EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Introduction The AAT2784 evaluation board provides a platform for test and evaluation of the AAT2784 3-channel 1.8MHz step-down converter. The input voltages (VP) of the three channels are connected, while their outputs are separate. The evaluation board demonstrates suggested size and placement of external components to achieve the best performance. The external components are limited and selected for small size to suit portable device applications, while the layout has been optimized to achieve high efficiency and low output noise with the TDFN34-16 package. The design operates across an input voltage range from 2.7V to 5.5V. The AAT2784 evaluation board provides an adjustable output voltage from 1V to VIN at 500mA maximum output current for channel 1 and 2, and 1.5A for channel 3. Resistors R1 and R2 program the channel 1 output to regulate at a voltage higher than 0.6V. Similarity, resistors R3 and R4 program the channel 2 output, and resistors R5 and R6 program the channel 3 output. The suggested value for R2 and R4 is 29.4kΩ, and the suggested value for R6 is 59kΩ. There are three enable pins: EN1, EN2, and EN3, corresponding to the three channels. Connecting each EN to VIN will turn on the channel, while connecting EN to GND will disable that channel. Schematic and BOM LX3 LX2 1 VIN LX1 1 1 L2 1 1 4.7µH C7 100pF R7 0 VOUT2 R3 133k 1 EN1 2 1 EN2 1 3 C5 10µF 2 C4 10µF 3 4 5 2 6 3 7 8 1 EN3 2 C1 10µF PGND2 FB2 EN1 EN2 GND VIN EN3 FB3 U1 LX2 VP1_2 LX1 PGND1 FB1 VP3 LX3 PGND3 15 L1 14 1 4.7µH 13 12 11 L3 10 C9 56pF R5 59K 3 R6 59K C6 4.7µF C2 4.7µF VOUT3 C10 10µF VOUT1 R1 133K C3 100pF 1 1.5µH 9 AAT2784 C8 10µF PGND R4 29.4k 16 R2 29.4K 1 1 PGND Figure 1: AAT2784 Evaluation Board Schematic. Symbol Description U1 C1,C4, C5, C8,C10 C2, C6 C3,C7 C9 L1, L2 L3 R1, R3 R2, R4 R5, R6 R7 AAT2784 TDFN34-16 10μF 10V 0805 4.7μF 10V 0805 100pF 10V 0402(Optional) 56pF 10V 0402 (Optional) 4.7μH 1.5μH 133KΩ 10V 0402 29.4kΩ 10V 0402 59kΩ 10V 0402 0Ω Table 1: AAT2784 Evaluation Board Build of Materials (BOM). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 1 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test Equipment 1. 2. 3. 4. 5. 6. 7. Unit under test (UUT) is the AAT2784 evaluation board. One (1) Keithley 2430 3A source meter or equivalent. Two (2) XT30-2 power supplies or equivalent. Two (2) 10Ω, 100W variable resistors, or DC electronic loads. Two (2) Fluke 189 multi-meters or equivalent. A HP33120A 15MHz function/ aArbitrary waveform generator; set to PWM setting. Oscilloscope: Tektronix TDS3054B or equivalent, three (3) Tek P6139A oscilloscope voltage probes or equivalent, and one Tektronix TCP202 300V 15A peak current probe. 8. A network analyzer. 9. Miscellaneous test leads (banana plug to clip lead type is recommended). Setup and Test Test: Line and Load Regulation Figure 2: AAT2784 Evaluation Board Connection Diagram for Line and Load Regulation Measurement. 1. 2. 3. 4. Configure the specified test equipment as shown in Figure 2. Enable channel 1 by connecting the jumper to the ‘ON’ position. Turn on the input power supply and set to desired input voltage based on the DC voltmeter. Vary the output load from 0 to 500mA and vary the input voltage from 2.7V to 5.5V while monitoring the output voltage. 5. % Error = % Error = VOUT - VNOMINAL · 100%, where VNOMINAL is the output voltage at 10mA output current. VNOMINAL 6. Repeat steps 2 through 5 for channels 2 and 3 (for channel 3, vary the output load from 0 to 1.5A). 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: Line Transient Response 1. Configure the specified test equipment as shown in Figure 3. 2. Enable channel 1 by connecting the jumper to the ‘ON’ position. 3. Use the Line Transient Response Board to generate the step input voltage 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 and over the range of VOUT and ILOAD. 6. Repeat the procedure for channels 2 and 3. Figure 3: AAT2784 Evaluation Board Connection Diagram for Line Transient Response Measurement. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 3 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: Load Transient Response 1. Configure the specified test equipment as shown in Figure 4. 2. Enable channel 3 by connecting the jumper to the ‘ON’ position. 3. Generate the step output load using a PWM (set VPP = 5V at 5KHz), a Power MOSFET, and adjustable resistors (R7, R8). 4. Adjust R7 and R8 to get the designed 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 VIN and VOUT. 6. Repeat the same procedure for channel 1 and then channel 2 with the step output load connected to VOUT1, then to VOUT2. Figure 4: AAT2784 Evaluation Board Connection Diagram for Load Transient Response Measurement. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: Quiescent Current vs. Input Voltage 1. 2. 3. 4. Configure the specified test equipment as shown in Figure 5. Enable channel 1 by connecting the jumper to the ‘ON’ position. Remove the output loads (open circuit). Replace the input power supply by Keithley 2400 3A Source meter or equivalent. Set VSRC to the designed input voltage (VSRC = VOUT + 1V), and set ICOM to 200µA. 5. Turn on the Keithley and read the compliance current (quiescent current). 6. Vary the input voltage VSRS = VOUT + 1V while monitoring the corresponding compliance current. Figure 5: AAT2784 Evaluation Board Connection Diagram for Quiescent Current. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 5 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: Startup using Enable 1. Configure the specified test equipment as shown in Figure 6. 2. Set the oscilloscope to single sequence, and trigger the rising edge of VOUT. 3. Turn on input power supply and toggle EN to ‘ON’ position while monitoring the EN1, VOUT1, LX1, and ILOAD1 on the oscilloscope. 4. Repeat steps 2 and 3 for different IOUT1, VIN, and VOUT1. 5. Repeat the same procedure for channels 2 and 3. Test: Startup using VIN 1. 2. 3. 4. 5. Configure the specified test equipment as shown in Figure 6. Enable channel 1 by connecting the jumper to the ‘ON’ position. Set the oscilloscope to single sequence, and trigger the rising edge of VOUT. Disconnect VIN from the input power supply. Turn on the input power supply and toggle VIN by plugging the banana clip to the power supply while monitoring the VIN, VOUT1, LX1, and ILOAD1 on the oscilloscope. 6. Repeat steps 3 through 5 for different IOUT1, VIN, and VOUT1. 7. Repeat the same procedure for channels 2 and 3. Figure 6: AAT2784 Evaluation Board Connection Diagram for Startup. 6 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: Efficiency vs. Output Current Figure 7: AAT2784 Evaluation Board Connection Diagram for Efficiency vs. Load Current Measurement. 1. Configure the specified test equipment as shown in Figure 7. Connect the voltmeter as closely as possible to the input and output capacitors (C4, C6) to avoid voltage drop along the trace resistance. 2. Enable channel 2 by connecting the jumper to the ‘ON’ position. 3. Set Keithley load to 4 Wire Sensing Mode (the two sensing wires should connect as closely as possible to the output cap C6). 4. Vary the output current (IOUT = ISRC ) from -1mA to -500mA and keep the input voltage the same while monitoring the input current (IIN), and the output voltage (VOUT). 5. Calculate the efficiency as the following equation: η= 100 ⋅ (VOUTIOUT) VINIIN 6. Repeat steps 4 and 5 for different input and output voltages. 7. Repeat the same procedure for channels 1 and 3. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 7 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: RDS(ON)H and RDS(ON)L Figure 8: AAT2784 Schematic Connection Diagram for RDS(ON) Measurement. 1. Configure the specified test equipment as shown in Figure 8. 2. Enable channel 1 by connecting the jumper to the ‘ON’ position, and connect the FB1 pin to GND to turn on the high side PMOS and turn off the low side NMOS. 3. Connect 4 wires (Force and Sense) from the Keithley power supply between VIN and LX node. The compliance set to VSRC = 40mV at Icomp = 300mA). 4. Power up and measure RDS(ON)H. RDS(ON)H = VSRC ICOMP 5. To measure RDS(ON)L, repeat steps 2 through 4 with the FB pin connected to VCC (to turn on the low side NMOS) and connect the 4 wires (Force and Sense) from the Keithley power supply between LX and GND. RDS(ON)L = VSRC ICOMP 6. Repeat the same procedure measurement for channels 2 and 3. 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Test: Gain and Phase Margin (Loop Gain) Analog Network Analyzer Oscilliscope SOURCE OUT CHA CHB LOAD Power Supply 5.00V 300mA 500mA L1 4.7uH 50 14 15 VIN ON/OFF 3 Isolation Transformer LX1 VP1_2 EN1 C4 10uF TDFN34-16 AAT2784 FB AGND 13 12 R1 133K . VOUT Broken Original Connection C3 100pF (Optional) 5 R2 29.4K C1 4.7uF PGND Figure 9: AAT2784 Schematic Connection Diagram for Gain and Phase Margin Measurement. 1. Break the feedback loop and insert a one-to-one isolation transformer between the broken original connection. A 50Ω resistor is connected in parallel with the secondary wire. 2. Configure the specified test equipment as shown in Figure 9. 3. Inject a signal from SOURCE OUT to the loop through the primary wire of the isolation transformer while monitoring the ratio of CHA and CHB on the network analyzer. 4. Set the output current to heavy load while monitoring the LX1 node of the converter on the Oscilloscope (to obtain a good result the converter must be in continuous PWM mode). 5. Sweep the frequency from SOURCE OUT of the network analyzer from 10Hz to 1MHz and adjust the magnitude of the injected signal (around 10mV to 100mV) in order to have a clean PWM waveform at the LX1 node. 6. Repeat the measurement for different VIN, VOUT, and ILOAD. 7. Repeat the same procedure for channels 2 and 3. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202283A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 22, 2012 9 EVALUATION BOARD DATA SHEET EV157 Evaluation Board for the AAT2784 Three-Channel Step-down DC/DC Converter Printed Circuit Board Figure 10: Top Layer (not to scale). Figure 11: Bottom Layer (not to scale). Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. 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