EV-107 AAT1155 EVAL 1MHz 2.5A Buck DC/DC Converter Introduction The AAT1155 evaluation board demonstrates performance, along with the suggested size and placement of external components, for the AAT1155 integrated buck regulator. The external components are selected for minimum size and optimum operation up to 2.5A output current. Please refer to the AAT1155 product datasheet for more details about this product. Component Summary Capacitor C4 is a high equivalent series resistance (ESR) tantalum capacitor for damping the high Q input network associated with the inductance of the leads feeding the input power to the evaluation board and the low ESR 10µF ceramic input capacitor (C1). R2 is a pull-up resistor to allow the enable pin to be used to enable and disable the IC by either shorting the enable pin to GND or leaving the pin open. Both R2 and C4 are for demonstration purposes only and are not necessary in the final solution. Resistors R3 and R4 are used with the 1V model to set the output voltage to any desired value from 1.0V to as high as 200mV below the minimum input voltage. They are not required for the fixed output voltage versions of the AAT1155. For fixed output voltage versions, R4 is omitted and R3 is replaced with a short. Layout As with all switching power supplies, the board layout for the AAT1155 is critical (see Figure 1). Special care has been taken with the placement of the external components. The input capacitor (C1) placement is critical and it must be located immediately adjacent to the AAT1155. As shown in Figure 2, the LX node trace has been routed under C1 in order to facilitate placement of C1 close 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 routed to avoid the LX node and associated noise. VIN+ VOUT+ R1 100 C4 100µF U1 AAT1155 R3 1 R2 100k 2 Enable C1 10µF C3 0.1µF VP 8 GND LX 7 FB 3 EN LX 6 4 VCC VP 5 LX R4 10.0k L1 1.5µH C2 CR1 B340LA 120µF GND C1: Murata 10µF 6.3V X5R GRM42-6X5R106K6.3 Figure 1: AAT1155 Evaluation Board Schematic. EV-107.2005.01.1.0 1 EV-107 AAT1155 EVAL 1MHz 2.5A Buck DC/DC Converter Specification Test Conditions Input Voltage Output Error Voltage Output Current Min Typ Max Units 2.7 3.6 ±3 5.5 V % A 0 2.5 Table 1: AAT1155 Evaluation Board Specifications. Figure 2: AAT1155 Evaluation Board PCB Top Side. Figure 3: AAT1155 Evaluation Board PCB Bottom Side. Test Equipment 1. 6V, 5A laboratory power supply: HP33401A or equivalent. 2. DC 0A to 2.5A load capable of operation down to 1.0V: Keithley 2400 or equivalent. When using the Keithley 2400, set the meter to zero volts 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 2.5A 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 board should not vary by more than ±3% of the nominal voltage. 2 EV-107.2005.01.1.0 EV-107 AAT1155 EVAL 1MHz 2.5A Buck DC/DC Converter 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 output returns to its initial value. C. Enable Input and Power OK 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. 3.600V Oscilloscope Voltmeter Power Supply 3.650V 0.147A 1.500V Voltmeter Load 0-2.5A Figure 4: AAT1155 Connection Diagram. EV-107.2005.01.1.0 3 EV-107 AAT1155 EVAL 1MHz 2.5A Buck DC/DC Converter Component Part Number U1 U1 U1 U1 CR1 C2 C4 C1 C3 R1 R2 L1 R3 R4 Description AAT1155IKS-1.0-T1 AAT1155IKS-1.8-T1 AAT1155IKS-2.5-T1 AAT1155IKS-3.3-T1 B340LA 594D127X96R6R3C2T 565D107X0016C GRM319R60J106KE01 GRM155R61A104KA01 Chip Resistor Chip Resistor CDRH6D28-1R5 Chip Resistor Chip Resistor 1.0V 850kHz 2.5A Buck Converter 1.8V 850kHz 2.5A Buck Converter 2.5V 850kHz 2.5A Buck Converter 3.3V 850kHz 2.5A Buck Converter Low VF 3A 40V Schottky Diode 120µF, 6.3V, Tantalum 100µF, 16V, Tantalum 10µF, 6.3V, X5R, 10%, 1206 0.1µF, 25V, X5R, 10%, 0402 100kΩ, 5%, 1/16W, 0402 100kΩ, 5%, 1/16W, 0402 1.5µH Shielded AAT1155IKS-1.0-T1 Table 3, 1%, 1/16W, 0402 AAT1155IKS-1.1-T1 thru 0Ω, 0402 AAT1155IKS-3.3 -T1 AAT1155IKS-1.0-T1 10kΩ, 1%, 1/16W; 0402 (when output is >1.0V only, otherwise not needed) AAT1155IKS-1.1-T1 thru AAT1155IKS-3.3 -T1 Manufacturer AnalogicTech AnalogicTech AnalogicTech AnalogicTech Diodes Inc. Vishay Vishay MuRata MuRata Vishay Vishay Sumida Vishay Vishay Vishay n/a Table 2: AAT1155 EVAL Bill of Materials. 4 EV-107.2005.01.1.0 EV-107 AAT1155 EVAL 1MHz 2.5A Buck DC/DC Converter Output Voltage For an adjustable output, set R4 to 10kΩ and select R3 according to Table 3 using the AAT1155IKS-1.0-T1. VO (V) Ω) R3 (kΩ 1.0 1.1 1.2 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 0.00 (short) 1.00 2.00 2.55 3.01 4.02 4.99 6.04 6.98 8.06 8.45 9.09 10.0 11.0 12.1 13.0 14.0 15.0 23.2 Ω). Table 3: Resistor Selection for Adjustable Output Voltage (R4 = 10kΩ EV-107.2005.01.1.0 5 EV-107 AAT1155 EVAL 1MHz 2.5A Buck DC/DC Converter EV-107.2005.01.1.0 6