Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter General Description Features The AP3431 is a high efficiency step-down DC-DC voltage converter. The chip operation is optimized by peak-current mode architecture with built-in synchronous power MOS switchers. The oscillator and timing capacitors are all built-in providing an internal switching frequency of 1MHz that allows the use of small surface mount inductors and capacitors for portable product implementations. • • • • • • • • • • Integrated Soft Start (SS), Under Voltage Lock Out (UVLO), Thermal Shutdown Detection (TSD) and short circuit protection are designed to provide reliable product applications. AP3431 High Efficiency Buck Power Converter Output Current: 2A Low RDS(ON) Internal Switches : 120mΩ(VIN=5V) Adjustable Output Voltage from 0.8V to 0.9×VIN Wide Operating Voltage Range: 2.7V to 5.5V Built-in Power Switches for Synchronous Rectification with High Efficiency Feedback Voltage: 800mV Switching Frequency: 1.0MHz Thermal Shutdown Protection Internal Soft Start Applications The device is available in adjustable output voltage versions ranging from 0.8V to 0.9×VIN when input voltage range is from 2.7V to 5.5V , and is able to deliver up to 2.0A. • • • • LCD TV Set Top Box Post DC-DC Voltage Regulation PDA and Notebook Computer The AP3431 is available in SOIC-8 package. SOIC-8 Figure 1. Package Type of AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 1 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Pin Configuration M Package (SOIC-8) 1 8 2 7 3 6 4 5 Figure 2. Pin Configuration of AP3431 (Top View) Pin Description Pin Number Pin Name 1 VCC 2 NC 3 GND 4 FB 5 EN 6 PGND 7 SW 8 VIN Nov. 2011 Function Supply input for the analog circuit No connection Ground pin Feedback pin. Receives the feedback voltage from a resistive divider connected across the output Chip enable pin. Active high, internal pull-high with 200kΩ resistor Power switch ground pin Switch output pin Power supply input for the MOSFET switch Rev. 1. 0 BCD Semiconductor Manufacturing Limited 2 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Functional Block Diagram Figure 3. Functional Block Diagram of AP3431 Ordering Information AP3431 A - Circuit Type G1:Green Package M: SOIC-8 Blank: Tube TR: Tape & Reel Package Temperature Range SOIC-8 -40 to 80°C Part Number Marking ID Packing Type AP3431M-G1 3431M-G1 Tube AP3431MTR-G1 3431M-G1 Tape & Reel BCD Semiconductor's Pb-free products, as designated with "G1" in the part number, are RoHS compliant and green. Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 3 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Absolute Maximum Ratings (Note 1) Parameter Symbol Value Unit Supply Input for the Analog Circuit VCC 0 to 6.0 V Power Supply Input for the MOSFET Switch VIN 0 to 6.0 V SW Pin Switch Voltage VSW -0.3 to VIN+0.3 V Enable Voltage VEN -0.3 to VIN+0.3 V SW Pin Switch Current ISW 2.9 A Power Dissipation (on PCB, TA=25°C) PD 1.45 W Thermal Resistance (Junction to Ambient, Simulation) θJA 68.63 °C/W Junction Temperature TJ 160 °C Operating Temperature TOP -40 to 85 °C Storage temperature TSTG -55 to 150 °C ESD (Human Body Model) VHBM 2000 V ESD (Machine Model) VMM 200 V Note 1: Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under “Recommended Operating Conditions” is not implied. Exposure to “Absolute Maximum Ratings” for extended periods may affect device reliability. Recommended Operating Conditions Parameter Symbol Min Max Unit Supply Input Voltage VIN 2.7 5.5 V Junction Temperature Range TJ -40 125 °C Ambient Temperature Range TA -40 80 °C Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 4 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Electrical Characteristics VIN=VCC=VEN=5V, VOUT=1.2V, VFB=0.8V, L=2.2µH, CIN=10µF, COUT=22µF, TA=25°C, unless otherwise specified. Parameter Symbol Conditions Min Typ Max Unit Input Voltage Range VIN Shutdown Current IOFF VEN=0V Active Current Regulated1Feedback Voltage Regulated Output Voltage Accuracy Peak Inductor Current ION VFB = 0.95V VFB For Adjustable Output Voltage Oscillator Frequency ∆VOUT/VOUT 2.7 VIN=2.7V to 5.5V, IOUT=0 to 2.0A V 4 µA 460 µA 0.8 -3 0.816 V 3 % 2.9 IPK fOSC 0.784 5.5 A VIN = 2.7V to 5.5V 1.0 MHz PMOSFET RON RON(P) VIN = 5V 120 mΩ NMOSFET RON EN High-level Input Voltage EN Low-level Input Voltage RON(N) VIN = 5V 120 mΩ 1.5 VEN_H V 0.4 VEN_L V EN Input Current IEN 2 µA Soft-start Time tSS 450 µs Maximum Duty Cycle Under Voltage Lock Out Threshold Thermal Shutdown Nov. 2011 90 DMAX TSD % Rising 2.4 V Falling 2.3 V Hysteresis 0.1 V Hysteresis=30°C 160 °C Rev. 1. 0 BCD Semiconductor Manufacturing Limited 5 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics Figure 4. Efficiency vs. Output Current Nov. 2011 Figure 5. Efficiency vs. Output Current Figure 6. 2.5V Load Regulation Figure 7. 1.8V Load Regulation Rev. 1. 0 BCD Semiconductor Manufacturing Limited 6 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Figure 8. 2.5V Line Regulation Figure 9. 1.8V Line Regulation Figure 10. Efficiency vs. Output Current Nov. 2011 Figure 11. Efficiency vs. Output Current Rev. 1. 0 BCD Semiconductor Manufacturing Limited 7 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Nov. 2011 Figure 12. 1.2V Load Regulation Figure 13. 1.0V Load Regulation Figure 14. 1.2V Line Regulation Figure 15. 1.0V Line Regulation Rev. 1. 0 BCD Semiconductor Manufacturing Limited 8 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Figure 16. Efficiency vs. Output Current Figure 17. Frequency vs. Input Voltage Figure 18. 3.3V Load Regulation Nov. 2011 Figure 19. Temperature vs. Output Current Rev. 1. 0 BCD Semiconductor Manufacturing Limited 9 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Figure 20. EN Pin Threshold vs. Input Voltage Figure 21. FB Voltage vs. Output Current Figure 22. VOUT Ripple (VIN=5V, VOUT=3.3V, IOUT=500mA) Nov. 2011 Figure 23. Dynamic Mode (Load=200mA to 1200mA, VIN=5V, VOUT=3.3V) Rev. 1. 0 BCD Semiconductor Manufacturing Limited 10 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Figure 24. VOUT Ripple (VIN=5V, VOUT=3.3V, IOUT=1A) Figure 25. Dynamic Mode (Rising) Figure 26. VOUT Ripple (VIN=5V, VOUT=3.3V, IOUT=2A) Nov. 2011 Figure 27. Dynamic Mode (Falling) Rev. 1. 0 BCD Semiconductor Manufacturing Limited 11 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Figure 28. EN Pin, Low to High (VIN=5V, VOUT=3.3V, IOUT=100mA) Figure 29. Soft Start (VIN=5V, VOUT=3.3V, IOUT=0A) Figure 30. EN Pin, Low to High (VIN=5V, VOUT=3.3V, IOUT=1A) Nov. 2011 Figure 31. Soft Start (VIN=5V, VOUT=3.3V, IOUT=1A) Rev. 1. 0 BCD Semiconductor Manufacturing Limited 12 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Performance Characteristics (Continued) Figure 32. EN Pin, High to Low (VIN=5V, VOUT=3.3V, IOUT=1A) Nov. 2011 Figure 33. OTP Rev. 1. 0 BCD Semiconductor Manufacturing Limited 13 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Application Information qw The basic AP3431 application circuit is shown in Figure 35, external components selection is determined by the load current and is critical with the selection of inductor and capacitor values. deviations do not much relieve. The selection of COUT is determined by the Effective Series Resistance (ESR) that is required to minimize output voltage ripple and load step transients, as well as the amount of bulk capacitor that is necessary to ensure that the control loop is stable. Loop stability can be also checked by viewing the load step transient response as described in the following section. The output ripple, △VOUT, is determined by: 1. Inductor Selection For most applications, the value of inductor is chosen based on the required ripple current with the range of 1µH to 6.8µH. ∆VOUT ≤ ∆I L [ ESR + V 1 ∆I L = VOUT (1 − OUT ) f ×L VIN The output ripple is the highest at the maximum input voltage since △IL increases with input voltage. The largest ripple current occurs at the highest input voltage. Having a small ripple current reduces the ESR loss in the output capacitor and improves the efficiency. The highest efficiency is realized at low operating frequency with small ripple current. However, larger value inductors will be required. A reasonable starting point for ripple current setting is △IL=40%IMAX . For a maximum ripple current stays below a specified value, the inductor should be chosen according to the following equation: L =[ 3. Load Transient A switching regulator typically takes several cycles to respond to the load current step. When a load step occurs, VOUT immediately shifts by an amount equal to △ILOAD×ESR, where ESR is the effective series resistance of output capacitor. △ILOAD also begins to charge or discharge COUT generating a feedback error signal used by the regulator to return VOUT to its steady-state value. During the recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. VOUT VOUT ][1 − ] f × ∆I L ( MAX ) VIN ( MAX ) 4. Output Voltage Setting The DC current rating of the inductor should be at least equal to the maximum output current plus half the highest ripple current to prevent inductor core saturation. For better efficiency, a lower DC-resistance inductor should be selected. The output voltage of AP3431 can be adjusted by a resistive divider according to the following formula: VOUT = V REF × (1 + 2. Capacitor Selection I RMS = I OMAX VOUT R1 FB 1 2 AP3431 R2 GND It indicates a maximum value at VIN=2VOUT, where IRMS=IOUT/2. This simple worse-case condition is commonly used for design because even significant Nov. 2011 R1 R ) = 0.8V × (1 + 1 ) R2 R2 The resistive divider senses the fraction of the output voltage as shown in Figure 34. The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: [V (V − VOUT )] × OUT IN VIN 1 ] 8 × f × COUT Figure 34. Setting the Output Voltage Rev. 1. 0 BCD Semiconductor Manufacturing Limited 14 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Application Information (Continued) the VIN and this effect will be more serious at higher input voltages. 5. Short Circuit Protection When the AP3431 output node is shorted to GND, as VFB drop under 0.4V, the chip will enter soft-start mode to protect itself, when short circuit is removed, and VFB rise over 0.4V, the AP3431 recover back to normal operation again. If the AP3431 reach OCP threshold while short circuit, the AP3431 will enter soft-start cycle until the current under OCP threshold. 6.2 I2R losses are calculated from internal switch resistance, RSW and external inductor resistance RL. In continuous mode, the average output current flowing through the inductor is chopped between power PMOSFET switch and NMOSFET switch. Then, the series resistance looking into the SW pin is a function of both PMOSFET and NMOSFET RDS(ON) resistance and the duty cycle (D) are as follows: 6. Efficiency Considerations The efficiency of switching regulator is equal to the output power divided by the input power times 100%. It is usually useful to analyze the individual losses to determine what is limiting efficiency and which change could produce the largest improvement. Efficiency can be expressed as: RDS(ON) resistance and the duty cycle (D): RSW = RDS (ON )P × D + RDS (ON ) N × (1 − D ) Therefore, to obtain the I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. Efficiency=100%-L1-L2-….. Other losses including CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2 % of total additional loss. Where L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the regulator produce losses, two major sources usually account for most of the power losses: VIN quiescent current and I2R losses. The VIN quiescent current loss dominates the efficiency loss at very light load currents and the I2R loss dominates the efficiency loss at medium to heavy load currents. 7. Thermal Characteristics In most applications, the part does not dissipate much heat due to its high efficiency. However, in some conditions when the part is operating in high ambient temperature with high RDS(ON) resistance and high duty cycles, such as in LDO mode, the heat dissipated may exceed the maximum junction temperature. To avoid the part from exceeding maximum junction temperature, the user should do some thermal analysis. The maximum power dissipation depends on the layout of PCB, the thermal resistance of IC package, the rate of surrounding airflow and the temperature difference between junction and ambient. 6.1 The VIN quiescent current loss comprises two parts: the DC bias current as given in the electrical characteristics and the internal MOSFET switch gate charge currents. The gate charge current results from switching the gate capacitance of the internal power MOSFET switches. Each cycle the gate is switched from high to low, then to high again, and the packet of charge, dQ moves from VIN to ground. The resulting dQ/dt is the current out of VIN that is typically larger than the internal DC bias current. In continuous mode, 8. PCB Layout Considerations When laying out the printed circuit board, the following checklist should be used to optimize the performance of AP3431. I GATE = f × (Q P + Q N ) Where QP and QN are the gate charge of power PMOSFET and NMOSFET switches. Both the DC bias current and gate charge losses are proportional to Nov. 2011 1) The power traces, including the GND trace, the SW trace and the VIN trace should be kept direct, short and wide. 2) Put the input capacitor as close as possible to the V Rev. 1. 0 BCD Semiconductor Manufacturing Limited 15 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Application Information (Continued) -IN and GND pins. 3) The FB pin should be connected directly to the feedback resistor divider. Nov. 2011 4) Keep the switching node, SW, away from the sensitive FB pin and the node should be kept small area. Rev. 1. 0 BCD Semiconductor Manufacturing Limited 16 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Typical Application Note 2: VOUT = V FB × (1 + R1 ) . R2 Figure 35. Typical Application Circuit of AP3431 Table 1. Component Guide Nov. 2011 VOUT(V) R1(kΩ) R2(kΩ) L1(µH) 3.3 31.25 10 2.2 2.5 21.5 10 2.2 1.8 12.5 10 2.2 1.2 5 10 2.2 1.0 3 10 2.2 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 17 Data Sheet 1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Mechanical Dimensions SOIC-8 4.700(0.185) 5.100(0.201) 7° Unit: mm(inch) 0.320(0.013) 1.350(0.053) 1.750(0.069) 8° 8° 7° 0.675(0.027) 0.725(0.029) D 5.800(0.228) 1.270(0.050) 6.200(0.244) TYP D 20:1 0.300(0.012) R0.150(0.006) 0.100(0.004) 0.800(0.031) 0.200(0.008) 0° 8° 1.000(0.039) 3.800(0.150) 4.000(0.157) 0.330(0.013) 0.510(0.020) 0.190(0.007) 0.250(0.010) 0.900(0.035) 1° 5° R0.150(0.006) 0.450(0.017) 0.800(0.031) Note: Eject hole, oriented hole and mold mark is optional. Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 18 BCD Semiconductor Manufacturing Limited http://www.bcdsemi.com IMPORTANT NOTICE IMPORTANT NOTICE BCD Semiconductor BCD Semiconductor Manufacturing Manufacturing Limited Limited reserves reserves the the right right to to make make changes changes without without further further notice notice to to any any products products or or specifispecifications herein. cations herein. BCD BCD Semiconductor Semiconductor Manufacturing Manufacturing Limited Limited does does not not assume assume any any responsibility responsibility for for use use of of any any its its products products for for any any particular purpose, particular purpose, nor nor does does BCD BCD Semiconductor Semiconductor Manufacturing Manufacturing Limited Limited assume assume any any liability liability arising arising out out of of the the application application or or use use of any of any its its products products or or circuits. circuits. 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