ev-109 aat1151 qfn eval 850khz 700ma buck regulator introduction the aat1151 evaluation board demonstrates performance, along with the suggested size and placement of external components, for the aat1151 integrated buck regulator. the external components are selected for minimum size and optimum operation up to 700ma output current. the output voltage can be adjusted with the use of the 1.0v version of the aat1151 and external resistors r3 and r4. please refer to the aat1151 product datasheet for more details about the aat1151. layout as with all switching power supplies, the board layout for the aat1151 is critical (see figure 1). special care has been taken with the placement of the external components. the input capacitor (c1) placement is critical. it must be located immediately adjacent to the aat1151. as shown in figure 2, the lx node trace has been routed under c1 in order to facilitate a close placement of c1 next to the ic. the output voltage feedback trace has been routed on the portion of backside of the board which has a ground plane on the top side (see figure 3). the trace is also routed to avoid the lx node and associated noise. figure 1: aat1151 qfn evaluation board schematic. table 1: aat1151 qfn evaluation board specifications. specification test conditions min typ max units input voltage 2.7 3.6 5.5 v output error voltage -3 +3 % output current 0 700 ma 3.3 h l1 4x 10 f (2x 22 f ) c3-c7 10 f c1 100 r1 0.1 f c2 100k r2 v o + v in + r3 10.0 k ? r4 gnd gnd enable fb 4 sgnd 5 en 7 vcc 9 vp 10 lx 13 lx 14 pgnd 3 vp 11 sgnd 6 pgnd 2 lx 15 n/c 16 pgnd 1 n/c 8 vp 12 aat1151-qfn u1 ev-109.2005.04.1.1 1
figure 2: aat1151 qfn evaluation figure 3: aat1151 qfn evaluation board pcb top side. board pcb bottom side. test equipment 1. 6.0v, 1.0a laboratory power supply: hp33401a or equivalent. 2. dc 0a to 700 ma electronic load, capable of operation down to 1.0v: keithley 2400 or equivalent. (when using the keithley 2400, set the meter to operate 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 v in + (positive terminal) and gnd (negative terminal or return). 2. apply a dc load and dc voltmeter to output terminals v o + and gnd. 3. vary the load from 0a to 0.7a 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 boards should not vary by more than 3% of the nominal voltage. b. short-circuit and over-temperature protection 1. raise the input voltage to 5.5v. 2. apply a short from v o + to gnd at the evaluation board terminals. 3. remove the short and verify that the output returns to its initial value. c. enable input 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. 2 ev-109.2005.04.1.1 ev-109 aat1151 qfn eval 850khz 700ma buck regulator
figure 4: aat1151 qfn connection diagram. note 1: either 4x 10f or 2x 22f capacitors can be used for c3-c7. table 2: aat1151 qfn eval bill of materials. component part number description quantity manufacturer u1 aat1151ivn-1.0-t1 1.0v 700ma adjustable buck converter 1 analogictech u1 aat1151ivn-1.8-t1 1.8v 700ma buck converter 1 analogictech u1 aat1151ivn-2.5-t1 2.5v 700ma buck converter 1 analogictech c3-c7 1 grm21br60j106ke19 10f, 6.3v, x5r, 10%, 0805 4 murata c3-c7 1 grm21br60j226ke39 22f, 6.3v, x5r, 10%, 0805 2 murata c1 grm319r60j106ke01 10f, 6.3v, x5r, 10%, 1206 1 murata c2 grm155r61a104ka01 0.1f, 25v,x5r, 10%, 0402 1 murata r1 chip resistor 100k ? , 5%, 1/16w; 0402 1 vishay r2 chip resistor 100k ? , 5%, 1/16w; 0402 1 vishay aat1151ivn-1.0-t1 see table 3, 1%, 1 1/16w; 0402 r3 chip resistor aat1151ivn-1.8-t1 0 ? , 0402 1 vishay aat1151ivn-2.5-t1 0 ? , 0402 1 r4 chip resistor 10k ? , 1%, 1/16w; 0402 1 vishay (aat1151ivn-1.0-t1 only) l1 cdrh3d16-3r3 3.3 h 85m ? 1.1a shielded 1 sumida voltmeter 1.500v load 0 - 700ma 3.650v 0.147a power supply oscilloscope voltmeter 3.600v ev-109.2005.04.1.1 3 ev-109 aat1151 qfn eval 850khz 700ma buck regulator
output voltage for an adjustable output, set r4 to 10k ? and select r3 according to table 3. for fixed output versions, r4 can be omitted and r3 is a short. table 3: resistor selection for adjustable output voltage for aat1151iks-1.0-t1 (r4 = 10k ? ? ). v o (v) r3 (k ? ? ) 1.0 0.00 (short) 1.1 1.00 1.2 2.00 1.25 2.55 1.3 3.01 1.4 4.02 1.5 4.99 1.6 6.04 1.7 6.98 1.8 8.06 1.85 8.45 1.9 9.09 2.0 10.0 2.1 11.0 2.2 12.1 2.3 13.0 2.4 14.0 2.5 15.0 3.3 23.2 4 ev-109.2005.04.1.1 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737-4600 fax (408) 737-4611 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 wi thout notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. all products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of l iability. analogictech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accorda nce with analogictech?s standard warranty. testing and other quality control techniques are utilized to the extent analogictech deems necessary to support this warranty. specific tes ting of all parameters of each device is not necessarily performed. ev-109 aat1151 qfn eval 850khz 700ma buck regulator
form#: for001 rev. d
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