AP3431 BCDSEMI | Alldatasheet

Document overview

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Technical content

Features

  • High Efficiency Buck Power Converter
  • Output Current: 2A
  • Low R DS(ON) Internal Switches : 120mΩ(VIN=5V)
  • Adjustable Output Voltage from 0.8V to 0.9×V IN
  • 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

  • LCD TV
  • Set Top Box
  • Post DC-DC Voltage Regulation
  • PDA and Notebook Computer

Figure 1. Package Type of AP3431

Figure 2. Pin Configuration of AP3431 (Top View)

1 VCC Supply input for the analog circuit

2 NC No connection

3 GND Ground pin

6 PGND Power switch ground pin

7 SW Switch output pin

8 VIN Power supply input for the MOSFET switch

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited Functional Block Diagram Figure 3. Functional Block Diagram of AP3431

Ordering Information

M: SOIC-8 Package Temperature Range Part Number Marking ID Packing Type AP3431M-G1 3431M-G1 Tube SOIC-8 -40 to 80°C AP3431MTR-G1 3431M-G1 Tape & Reel BCD Semiconductor's Pb-free products, as designated wi th "G1" in the part number, are RoHS compliant and green. G1:Green Blank: Tube TR: Tape & Reel

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited Absolute Maximum Ratings (Note 1) Parameter Symbol Value Unit Supply Input for the Analog Circuit V CC 0 to 6.0 V Power Supply Input for the MOSFET Switch V IN 0 to 6.0 V SW Pin Switch V oltage V SW -0.3 to VIN+0.3 V Enable V oltage V EN -0.3 to V IN+0.3 V SW Pin Switch Current I SW 2.9 A Power Dissipation (on PCB, TA=25°C) P D 1.45 W Thermal Resistance (Junction to Ambient, Simulation) θJA 68.63 °C/W Junction Temperature T J 160 °C Operating Temperature T OP -40 to 85 °C Storage temperature T STG -55 to 150 °C ESD (Human Body Model) V HBM 2000 V ESD (Machine Model) V MM 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 Co nditions” 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 V IN 2.7 5.5 V Junction Temperature Range T J -40 125 °C Ambient Temperature Range T A -40 80 °C

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited

Electrical Characteristics

VIN=VCC=VEN=5V , VOUT=1.2V , VFB=0.8V , L=2.2µH, C IN=10µF, COUT=22µF, TA=25°C, unless otherwise specified. Parameter Symbol Conditions Min Typ Max Unit Input V oltage Range V IN 2.7 5.5 V Shutdown Current I OFF V EN=0V 4 µA Active Current I ON V FB = 0.95V 460 µA Regulated1Feedback V oltage VFB For Adjustable Output V oltage 0.784 0.8 0.816 V Regulated Output V oltage Accuracy ∆VOUT/VOUT VIN=2.7V to 5.5V , IOUT=0 to 2.0A -3 3 % Peak Inductor Current IPK 2.9 A Oscillator Frequency f OSC V IN = 2.7V to 5.5V 1.0 MHz PMOSFET RON R ON(P) V IN = 5V 120 m Ω NMOSFET RON R ON(N) V IN = 5V 120 m Ω EN High-level Input V oltage VEN_H 1.5 V EN Low-level Input V oltage VEN_L 0.4 V EN Input Current I EN 2 µA Soft-start Time t SS 450 µs Maximum Duty Cycle DMAX 90 % Rising 2.4 V Falling 2.3 V Under V oltage Lock Out Threshold Hysteresis 0.1 V Thermal Shutdown T SD Hysteresis=30°C 160 °C

Figure 32. EN Pin, High to Low Figure 33. OTP (VIN=5V, VOUT=3.3V, IOUT= 1 A )

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited FB GND VOUT R2AP3431

Application Information

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. 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. 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 △I L=40%IMAX . For a maximum ripple current stays below a specified value, the inductor should be chosen according to the following equation: 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. 2. Capacitor Selection The input capacitance, C IN, 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 RM S capacitor current is given by: It indicates a maximum value at V IN=2VOUT, where IRMS=IOUT/2. This simple worse-case condition is commonly used for design because even significant qw deviations do not much relieve. The selection of C OUT 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, △V OUT, is determined by: The output ripple is the highest at the maximum input voltage since △IL increases with input voltage. 3. Load Transient A switching regulator typically takes several cycles to respond to the load curren t 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 V OUT to its steady-state value. During the recovery time, V OUT can be monitored for overshoot or ringing that would indicate a stability problem. 4. Output Voltage Setting The output voltage of AP3431 can be adjusted by a resistive divider according to the following formula: The resistive divider senses the fraction of the output voltage as shown in Figure 34. Figure 34. Setting the Output Voltage

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited Application Information (Continued) 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 V FB 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. 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: Efficiency=100%-L1-L2-….. 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: V IN quiescent current and I2R losses. The V IN 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.

6.1 The V

IN 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 V IN to ground. The resulting dQ/dt is the current out of V IN that is typically larger than the internal DC bias current. In continuous mode, Where Q P and Q N are the gate charge of power PMOSFET and NMOSFET switches. Both the DC bias current and gate charge losses are proportional to the V IN and this effect will be more serious at higher input voltages. 6.2 I 2R losses are calculated from internal switch resistance, R SW and external inductor resistance R L. 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 R DS(ON) resistance and the duty cycle (D) are as follows: R DS(ON) resistance and the duty cycle (D): Therefore, to obtain the I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. Other losses including C IN and C OUT ESR dissipative losses and inductor core losses generally account for less than 2 % of total additional loss. 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 R DS(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. 8. PCB Layout Considerations When laying out the printed circuit board, the following checklist should be used to optimize the performance of AP3431. 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 )( NPGATE QQfI +×= () () )( DRDRR NONDSPONDSSW −×+×= 1

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited Application Information (Continued) -IN and GND pins. 3) The FB pin should be connected directly to the feedback resistor divider. 4) Keep the switching node, SW, away from the sensitive FB pin and the node should be kept small area.

Figure 35. Typical Application Circuit of AP3431 Table 1. Component Guide

1.0MHz, 2.0A, Synchronous Step Down DC-DC Converter AP3431 Nov. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited Mechanical Dimensions S O I C - 8 U n i t : m m ( i n c h ) R0.150(0.006) R0.150(0.006) 1.000(0.039) 0.330(0.013) 0.510(0.020) 1.350(0.053) 1.750(0.069) 0.100(0.004) 0.300(0.012) 0.900(0.035) 0.800(0.031) 0.200(0.008) 3.800(0.150) 4.000(0.157) 20:1 D 1.270(0.050) TYP 0.190(0.007) 0.250(0.010) D 5.800(0.228) 6.200(0.244) 0.675(0.027) 0.725(0.029) 0.320(0.013) 0.450(0.017) 0.800(0.031) 4.700(0.185) 5.100(0.201) Note: Eject hole, oriented hole and mold mark is optional.

BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifi- cations herein. BCD Semiconductor Manufacturing Limited does not assume any responsibility for use of any its products for any particular purpose, nor does BCD Semiconductor Manufacturing Limited assume any liability arising out of the application or use of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or other rights nor the rights of others. - Wafer Fab Shanghai SIM-BCD Semiconductor Manufacturing Limited 800, Yi Shan Road, Shanghai 200233, China Tel: +86-21-6485 1491, Fax: +86-21-5450 0008 BCD Semiconductor Manufacturing Limited MAIN SITE REGIONAL SALES OFFICE Shenzhen Office Shanghai SIM-BCD Semiconductor Manufacturing Co., Ltd. Shenzhen Office Advanced Analog Circuits (Shanghai) Corporation Shenzhen Office Room E, 5F, Noble Center, No.1006, 3rd Fuzhong Road, Futian District, Shenzhen 518026, China Tel: +86-755-8826 7951 Fax: +86-755-8826 7865 Taiwan Office BCD Semiconductor (Taiwan) Company Limited 4F, 298-1, Rui Guang Road, Nei-Hu District, Taipei, Taiwan Tel: +886-2-2656 2808 Fax: +886-2-2656 2806 USA Office BCD Semiconductor Corporation 30920 Huntwood Ave. Hayward, CA 94544, U.S.A Tel : +1-510-324-2988 Fax: +1-510-324-2788 - IC Design Group Advanced Analog Circuits (Shanghai) Corporation 8F, Zone B, 900, Yi Shan Road, Shanghai 200233, China Tel: +86-21-6495 9539, Fax: +86-21-6485 9673 BCD Semiconductor Manufacturing Limited http://www.bcdsemi.com BCD Semiconductor Manufacturing Limited IMPORTANT NOTICE BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifi- cations herein. BCD Semiconductor Manufacturing Limited does not assume any responsibility for use of any its products for any particular purpose, nor does BCD Semiconductor Manufacturing Limited assume any liability arising out of the application or use of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or other rights nor the rights of others. - Wafer Fab Shanghai SIM-BCD Semiconductor Manufacturing Co., Ltd.

800 Yi Shan Road, Shanghai 200233, China

Tel: +86-21-6485 1491, Fax: +86-21-5450 0008 MAIN SITE REGIONAL SALES OFFICE Shenzhen Office Shanghai SIM-BCD Semiconductor Manufacturing Co., Ltd., Shenzhen Office Unit A Room 1203, Skyworth Bldg., Gaoxin Ave.1.S., Nanshan District, Shenzhen, China Tel: +86-755-8826 7951 Fax: +86-755-8826 7865 Taiwan Office BCD Semiconductor (Taiwan) Company Limited 4F, 298-1, Rui Guang Road, Nei-Hu District, Taipei, Taiwan Tel: +886-2-2656 2808 Fax: +886-2-2656 2806 USA Office BCD Semiconductor Corp. 30920 Huntwood Ave. Hayward, CA 94544, USA Tel : +1-510-324-2988 Fax: +1-510-324-2788 - Headquarters BCD Semiconductor Manufacturing Limited No. 1600, Zi Xing Road, Shanghai ZiZhu Science-based Industrial Park, 200241, China Tel: +86-21-24162266, Fax: +86-21-24162277