ev138 aat1106 eval: 600ma step-down converter introduction the aat1106 evaluation board contains a fully tested 600ma, 1.5mhz step-down dc/dc regulator. the cir- cuit has an input voltage range of 2.5v to 5.5v and four preset selectable outputs (1.2v, 1.5v, 1.8v and 2.5v). the device is capable of delivering up to 600ma of output current with a 3.0v vin. the circuit can provide up to 96% efficiency and it consumes less than 1ua in shutdown mode. in light load mode operation there is very low output ripple voltage for noise sensitive applications. the aat1106 comes in a small 5-pin tsot23 pack- age and the board has been optimized to fit small form factor designs. an optional tvs (sm6t6v8a) is con- nected between vin and gnd so that the evaluation board can be used in a hot-plug application. these fea- tures, plus the nominal operating frequency of 1.5mhz allowing the use of low profile surface mount compo- nents, make the aat1106 evaluation board an ideal circuit for use in battery-powered, hand-held applications. board picture figure 1: aat1106 evaluation board. layout guidelines the following guidelines should be followed to ensure proper operation of the aat1106: 1. the power traces, including the gnd trace, lx-to-l1, l1-to-vout traces and the vin-to-in trace should be kept short, direct and wide to allow large current flow. put many multiple-layer via pads when con- necting traces between layers. 2. connect the input capacitor c1 to the in pin as close as possible to get good power filtering. 3. keep the switching node, lx pin 3, away from the sensitive fb/out node. ev-138.2007.08.1.0 1
ev138 aat1106 eval: 600ma step-down converter 2 ev-138.2007.08.1.0 figure 2: aat1106 evaluation board schematic. table 1: aat1106 evaluation board specifications. specification test conditions min typ max units input voltage 2.5 3.6 5.5 v output error voltage -3 +3 % output current 0 600 ma en 1 gnd 2 u1 aat1106 jp1 c1 4.7h l1 2.2h r2a 316k r1 316k c3 10h vin vout lx in 4 fb/vout 5 lx 3 c2 22pf 1 2 jp2 3 5 4 6 78 r2b 470k r2c 634k r2d 1m 1.2v, 1.5v, 1.8v, 2.5 v 2. 5v ~ 5.5v
figure 3: aat1106 evaluation board figure 4: aat1106 evaluation board pcb pcb top side. bottom side. figure 5: aat1106 evaluation board figure 6: aat1106 evaluation board pcb midlayer 1 side. pcb midlayer 2 side. test equipment 1. 8.0v 5.0a laboratory power supply: agilent e3648a or equivalent. 2. electronic load: agilent n3301a 3. dc voltmeter: agilent34401a or equivalent. 4. oscilloscope: tektronix tds3034b or equivalent. ev138 aat1106 eval: 600ma step-down converter ev-138.2007.08.1.0 3
setup and test (see connection diagram in figure 7) a: load and line regulation 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: vout and gnd. 3. before powering on the supply, set the fb setting jumper (jp2) to choose the vout voltage position (1.2v, 1.5v, 1.8v or 2.5v) and set the en jumper (jp1) from off state to on. 4. vary the load from 0 to 600ma and the input voltage from 2.5v to 5.5v while monitoring the output voltage. 5. 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: ripple and shutdown current 1. apply a dc power supply set to 3.6v at vin. set the output load current between 0 ma and 600 ma, and measure the output ripple voltage; the measurement should be less than 20 mvac. 2. apply a dc power supply set to 4.2v at vin. set the jumper from on state to off. measure the shut- down supply current at this point by removing the tvs device. the tvs (sm6t6v8a) is connected between vin and gnd. the supply current will be less than 1ua in shutdown. c: short-circuit protection 1. raise the input voltage to 5.5v. 2. apply a short from vout to gnd at the evaluation board terminals. 3. remove the short and verify that the output returns to its initial value. d: enable output 1. short the en pin to gnd using jp1. the output will decay to zero. 2. remove the short applied to the en pin. the output will recover to its initial value. figure 7: aat1106 connection diagram. v + - + - + a - v + - + - + a - load ev138 aat1106 eval: 600ma step-down converter 4 ev-138.2007.08.1.0
waveform a: normal waveform condition: v in = 3.6v, v out = 1.8v, no load condition: v in = 3.6v, v out = 1.8v, 1.2a load ch1: lx, ch2: i inductor , ch3: v out (ac). ch1: lx, ch2: i inductor , ch3: v out (ac). b: startup time condition: v in = 3.6v, v out = 1.8v, 3? load ch1: en, ch2: i in , ch3: v out . ev138 aat1106 eval: 600ma step-down converter ev-138.2007.08.1.0 5
table 2: aat1106 eval bill of materials. output voltage the board has an r1 value of 316k?. to adjust the output from the 1.8v default, select r2 according to table 3 or use the jumper jp2. a smaller value resistor divider can be used for better noise immunity, values are shown in column 3. a larger value resistor divider is used as default for lower current consumption. standard 1% resistor values are substituted for calculated values. table 3: resistor selection for adjustable output voltage. component part number description manufacturer u1 aat1106 1.5 mhz, 600ma synchronous analogic tech step-down converter l1 sf32-2r2m-r inductor 2.2uh 1.8a smd fenfa c1 grm42-6x7r475k16pt cap ceramic 4.7f16v x7r 10% 1206 murata c2 c1005cog1h220jt000p cap ceramic 22pf 50v c0g 5% 0402 tdk c3 grm31br71c106ka01l cap ceramic 10f 16v x7r 10% 1206 murata r1, r2a chip resistor resistor 316k? 1/16w 1% 0402 smd r2b chip resistor (optional) resistor 470k? 1/16w 1% 0402 smd r2c chip resistor (optional) resistor 634k? 1/16w 1% 0402 smd r2d chip resistor (optional) resistor 1m? 1/16w 1% 0402 smd no designator sm6t6v8a (optional) 6.8v tvs st r1 = 316k? r1 = 59k? r1 = 316k? r1 = 59k? v out (v) r2 (k?) r2 (k?) v out (v) r2 (k?) r2 (k?) 0.6 0(short) 0(short) 0.6 0(short) 0(short) 0.80 105 19.6 1.90 681 127 1.00 210 39.2 2.00 732 137 1.20 316 59.0 2.10 787 147 1.30 365 68.1 2.20 845 158 1.40 422 78.7 2.32 909 169 1.50 475 88.7 2.40 953 178 1.60 523 97.6 2.50 1000 187 1.70 576 107 3.30 1430 267 1.80 634 118 ev138 aat1106 eval: 600ma step-down converter 6 ev-138.2007.08.1.0
ev138 aat1106 eval: 600ma step-down converter ev-138.2007.08.1.0 7 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.
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