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ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter introduction the aat1149 evaluation board provides a platform for test and evaluation of the aat1149 3mhz fast transient 400ma step-down converter. 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 efficien- cy and low output noise with the sc70jw-8 package. the design operates across an input voltage range from 2.7v to 5.5v. the aat1149 evaluation board provides an adjustable output voltage from 1v to v in at 400ma maximum out- put current. resistors r1 and r2 program the output to regulate at a voltage higher than 0.6v. the suggest- ed value for r2 is 59k. table 2 summarizes the resistor values for various output voltages. connecting en to in will turn on the part while connecting en to gnd will disable the part. schematic and bom figure 1: aat1149 evaluation board schematic. table 1: aat1149 evaluation board build of materials (bom). symbol description u1 aat1149 sc70jw-8 c1, c2, 4.7f 10v 0805 c3 100pf 10v 0402(optional) l1 1.8h sumida cdrh2do9 r1 see table 2; 10v 0402 r2 59k 10v 0402 ev-139.2007.08.1.0 1
table 2: aat1149 adjustable resistor values. test equipment 1. unit under test (uut) is the aat1149 evaluation board. 2. one (1) keithley 2430 3a source meter or equivalent. 3. two (2) xt30-2 power supplies or equivalent. 4. two (2) 10, 100w variable resistors, or dc electronic loads. 5. two (2) fluke 189 multi-meters or equivalent. 6. a hp33120a 15mhz function/ arbitrary waveform generator. set to pwm setting. 7. 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). r2 = 59k r2 = 221k v out (v) r1 (k ) r1 (k ) 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59.0 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 1.85 124 464 2.0 137 523 2.5 187 715 3.3 267 1000 3.6 295 1105 ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter 2 ev-139.2007.08.1.0
setup and test test: line-load regulation 1. configure the specified test equipment as shown in figure 2. 2. enable uut by connecting the jumper 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 400ma and vary the input voltage from 2.7v to 5.5v while monitoring the output voltage. 5. where v nominal is the output voltage at 10ma output current. figure 2: aat1149 evaluation board connection diagram for line and load regulation. ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter ev-139.2007.08.1.0 3 % error = v out - v nominal v nominal
test: line transient response 1. configure the specified test equipment as shown in figure 3. 2. 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 supply to 3.6v and the second one to 4.2v. 4. toggle the input voltage from 3.6v to 4.2v 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 v out . figure 3: aat1149 evaluation board connection diagram for line transient response. ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter 4 ev-139.2007.08.1.0 vin(ac) vout(ac)
test: load transient response 1. configure the specified test equipment as shown in figure 4. 2. enable uut by connecting the jumper to the on position. 3. generate the step output load 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 output current while monitoring the step output current and the out- put voltage response (ac coupling) on the oscilloscope. 5. repeat step 4 for different output current steps and over the ranges of v in and v out . figure 4: aat1149 evaluation board connection diagram for load transient response. ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter ev-139.2007.08.1.0 5 iload vout(ac)
test: quiescent current vs. input voltage 1. configure the specified test equipment as shown in figure 5. 2. enable uut by connecting the jumper to the on position. 3. remove the output loads (open circuit). 4. replace the input power supply by keithley 2400 3a source meter or equivalent. set v src to the designed input voltage (v src = v out + 1v), and set the i com to 200a. 5. turn on the keithley and read the compliance current (quiescent current). 6. vary the input voltage v src = v out + 1v while monitoring the corresponding compliance current. figure 5: aat1149 evaluation board connection diagram for quiescent current. ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter 6 ev-139.2007.08.1.0
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 v out . 3. turn on input power supply and toggle en to the on position while monitoring the en, v out , lx, and i load on the oscilloscope. 4. repeat steps 2 and 3 for different i out , v in , and v out . test: startup using v in 1. configure the specified test equipment as shown in figure 6. 2. enable uut by connecting the jumper to the on position. 3. set the oscilloscope to single sequence, and trigger the rising edge of v out . 4. disconnect v in to input power supply. 5. turn on input power supply and toggle v in by connecting the banana clip to the power supply while mon- itoring the v in , v out , lx, and i load on the oscilloscope. 6. repeat steps 3 through 5 for different i out , v in , and v out . figure 6: aat1149 evaluation board connection diagram for startup. ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter ev-139.2007.08.1.0 7
ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter 8 ev-139.2007.08.1.0 test: efficiency vs. output current 1. configure the specified test equipment as shown in figure 7. connect voltmeters as closely as possible to the input and output capacitors to avoid voltage drop along the trace resistance. 2. enable uut 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. 4. vary the output current (i out = i src ) from -1ma to -400ma and keep the input voltage the same while mon- itoring the input current (i in ), and the output voltage (v out ). 5. calculate the efficiency as the following equation: 6. repeat steps 4 and 5 for different input and output voltages. figure 7: aat1149 evaluation board connection diagram for efficiency vs. load current. efficiency =
test: r ds(on)h and r ds(on)l 1. configure the specified test equipment as shown in figure 8. 2. enable uut by connecting the jumper to the on position, and connect the fb 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 v in and lx node. set the compliance to v src = 40mv at i comp = 300ma. 4. power up and measure 5. to measure the r ds(on)l , repeat steps 2 through 4 with the fb pin connected to v cc (to turn on the low side nmos) and connect the 4 wires (force and sense) between lx and gnd. figure 8: aat1149 schematic connection diagram for r ds(on) . ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter ev-139.2007.08.1.0 9 r ds(on)h = v src i com p r ds(on)l = v src i com p
test: gain and phase margin (loop gain) 1. break the feedback loop and insert a one-to-one isolation transformer between the broken original con- nection. configure the specified test equipment as shown in figure 9. 2. inject a signal from source out to the loop through the isolation transformer while monitoring the ratio of cha and chb on the network analyzer. 3. set the output current to heavy load while monitoring the lx node of the converter on the oscilloscope (to obtain a good result the converter must be in continuous pwm mode). 4. sweep the frequency from source out of the network analyzer from 10hz to 1mhz and adjust the mag- nitude of the injected signal (around 10mv to 100mv) in order to have a clean pwm waveform at the lx node. 5. repeat the measurement for different v in , v out , and i load . figure 9: aat1149 schematic connection diagram for gain and phase margin. ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter 10 ev-139.2007.08.1.0 vout in en lx c2 4.7uf c6 100pf agnd 7 3 2 6 vin fb c1 4.7uf 5 1 4 on/off r1 adj. r2 59k (optional) pgnd pgnd pgnd 8 l1 1.8uh 50 isolation transformer broken original connection
advanced analogic technologies, inc. 3230 scott boulevard, santa clara, ca 95054 phone (408) 737- 4600 fax (408) 737- 4611 ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. 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 with- out notice. except as provided in analogictechs terms and conditions of sale, analogictech assumes no liability whatsoever, an d analogictech disclaims any express or implied war- ranty relating to the sale and/or use of analogictech products including liability or warranties relating to fitness for a part icular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. in order to minimize risks associated with the customers applications, adequa te design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. testing and other quality control techniques are utilized to the extent an alogictech deems necessary to support this warranty. specific testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trad emarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holder s. printed circuit board figure 10: aat1149 evaluation board top layer (not to scale). figure 11: aat1149 evaluation board bottom layer (not to scale). ev-139 aat1149 eval: 3mhz fast transient 400ma step-down converter ev-139.2007.08.1.0 11

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