Evaluation Board for the AAT1275 Boost Converter with USB Power Switch

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1 Introduction EVALUATION BOARD DATA SHEET The AAT1275 evaluation board provides a platform for test and evaluation of the AAT1275 switching boost converter with USB Power Switch. The evaluation board demonstrates suggested size and placement of external components to achieve 5V output voltages and up to 500mA output load current to support USB V BUS operation from an input supply as low as 2.7V. The external components are selected for small size to suit portable applications while the layout has been optimized to achieve high efficiency and low output noise with the TSOPJW-12 package. The design operates across an input voltage range from 2.7 to 5V. This document provides details on the operation and test of the AAT1275 Evaluation Board. Modification of the resistor divider network (R2, R3) allows different output voltages. The load switch current limit level at OUT2 is determined by R SET (R4) value (see Table 1). When the OUT2 pin load current has exceeded current limit level the AAT1275 shuts down to minimize the power dissipation and component stresses under over load and short circuit conditions. Schematic and BOM V IN L1 2.2µH 4 U1 AAT1275 SW FLT 8 R1 10kΩ FLT V IN GND C6 120µF CCase R4 16.9kΩ C3 4.7µF 10V LIN SET GND VCC VIN OUT2 OUT1 6 5 EN 12 FB 9 PGND 3 R2 432kΩ R3 59kΩ V O1 J5 C2 4.7µF 10V C1 4.7µF V O2 GND V IN GND Enable Figure 1: AAT1275 Evaluation Board Schematic (AAT1275-DB1) Symbol Description U1 AAT1275 TSOPJW-12 L1 2.2μH, CDRH2D14-2R2 Sumida 3.2x3.2x1.55mm, 94mΩ C1, C2, C3, C5 4.7μF 10V 0805 C4 100pF 10V 0402 C6 120μF 10V (optional) R1 10kΩ 1% 0402 R2 432kΩ 1% 0402 R3 59kΩ 1% 0402 R4 16.9kΩ 1% 0402 R5 10Ω 1% 0402 Table 1: AAT1275 Bill of Materials. 1

2 Test Equipment EVALUATION BOARD DATA SHEET 1. Unit under test (UUT) is the AAT1275 Evaluation Board. 2. One (1) XT30-2 Power Supplies or equivalent. 3. HP6060B DC Electronic Load or equivalent. 4. Two (2) Fluke 189 DC voltmeters or equivalent. Set to DCV setting. 5. Oscilloscope Tektronix TDS3054B or equivalent, three (3) Tek P6139A oscilloscope voltage probes or equivalent, and one Tektronix TCP V 15A peak current probe. 6. Line Transient and Load Transient boards. 7. Miscellaneous test leads (banana plug to clip lead type is recommended). Setup and Test Test: Load Switch Current Limit versus R SET 1. Configure the specified test equipment as shown in Figure Enable the UUT jumper JP1 to the ON position. 3. Set the HP6060B DC Electronic Load to Constant Voltage Mode (CV) and clamp its voltage at 4.9V. 4. Turn on input power supply and set to the designed voltage (4.0V) while monitoring the V OUT2, and I OUT2 on the oscilloscope. 5. Vary the clamped voltage on the HP6060B DC Electronic Load with different values (4.8V, 4.7V,,4.0V) until the V OUT2 and I OUT2 turn OFF and ON periodically. 6. Use horizontal cursors to measure the Load Switch Current Limit on the oscilloscope. 7. Repeat step 2 to 5 for different values of R SET (R4) in Table 2 below. R SET (KΩ) I OUT (ma) Table 2: Load Switch Current versus R SET. 2

3 Figure 2: AAT1275 Evaluation Board Connection Diagram for Load Switch Current Limit Measurement. 3

4 Test: Load and Line Regulation 1. Configure the specified test equipment as shown in Figure Enable the UUT jumper JP1 to the on position. 3. Turn on the input power supply and set to desired input voltage based on the DC voltmeter. 4. Vary the output load from 0 to 500mA and vary the input voltage from 2.7V to 5V while monitoring the output voltage. Figure 3: AAT1275 Evaluation Board Connection Diagram for Load and Line Regulation Measurement. 4

5 Test: Start up using Enable 1. Configure the specified test equipment as shown in Figure Set the Oscilloscope to single sequence, and trigger the rising edge of V OUT. 3. Turn on input power supply and toggle EN to ON position while monitoring the EN, V OUT1, V OUT2, and I IN on the oscilloscope. 4. Repeat step #2 and step #3 for different I OUT, and V IN. Figure 4: AAT1275 Evaluation Board Connection Diagram for Start Up Measurement. 5

6 Test: Output Ripple Measurement 1. Configure Oscilloscope CH1 for output ripple measurement. Plug probe into CH1 as shown in Figure 4. a. AC Coupling, 25mV/div. b. BW 100MHz to limit high frequency pickup 2. Configure Oscilloscope auto-trigger. 3. Turn on input power supply. Set input voltage between 2.7 and 5V and adjust output load from 0 to 500mA, as desired. It should be noted that light load measurements (<20mA) may be affected by electronic load characteristics. As an alternative, parallel arrangement of 1/4W carbon film resistor(s) can be used. 4. To minimize high frequency noise pickup due to PCB parasitic and guarantee consistent results, CH1 output ripple should be measured directly across output capacitor C1, as shown in Figure 3. Probe tip contacting capacitor positive terminal. Probe ground consisting of a small bus wire wrapped around probe ground (see Figure 4). Probe Tip Probe GND Bus wire wrapped around probe ground, with probe spring tip removed Figure 5: Oscilloscope Probe Setup for Output Ripple Measurement. 6

7 Test: Line Transient Response 1. Configure the specified test equipment as shown in Figure Enable UUT by connecting the jumper to the on position. 3. Use Line Transient Response Board to generate the input voltage step by setting the first power supplies to 3.6V and the second one to 4.2V. 4. Toggle the input voltage from 3.6V to 4.2 V by setting the magnitude of the PWM to 5Vpp at 5MHz while monitoring the AC input voltage and the AC output voltage on the oscilloscope. 5. Repeat step #4 for different input voltage steps. Figure 6: AAT1275 Evaluation Board Connection Diagram for Line Transient Measurement. 7

8 Test: Load Transient Response 1. Configure the specified test equipment as shown in Figure Enable UUT by connecting the jumper to the on position. 3. Generate the step output current using a PWM (set V PP = 5V at 5KHz), a Power MOSFET, and adjustable resistors (R7, R8). 4. Adjust R7 and R8 to get the designed step output current while monitoring the step output current and the output voltage response (AC coupling) on the oscilloscope. 5. Repeat step #4 for different output current steps and over the ranges of V IN. Figure 7: AAT1275 Evaluation Board Connection Diagram for Load Transient Measurement. 8

9 Printed Circuit Board Figure 8: Top Layer (not to scale). Figure 9: Bottom Layer (not to scale) 9

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