EV136 AAT1145 EVAL:1.5 MHz, 1.2A Step-Down DC/DC Converter with Low Quiescent Current Introduction The AAT1145 Evaluation Board contains a fully tested 1.2A, 1.5MHz step-down DC/DC regulator. The circuit has an input voltage range of 2.5V to 5.5V and a 1.8V output capable of delivering up to 1.2A output current with a 3.6V VIN. The output is adjustable from 0.6V to VIN. The circuit can provide up to 96% efficiency and it consumes less than 1µA in shutdown mode. In light load mode operation there is very low output ripple voltage for noise-sensitive applications. The AAT1145 comes in a small 10-pin DFN package, which has an exposed pad on the bottom-side of the IC for better thermal performance. The board has a ground pad just below the exposed pad for reliable soldering and better thermal dissipation. These features, plus the nominal operating frequency of 1.5MHz allowing the use of low profile surface mount components, make the AAT1145 an ideal circuit for use in battery-powered, hand-held applications. Figure 1: AAT1145 Evaluation Board. Layout Guidelines The following guidelines should be followed to ensure proper operation of the AAT1145: 1. The Exposed Pad (EP) must be reliably soldered to GND. A large pad under the device is strongly recommended for heat sinking purposes. 2. The power traces, including the GND trace, the LX-to-L1-to-VOUT trace and the VIN-to-IN trace should be kept short, direct and wide to allow large current flow. Put many multiple-layer VIA pads when connecting traces change between layers. 3. Connect the input capacitor C1 to the IN and AIN pins as close as possible to get good power filtering. 4. Keep the switching node, LX pin 7 and 8, away from the sensitive FB/OUT node. 5. To avoid large GND noise affecting the accurate reference circuit, it is recommended that pin 4 and pin 6 AGND connect to the GND plane to a single point under the device. EV-136.2007.08.1.1 1 EV136 AAT1145 EVAL:1.5 MHz, 1.2A Step-Down DC/DC Converter with Low Quiescent Current JP1 U1 AAT1145 1 2 VIN 3 C1 10μF 4 5 EN PGND IN PGND LX AIN LX AGND FB/OUT EP AGND 10 9 L1 2.2μH 8 7 VOUT SW C3 22pF R2 634k 6 C2 22μF R1 316k Figure 2: AAT1145 Evaluation Board Schematic. Specification Test Conditions Input Voltage Output Error Voltage Output Current Min Typ Max Units 2.5 3.6 ±3 5.5 V % mA 0 1200 Table 1: AAT1145 Evaluation Board Specifications. Figure 3: AAT1145 Evaluation Board PCB Top Side. 2 Figure 4: AAT1145 Evaluation Board PCB Bottom Side. EV-136.2007.08.1.1 EV136 AAT1145 EVAL:1.5 MHz, 1.2A Step-Down DC/DC Converter with Low Quiescent Current Test Equipment 1 2. 3. 4. 8.0V 5.0A laboratory power supply: Agilent E3648A or equivalent. Electronic load: Agilent N3301A DC voltmeter: Agilent 34401A or equivalent. Oscilloscope: Tektronix TDS3034B or equivalent. Setup and Test (see connection diagram in Figure 5) A: Load and Line Regulation 1. Apply a DC power supply and DC voltmeter across the input voltage terminals: VIN (positive terminal) and GND (negative terminal or return). 2. Apply a DC load and DC voltmeter to the output terminals: VOUT and GND. 3. Before turning on the supply, set the jumper to the side labeled “Enable”. 4. Vary the load from 0 to 1.2A and the input voltage from 2.5V to 5.5V while monitoring the output voltage. 5. The output voltage as measured at the output terminals of the evaluation boards should not vary by more than ±3% of the nominal voltage. B: Ripple and Shutdown Current 1. Set the output load current between 0A and 1.2A, and measure the output ripple voltage; the measurement should be less than 20 mVAC. 2. Apply 4.2V at VIN. Set the jumper from “Enable” state to GND. Measure the shutdown supply current. The supply current will be less than 1µA. C: Short-Circuit and Over-Temperature Protection 1. Raise the input voltage to 5.5V. 2. Apply a short from VOUT to GND at the evaluation board terminals. 3. Remove the short and verify that the output returns to its initial value. D: Enable Output 1. Short the Enable pin to GND. The output should decay to zero. 2. Remove the short applied to the Enable pin. The output should recover to its initial value. EV-136.2007.08.1.1 3 EV136 AAT1145 EVAL:1.5 MHz, 1.2A Step-Down DC/DC Converter with Low Quiescent Current Figure 5: AAT1145 Connection Diagram. Waveforms Ch1 (2V/div) Ch2 (10mV/div) Ch3 (200mA/div) Time (1μs/div) Figure 6: Light Load Switching Waveforms (VIN = 3.6V, VOUT = 1.8V, No Load; Ch1: (SW) LX pin, Ch2: VOUT (AC), Ch3: LX IINDUCTOR). 4 EV-136.2007.08.1.1 EV136 AAT1145 EVAL:1.5 MHz, 1.2A Step-Down DC/DC Converter with Low Quiescent Current Ch1 (2V/div) Ch2 (10mV/div) Ch3 (500mA/div) Time (1μs/div) Figure 7: Full Load Switching Waveforms (VIN = 3.6V, VOUT = 1.8V, 1.2A Load; Ch1: (SW) LX pin, Ch2: VOUT (AC), Ch3: LX IINDUCTOR). Ch1 (2V/div) Ch2 (2V/div) Ch3 (500mA/div) Time (400μs/div) Figure 8: Startup Waveforms VIN = 3.6V, VOUT = 1.8V, 3Ω Load; Ch1: EN, Ch2: VOUT, Ch3: IIN). EV-136.2007.08.1.1 5 EV136 AAT1145 EVAL:1.5 MHz, 1.2A Step-Down DC/DC Converter with Low Quiescent Current Component U1 L1 C1 C2 C3 R1 R2 Part Number Description Manufacturer AAT1145 CDRH2D14NP-2R2NC GRM21BR61C106K GRM21BR60J226M C1005COG1H220JT000P Chip Resistor Chip Resistor 1.5 MHz,1.2A Synchronous Step-Down Converter Inductor 2.2uH 1.5A SMD Cap Ceramic 10uF 0805 X5R 16V10% Cap Ceramic 10uF 0805 X5R 6.3V 20% Cap Ceramic 22pF 0402 C0G 50V 5% Res 316KΩ 1/16W 1% 0402 SMD Res 634kΩ 1/16W 1% 0402 SMD Analogic Tech Sumida Murata Murata TDK Any Any Table 2: AAT1145 EVAL Bill of Materials. Output Voltage There are two versions of the AAT1145, a fixed 1.8V output (AAT1145IDE-1.8) without feedback resistors R1 and R2, and an adjustable version that is set to 0.6V. To adjust the output from the 0.6V default, set R1 to 316kΩ a nd select R2 according to Table 3. A smaller value resistor divider can be used for better noise immunity, values are shown in columns 2 and 5. A larger value resistor divider is used as default for lower current consumption in columns 3 and 6. Standard 1% resistor values are substituted for calculated values. VOUT (V) R1=59kΩ R2 (kΩ) R1=316kΩ R2 (kΩ) VOUT (V) R1=59kΩ R2 (kΩ) R1=316kΩ R2 (kΩ) 0.6 0.8 0.9 1.0 1.1 1.2 1.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 0(short) 105 158 210 261 316 365 1.4 1.5 1.8 1.85 2.5 3.0 3.3 88.7 118 124 137 187 294 267 422 475 634 655 1000 1270 1430 Table 3: Resistor Selection for Adjustable Output Voltage. © 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. 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All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737- 4600 Fax (408) 737- 4611 6 EV-136.2007.08.1.1