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rev. 1.0 november 2011 page 1 of 14 www.aosmd.com AOZ1615 1.5a/3mhz buck regulator general description the AOZ1615 is a high - performance, easy - to - use b uck regulator. its 3mhz switching frequency, low quiescent current and small solution size make it an ideal choice for portable applications. the AOZ1615 has a patented light load mode architecture allowing up to 85% efficiency at 1ma load currents, enabling longer standby times in battery operated systems. the AOZ1615 has and input voltage range of 2.5v to 5.5v and provides up to 1 . 5a of output current with an output voltage adjustable down to 0.6v. the AOZ1615 is available in a tiny 2mm x 3 mm 8 - pin dfn package and is rated over a - 40c to +85c ambient temperature range . features ? 2.5v to 5.5v input voltage range ? 0.1 a shutdown current ? automatic pfm/pwm mode switching ? output voltage adjustable down to 0.6v ? fixed output voltages available ? 2 % initial accuracy ? up to 1 . 5a continuous output current ? 3mhz constant frequency operation ? low drop - out operation ? 100% duty c ycle ? cycle - by - cycle current - limit ? thermal overload protection ? excellent load transient response ? internal soft - start ? tiny 2mm x 3 mm dfn - 8 package applications ? smart phones ? personal media players ? mp3 players ? digital still cameras ? wireless modems and lans ? portable usb devices typical application AOZ1615di vin 2.5v to 5.5v c2 r1 r2 analog ground power ground off on in pgnd en c1 10f lx fb agnd l1 1.0h vout 1.5a
page 2 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 ordering information part number temperature range package environmental aoz1 615di - 40c to +85c 8 - pin 2 mm x 3 mm d fn green product aos green products use reduced levels of halogens, and are also rohs compliant. please visit www.aosmd.com/web/quality/rohs_compliant.jsp for additional information. pin configuration 8 - pin 2 mm x 3 mm d fn (top view) pin description part number pin name pin function 1 pgnd power g round . 2 in input supply . 3 , 7 nc no connect . 4 agnd analog ground. 5 fb feedback input. connect an external resistive voltage divider to fb to set the output voltage . 6 en enable input . the device is enabled when en is high and disabled with en is low. 8 lx switching node . pad agnd analog ground . lx nc en fb pgnd vin nc agnd 8 7 6 5 1 2 3 4 agnd
page 3 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 absolute maximum ratings exceeding the absolute maximum ratings may damage the device. parameter rating in , e n , fb to agnd - 0.3v to +6 v lx to agnd - 0.3 v to v in + 0 .3 v pgnd to agnd - 0.3v to +0. 3 v storage temperature (t s ) - 65c to +150c junction temperature (t j ) +150c max. soldering temperature ( 10s) + 30 0c esd rating (1) 2kv note: 1. devices are inherently esd sensitive, handling precautions are required. human body model rating: 1.5k in series with 100pf. recommended operating ratings this device is not guaranteed to operate beyond the recommended operating ratings. parameter rating supply voltage (v i n ) 2. 5 v to 5.5 v ambient temperature (t a ) - 40c to +85c junction temperature (t j ) internally limited package thermal resistance 2x3 dfn - 8 ( t ja ) 5 5 c/w electrical characteristics t a = 25c, v in = 3.6 v, en = in unless otherwise specified. specifications in bold indicate a temperature range of - 40c to +85c. symbol parameter conditions min. typ. max units v in input voltage range 2.5 5.5 v v uv under - voltage lockout 2.11 2.3 2.49 v under - voltage lockout hysteresis 100 m v i in input supply current en = in, v fb = 1v, no load en = agnd 40 0.01 65 0.1 a v fb feedback reference voltage t a = 25c , no load t a = -40 c to + 85c , no load 0. 588 0.585 0. 6 00 0.600 0. 612 0.615 v i fb feedback bias current 0.01 0.1 a enable input high voltage 1.5 v enable input low voltage 0.8 v i en enable bias current v en = 5.5v 0.01 0.1 a oscillator f sw switching frequency 2.25 3 3.75 mhz operating duty cycle 100 % t (on)min minimum on - time 70 ns protection i lim+ positive current limit 1.7 2.2 3 a thermal shutdown threshold +145 c thermal shutdown hysteresis 40 c output stage r ds(on) p p fet on resistance i lx = 50ma sourcing 150 m r ds(on) n n fet on resistance i lx = 50ma sinking 120 m lx leakage current v en = 0 v , v lx = 0 v or v in , v in = 5v -1 1 a
page 4 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 output voltage selection for AOZ1615 the output voltage of the AOZ1615 can be programmed through the resistor network connected from v out to f b to a gnd . the resistor from fb to agnd should be 100k to keep the current drawn through this network below the 6a quie s cent current level in pfm mode. the output voltage of the adjustable AOZ1615 parts ranges from 0.6v to 3.3v. the output voltage formula is: ? 1 ? 1 2 1 r r v v fb out where; v out = output voltage (v) v fb = feedback voltage (0.6v typical) r1 = feedback resistor from v out to fb () r2 = feedback resistor from fb to agnd () a 10pf bypass capacitor c5 on the evaluation board, in parallel with the feedba ck resistor from v out to fb is chosen for increased stability throughout the voltage range . table 1. output voltage resistor selection table for various v out voltages v out r1 r2 l c in c out c5 (v) (k) (k) (h) (f) (f) (pf) 1.1 83 100 1 10 22 10 1.2 100 100 1 10 22 10 1.3 117 100 1 10 10 10 1.5 150 100 1 10 10 10 1.6 167 100 1 10 10 10 1.7 183 100 1 10 10 10 1.8 200 100 1 10 10 10 1.875 213 100 1 10 10 10 2.5 317 100 1 10 10 10 2.8 367 100 1 10 10 10 3.3 450 100 1 10 10 10
page 5 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 functional block output logic control lx pgnd agnd in en fb 3mhz oscillator uvlo thermal shutdown i sense amp i limit comp i min threshold pwm pfm master logic error amp vref 600mv
page 6 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 typical performance characteristics
page 7 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 typical performance characteristics (continued)
page 8 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 application information the AOZ1615 has a patented light load mode architecture which allows up to 85% efficiency at 1ma load currents , enabling longer standby times in battery operated systems. the AOZ1615 is a high efficiency step down dc - dc buck converter that operates typically at 3mhz fixed pulse width modulation (pwm) at medium to heavy load currents. the AOZ1615 can deliver a constant voltage from a single li - ion battery with an input voltage range from 2.5v to 5.5 v . by using voltage mode architecture with synchronous rectification, the AOZ1615 has the ability to deliver up 1.5 a of continuous current depending on the input voltage, output voltage, ambient temperature and inductor chosen. there are two modes of operations depending on the current consumption, pfm (pulse frequency modulation) and pwm (pulse width modulation). for ultra - low current , the device operates in the pfm mode to obtain high efficiency that is characteristic of the pfm mode. the device operates in the pwm mode when the output current exceed s the load current of approximately 100ma or higher. additional feature s include under voltage lockout, over current protection, thermal shutdown and soft - start. inductor selection there are two main considerations when choosing an inductor; the inductor should not saturate and the inductor current ripple should be sm all enough to achieve the desire output voltage ripple. a 1 h inductor with a saturation current of at least 2 a is recommended for the aoz16 1 5 full load application. for maximum efficiency, the inductor?s resistance (dcr) should be as low as possible. for given input and output voltage, inductance and switching frequency together decide the inductor ripple current, which is: ? ? 1 ? u u ' in out out l v v l f v i 1 the peak inductor current is: 2 l out peak i i i ' high inductance gives low inductor ripple current but requires a larger size inductor to avoid saturation. l ow ripple current reduces inductor core losses. it also reduces rms current through inductor and switches, which results in less conduction loss. usually, peak - to - peak ripple current on inductor is designed to be 20% to 30% of output current. when selecting the inductor, make sure that it is able to handle the peak current without saturation even at the highest operating temperature. the inductor takes the highest current in a buck circuit. the condu ction loss es on an inductor need to be checked for thermal and efficiency requirements. surface mount inductors in different shape s and styles are available from coilcraft, elytone and murata. shielded inductors are small and radiate less emi noise , but th ey cost more than unshielded inductors. the choice depends on emi requirement, price and size . input capacitor the input capacitor must be connected to the vin and pgnd pin s of aoz16 1 5 to maintain steady input voltage and filter out the pulsing input current. the voltage rating of input capacitor must be greater than maximum input voltage plus ripple voltage. for greater capacitor performance, the working capacitance voltage should be twice v in . the input ripple voltage can be approximated by using the equation below: in out in out in out in v v v v c f i v u ? ? 1 ? u u ' 1 since the input current is discontinuous in a buck converter, the current stress on the input capacitor is another concern when selecting the capacitor. for a buck circuit, the rms value of input capacitor current can be calculated by: ? ? 1 ? u in out in out out rms cin v v v v i i 1 _ if we let m equal the conversion ratio: m v v in out the relationship between the input capacitor rms current and voltage conversion ratio is calculated and shown below in figure 1. it can be seen that when v out is half of v in , c in is under the worst current stress. the worst current stress on c in is 0.5 x i o ut .
page 9 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 figure 1 . i cin vs. voltage conversion ratio for reliable operation and best performance, the input capacitors must have current rating higher than i cin_rms at worst operating conditions. ceramic capacitors are preferred for input capacitors because of their low esr and high current rating. when selecting ceramic capacitors, x5r or x7r type dielectric ceramic capacitors should be used for their better temperature and voltage characteristics. note that the ripple current rating from capacitor manufactures , are based on certain amount of life time. further de - rating may be necessary in practical design. output capacitor the output capacitor is selected based on the dc output voltage rating, output ripple voltage specification and ripple current rating. the selected output capacitor must have a higher rated voltage specification than the maximum desired output voltage including ripple. de - rati ng needs to be considered for long term reliability. output ripple voltage specification is another important factor for selecting the output capacitor. in a buck converter circuit, output ripple voltage is determined by inductor value, switching frequency , output capacitor value and esr. it can be calculated by : ? ? ? ? ? ? ? ? + ? = ? o co l o c f esr i v 8 1 where , c o is output capacitor value and esr co is the equivalent series resistor of output capacitor. when low esr ceramic capacitor is used as output capacitor, the impedance of the capacitor at the switching frequency dominates. output ripple is mainly caused by capacitor value and inductor ripple current. the output ripple voltage calculation can be simplified to: o l o c f i v ? = ? 8 1 if the impedance of esr at switching frequency dominates, the output ripple voltage is mainly decided by capacitor esr and inductor ripple current. the output ripple voltage calculation can be further simplified to: co l o esr i v ? = ? for lower output ripple voltage across the entire oper ating temperature range, x5r or x7r dielectric type of ceramic, or other low esr tantalum are recommended to be used as output capacitors. in a buck converter, output capacitor current is continuous. the rms current of the output capacitor is decided by the peak - to - peak inductor ripple current. it can be calculated by: 12 _ l rms co i i ? = usually, the ripple current rating of the output capacitor is a smaller issue because of the low current stress. when the buck inductor is selected to be very small a nd the inductor ripple current is high, the output capacitor could be overstressed. thermal shutdown in most applications the aoz16 1 5 does not dissipate much heat due to its high efficiency. but in an application where the aoz16 1 5 is running at high ambient temperature with low supply voltage and high duty cycle, the heat dissipated may exceed the maximum junction temperature. if the junction temperature reaches approximately 140c (typical), the internal high side and low side mosfet switching is dis abled until the temperature on the die has fallen sufficiently below 105c. the device remains in thermal shutdown until the junction temperature falls below the thermal shutdown hysteresis. i cin_rms(m) i ou t 0.5 0.4 0.3 0.2 0.1 0 0 0.5 m 1
page 10 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 undervoltage lockout the undervoltage lockout circuit prevents the device from malfunctioning at low input voltages and from excessive discharge of the battery by disabling the output stage of the converter. the aoz16 1 5 will resume normal operation when the input supply voltage rises high enough to properly function. the undervoltage lockout threshold is typically 2.3v . soft start the aoz16 1 5 has a soft - start circuit that limits the inrush current during startup. soft start is activated when en goes from logic low to logic high after v in reaches 2.3v . ov er current protection (ocp) the sensed inductor current signal is also used for over current protection. since the AOZ1615 employs peak current mode control, the comp voltage is proportional to the peak inductor current. the comp voltage is limited to be b etween 0.4v and 2.5v internally. the peak inductor current is automatically limited cycle - by - cycle. when the output is shorted to ground under fault conditions, the vfb is lower than 0.425v, the high side switch will turn off, then AOZ1615 will initiate a soft start. enable the en pin of the aoz16 1 5 is active high. connect the en pin to vin if the enable function is not used, p ull ing it to ground will disable the aoz16 1 5. do not leave it open. the voltage on en must be above 2v to enable the aoz16 1 5. when voltage falls below 0.6v, the aoz16 1 5 is disabled. if an application circuit requires the aoz16 1 5 to be disabled, an open drain or open collector circuit should be used to interface with the en pin. low drop out operation the aoz16 1 5 can operate at 1 00% duty cycle. in this state, the high side p - channel mosfet is always on. this allow s the output to follow the input voltage as it drops below the regulation voltage . thermal management and layout consideration in the aoz16 1 5 buck regulator circuit, high pulsing current flows through two circuit loops. the first loop starts from the input capacitors, to the vin pin, to the lx pin, to the filter inductor, to the output capacitor and load, and then return s to the input capacitor through ground. current flows in the first loop when the high side switch is on. the second loop starts from inductor, to the output capacitors and load, to the low side n - mosfet. current flows in the second loop when the low side n - mosfet is on. in pcb layout, minimizing the two loops area reduces the noise of the circuit and improves efficiency. a ground plane is strongly recommended to connect the input and output capacitor s , a s well as the pgnd pin of the AOZ1615. in the AOZ1615 buck regulator circuit, the major power dissipat ing components are the AOZ1615 and the output inductor. the total power dissipation of converter circuit can be measured by input power minus output power. o o in in loss total i v i v p ? = _ the power dissipation of the inductor can be approximately calculated by output current and dcr of inductor. 1 . 1 2 _ = inductor o loss inductor r i p the actual junction temperature can be calculated with power dissipation in the aoz16 1 5 and thermal impedance from junction to ambient. ( ) ja loss inductor loss total junction p p t ? = _ _ the maximum junction temperature of AOZ1615 is 140oc, which limits the maximum load current capability. please see the thermal de - rating curves for maximum load current of the AOZ1615 under different ambient temperature. the thermal performance of the AOZ1615 is strongly affected by the pcb layout. extra care should be taken by users during design process to ensure that the ic will operate under the r ecommended environmental conditions .
page 11 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 the aoz16 1 5 is an exposed pad dfn - 8 package. several layout tips are listed below for the best electric and thermal performance . 1. the exposed pad is connected to pgnd. connect a large copper plane to this pad to help thermal dissipation . 2. do not use thermal relief connection from the vin pin and the pgnd pin. pour a maximized copper area to the pgnd pin and the vin pin to help thermal dissipation . 3. input capacitor should be connected as close as possible to the vin pin and the pgnd pin. for optimal performance of the device, place bulk capacitor and de - coupling capacitor no further than 50mils from the devic e . 4. a ground plane is preferred. if a ground plane is not used, separate pgnd from agnd and connect them only at one point to avoid the pgnd pin noise coupling to the agnd pin . 5. make the current trace from lx pin to l to c o to pgnd as short as possible . 6. po ur copper planes on all unused board area and connect them to stable dc nodes, like vin, gnd or vout . 7. keep sensitive signal traces away from the lx pin .
page 12 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 package dimensions, d fn 2x3, 8 l ead ep 1 _s recommended land pattern unit: mm dimensions in millimeters dimensions in inches symbols min. nom. max. min. nom. max. a 0.70 0.75 0.80 0.028 0.030 0.031 a1 -- -- 0.05 -- -- 0.002 b 0.20 0.25 0.30 0.008 0.010 0.012 c 0.195 0.203 0.211 0.0076 0.008 0.0083 d 2.00 bsc 0.079 bsc d1 1.55 1.60 1.65 0.061 0.063 0.065 d2 0.15 0.20 0.25 0.006 0.008 0.010 d3 0.125 bsc 0.005 bsc e 3.00 bsc 0.118 bsc e1 0.35 0.40 0.45 0.014 0.016 0.018 e2 0.60 0.65 0.70 0.024 0.026 0.028 e3 1.65 1.70 1.75 0.065 0.067 0.069 e 0.50 bsc 0.002 bsc note 1. controlling dimension is millimeter. converted inch dimensions are not necessarily exact.
page 13 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 tape and reel dimensions, dfn 2x3, 8 lead ep1_s carrier tape unit: mm package a0 b0 k0 d0 d1 e e1 e2 p0 p1 p2 t dfn 2x3 (8mm) 3.35 0.10 3.20 0.10 1.10 0.10 1.50 +0.10 - 0.00 1.00 +0.25 - 0.00 8.00 +0.30 - 0.10 1.75 0.10 3.50 0.05 4.00 0.10 4.00 0.10 2.00 0.05 0.23 0.020 reel unit: mm tape size reel size m n w1 h s k r 8mm ? 180 ? 180.0 0.50 60.0 0.50 8.4 +1.5 - 0 13.0 0.20 1.5 min. 13.5 min. 3.0 0.50 leader/trailer and orientation feeding direction p2 d0 d0 a p1 a - a k0 t p0 a0 a e1 e2 e b0 r m n w1 s h k t railer t ape 300mm min. components t ape orientation in pocket leader t ape 500mm min.
page 14 of 14 rev. 1.0 november 2011 www.aosmd.com AOZ1615 this datasheet contains preliminary data; supplementary data may be published at a later date. alpha and omega semiconductor reserves the right to make changes at any time without notice. life support policy alpha & omega semiconductor products are not authorized for use as critical components in life support devices or systems. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. a critical component in any component of a life support, device, or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.

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