SYMBOL VALUE UNIT Supply Voltage (VDD, SW) VDD –0.3 to 15.0 V Pin Voltage (IN, ENC, EO) VI –0.3 to (VDD +0.3) V SW Current ISW 6.5 A Operating Temperature Range TC –40 C to +85 C C TSTORAGE –65 C to +150 C C Storage Temperature Range – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 2 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 ELECTRICAL CHARACTERISTICS ( VDD = 4V~15V, TC = –40 C to 85 C , Tested at TC = 25 C ,VDD = 12V, unless otherwise specified.) General Item PARAMETER Input Voltage Range SYMBOL VDD VUVLO Under Voltage Lockout Hysteresis VUHYS VDD Falling 3.33 3.48 MAX UNIT 15 V 3.63 V 150 mV VIN = 1.5V 1 mA IDD-ON VIN = 0.85V 5.5 mA ISHDN OSC Frequency fOSC 1.70 VSHORT EN Low Level VIL EN High Level VIH Thermal Shutdown TYP IDD-OFF Shutdown Current into VDD Short Detection Voltage MIN 4 Under Voltage Lockout Input Current into VDD TEST CONDITION 10.00 µA Normal Operation 380 kHz Short-Circuit 47.5 kHz VIN Falling 0.67 0.70 0.73 V 0.4 V 1.6 TSHDN V 160 C Buck PWM PARAMETER SYMBOL TEST CONDITION MIN TYP MAX UNIT IN Regulation Voltage VIN IN = EO 0.88 0.90 0.92 V IN to EO Transconductance Gm IN = EO 35 80 125 µS Maximum Duty Cycle 90 IN Input Leakage Current IL Current-Sense Amplifier Transresistance RCS SW Leakage Current ILSW Switch On-Resistance RON SW Current Limit ILIMIT Soft-Start Time IN = 0V to 1.5V 0.01 +100.00 0.2 VSW = 15V – 0.1 2.5 tSS – −100.00 % 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 3 of 11 nA V/A 5.0 µA 200 mΩ 3.7 A 700 µs Advanced Analog Technology, Inc. October 2007 AAT7301 TYPICAL OPERATING CHARACTERISTICS – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 4 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 TYPICAL OPERATING CHARACTERISTICS – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 5 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 PIN DESCRIPTION PIN NO. NAME I/O FUNCTION 1 NC - Not Connected 2 VDD I Power Input 3 SW I/O 4 GND - Ground 5 IN I Feedback Input 6 EO I/O 7 ENC I Enable Control 8 NC - Not Connected Switching Node Error Amplifier Compensation Output FUNCTION BLOCK DIAGRAM AAT7301 – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 6 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 TYPICAL APPLICATION CIRCUIT AAT7301 – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 7 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 DETAILED DESCRIPTION DESIGN PROCEDURE The AAT7301 is a current-mode buck switch-mode Programming the Output Voltage regulator with a fixed switching frequency of 380kHz. It The output voltage for the AAT7301 is programmed uses an internal P-channel MOSFET switch to step using a resistor divider from the output connected to the down the input voltage to the regulated output voltage. feedback pins (Figure 1). When setting the output The converter regulates input voltages from 4V to 15V voltage, connect a resistive voltage divider from the down to an output voltage as low as 0.9V, and is able to output to IN pin and then to GND. Choose the supply up to 2A of load current. lower-side (IN-to-GND) resistor, then calculate the upper-side (output-to-IN) resistor as follows: ENC Control Input The AAT7301 contains built-in pull high logic. The IC is enabled even ENC left floating (ENC pin voltage ＞ V RUPPER = RLOWER OUT − 1 VIN 1.6V). When the voltage is lower than 0.4V, the IC is disabled. Where VIN is the feedback regulation voltage, 0.9V (typ). Typical values for RLOWER are in the range of 10kΩ to Soft-Start 100kΩ. The AAT7301 has built-in 700µs soft-start time. Upon power turn-on, if ENC pin is not pulled low; and VDD is above VUVLO (typ. 3.48V), IN pin will climb from 0V to 0.9V during 700µs soft-start time to reduce inrush current. Short Circuit Protection When short circuit happens, and the feedback voltage (IN) is less than 0.7V, the switching frequency will change to 47kHz to reduce the power supply from input Figure 1. Feedback Network to output to protect the system. The frequency will switch back to 380kHz after the short circuit is released. Thermal Shutdown The AAT7301 includes a thermal-limit circuit that shuts down the IC at approximately +160 C . The part turns on after the IC cools by approximately 20 C . – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 8 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 Inductor Selection Input Capacitor A good rule of thumb when choosing the inductance is The input capacitor in a DC-to-DC converter reduces to allow the peak inductor current in the inductor to be current peaks drawn from the input power source and approximately 115% of the maximum load current. Also, reduces make sure that the peak inductor current is below the impedance of the input capacitor at the switching 2.5A minimum current limit. frequency should be less than that of the input source The inductance value can be calculated by the so high-frequency switching currents do not pass equation: through the input source. Ceramic capacitors are switching preferred, but noise tantalum in or the controller. low-ESR The electrolytic V VOUT ⋅ (1 − OUT ) VI L≈ 0.3 ⋅ IOUT ⋅ fSW capacitors may also satisfy. For insuring stable Where VOUT is the output voltage, VI is the input voltage, Output Capacitor fSW is the switching frequency (380kHz), and IOUT is the The output capacitor keeps output ripple small and maximum load current. ensures control-loop stability. The output capacitor When the inductance value is determined, then the must also have low impedance at the switching peak inductor current can be calculated by the frequency. Ceramic, polymer, and tantalum or low-ESR equation: electrolytic capacitors are suitable. operation the IC must be bypassed with a 0.22 µF ceramic capacitor placed close to the VDD. Output ripple with a ceramic output capacitor is V VOUT ⋅ (1 − OUT ) VI IL(peak) = IOUT + 2 ⋅ fSW ⋅ Lsetting approximately as follows: Vripple ≈ Where IOUT is maximum load current, VOUT is the output voltage, VI is the input voltage, fSW is the switching frequency (380kHz), and Lsetting is the inductance value. V VOUT ⋅ (1 − OUT ) VI 8 ⋅ L setting ⋅ COUT ⋅ fSW 2 Where VOUT is the output voltage, VI is the input voltage, Choose an inductor that does not saturate under the fSW is the switching frequency (380kHz), COUT is the peak inductor current. output capacitance, and Lsetting is the inductance value. If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows: Schottky Diode Selection Choose a Schottky diode whose maximum reverse voltage rating is greater than the maximum input Vripple ≈ 2 ⋅ (IL(peak) − IOUT ) × RESR voltage, and whose current rating is greater than the Where IL(peak) is the peak inductor current, IOUT is peak inductor current. maximum load current, and RESR is the capacitor’s ESR. – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 9 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 Compensation from EO to GND: The AAT7301 employs current-mode control, thereby simplifying the control-loop compensation. When the AAT7301 operates with continuous inductor current (typically the case), a RLOAD COUT pole appears in the CP = C OUT × RESR RC If CP is calculated to be < 10pF, it can be omitted. loop-gain frequency response. To ensure stability, set the compensation RCCC to zero to compensate for the RLOAD COUT pole. Set the loop crossover below the lower of 1/10 the switching frequency (380kHz). The compensation resistor and capacitor are then chosen to optimize control-loop stability. Choose the compensation resistor RC to set the desired crossover frequency fC. Determine the value by the following equation: RC = LAYOUT CONSIDERATIONS Conductors carrying discontinuous currents and any high-current path should be made as short and wide as possible. The compensation network should be very close to the EO pin and avoid through VIA. The IC must be bypassed with a 0.22 µF ceramic capacitor placed close to the VDD. Tie the feedback resistor divider to be very close to output capacitor and far away from the inductor or Schottky diode. Keep the 2π × COUT × VOUT × RCS × fC Gm × VIN feedback network IN close to the IC. Switching nodes (SW) should be kept as small as possible and should Where COUT is the output capacitance, VOUT is the be routed away from high-impedance nodes such as output voltage, RCS is the current-sense amplifier IN. transresistance (0.2V/A), Gm is the error amplifier transconductance (80 µS ) and VIN is the feedback threshold voltage (0.9V). If the value calculated for RC is greater than 100 kΩ , recommend 100 kΩ . Choose the compensation capacitor CC to set the zero to 1/4 of the crossover frequency. CC < COUT × VOUT 4 × RC If the output filter capacitor COUT has significant ESR, a zero occurs at the following: ZESR = 1 2π × C OUT × RESR If ZESR > fC / 4, it can be ignored, as is typically the case with ceramic output capacitors. If ZESR < fC / 4, it should be cancelled with a pole set by capacitor CP connected – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 10 of 11 Advanced Analog Technology, Inc. October 2007 AAT7301 PACKAGE DIMENSION SOP-8 Symbol A A1 A2 b C D E E1 e L y θ Dimensions In Millimeters MIN TYP MAX 1.35 1.60 1.73 0.05 -----0.15 -----1.45 -----0.33 0.41 0.51 0.19 0.20 0.25 4.80 4.85 4.95 5.79 5.99 6.20 3.81 3.91 3.99 1.27 BSC 0.406 0.710 1.270 ----------0.076 0˚ -----8˚ – – 台灣類比科技股份有限公司 – Advanced Analog Technology, Inc. – Version 1.00 Page 11 of 11