AOZ1282CI EZBuck™ 1.2A Simple Buck Regulator General Description Features The AOZ1282CI is a high efficiency, simple to use, 1.2A  4.5V to 36V operating input voltage range buck regulator flexible enough to be optimized for a  420mΩ internal NMOS variety of applications. The AOZ1282CI works from a  Up to 95% efficiency 4.5V to 36V input voltage range, and provides up to 1.2A of continuous output current. The output voltage is  Internal compensation adjustable down to 0.8V. The fixed switching frequency  1.2A continuous output current of 450kHz PWM operation reduces inductor size.  Fixed 450kHz PWM operation  Internal soft start  Output voltage adjustable down to 0.8V  Cycle-by-cycle current limit  Short-circuit protection  Thermal shutdown  Small size SOT23-6L Applications  Point of load DC/DC conversion  Set top boxes and cable modems  DVD drives and HDDs  LCD Monitors & TVs  Telecom/Networking/Datacom equipment Typical Application VIN C3 C1 4.7µF VIN BS EN L1 VOUT AOZ1282CI LX 22µH R1 FB C2 GND 10µF R2 Figure 1. 1.2A Buck Regulator Rev. 1.2 March 2016 www.aosmd.com Page 1 of 13

AOZ1282CI Ordering Information Part Number Ambient Temperature Range Package Environmental AOZ1282CI -40 °C to +85 °C SOT23-6L Green Product AOS Green Products use reduced levels of Halogens, and are also RoHS compliant. Please visit www.aosmd.com/media/AOSGreenPolicy.pdf for additional information. Pin Configuration BST 1 6 LX GND 2 5 VIN FB 3 4 EN SOT23-6L (Top View) Pin Description Pin Number Pin Name Pin Function 1 BST Bootstrap Voltage Input. High side driver supply. Connected to 100nF capacitor between BST and LX. 2 GND Ground. 3 FB Feedback Input. It is regulated to 0.8V. The FB pin is used to determine the PWM output voltage via a resistor divider between the output and GND. 4 EN Enable Pin. The enable pin is active high. Connect EN pin to VIN through current limiting resistor. Do not leave the EN pin floating. 5 VIN Supply Voltage Input. Range from 4.5V to 36V. When VIN rises above the UVLO threshold the device starts up. 6 LX PWM Output. Connect to inductor. Rev. 1.2 March 2016 www.aosmd.com Page 2 of 13

AOZ1282CI Absolute Maximum Ratings Recommended Operating Conditions Exceeding the Absolute Maximum Ratings may damage the The device is not guaranteed to operate beyond the device. Recommended Operating Conditions. Parameter Rating Parameter Rating Supply Voltage (V ) 40V Supply Voltage (V ) 4.5V to 36V IN IN LX to GND -0.7V to V + 0.3V Output Voltage (V ) 0.8V to V VIN OUT VIN EN to GND -0.3V to 40V Ambient Temperature (T ) -40°C to +85°C A FB to GND -0.3V to 6V Package Thermal Resistance (Θ ) JA SOT23-6L 220°C/W BST to GND V + 6V LX Junction Temperature (T ) +150°C J Storage Temperature (T ) -65°C to +150°C S ESD Rating(1) 2kV Note: 1. Devices are inherently ESD sensitive, handling precautions are required. Human body model rating: 1.5kΩ in series with 100pF. Electrical Characteristics T = 25 °C, V = V = 12V, unless otherwise specified. Specifications in BOLD indicate a temperature range of -40°C to +85°C. A IN EN These specifications are guaranteed by design. Symbol Parameter Conditions Min. Typ. Max. Units V Supply Voltage 4.5 36 V IN V Input Under-Voltage Lockout Threshold V rising 2.9 V UVLO IN V falling 2.3 V IN UVLO Hysteresis 260 mV I Supply Current (Quiescent) I = 0, V = 1V, V > 1.2V 1 1.5 mA IN OUT FB EN I Shutdown Supply Current V = 0V 8 μA OFF EN V Feedback Voltage T = 25ºC 784 800 816 mV FB A V Load Regulation 120mA < Load < 1.08A 0.5 % FB_LOAD V Line Regulation Load = 600mA 0.03 %/V FB_LINE I Feedback Voltage Input Current V = 800mV 500 nA FB FB ENABLE V EN Input Threshold Off threshold 0.4 V EN_OFF V On threshold 1.2 V EN_ON V EN Input Hysteresis 200 mV EN_HYS I Enable Input Current 3 μA EN MODULATOR f Frequency 360 450 540 kHz O D Maximum Duty Cycle 87 % MAX T Minimum On Time 150 ns ON_MIN I Current Limit 1.5 1.9 A LIM Over-Temperature Shutdown Limit T rising 150 °C J T falling 110 °C J T Soft Start Interval 1.5 ms SS POWER STATE OUTPUT I NMOS Leakage V = 0V, V = 0V 10 μA LEAKAGE EN LX R NMOS On-Resistance V = 12V 420 mΩ DS(ON) IN Rev. 1.2 March 2016 www.aosmd.com Page 3 of 13

AOZ1282CI Block Diagram VIN Regulator EN Enable SoftStart Current BST BST Detect Sense LDO Ramp Generator OC CLK OSC Driver FB PWM Logic LX 0.8V Error Amplifier PWM Comparator GND Rev. 1.2 March 2016 www.aosmd.com Page 4 of 13

AOZ1282CI Typical Performance Characteristics Circuit of Figure 1. T = 25°C, V = V = 12V, V = 3.3 V, unless otherwise specified. A IN EN OUT Light Load Operation Full Load Operation IN IN Voltage Voltage (500mV/div) (1V/div) OUT OUT Voltage Voltage (100mV/div) (100mV/div LX LX Voltage Voltage (10V/div) (10V/div) LOAD LOAD Current Current (1A/div) (1A/div) 2µs/div 2µs/div Start Up to Full Load Load Transient IN Voltage (5V/div) OUT Voltage OUT (100mV/div Current (1A/div) OUT Voltage OUT (2V/div) Current (1A/div) 5ms/div 200µs/div Short Circuit Protection Short Circuit Recovery LX LX Voltage Voltage (10V/div) (10V/div) OUT OUT Voltage Voltage (2V/div) (2V/div) LOAD LOAD Current Current (1A/div) (1A/div) 2ms/div 2ms/div Rev. 1.2 March 2016 www.aosmd.com Page 5 of 13

AOZ1282CI Typical Performance Characteristics (continued) Efficiency (Vo=5V) Efficiency (Vo=3.3V) vs. Load Current vs. Load Current 95 95 12V–5V 5V–3.3V 90 90 12V–3.3V 85 85 %) 80 24V–5V %) 80 cy ( 75 18V–5V cy ( 75 24V–3.3V n n cie 70 cie 70 Effi 65 Effi 65 18V–3.3V 60 60 55 55 50 50 0 0.2 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 0.8 1.0 1.2 Load Current (A) Load Current (A) Current Limit vs. Input Voltage (Vo=3.3V) 2.0 1.8 A) 1.6 mit ( 1.4 Li ent 1.2 r r u C 1.0 0.8 0.6 5 9 13 17 21 25 29 33 37 Input Voltage (V) Rev. 1.2 March 2016 www.aosmd.com Page 6 of 13

AOZ1282CI Detailed Description The AOZ1282CI is a current-mode step down regulator Switching Frequency with integrated high side NMOS switch. It operates from The AOZ1282CI switching frequency is fixed and set by a 4.5V to 36V input voltage range and supplies up to an internal oscillator. The switching frequency is set 1.2A of load current. Features include enable control, internally 450kHz. under voltage lock-out, internal soft-start, output over- voltage protection, over-current protection and thermal Output Voltage Programming shut down. Output voltage can be set by feeding back the output to the FB pin with a resistor divider network. In the The AOZ1282CI is available in SOT23-6L package. application circuit shown in Figure 1. The resistor divider network includes R1 and R2. Usually, a design is started Enable and Soft Start by picking a fixed R2 value and calculating the required The AOZ1282CI has internal soft start feature to limit in- R1 with equation below. rush current and ensure the output voltage ramps up smoothly to regulation voltage. A soft start process  R  begins when the input voltage rises to the voltage higher VO = 0.8×1+-----1--  R  than UVLO and voltage on EN pin is HIGH. In soft start 2 process, the output voltage is ramped to regulation Some standard values of R1 and R2 for the most voltage in typically 400µs. The 400µs soft start time is set commonly used output voltage values are listed in internally. Table1. The EN pin of the AOZ1282CI is active high. Connect the EN pin to VIN if enable function is not used. Pull it to Vo (V) R1 (kΩ) R2 (kΩ) ground will disable the AOZ1282CI. Do not leave it open. 1.8 80.6 64.2 The voltage on EN pin must be above 1.2 V to enable the AOZ1282CI. When voltage on EN pin falls below 0.4V, 2.5 49.9 23.4 the AOZ1282CI is disabled. 3.3 49.9 15.8 5.0 49.9 9.53 Steady-State Operation Under steady-state conditions, the converter operates in Table 1. fixed frequency and Continuous-Conduction Mode (CCM). The combination of R1 and R2 should be large enough to avoid drawing excessive current from the output, which The AOZ1282CI integrates an internal NMOS as the will cause power loss. high-side switch. Inductor current is sensed by amplifying the voltage drop across the drain to source of the high Protection Features side power MOSFET. Output voltage is divided down by The AOZ1282CI has multiple protection features to the external voltage divider at the FB pin. The difference prevent system circuit damage under abnormal of the FB pin voltage and reference is amplified by the conditions. internal transconductance error amplifier. The error voltage is compared against the current signal, which is Over Current Protection (OCP) sum of inductor current signal and ramp compensation The sensed inductor current signal is also used for over signal, at PWM comparator input. If the current signal is current protection. less than the error voltage, the internal high-side switch is on. The inductor current flows from the input through The cycle by cycle current limit threshold is set normal the inductor to the output. When the current signal value of 1.9A. When the load current reaches the current exceeds the error voltage, the high-side switch is off. The limit threshold, the cycle by cycle current limit circuit turns inductor current is freewheeling through the external off the high side switch immediately to terminate the Schottky diode to output. current duty cycle. The inductor current stop rising. The cycle by cycle current limit protection directly limits inductor peak current. The average inductor current is also limited due to the limitation on peak inductor current. When cycle by cycle current limit circuit is triggered, the output voltage drops as the duty cycle decreasing. Rev. 1.2 March 2016 www.aosmd.com Page 7 of 13

AOZ1282CI The AOZ1282CI has internal short circuit protection to The relationship between the input capacitor RMS protect itself from catastrophic failure under output short current and voltage conversion ratio is calculated and circuit conditions. The FB pin voltage is proportional to shown in Figure 2. It can be seen that when V is half of O the output voltage. Whenever FB pin voltage is below V , C is under the worst current stress. The worst IN IN 0.2V, the short circuit protection circuit is triggered. As a current stress on C is 0.5 x I . IN O result, the converter is shut down and hiccups. The 0.5 converter will start up via a soft start once the short circuit condition disappears. In short circuit protection mode, the 0.4 inductor average current is greatly reduced. Under Voltage Lock Out (UVLO) I (m) 0.3 CIN_RMS An UVLO circuit monitors the input voltage. When the I O 0.2 input voltage exceeds 2.9V, the converter starts operation. When input voltage falls below 2.3V, the 0.1 converter will stop switching. Thermal Protection 0 0 0.5 1 An internal temperature sensor monitors the junction m temperature. It shuts down the internal control circuit and high side NMOS if the junction temperature exceeds Figure 2. I vs. Voltage Conversion Ratio CIN 150ºC. The regulator will restart automatically under the control of soft-start circuit when the junction temperature For reliable operation and best performance, the input decreases to 110°C. capacitors must have current rating higher than I CIN-RMS at worst operating conditions. Ceramic capacitors are Application Information preferred for input capacitors because of their low ESR and high ripple current rating. Depending on the The basic AOZ1282CI application circuit is shown in application circuits, other low ESR tantalum capacitor or Figure1. Component selection is explained below. aluminum electrolytic capacitor may also be used. When selecting ceramic capacitors, X5R or X7R type dielectric Input Capacitor ceramic capacitors are preferred for their better The input capacitor must be connected to the VIN pin temperature and voltage characteristics. Note that the and PGND pin of the AOZ1282CI to maintain steady ripple current rating from capacitor manufactures is input voltage and filter out the pulsing input current. The based on certain amount of life time. Further de-rating voltage rating of input capacitor must be greater than may be necessary for practical design requirement. maximum input voltage plus ripple voltage. Inductor The input ripple voltage can be approximated by The inductor is used to supply constant current to output equation below: when it is driven by a switching voltage. For given input I  V  V and output voltage, inductance and switching frequency ΔVIN = f----×----OC--------- ×1–V-----O---- ×V-----O---- together decide the inductor ripple current, which is: IN IN IN V  V  ΔI = ------O-----×1–-----O---- Since the input current is discontinuous in a buck L f×L  V  IN converter, the current stress on the input capacitor is another concern when selecting the capacitor. For a buck The peak inductor current is: circuit, the RMS value of input capacitor current can be calculated by: ΔI L I = I +-------- Lpeak O 2 V  V  I = I × -----O----1–-----O---- CIN_RMS O VIN VIN High inductance gives low inductor ripple current but requires larger size inductor to avoid saturation. Low if we let m equal the conversion ratio: ripple current reduces inductor core losses. It also reduces RMS current through inductor and switches, V O which results in less conduction loss. --------- = m V IN Rev. 1.2 March 2016 www.aosmd.com Page 8 of 13

AOZ1282CI When selecting the inductor, make sure it is able to For lower output ripple voltage across the entire handle the peak current without saturation even at the operating temperature range, X5R or X7R dielectric type highest operating temperature. of ceramic, or other low ESR tantalum capacitor or aluminum electrolytic capacitor may also be used as The inductor takes the highest current in a buck circuit. output capacitors. The conduction loss on inductor needs to be checked for thermal and efficiency requirements. In a buck converter, output capacitor current is continuous. The RMS current of output capacitor is Surface mount inductors in different shape and styles are decided by the peak to peak inductor ripple current. available from Coilcraft, Elytone and Murata. Shielded It can be calculated by: inductors are small and radiate less EMI noise. But they ΔI cost more than unshielded inductors. The choice I = --------L-- CO_RMS depends on EMI requirement, price and size. 12 Output Capacitor Usually, the ripple current rating of the output capacitor is The output capacitor is selected based on the DC output a smaller issue because of the low current stress. When voltage rating, output ripple voltage specification and the buck inductor is selected to be very small and ripple current rating. inductor ripple current is high, output capacitor could be overstressed. The selected output capacitor must have a higher rated voltage specification than the maximum desired output Schottky Diode Selection voltage including ripple. De-rating needs to be The external freewheeling diode supplies the current to considered for long term reliability. the inductor when the high side NMOS switch is off. To reduce the losses due to the forward voltage drop and Output ripple voltage specification is another important recovery of diode, Schottky diode is recommended to factor for selecting the output capacitor. In a buck use. The maximum reverse voltage rating of the chosen converter circuit, output ripple voltage is determined by Schottky diode should be greater than the maximum inductor value, switching frequency, output capacitor input voltage, and the current rating should be greater value and ESR. It can be calculated by the equation than the maximum load current. below: ΔV = ΔI ×ESR +------------1------------- Thermal Management and Layout O L  CO 8×f×C  Consideration O In the AOZ1282CI buck regulator circuit, high pulsing where, current flows through two circuit loops. The first loop C is output capacitor value, and starts from the input capacitors, to the VIN pin, to the LX O pins, to the filter inductor, to the output capacitor and ESR is the equivalent series resistance of the output CO load, and then return to the input capacitor through capacitor. ground. Current flows in the first loop when the high side switch is on. The second loop starts from inductor, to the When low ESR ceramic capacitor is used as output output capacitors and load, to the anode of Schottky capacitor, the impedance of the capacitor at the switching diode, to the cathode of Schottky diode. Current flows in frequency dominates. Output ripple is mainly caused by the second loop when the low side diode is on. capacitor value and inductor ripple current. The output ripple voltage calculation can be simplified to: In PCB layout, minimizing the two loops area reduces the ΔV = ΔI ×------------1------------- noise of this circuit and improves efficiency. A ground O L 8×f×C  plane is strongly recommended to connect input O capacitor, output capacitor, and PGND pin of the AOZ1282CI. If the impedance of ESR at switching frequency dominates, the output ripple voltage is mainly decided by In the AOZ1282CI buck regulator circuit, the major power capacitor ESR and inductor ripple current. The output dissipating components are the AOZ1282CI, the ripple voltage calculation can be further simplified to: Schottky diode and output inductor. The total power dissipation of converter circuit can be measured by input ΔV = ΔI ×ESR O L CO power minus output power. P = (V ×I )–(V ×V ) total_loss IN IN O IN Rev. 1.2 March 2016 www.aosmd.com Page 9 of 13

AOZ1282CI The power dissipation in Schottky can be approximated Several layout tips are listed below for the best electric as: and thermal performance. P = I ×(1–D)×V 1. The input capacitor should be connected as close as diode_loss O FW_Schottky possible to the VINpin and the GND pin. where, 2. The inductor should be placed as close as possible to the LX pin and the output capacitor. V is the Schottky diode forward voltage drop. FW_Schottky 3. Keep the connection of the schottky diode between The power dissipation of inductor can be approximately the LX pin and the GND pin as short and wide calculated by output current and DCR of inductor. as possible. P =I 2×R ×1.1 4. Place the feedback resistors and compensation inductor_loss O inductor components as close to the chip as possible. 5. Keep sensitive signal traces away from the LX pin. The actual junction temperature can be calculated with power dissipation in the AOZ1282CI and thermal 6. Pour a maximized copper area to the VIN pin, the impedance from junction to ambient. LX pin and especially the GND pin to help thermal dissipation. (P –P –P ) total_loss diode_loss inductor_loss T = -------------------------------------------------------------------------------------------------------------------------- 7. Pour a copper plane on all unused board area and junction θ +T JA ambient connect the plane to stable DC nodes, like VIN, GND or VOUT. The maximum junction temperature of AOZ1282CI is 150ºC, which limits the maximum load current capability. The thermal performance of the AOZ1282CI 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 recommended environmental conditions. Rev. 1.2 March 2016 www.aosmd.com Page 10 of 13

AOZ1282CI Package Dimensions, SOT23-6 Gauge Plane Seating Plane D 0.25mm e1 c L E E1 θ1 e b A A2 .010mm A1 Dimensions in millimeters Dimensions in inches Symbols Min. Nom. Max. Symbols Min. Nom. Max. RECOMMENDED LAND PATTERN A 0.80 — 1.25 A 0.031 — 0.049 A1 0.00 — 0.15 A1 0.000 — 0.006 A2 0.70 1.10 1.20 A2 0.028 0.043 0.047 b 0.30 0.40 0.50 b 0.012 0.016 0.020 2.40 c 0.08 0.13 0.20 c 0.003 0.005 0.008 0.80 D 2.70 2.90 3.10 D 0.106 0.114 0.122 E 2.50 2.80 3.10 E 0.098 0.110 0.122 E1 1.50 1.60 1.70 E1 0.059 0.063 0.067 0.95 0.63 e 0.95 BSC e 0.037 BSC UNIT: mm e1 1.90 BSC e1 0.075 BSC L 0.30 — 0.60 L 0.012 — 0.024 θ1 0° — 8° θ1 0° — 8° Notes: 1. Package body sizes exclude mold flash and gate burrs. Mold flash at the non-lead sides should be less than 5 mils each. 2. Dimension “L” is measured in gauge plane. 3. Tolerance ±0.100 mm (4 mil) unless otherwise specified. 4. Followed from JEDEC MO-178C & MO-193C. 5. Controlling dimension is millimeter. Converted inch dimensions are not necessarily exact. Rev. 1.2 March 2016 www.aosmd.com Page 11 of 13

AOZ1282CI Tape and Reel Dimensions, SOT23-6 Tape P1 T D1 P2 E1 E2 E B0 K0 A0 D0 P0 Feeding Direction Unit: mm Package A0 B0 K0 D0 D1 E E1 E2 P0 P1 P2 T SOT-23 3.15 3.27 1.34 1.10 1.50 8.00 1.75 3.50 4.00 4.00 2.00 0.25 ±0.10 ±0.10 ±0.10 ±0.01 ±0.10 ±0.20 ±0.10 ±0.05 ±0.10 ±0.10 ±0.10 ±0.05 Reel W1 S G N M K V R H W Unit: mm Tape Size Reel Size M N W W1 H K S G R V 8 mm ø180 ø180.00 ø60.50 9.00 11.40 ø13.00 10.60 2.00 ø9.00 5.00 18.00 ±0.50 Min. ±0.30 ±1.0 +0.50 / -0.20 ±0.50 Leader/Trailer and Orientation Trailer Tape Components Tape Leader Tape 300mm min. or Orientation in Pocket 500mm min. or 75 Empty Pockets 125 Empty Pockets Rev. 1.2 March 2016 www.aosmd.com Page 12 of 13

AOZ1282CI Part Marking AOZ1282CI (SOT23-6) B N 20DW 1 Assembly Lot Code 1 Part Number Code Week & Year Code Option / Assembly Location Code LEGAL DISCLAIMER Alpha and Omega Semiconductor makes no representations or warranties with respect to the accuracy or completeness of the information provided herein and takes no liabilities for the consequences of use of such information or any product described herein.Alpha and Omega Semiconductor reserves the right to make changes to such information at any time without further notice. This document does not constitute the grant of any intellectual property rights or representation of non-infringement of any third party’s intellectual property rights. LIFE SUPPORT POLICY ALPHA AND 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 2. A critical component in any component of a life systems which, (a) are intended for surgical implant into support, device, or system whose failure to perform can the body or (b) support or sustain life, and (c) whose be reasonably expected to cause the failure of the life failure to perform when properly used in accordance support device or system, or to affect its safety or with instructions for use provided in the labeling, can be effectiveness. reasonably expected to result in a significant injury of the user. Rev. 1.2 March 2016 www.aosmd.com Page 13 of 13