Advanced Power Electronics Corp. APE1596A 3A/23V High Efficiency Synchronous Rectified Step-Down DC/DC Converter FEATURES DESCRIPTION The APE1596A is a high efficiency synchronous stepdown DC/DC converter series with 3A continuous output current supplied. Included on the substrate with the features listed is a high performance trans-conductance error amplifier that provides tight voltage regulation and accuracy under transient conditions. A built-in under voltage lockout circuit is provided to prevent start-up until the input voltage reaches to 4.5V. In addition, it features over-current protection and thermal shutdown. The APE1596A is available in ESOP-8 package. Input Voltage Supply Range from 4.5V to 23V High Efficiency up to 95% Adjustable Output Voltage from 0.925V to 12V 3A Continuous Output Current 330kHz Constant Frequency Operation Current Mode Operation Programmable Soft-start Over-temperature Protection Over-current Protection Input Under Voltage Lockout 15μA Shutdown Current ESOP-8 Package RoHS Compliant APPLICATION Data comm. xDSL CPE Graphics Cards Set-Top-Box, DVD Servers/Networking DSP and FPGA Power Supply Telecomm Equipments DC-DC Regulator Modules LCD Monitor and LCD TV TYPICAL APPLICATION Input 4.5 to 23V BS VIN Cin 22uF/ 25V X5R MLCC Css 10nF VSW EN SS APE1596A Cbs 10nF L 10uH Output 3.3V R1 26.1K Cup Option COMP FB GND Cs Cout 22 uFx2 X5R R2 10K Cp Rc Data and specifications subject to change without notice 1 201205091 Advanced Power Electronics Corp. APE1596A PACKAGE ORDERING INFORMATION ( Top View ) APE1596A X BS 1 Package Type VIN 2 MP : ESOP-8 SW 3 GND 4 8 SS EXPOSED PAD 7 EN 6 COMP 5 FB ESOP-8 ABSOLUTE MAXIMUM RATINGS (at TA=25°C) Input Supply Voltage(VIN) --------------------------------- GND - 0.3V to +26V SW PIN Voltage(VSW ) -------------------------------------- - 1V (-5V for 10nS) toVIN+0.3V EN PIN Voltage(VEN) --------------------------------------- - 0.3 to VIN+0.3V Other Pins Voltage ----------------------------------------- - 0.3V to +6V Boost Voltage ------------------------------------------------ Vsw+6V SW Peak Current ------------------------------------------- 4.5A Power Dissipation(PD)@TA=25oC ---------------------- 1.96W Storage Temperature Range(T ST) ---------------------- -65°C To 150°C Junction Temperature Range(T j) ----------------------- -40°C To 150°C Lead Temperature (Soldering 10s) --------------------- 260oC Thermal Resistance from Junction to Case(Rth JC) 13°C/W Thermal Resistance from Junction to Ambient(RthJA) 51°C/W RECOMMENDED OPERATING CONDITIONS Input Supply Voltage(VIN) --------------------------------- 4.5V to +23V Operating Temperature ----------------------------------- -30°C To 85°C Note 1: Stresses beyond above listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability. Note 2: Guaranteed by design, not production tested. Note3: For the measuring condition of Rthja, it is under the natural convection at TA = 25oC and on a four-layer test board with highly effective thermal conductivity following the JEDEC 51-7 thermal measurement standard. As for the case position of Rthjc, it is on the exposed pad of the package. ELECTRICAL SPECIFICATIONS (Recommended Operating Conditions, Unless Otherwise Noted; VIN = 12V; TA = 25 oC) MIN TYP MAX UNITS 4.5 - 23 V VEN = 0V - 15 - uA Regulated Feedback Voltage 4.5V≦VIN≦23V 0.9 0.925 0.95 V Error Amplifier Transconductance △ICOMP = +10uA - 700 - uA/V Parameter SYM Supply Voltage VIN Shutdown Supply Current ISD TEST CONDITION 2 Advanced Power Electronics Corp. APE1596A ELECTRICAL SPECIFICATIONS MIN TYP MAX UNITS - 2.2 - A/V - 4.5 - A - - 10 uA High Side On Resistance - 0.1 - Ω Low Side On Resistance - 0.1 - Ω Parameter Current Sense Transconductance SYM to TEST CONDITION COMP Current Limit SW Leakage Current VEN = 0V, VSW = 0V Oscillation Frequency 260 330 400 kHz VFB=0V - 82.5 - kHz VFB=0.7V - 90 - % - 100 - ns 3.9 4.2 4.3 V - 400 - mV Thermal Shutdown Threshold - 155 - EN High Level - 2.35 - V EN Low Level - 1.2 - V VEN = 0V 0.8 1 1.2 uA Css=0.1uF - 21 - ms Short Circuit Oscillation Frequency Maximum Duty Cycle Minimum On Time Under Voltage Lockout Threshold Under Voltage Lockout Threshold Hysteresis VIN Rising EN Input Current Soft Start o C o Note: Fully production test at +25 C. Specifications over the temperature range are guaranteed by design and characterization. PIN DESCRIPTIONS PIN SYMBOL BS FB EN GND PIN DESCRIPTION It is required to connect SW and BS by a capacitor, which is able to boost the gate drive to the internal NMOS above VIN to fully turn it ON. This is the input to an error amplifier, which drives the PWM controller. It is necessary to connect this pin to the actual output of power supply to set the DC output voltage. This input provides an electrical ON/OFF control of the power supply. If the EN pin is open, it will be pulled to high by the internal circuit. This is the reference of the ground connection for all components in the power supply. SW This is the output of a power MOSFET switch. VIN The input voltage for the power supply is connected to this pin. SS COMP This pin is connected to an external capacitor to control soft-start timing. 21ms soft-start period can be obtained by connecting a 0.1uF capacitor. This pin is to compensate the regulation control loop by connecting a series of RC network from COMP pin to GND pin. 3 Advanced Power Electronics Corp. APE1596A BLOCK DIAGRAM Current Sense Amplifier EN VIN Slope Compensation Σ Reference 0.925V VCS PWM Comparator PWM Error Amplifier FB BS UG M1 PWM/ PSM Logic SW Clock Oscillator LG COMP SS M2 GND FUNCTION PIN DESCRIPTION The APE1596A is a current mode PWM synchronous step-down converter with a constant switching frequency. It regulates the input voltage from 4.5V to 23V and a low output voltage of 0.925V.The supplied load current is up to 3A. Pulse Skip Mode The APE1596A enters a pulse-skipping mode at light load to minimize the switching loss by reducing the switching frequency. A zero-cross sensing circuit monitors the low side N-MOSFET current for zero crossing. When the inductor current crossing zero is detected, the regulator enters the skip mode. Oscillator Frequency Slope compensated current mode PWM control provides not only stable switching and cycle-by-cycle current limit for superior load and line response but also protection of the internal main switch and synchronous rectifier. The APE1596A switches at a constant frequency (330 kHz) and regulates the output voltage. The PWM comparator modulates the power transferred to the load by changing the inductor ’ s peak current based on the feedback error voltage during each cycle. The main switch is turned on for a certain period to ramp the inductor ’ s current at each rising edge of the internal oscillator under normal operation whereas off when the inductor ’ s peak current is above the error voltage. After the main switch is turned off, the low side MOS will be turned on immediately and stay on until the next cycle starts. 4 Advanced Power Electronics Corp. APE1596A Short Circuit Protection The APE1596A provides short circuit protection. When the output is shorted to ground, the oscillator ’ s frequency is reduced to prevent the inductor ’ s current from increasing beyond the NMOS current limit. The NMOS current limit is also reduced to lower the short circuit current. The frequency and current limit will return to the normal values once the short circuit condition is removed and the feedback voltage reaches 0.925V. Maximum Load current The APE1596A can operate down to 4.5V input voltage; however the maximum load current decreases at lower input due to large IR voltage drop on the main switch and low side switch. The slope compensation signal reduces the inductor ’ s peak current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Enable The EN pin provides electrical on/off control of the regulator. Once the voltage of the EN pin exceeds the threshold voltage, the regulator starts operation and the internal slow start begins to ramp. If the voltage of the EN pin is pulled below the threshold, the regulator will stop switching and the internal slow start reset. If the EN pin is open, it will be pulled to high by the internal circuit. Under Voltage Lockout The APE1596A incorporates an under voltage lockout circuit to keep the device disabled when VIN is below the UVLO start threshold. During power-up, the internal circuit is held inactive until VIN exceeds the UVLO start threshold voltage. Once this threshold voltage is reached, device start-up begins. The device operates until VIN falls below the UVLO stop threshold voltage. The typical hysteretic in the UVLO comparator is 400mV. Soft-start The built-in soft-start function is provided by APE1596A to reduce the input inrush current after power-on. If the SS pin is activated, it will provide about 150us to make the duty transferred from small to specific duty during the power-on period. Thus this function can lower the current stress on input power, MOSFET, and freewheeling diode. The soft start time can be programmed by connecting this pin with a capacitor, which is defined as the following. 21mS soft-start period can be obtained by connecting a 0.1uF capacitor. Tss = Css × Vref Iss Boost Capacitor The BS pin and SW pin can be connected by a 10nF low ESR ceramic capacitor, providing the gate drive voltage for the high side MOSFET. 5 Advanced Power Electronics Corp. APE1596A Thermal Shutdown The APE1596A protects itself from overheating with an internal thermal shutdown circuit. If the junction temperature exceeds the thermal shutdown threshold, the voltage reference will be grounded and high side MOSFET turned off. Compensation The system stability is controlled through COMP pin. It will present a general design procedure to ensure a stable and operational circuit. The design in this data sheet is optimized for particular requirements. Some components may need to be changed to ensure stability if there are different requirements. First of all, the power components and their corresponding effects need to be determined. Following are the compensation components, which are to produce stability. The compensation steps for the converter are listed below: (1). Choose an appropriate inductor and output capacitance based on the allowed output voltage ripple and load transient. (2). Placing FC as high as possible can respond quickly to the load transient. Considering the output capacitor’s tolerances and temperature effects, typically place FC approximately 1/10 of FS for the multi-layer ceramic output capacitor (X5R, X7R). However, if the type of the output capacitor is the aluminum electrolytic or that largely variable with the temperature, place FC approximately 1/20 of FS. (3). Set the compensation RC to zero to cancel the RLOAD COUT pole. RC = 2π × FC × COUT × VOUT G M × G CS × VREF CC = COUT × R LOAD RC GM : error amp transconductance GCS : current sense transconductance (4). Determine CP if required. If ZESR (zero occurs by output capacitor ESR) is less than FC, it should be cancelled with a pole set by capacitor CP connected between CC to GND. C P = C OUT × R ESR RC 6 Advanced Power Electronics Corp. APE1596A APPLICATION INFORMATION Input Capacitor Selection It is necessary for the input capacitor to sustain the ripple current produced during the period of “on” state of the upper MOSFET, so a low ESR is required to minimize the loss. The RMS value of this ripple can be obtained by the following: I IN RMS = I OUT D × (1 − D ) Where D is the duty cycle, linRMS is the input RMS current, and IOUT is the load current. The equation reaches its maximum value with D = 0.5. The loss of the input capacitor can be calculated by the following equation: PCIN = ESR CIN × I IN RMS 2 Where PCIN is the power loss of the input capacitor and ESRCIN is the effective series resistance of the input capacitance. Due to large dI/dt through the input capacitor, electrolytic or ceramics should be used. If a tantalum must be used, it must be surge-protected. Otherwise, capacitor failure could occur. Output Inductor Selection The output inductor selection is to meet the requirements of the output voltage ripple and affects the load transient response. The higher inductance can reduce the inductor's ripple current and induce the lower output ripple voltage. The ripple voltage and current can be approximately calculated approximated by the following equations: ∆I = V in − V out V out • FS × L Vin ∆ Vout = ∆ I × ESR Although the increase of the inductance reduces the ripple current and voltage, it contributes to the decrease of the response time for the regulator to load transient as well. Increasing the switching frequency (Fs) for a given inductor also can reduce the ripple current and voltage but it will increase the switching loss of the power MOS. The way to set a proper inductor value is to have the ripple current ( △ I) be approximately 10%~50% of the maximum output current. Once the value has been determined, select an inductor capable of carrying the required peak current without going into saturation. It is also important to have the inductance tolerance specified to keep the accuracy of the system controlled. Using 20% for the inductance (at room temperature) is reasonable tolerance able to be met by most manufacturers. For some types of inductors, especially those with core made of ferrite, the ripple current will increase abruptly when it saturates, resulting in a larger output ripple voltage. 7 Advanced Power Electronics Corp. APE1596A Output Capacitors Selection An output capacitor is required to filter the output and supply the load transient current. The high capacitor value and low ESR will reduce the output ripple and the load transient drop. These requirements can be met by a mix of capacitors and careful layout. In typical switching regulator design, the ESR of the output capacitor bank dominates the transient response. The number of output capacitors can be determined by the following equations: ∆VESR ESR MAX = ∆I OUT Number Of Capacitors = ESR CAP ESR MAX △VESR = change in output voltage due to ESR (assigned by the designer) △IOUT = load transient. ESRCAP = maximum ESR per capacitor (specified in manufacturer’s data sheet). ESRMAX = maximum allowable ESR. High frequency decoupling capacitors should be placed as close to the power pins of the load as physically possible. For the decoupling requirements, please consult the capacitor manufacturers for confirmation. Output Voltage The output voltage is set using the FB pin and a resistor divider connected to the output as shown in the following AP Circuit. The output voltage (VOUT) can be calculated according to the voltage of the FB pin (VFB) and ratio of the feedback resistors by the following equation, where (VFB) is 0.925V: VFB = Vout × R2 ( R1 + R 2 ) Vout = 0 .925 × ( R1 + R 2 ) R2 Thus the output voltage is: 8 Advanced Power Electronics Corp. APE1596A External Bootstrap Diode It is strongly recommended that an external bootstrap diode be added when there is a 5V fixed input for the system or the power supply generates a 5V output in order to improve the efficiency of the APE1596A regulator. The boost diode can be the one with lost cost such as IN4148 or BAT54. 5V VIN BS 10nF APE1596A SW This diode is also recommended for high duty cycle operation when Duty Cycle>65% (Example: VIN=5V & VOUT=3.3V; Duty Cycle=66%) and high output voltage (VOUT>12V) applications. Layout Consideration For proper operation of the converter, some layout rules should be followed. It is necessary to understand which pin of APE1596A is sensitive and which is insensitive. Please refer the following for the location where noise comes from on the circuit and where the clear ground is for the small signal ground. R2 10K Input 4.5 to 23V FB VIN BS Cbs 10nF L 10uH Cin 22uF/25V EN SW APE1596A R1 26.1K Output 3.3V/3A SS Css GND COMP Cp Cout 22uF/6.3V x2 Ceramic Cs Rs PGND Return Path 1.) First, put the input capacitor (CIN) as close as possible to the VIN pin. 2.) Secondly, place the Cs, Rs, Cp, Css and R2 as close as APE1596A and connect these analog grounds (Clear AGND) to APE1596A ’ s GND pin. It is recommended to use a dot short for these AGND pins or connect the GND pin via contact. 3.) The large current loop shown in bold lines in the above figure circuit should be routed as short and wide as possible and the switch node is a high dv/dt. It easily couples noise to other traces by the capacitive path. Therefore the sensitive signals like FB, COMP and AGND should be routed away with this noise source. 4.) The feedback network resistors (R1 & R2) should be routed away from the inductor and switch node to minimize noise and EMI issue. And the R1 resistor should be sensed the output capacitor or device loading, not the inductor’s output node. 9 Advanced Power Electronics Corp. APE1596A PCB Layout Guide Top Layer Bottom Layer (Top view) 10 Advanced Power Electronics Corp. APE1596A APE1596A EVB Schematic Application 1 C12 NC R1 R2 10K U1 APE1596A FB COMP EN SS EP GND SW VCC BST Vout L1 1 2 Vin 12V BST R3 C9 10nF C13 NC SW C1 22uF C5 C6 0.1uF 22uF/25V 9 C7 FB COMP EN SS R5 NC C2 22uF C8 C10 10nF Vin R4 100K EN Qty Ref Value Description Package 2 C1, C2, 22µF Ceramic Capacitor X5R 16V 1206 1 C6 22uF Ceramic Capacitor X5R 25V 1206 1 C5 0.1µF Ceramic Capacitor 0603 Inductor, Rated Current 4.5A 1 L1 10uH WE-part number: 744 771 4100---10uH SMD 1 R4 100KΩ Resistor, ±1% 0603 Resistor, ±1% 0603 Resistor, ±1% 0603 Ceramic Capacitor 0603 C7 value is adjustable for the ESR of Cout. 0603 Vout=12V 120K Ω Vout=5V 44.2KΩ Vout=3.3V 26.1KΩ Vout=2.5V 17.4KΩ Vout=1.8V 9.53KΩ Vout=1.5V 6.34KΩ Vout=1.2V 3K Ω 1 R1 Vout=1V 1 R2 10k Ω 820Ω Vout=12V 9.1K Ω Vout=5V 8.87KΩ Vout=3.3V 7.5K Ω Vout=2.5V 5.1K Ω Vout=1.8V 4.7K Ω Vout=1.5V 4.7K Ω Vout=1.2V 3.9K Ω 1 R3 3 C9, C10, C11 10nF Vout=1V 3.0K Ω Vout=12V 18pF Vout=5V 33pF Vout=3.3V 68pF Vout=2.5V 82pF Vout=1.8V 100pF Vout=1.5V 120pF Vout=1.2V 150pF 1 C7 Vout=1V 180pF Vout=12V 1nF Vout=5V 2.2nF Vout=3.3V 4.7nF Vout=2.5V 8.2nF Vout=1.8V 8.2nF Vout=1.5V 8.2nF Vout=1.2V 8.2nF 1 C8 Vout=1V 1 U1 APE1596AMP 8.2nF Ceramic Capacitor 0603 Step-Down DC/DC Converter ESOP-8 11 Advanced Power Electronics Corp. APE1596A Application 2 C12 NC R1 R2 10K U1 APE1596A FB COMP EN SS EP R3 C9 0.1uF 9 C7 FB COMP EN SS GND SW VCC BST C13 NC R5 NC Vout L1 SW 1 2 Vin 12V BST C5 C6 0.1uF 22uF/25V C1 10uF C4 470uF C8 C10 10nF Vin R4 100K EN Qty Ref Description Value Package 1 C6 22µF Ceramic Capacitor X5R 25V 1 C1 10uF Ceramic Capacitor X5R 16V 1206 1 C4 470uF EC470uF/Breakdown Voltage > 2~3 time Vo 6.3x11mm( DIP) 2 C5,C9 0.1µF Ceramic Capacitor 0603 1206 Inductor, Rated Current 4.5A 1 L1 10uH WE-part number: 744 771 4100---10uH SMD 1 R4 100K Ω Resistor, ±1% 0603 Resistor, ±1% 0603 Vout=12V 120K Ω Vout=5V 44.2K Ω Vout=3.3V 26.1K Ω Vout=2.5V 17.4K Ω Vout=1.8V 9.53K Ω Vout=1.5V 6.34K Ω Vout=1.2V 3KΩ 1 R1 Vout=1V 1 R2 10k Ω 820Ω Vout=12V 250K Ω Vout=5V 120K Ω Vout=3.3V 75K Ω Vout=2.5V 59K Ω Vout=1.8V 47K Ω Vout=1.5V 33K Ω Vout=1.2V 27K Ω 1 R3 Vout=1V 2 C10, C11 10nF 22K Ω Vout=12V 470pF Vout=5V 470pF Resistor, ±1% 0603 Ceramic Capacitor 0603 C7 value is adjustable for the ESR of Cout. 0603 Vout=3.3V 470pF Vout=2.5V 470pF Vout=1.8V 470pF Vout=1.5V 470pF Vout=1.2V 470pF 1 C7 Vout=1V 470pF Vout=12V 4.7nF 4.7nF Vout=5V Vout=3.3V 4.7nF Vout=2.5V 4.7nF Vout=1.8V 4.7nF Vout=1.5V 4.7nF 1 C8 Vout=1.2V 4.7nF 4.7nF Vout=1V Ceramic Capacitor 0603 1 U1 APE1596AMP Step-Down DC/DC Converter ESOP-8 12 Advanced Power Electronics Corp. APE1596A TYPICAL PERFORMANCE CHARACTERISTICS Vin=12V Efficiency Vin=5V Efficiency 100 90 90 80 80 70 60 Vo=3.3V Vo=2.5V Vo=1.8V Vo=1.5V Vo=1.2V Vo=1V 50 40 30 20 E ffic ie n c y (% ) E ffic ie n c y (% ) 100 60 Vo=3.3V 50 Vo=2.5V Vo=1.8 40 Vo=1.5V Vo=1.2V Vo=1V 30 20 Vo=5V 10 70 10 0 0 1 10 100 1000 10000 1 10 100 Iout(mA) VIN=12V, VOUT=3.3V, Io=0.5A Oscillator Frequency vs Temperature Feedback Voltage vs Temperature 950 945 940 935 930 925 920 915 910 905 900 350 340 330 320 310 300 290 280 270 260 250 O s cillator F requency (K H z) F eedback V oltage(m V ) 10000 Iout(mA) VIN=12V, VOUT=3.3V, Io=0.5A -40 -20 0 20 40 60 80 100 -40 -20 0 20 Temperature(℃) O u tp u t V o lta g e (V ) 0 20 40 Temperature(℃) 80 100 3 3.5 Output Voltage vs Output Current Current Limit vs Temperature -20 60 VIN=12V, VOUT=3.3V 6 5.8 5.6 5.4 5.2 5 4.8 4.6 4.4 4.2 4 -40 40 Temperature(℃) VIN=12V, VOUT=3.3V, 0.5A C urrent L im it(A ) 1000 60 80 100 3.5 3.47 3.44 3.41 3.38 3.35 3.32 3.29 3.26 3.23 3.2 0 0.5 1 1.5 2 2.5 Output Current(A) 13 Advanced Power Electronics Corp. APE1596A TYPICAL PERFORMANCE CHARACTERISTICS Load Transient Response VIN=12V, VOUT=3.3V, IOUT=0.5A~1A Load Transient Response VIN=12V, VOUT=3.3V, IOUT=1A~2A VO(Ac) (200mV/Div) VO(Ac) (200mV/Div) Vsw (20V/Div) Vsw (20V/Div) Io (2A/Div) Io (2A/Div) Time: (40uS/Div) Power On VIN=12V, VOUT=3.3V, IOUT=No Load Time: (40uS/Div) Power Off VIN=12V, VOUT=3.3V, IOUT=No Load VIN (5V/Div) VIN (5V/Div) VO (2V/Div) VO (2V/Div) Sw (10V/Div Sw (10V/Div IL (2A/Div) IL (2A/Div) Time: (2mS/Div) Power On VIN=12V, VOUT=3.3V, IOUT=3A Time: (200mS/Div) Power Off VIN=12V, VOUT=3.3V, IOUT=3A VIN (5V/Div) VIN (5V/Div) VO (2V/Div) VO (2V/Div) Sw (10V/Div Sw (10V/Div IL (5A/Div) IL (5A/Div) Time: (2mS/Div) Time: (400mS/Div) 14 Advanced Power Electronics Corp. APE1596A TYPICAL PERFORMANCE CHARACTERISTICS Steady State Waveforms VIN=12V, VOUT=3.3V, IOUT=100mA Steady State Waveforms VIN=12V, VOUT=3.3V, IOUT=3A VIN (200mV/Div ) VIN (1V/Div ) Vo(AC) (10mV/Div) Vo(AC) (20mV/Div) Sw (10V/Div ) Sw (10V/Div ) IL (5A/Div) IL (200mA/Div) Time: (4uS/Div) Time: (4uS/Div) 15 Advanced Power Electronics Corp. APE1596A MARKING INFORMATION ESOP-8 Part Number Package Code 1596AMP YWWSSS Date Code (YWWSSS) Y：Last Digit Of The Year WW：Week SSS：Sequence 16