EVALUATION BOARD DATASHEET EV-143

Transcription

1 Introduction The AAT27 is a.2mhz constant frequency, current mode PWM stepup converter. It can supply a.v output voltage at 00mA from a single AA cell. The device integrates a main switch and a synchronous rectifier for high efficiency without an external Schottky diode. A switching frequency of.2mhz allows the use of small, low profile inductors and ceramic capacitors. This demo board is designed for evaluating the AAT27. The device can supply 400mA to a.v load from a two AA cell input. Every demo board circuit is fully tested and supported with test data before shipping. Two versions of the evaluation board are introduced in this manual. The Rev. A is a more complete board with jumpers to select output voltage, bypass load disconnect circuitry, shutdown pin status, and the possibility to use a current probe to capture the inductor current waveform. The Rev. 2B evaluation board demonstrates a simplified circuit with only the essential external parts in the smallest possible solution size. This simplified board helps the user to evaluate the AAT27 s performance for minimal footprint applications. Board Picture Rev. A Rev. 2B Figure : Picture of AAT27 Rev. A and Rev. 2B Evaluation Boards. Parameter Test Conditions Min Typ Max Units Input Voltage Minimum StartUp Input Voltage 0.8 V Output Voltage Accuracy ± % Output Voltage Range 2.. V Output Current V IN =.2V, V OUT =.V 0 00 V IN = 2.4V, V OUT =.V ma Table : AAT27 Evaluation Board Specifications

2 L 4.7μH JP2 D MBR020 JP4 V IN C IN 6 4 VIN SHDN SW VOUT AAT27 FB R4 0k Q Si 20DS R.02M JP V OUT C OUT GND 2 ON /OFF Control (JP) R 0k R2A:002k 2.V B: 696 k.0v C: 604 k.v Q2 D: 24 k.0v 2N 904 Figure 2: AAT27 Evaluation Board Rev. A Schematic. L 4.7μH D MBR020 C 00pF (Opt) SW V IN C IN 6 4 VIN SHDN VOUT AAT27 FB R.02M V OUT C OUT GND R2 2 R2A:002k 2.V B:696k.0V C:604k.V D:24k.0V ON /OFF Control (JP) Figure : AAT27 Evaluation Board Rev. 2B Schematic. PCB Layout The AAT27 typically operates at.2mhz. This is a significantly high frequency for DCDC converters. For satisfactory performance, PCB layout is important with high operational frequencies. The PCB traces should be as wide and as short as possible. The inductor, input capacitor, and output capacitor should be as close as possible to the AAT27. The feedback and shutdown pin PCB traces should avoid proximity to large AC signals, such as the power inductor and switching nodes. The optional rectifier diode (D in Figure 4 and Figure 7) can improve efficiency and alleviate the stress 2

3 on the integrated power MOSFET. The diode should also be close to the inductor and the chip to form the shortest possible switching loop. While a two layer PCB layout is adequate for most applications, large multilayer ground planes are ideal for high power applications. A large area of copper has lower resistance and would help dissipate heat from the AAT27. The two demo boards described in this manual are four layer PCBs with two internal ground layers. The converter s ground should join the system ground to which it supplies power at one point only. Figure 4: AAT27 Evaluation Board Rev. A PCB Top Side. Figure : AAT27 Evaluation Board Rev. A PCB Bottom Side. Figure 6: AAT27 Evaluation Board Rev. 2B PCB Top Side. Figure 7: AAT27 Evaluation Board Rev. 2B PCB Bottom Side

4 Evaluation Setup (see Figures 4, 6, and 8) Jumper Setting JP JP2 JP JP4 Description Output voltage selector. R2A:2.V, R2B:V, R2C:.V, R2D:V (Rev.A only) Connection between inductor and SW pin, Inductor current can be probed here (Rev.A Only) Run/Shutdown selector Connection between VOUT pin and board output. Q and Q2 are designed to disconnect load from the VOUT pin when the device is shut down. Shorting this jumper will bypass this circuit and connect the VOUT pin to board output directly. (Rev.A only) Operating the Evaluation Board Apply a DC power supply and DC voltmeter across the input voltage terminals. Set the voltage at least 0.V below the output voltage, otherwise the board may not be able to work properly. Connect a dummy load between VOUT and GND. The board can operate with both electronic and resistor loads. When the load current is too high, the device may begin to limit the inductor current, and thus the output voltage may drop. Since the body diode of the integrated Pchannel synchronous rectifier MOSFET exists from the SW pin to the VOUT pin, when VOUT < VIN, current can flow from VIN to VOUT. This happens when the device is shut down. On the Rev.A board, a simple circuit has been added to isolate the load from VIN; during shutdown, the Q2 collector pin is pulled low to ground, or logic low, which will shut down Q. In normal operation, the base pin of Q2 is logic high, thus the gate of Q2 is low and Q is conducting. The user can bypass this function by connecting JP4. Load and Line Regulation. Before beginning operation, set JP to the VOUT voltage position (R2A = 2.V, R2B =.0V, R2C =.V and R2D =.0V) and set JP from SHDN to RUN. 2. Vary the load and the input voltage while monitoring the output voltage.. The output voltage as measured at the output terminals of the evaluation boards should not vary by more than ±% of the nominal voltage. A V V A Load Figure 8: AAT27 Connection Diagram. 4

5 Component Part Number Description Manufacturer U AAT27.2 MHz, 600mA Micropower Synchronous StepUp Converter Analogic Tech L CDRHD6NP4R7NC Inductor 4.7μH 2.A Sumida C IN, C OUT GRM426X7R47K6PT Ceramic Cap 6V X7R 206 Murata D MBR020LT Schottky Diode 0.A 20V Onsemi Q Si20DS (optional) PChannel.2W,.8V (GS) MOSFET Vishay Q2 2N904 NPN General Purpose Amplifier Fairchild R, R2A, R ERJEKF004V Res MΩ /6W % 060 Panasonic R2B ERJEKF698V Res 698kΩ /6W % 060 Panasonic R2C ERJEKF604V Res 604KΩ /6W % 060 Panasonic R2D ERJEKF24V Res 24KΩ /6W % 060 Panasonic R4, R ERJEKF0V Res 0KΩ /6W % 060 Panasonic Table 2: AAT27 Evaluation Board Rev. A Bill of Materials. Component Part Number Description Manufacturer C GRM88CH0JA0 Ceramic Cap 00pF 0V C0G 060 Murata C LLL8R7A04MA0 Ceramic Cap 00nF 0V X7R 060 Murata C IN GRM29R6A47KE9 Ceramic Cap 0V XR 080 Murata C OUT GRM29R6A47KE9 Ceramic Cap 0V XR 080 Murata D MBR020LT Schottky Diode 0.A 20V Onsemi L CDRH2D094R7NC 4.7μH Sumida R ERJEKF004V Res MΩ /6W % 060 Panasonic R2 ERJEKF604V Res 604kΩ /6W % 060 Panasonic R ERJEKF004V Res MΩ /6W % 060 Panasonic U AAT27.2MHz, 600mA Micropower Synchronous StepUp Converter AnalogicTech Table : AAT27 Evaluation Board Rev. 2B Bill of Materials. Output Voltage Setting The reference voltage of AAT27 is.2v. The user can change R and R2 to obtain needed output voltage by this formula: V = R R2 OUT R2.2V The maximum V OUT is.v. Advanced Analogic Technologies, Inc. 20 Scott Boulevard, Santa Clara, CA 904 Phone (408) Fax (408) 7746 Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders