EV-110 AAT1157 EVAL 1MHz 1.4A Buck Regulator Introduction The AAT1157 evaluation board demonstrates performance, along with the suggested size and placement of external components, for the AAT1157 integrated buck regulator. The external components are selected for minimum size and optimum operation up to 1.4A output current. Resistors R3 and R4 set the output voltage. Please refer to the AAT1157 product datasheet for more details about this product. Layout As with all switching power supplies, board layout for the AAT1157 is critical (see Figure 1). Special care has been taken with the placement of the external components. The input capacitor (C1) placement is critical. It must be located immediately adjacent to the AAT1157. As shown in Figure 2, the LX node trace has been routed under C1 in order to facilitate a close placement of C1 next to the IC. The output voltage feedback trace has been routed on the portion of the back side of the board which has a ground plane on the top side (see Figure 3). The trace is also routed to avoid the LX node and associated noise. Enable 12 C1 10µF VP FB VP LX VP LX 7 100kΩ 9 14 13 EN LX N/C 6 R6 100kΩ L1 3.0µH 16 VCC C2 0.1µF R3 15 10 R2 VOUT+ 4 11 R1 100Ω LX U1 AAT1157 VIN+ 3 LL PGND N/C PGND 8 2 5 C3-C7 2x 22µF R4 59kΩ 1 SGND PGND GND LL GND Figure 1: AAT1157 Evaluation Board Schematic. Specification Input Voltage Output Error Voltage Output Current Test Conditions Min Typ Max Units 2.7 3.6 ±3 5.5 V % A 0 1.4 Table 1: AAT1157 Evaluation Board Specification. EV-110.2005.04.1.1 1 EV-110 AAT1157 EVAL 1MHz 1.4A Buck Regulator Figure 2: AAT1157 Evaluation Board PCB Top Side. Figure 3: AAT1157 Evaluation Board PCB Bottom Side. Test Equipment 1. 6.0V, 2.0A laboratory power supply: HP33401A or equivalent. 2. DC 0A to 1.4A capable of operation down to 0.6V: Keithley 2400 or equivalent. (When using the Keithley 2400, set the meter to operate in voltage source mode and set the load current by varying the current compliance [maximum current] of the meter.) 3. DC voltmeter: HP34401A or equivalent. 4. Oscilloscope: Tektronix TDS744A or equivalent. Setup and Test A. Load and Line Regulation (see connection diagram in Figure 4) 1. Apply a DC power supply and DC voltmeter across input voltage terminals VIN+ (positive terminal) and GND (negative terminal or return). 2. Apply a DC load and DC voltmeter to output terminals VO+ and GND. 3. Vary the load from 0A to 1.4 A and the input voltage from 2.7V to 5.5V while monitoring the output voltage. 4. 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. Short-Circuit and Over-Temperature Protection 1. Raise the input voltage to 5.5V. 2. Apply a short from VO+ to GND at the evaluation board terminals. 3. Remove the short and verify that the output returns to its initial value. C. Light Load Select 1. Remove the load from the output. 2. While monitoring the input current and the LX node with an oscilloscope, short the LL pin high to the input voltage. 3. The input current should increase from approximately 270µA to 5.5mA and the LX node should increase from single pulse light load (LL) mode to a 1.25MHz constant switching frequency. 2 EV-110.2005.04.1.1 EV-110 AAT1157 EVAL 1MHz 1.4A Buck Regulator D. Enable Input 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. 1.500V Voltmeter Load 0-1.4A Power Supply 3.650V 0.147A Oscilloscope 3.600V Voltmeter Figure 4: AAT1157 Connection Diagram. Component U1 C3-C7 C1 C2 R1 R2 R3 R4 L1 Part Number Description AAT1157IVN-0.6-T1 GRM21BR60J106KE19 GRM21BR60J226KE19 GRM319R60J106KE01 GRM155R61A104KA01 Chip Resistor Chip Resistor Chip Resistor Chip Resistor CDRH5D28-3R0 CDRH5D28-2R5 1MHz 1.4A Buck Converter 10µF, 6.3V, X5R, 10%, 0805 (see Table 3) 22µF, 6.3V, X5R, 10%, 0805 (see Table 3) 10µF, 6.3V, X5R, 10%, 1206 0.1µF, 25V,X5R, 10%, 0402 100kΩ, 5%, 1/16W, 0402 100kΩ, 5%, 1/16W, 0402 See Table 3, 1%, 1/16W, 0402 59K, 1%, 1/16W, 0402 3.0µH 24mΩ 2.4A Shielded (see Table 3) 2.5µH 18mΩ 2.6A Shielded (see Table 3) Manufacturer AnalogicTech MuRata MuRata MuRata Vishay Vishay Vishay Vishay Sumida Table 2: AAT1157 EVAL Bill of Materials. EV-110.2005.04.1.1 3 EV-110 AAT1157 EVAL 1MHz 1.4A Buck Regulator Output Voltage For an adjustable output, set R4 to 59kΩ and select R3 according to Table 3. VO (V) Ω) R1 (kΩ C3-C7 (µF) L1 (µH) 0.8 1.0 1.25 1.3 1.4 1.5 1.6 1.7 1.8 1.85 1.9 2.0 2.1 2.2 2.3 2.4 2.5 3.3 19.6 39.2 63.4 68.1 78.7 88.7 97.6 110 118 121 127 137 147 158 169 178 187 267 3x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 2x 22 22 2.5 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Ω). Table 3: Component Selection for Adjustable Output Voltage (R4 = 59kΩ 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, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. 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. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 4 EV-110.2005.04.1.1 Form#: FOR001 Rev. D