AOZ2151EQI-30

AOZ2151EQI-30 28V/4A Synchronous EZBuckTM Regulator General Description Features The AOZ2151EQI-30 is a high-efficiency, easy-to-use DC/DC synchronous buck regulator that operates up to 28V. The device is capable of supplying 4A of continuous output current with an output voltage adjustable down to 0.8V ±1%.  Wide input voltage range – 6.5V to 28V  4A continuous output current  Output voltage adjustable down to 0.8V (±1.0%)  Low RDS(ON) internal NFETs The AOZ2151EQI-30 integrates an internal linear regulator to generate 5.3V VCC from input. If input voltage is lower than 5.3V, the linear regulator operates at low drop output mode, which allows the VCC voltage is equal to input voltage minus the drop-output voltage of the internal linear regulator. – 28m high-side – 28m low-side  Constant On-Time with input feed-forward  Ceramic capacitor stable  Adjustable soft start A proprietary constant on-time PWM control with input feed-forward results in ultra-fast transient response while maintaining relatively constant switching frequency over the entire input voltage range.  Integrated bootstrap diode The device features multiple protection functions such as VCC under-voltage lockout, cycle-by-cycle current limit, output over-voltage protection, short-circuit protection, and thermal shutdown.  Thermally enhanced 3mm x 3mm QFN-18L package  Cycle-by-cycle current limit  Short-circuit protection  Thermal shutdown Applications  Compact desktop PCs The AOZ2151EQI-30 is available in a 3mm×3mm QFN18L package and is rated over a -40°C to +85°C ambient temperature range.  Graphics cards  Set-top boxes  LCD TVs  Cable modems  Point-of-load DC/DC converters  Telecom/Networking/Datacom equipment Typical Application RTON CTON 100pF 5.3V C4 4.7µF TON BST VCC C2 22µF C5 0.1µF AOZ2151EQI-30 LX Off On INPUT 6.5V to 28V IN EN L1 1.5µH R2 FB R1 CSS SS Output 3.3V, 4A C3 88µF AGND PGND Analog Ground Power Ground Rev 1.2 September 2018 www.aosmd.com Page 1 of 15 AOZ2151EQI-30 Option Table PFM / Force PWM for Light Load Operation Part Number PFM AOZ2151EQI-30 V Force PWM AOZ2151EQI-31 V Recommended Start-up Sequence VIN EN 50µs Rev 1.2 September 2018 www.aosmd.com Page 2 of 15 AOZ2151EQI-30 Ordering Information Part Number Ambient Temperature Range Package Environmental AOZ2151EQI-30 -40°C to +85°C 18-Pin 3mm x 3mm QFN 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 SS VCC BST TON 18 17 16 15 EN 1 14 LX FB 2 13 LX AGND 3 12 PGND IN 4 11 PGND IN 5 10 PGND 6 7 8 9 IN IN LX LX IN IN 18-Pin 3mm x 3mm QFN (Top View) Pin Description Pin Number Pin Name Pin Function 1 EN Enable Input. The AOZ2151EQI-30 is enabled when EN is pulled high. The device shuts down when EN is pulled low. 2 FB Feedback Input. Adjust the output voltage with a resistive voltage-divider between the regulator’s output and AGND. 3 AGND Analog Ground. 4, 5, 6, 7, 8 IN Supply Input. IN is the regulator input. All IN pins must be connected together. 9, 13, 14 LX Switching Node. 10, 11, 12 PGND Power Ground. 15 TON On-Time Setting Input. Connect a resistor between VIN and TON to set the on time. 16 BST Bootstrap Capacitor Connection. The AOZ2151EQI-30 includes an internal bootstrap diode. Connect an external capacitor between BST and LX as shown in the Typical Application diagram. 17 VCC Supply Input for analog functions. Bypass VCC to AGND with a 4.7µF~10µF ceramic capacitor. Place the capacitor close to VCC pin. 18 SS Rev 1.2 September 2018 Soft-Start Time Setting Pin. Connect a capacitor between SS and AGND to set the soft-start time. www.aosmd.com Page 3 of 15 AOZ2151EQI-30 Absolute Maximum Ratings Maximum Operating Ratings Exceeding the Absolute Maximum Ratings may damage the device. The device is not guaranteed to operate beyond the Maximum Operating ratings. Parameter Rating IN, TON to AGND Parameter -0.3V to 30V Supply Voltage (VIN) LX to AGND -0.3V to 30V Output Voltage Range BST to AGND -0.3V to 36V Ambient Temperature (TA) (1) SS, FB, EN, VCC to AGND -0.3V to +0.3V Junction Temperature (TJ) +150°C Storage Temperature (TS) -65°C to +150°C ESD Rating(2) 6.5V to 28V 0.8V to 0.85*VIN -40°C to +85°C Package Thermal Resistance (JA) (JC) -0.3V to 6V PGND to AGND Rating 40°C/W 6°C/W 2kV Notes: 1. LX to PGND Transient (t 2V, PFM IOFF Shutdown Supply Current VEN = 0V VFB Feedback Voltage TA = 25°C TA = 0°C to 85°C IFB Min. 3.2 0.792 0.788 4.0 3.7 Max Units 28 V 4.4 V 0.16 mA 15 A 0.800 0.800 0.808 0.812 V Load Regulation 0.5 % Line Regulation 1 % FB Input Bias Current 200 nA Enable Off threshold On threshold 0.5 VEN EN Input Threshold VEN_HYS EN Input Hysteresis 300 mV TON_MIN Minimum On Time 60 ns TON_MAX Maximum On Time 2.6 s TOFF_MIN Minimum Off Time 300 ns 1.6 V Modulator Soft-Start ISS_OUT SS Source Current VSS = 0 CSS = 0.001F to 0.1F 7 11 15 A Under Voltage and Over Voltage Protection VPL Under Voltage Threshold TPL Under Voltage Delay Time VPH Over Voltage Threshold Rev 1.2 September 2018 FB falling FB rising www.aosmd.com 70 % 32 s 120 % Page 4 of 15 AOZ2151EQI-30 Electrical Characteristics TA = 25°C, VIN=12V, EN = 5V, unless otherwise specified. Specifications in BOLD indicate a temperature range of -40°C to +85°C. Symbol Parameter Conditions Min. Typ. Max Units Power Stage Output RDS(ON) RDS(ON) High-Side NFET On-Resistance VIN = 12V High-Side NFET Leakage VEN = 0V, VLX = 0V Low-Side NFET On-Resistance VLX = 12V Low-Side NFET Leakage VEN = 0V 28 m 10 28 A m 10 A Over-current and Thermal Protection ILIM Current Limit Thermal Shutdown Threshold Rev 1.2 September 2018 6 TJ rising TJ falling www.aosmd.com A 150 100 °C Page 5 of 15 AOZ2151EQI-30 Functional Block Diagram BST IN LDO VCC EN UVLO Reference & Bias Error Comp 0.8V TOFF_MIN Q Timer SS FB ISENSE (AC) S Q R FB Decode LX ILIM Comp ILIM Current Information Processing ISENSE OTP TON Timer TON Generator Light Load Threshold EN Light Load Comp ISENSE PGND Rev 1.2 September 2018 ISENSE (AC) Vcc TON Q ISENSE www.aosmd.com AGND Page 6 of 15 AOZ2151EQI-30 Typical Performance Characteristics Circuit of Typical Application. TA = 25°C, VIN = 19V, VOUT = 3.3V, unless otherwise specified. Load Transient 0A to 4A Normal Operation VLX (10V/div) ILX (5A/div) ILX (5A/div) V O ripple (100mV/div) V O ripple (50mV/div) 500µs/div 10µs/div Full Load Start-up Short Circuit Protection VLX (20V/div) VLX (20V/div) EN (5V/div) ILX (5A/div) ILX (5A/div) VO (2V/div) VO (2V/div) 5µs/div 1m s/div Efficiency vs. Load Current 100 VOUT = 3.3V Efficiency (%) 95 90 85 80 Vin = 6.5V Vin = 12V Vin = 19V 75 Vin = 24V 70 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Output Current (A) Rev 1.2 September 2018 www.aosmd.com Page 7 of 15 AOZ2151EQI-30 Detailed Description The AOZ2151EQI-30 is a high-efficiency, easy-to-use, synchronous buck regulator optimized for notebook computers. The regulator is capable of supplying 4A of continuous output current with an output voltage adjustable down to 0.8V. The input voltage of AOZ2151EQI-30 can be as low as 6.5V. The highest input voltage of AOZ2151EQI-30 can be 28V. Constant on-time PWM with input feed-forward control scheme results in ultra-fast transient response while maintaining relatively constant switching frequency over the entire input range. True AC current mode control scheme guarantees the regulator can be stable with ceramics output capacitor. Protection features include VCC under-voltage lockout, cycle-by-cycle current limit, output over voltage and under voltage protection, shortcircuit protection, and thermal shutdown. The AOZ2151EQI-30 is available in 18-pin 3mm×3mm QFN package. Input Power Architecture The AOZ2151EQI-30 integrates an internal linear regulator to generate 5.3V (±5%) VCC from input. If input voltage is lower than 5.3V, the linear regulator operates at low drop-output mode; the VCC voltage is equal to input voltage minus the drop-output voltage of internal linear regulator. Enable and Soft Start The AOZ2151EQI-30 has external soft start feature to limit in-rush current and ensure the output voltage ramps up smoothly to regulate voltage. A soft start process begins when VCC rises to 4.5V and voltage on EN pin is HIGH. An internal current source charges the external soft-start capacitor; the FB voltage follows the voltage of soft-start pin (VSS) when it is lower than 0.8V. When VSS is higher than 0.8V, the FB voltage is regulated by internal precise band-gap voltage (0.8V). The soft-start time for FB voltage can be calculated by the following formula: TSS(s) = 80 x CSS(nF) If CSS is 1nF, the soft-start time will be 80µ seconds; if CSS is 10nF, the soft-start time will be 800µ seconds. VOUT VSS VSS = 3.3V VSS = 0.8V Figure 1. Soft Start Sequence of AOZ2151EQI-30 Constant-On-Time PWM Control with Input Feed-Forward The control algorithm of AOZ2151EQI-30 is constant-ontime PWM control with input feed-forward. The simplified control schematic is shown in Figure 2. The high-side switch on-time is determined solely by a one-shot whose pulse width is inversely proportional to input voltage (IN). The one-shot is triggered when the internal 0.8V is higher than the combined information of FB voltage and the AC current information of inductor, which is processed and obtained through the sensed low-side MOSFET current once it turns-on. The added AC current information can help the stability of constant-on time control even with pure ceramic output capacitors, which have very low ESR. The AC current information has no DC offset, which does not cause offset with output load change, which is fundamentally different from other V2 constant-on time control schemes. IN – PWM Programmable One-Shot FB Voltage/AC Current Information Comp + 0.8V Figure 2. Simplified Control Schematic of AOZ2151EQI-30 The constant-on-time PWM control architecture is a pseudo-fixed frequency with input voltage feed-forward. The internal circuit of AOZ2151EQI-30 sets the on-time of high-side switch inversely proportional to the IN. Ton  Rton () Vin (V ) (1) To achieve the flux balance of inductor, the buck converter has the equation: Fsw  Rev 1.2 September 2018 www.aosmd.com Vout Vin * Ton (2) Page 8 of 15 AOZ2151EQI-30 Once the product of Vin*Ton is constant, the switching frequency keeps constant and is independent of input voltage. An external resistor between the IN and TON pins sets the switching on-time according to the following curves: TON (nS) TON vs. RTON @ VIN=6.5V ~ 16V an effective current-sense resistor. Ceramic capacitors usually can not be used as output capacitor. The AOZ2151EQI-30 senses the low-side MOSFET current and processes it into DC current and AC current information using AOS proprietary technique. The AC current information is decoded and added on the FB pin on phase. With AC current information, the stability of constant-on-time control is significantly improved even without the help of output capacitor’s ESR; and thus the pure ceramic capacitor solution can be applicant. The pure ceramic capacitor solution can significantly reduce the output ripple (no ESR caused overshoot and undershoot) and less board area design. Current-Limit Protection The AOZ2151EQI-30 has the current-limit protection by using Rdson of the low-side MOSFET to be as current sensing. To detect real current information, a minimum constant off time (300ns typical) is implemented after a constant-on time. If the current exceeds the current-limit threshold, the PWM controller is not allowed to initiate a new cycle. The actual peak current is greater than the current-limit threshold by an amount equal to the inductor ripple current. Therefore, the exact current-limit characteristic and maximum load capability are a function of the inductor value and input and output voltages. The current limit will keep the low-side MOSFET on and will not allow another high-side on-time, until the current in the low-side MOSFET reduces below the current limit. RTON (kȟ) TON (nS) TON vs. RTON @ VIN=6.5V ~ 16V After 8 switching cycles, the AOZ2151EQI-30 considers this is a true failed condition and thus turns-off both highside and low-side MOSFET and shuts down. The AOZ2151EQI-30 enters hiccup mode to periodically restart the part. When the current limit protection is removed, the AOZ2151EQI-30 exits hiccup mode. Output Voltage Under-Voltage Protection RTON (kȟ) Figure 3. Ton vs. Rton Curves for AOZ2151EQI-30 A further simplified equation will be: Fsw ( KHz)  Vout (V ) 106 Vin (V )  Ton (nS ) (3) If the output voltage is lower than 70% by over-current or short circuit, AOZ2151EQI-30 will wait for 32µs (typical) and turns-off both high-side and low-side MOSFET and shuts down. When the output voltage under-voltage protection is removed, the AOZ2151EQI-30 restarts again. Output Voltage Over-voltage Protection If Vo is 1V, Vin is 19V, and set Fs=400kHz. According to eq.(3), Ton= 131.6nS is needed. Finally, use the Ton to Rton curve, we can find out Rton is 300k. This algorithm results in a nearly constant switching frequency despite the lack of a fixed-frequency clock generator. The threshold of OVP is set 20% higher than 0.8V. When the VFB voltage exceeds the OVP threshold, high-side MOSFET is turned-off and low-side MOSFET is turnedon 1µs, then shuts down. When the output voltage overvoltage protection is removed, the AOZ2151EQI-30 restarts again. True Current Mode Control The constant-on-time control scheme is intrinsically unstable if output capacitor’s ESR is not large enough as Rev 1.2 September 2018 www.aosmd.com Page 9 of 15 AOZ2151EQI-30 Application Information The basic AOZ2151EQI-30 application circuit is shown in the Typical Application section. The component selection is explained below. Input capacitor The input capacitor must be connected to the IN pins and PGND pin of the AOZ2151EQI-30 to maintain steady input voltage and filter out the pulsing input current. A small decoupling capacitor, usually 4.7µF, should be connected to the VCC pin and AGND pin for stable operation of the AOZ2151EQI-30. The voltage rating of input capacitor must be greater than maximum input voltage plus ripple voltage. The input ripple voltage can be approximated by equation below: VO  VO IO  V IN = -----------------   1 – ---------  --------V IN V IN f  C IN  (4) 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: VO  VO  I CIN_RMS = I O  ---------  1 – --------- V IN  V IN (5) if let m equal the conversion ratio: VO -------- = m V IN (6) The relation between the input capacitor RMS current and voltage conversion ratio is calculated and shown in Figure 4. It can be seen that when VO is half of VIN, CIN it is under the worst current stress. The worst current stress on CIN is 0.5 x IO. 0.5 Inductor The inductor is used to supply constant current to output when it is driven by a switching voltage. For given input and output voltage, inductance and switching frequency together decide the inductor ripple current, which is: VO  VO  I L = -----------   1 – --------- V IN fL  (7) The peak inductor current is: I L I Lpeak = I O + -------2 (8) High inductance gives low inductor ripple current but requires larger size inductor to avoid saturation. Low 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 30% to 50% of output current. When selecting the inductor, make sure 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 conduction loss on inductor needs to be checked for thermal and efficiency requirements. Surface mount inductors in different shape and styles are available from Coilcraft, Elytone and Murata. Shielded inductors are small and radiate less EMI noise. But they cost more than unshielded inductors. The choice depends on EMI requirement, price and size. 0.4 ICIN_RMS(m) 0.3 IO 0.2 Output Capacitor 0.1 0 For reliable operation and best performance, the input capacitors must have current rating higher than ICIN-RMS at worst operating conditions. Ceramic capacitors are preferred for input capacitors because of their low ESR and high ripple current rating. Depending on the application circuits, other low ESR tantalum capacitor or aluminum electrolytic capacitor may also be used. When selecting ceramic capacitors, X5R or X7R type dielectric ceramic capacitors are preferred for their better temperature and voltage characteristics. Note that the ripple current rating from capacitor manufactures is based on certain amount of life time. Further de-rating may be necessary for practical design requirement. 0 0.5 m Figure 4. ICIN vs. Voltage Conversion Ratio Rev 1.2 September 2018 1 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 www.aosmd.com Page 10 of 15 AOZ2151EQI-30 voltage including ripple. De-rating considered for long term reliability. needs to be 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 the equation below: 1 V O = I L   ESR CO + -------------------------  8fC  (9) O where, CO is output capacitor value and ESRCO 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: 1 V O = I L  ------------------------8fC (10) O 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: V O = I L  ESR CO (11) For lower output ripple voltage across the entire operating 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 output capacitor is decided by the peak to peak inductor ripple current. It can be calculated by: I L I CO_RMS = ---------12 (12) 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 and inductor ripple current is high, output capacitor could be overstressed. Rev 1.2 September 2018 Thermal Management and Layout Consideration In the AOZ2151EQI-30 buck regulator circuit, high pulsing current flows through two circuit loops. The first loop starts from the input capacitors, to the IN pin, to the LX pins, to the filter inductor, to the output capacitor and load, and then return 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 switch. Current flows in the second loop when the low side low side switch is on. In PCB layout, minimizing the two loops area reduces the noise of this circuit and improves efficiency. A ground plane is strongly recommended to connect input capacitor, output capacitor, and PGND pin of the AOZ2151EQI-30. In the AOZ2151EQI-30 buck regulator circuit, the major power dissipating components are the AOZ2151EQI-30 and the output inductor. The total power dissipation of converter circuit can be measured by input power minus output power. (13) P total_loss = V IN  I IN – V O  I O The power dissipation of inductor can be approximately calculated by output current and DCR of inductor and output current.The actual junction temperature can be P inductor_loss = IO2  R inductor  1.1 (14) calculated with power dissipation in the AOZ2151EQI-30 and thermal impedance from junction to ambient. T junction  ( Ptotal _ loss  Pinductor _ loss )   JA  T A (15) The maximum junction temperature of AOZ2151EQI-30 is 150ºC, which limits the maximum load current capability. The thermal performance of the AOZ2151EQI-30 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. www.aosmd.com Page 11 of 15 AOZ2151EQI-30 4. Decoupling capacitor CVCC should be connected to VCC and AGND as close as possible. Layout Considerations Several layout tips are listed below for the best electric and thermal performance. 5. Voltage divider R1 and R2 should be placed as close as possible to FB and AGND. 1. The LX pins and pad are connected to internal low side switch drain. They are low resistance thermal conduction path and most noisy switching node. Connected a large copper plane to LX pin to help thermal dissipation. 6. Keep sensitive signal traces such as feedback trace far away from the LX pins. 7. Pour copper plane on all unused board area and connect it to stable DC nodes, like VIN, GND or VOUT. 2. The IN pins and pad are connected to internal high side switch drain. They are also low resistance thermal conduction path. Connected a large copper plane to IN pins to help thermal dissipation. 3. Input capacitors should be connected to the IN pin and the PGND pin as close as possible to reduce the switching spikes. CVCC SS VCC BST TON 18 17 16 15 1 14 LX FB 2 13 LX AGND 3 12 PGND IN 4 11 PGND IN 5 10 PGND 7 8 9 IN IN LX LX 6 IN IN V OUT EN VOUT Cout PGND VIN Cin Rev 1.2 September 2018 www.aosmd.com Page 12 of 15 AOZ2151EQI-30 Package Dimensions, QFN 3x3, 18 Lead EP2_S 1 RECOMMENDED LAND PATTERN UNIT: mm NOTE CONTROLLING DIMENSION IS MILLIMETER. CONVERTED INCH DIMENSIONS ARE NOT NECESSARILY EXACT. Rev 1.2 September 2018 www.aosmd.com Page 13 of 15 AOZ2151EQI-30 Tape and Reel Dimensions, QFN 3x3, 18 Lead EP2_S Carrier Tape Reel Leader/Trailer & Orientation Rev 1.2 September 2018 www.aosmd.com Page 14 of 15 AOZ2151EQI-30 Part Marking AOZ2151EQI-30 (QFN 3x3) A B EM Part Number Code Option Code YW LT Assembly Lot Code Year & Week Code Part Number Part Number Code of Marking AOZ2151EQI-30 ABEM AOZ2151EQI-31 ABEW LEGAL DISCLAIMER Applications or uses as critical components in life support devices or systems are not authorized. AOS does not assume any liability arising out of such applications or uses of its products. AOS reserves the right to make changes to product specifications without notice. It is the responsibility of the customer to evaluate suitability of the product for their intended application. Customer shall comply with applicable legal requirements, including all applicable export control rules, regulations and limitations. AOS' products are provided subject to AOS' terms and conditions of sale which are set forth at: http://www.aosmd.com/terms_and_conditions_of_sale 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 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. Rev 1.2 September 2018 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. www.aosmd.com Page 15 of 15