AME AME5287 n General Description The AME5287 is a Synchronous Rectified Step-Down Converter with internal power MOSFETs. It achieves 3A continuous output current over a wide switching frequency range with excellent load and line regulation. Current mode operation provides fast transient response and eases of loop stabilization. Internal soft-start minimizes the inrush supply current at startup. The circuit protection includes cycle-by-cycle current limiting, output short circuit frequency protection and thermal shutdown. In shutdown mode, the regulator reduces the current less than 1µA of supply current. This device is available in SOP-8/PP ,DFN-8 package with exposed pad for low thermal resistance. 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter n Typical Application L 2.2µH VIN 5V IN CIN 10µF OFF ON SW R1 75KΩ EN AME5287 VOUT 3.3V COUT 22µF FB COMP C2 Optional C1 680pF R3 25KΩ GND FREQ R2 24KΩ RFREQ 18KΩ Figure 1. 3.3V at 3A Step-Down Regulators. n Features l 3A Output Current l Stable with Low ESR Output Ceramic L 1.5µH VIN 3V~5V IN Capacitors l Pre-Regulator for Linear Regulators l Up to 95% Efficiency CIN 10µF OFF ON 300KHz~2MHz l Thermal Protection R1 6KΩ EN AME5287 VOUT 1V C OUT 22µF FB COMP l Less than 1µA Shutdown Current l Wide Switching Frequency Range from SW C2 Optional C1 680pF R3 8.2KΩ GND FREQ R2 24KΩ RFREQ 18KΩ l Cycle-by-Cycle Over Current Protection l Output Adjustable from 0.8V to VIN Figure 2. 1V at 3A Step-Down Regulators. l Short Circuit Protection l Green Products Meet RoHS Standards n Applications l TV l Distributed Power Systems l Pre-Regulator for Linear Regulators l Digital Cameras Rev. A.01 1 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Functional Block Diagram IN CURRENT SENSE EN ENABLE CURRENT LIMIT UVLO FREQ OSC SW SLOPE + + COMP 0.8V VREF + EA - GND SOFT START - DRIVER LOGIC PWM IRCMP OTP FB SW + Short circuit PGND n Pin Configuration DFN-8C (3mmx3mmx0.75mm) Top View SOP-8/PP Top View 8 7 6 5 AME5287-AZAADJ 8 7 6 5 1. COMP 1. COMP 2. GND 9 2 3 4 9 4. IN 5. SW 1 2. GND AME5287 3. EN AME5287 AME5287-AVAADJ 3. EN 4. IN 1 2 3 4 5. SW 6. SW 6. SW 7. FREQ 7. FREQ 8. FB 8. FB 9. GND (Exposed Pad) 9. GND (Exposed Pad) * Die Attach: Conductive Epoxy * Die Attach: Conductive Epoxy Note. Connect exposed pad (heat sink on the back) to GND. 2 Rev. A.01 AME AME5287 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter n Pin Description Pin No. Pin Name Pin Description 1 COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. 2 GND 3 EN Enable. Pull EN below 0.4V to shut down the regulator. 4 IN Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Bypass IN to GND with a suitable large capacitor to eliminate noise on the input to the IC. 5, 6 SW 7 FREQ 8 FB 9 GND Rev. A.01 Ground. Connect the exposed pad to GND. Power Switching Output. SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Frequency Adjust Pin. Add a resistor from this pin to ground determines the switching frequency. Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback reference voltage is 0.8V. Ground. Connect the exposed pad to GND. 3 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Ordering Information AME5287 - x x x xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration A (SOP-8/PP) (DFN-8C) 4 1. COMP 2. GND 3. EN 4. IN 5. SW 6. SW 7. FREQ 8. FB 9. GND Package Type Z: SOP/PP V: DFN Number of Pins A: 8 Output Voltage ADJ: Adjustable Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Absolute Maximum Ratings Parameter Symbol Maximum Unit Supply Voltage VIN 6 V Switch Voltage VSW -1.5V to VIN +0.7V V -0.3V to VIN +0.3V V HBM 2 kV MM 200 V EN, FB, COMP, FREQ to GND ESD Classification n Recommended Operating Conditions Parameter Symbol Rating Ambient Temperature Range TA -40 to +85 Junction Temperature Range TJ -40 to +125 Storage Temperature Range TSTG -65 to +150 Unit o C n Thermal Information Parameter Package Thermal Resistance* (Junction to Case) SOP-8/PP Thermal Resistance (Junction to Ambient) SOP-8/PP Internal Power Dissipation Die Attach θ JC DFN-8C DFN-8C SOP-8/PP DFN-8C Symbol Maximum Conductive Epoxy θJA PD Unit 15 8.2 75 o C/W 70 1.333 W 1.429 Maximum Junction Temperature 150 o C Lead Temperature (soldering 10 sec)** 260 o C * Measure θJC on backside center of Exposed Pad. ** MIL-STD-202G 210F Rev. A.01 5 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Electrical Specifications VIN=5V, TA=25oC, unless otherwise noted. Parameter Input Voltage Input UVLO Symbol Test Condition VIN Min Typ 3 VUVLO Quiescent Current IQ VEN=5V, VFB=0.7V (No Switching) Shutdown Current ISHDN VEN=0V Feedback Voltage VFB 0.784 Feedback Current IFB -50 Units 5.5 V 2.3 V 600 µA 0.8 1 µA 0.816 V 50 nA Load Regulation REGLOAD 0A<I OUT <2A 0.25 % Line Regulation REG LINE 2.7V<VIN<5.5V 0.25 %/V EN Voltage High 1.4 VEN V EN Voltage Low EN Leakage Current Switching Frequency IENLK FSW VEN=3V Error Amp Transconductance GEA Switch Leakage Current ISWLK 0.4 V 0.1 1 µA R FREQ=NC 240 300 360 KHz R FREQ=120K Ω 480 600 720 KHz RFREQ=47K Ω 0.8 1 1.2 MHz RFREQ=18KΩ 1.6 2 MHz 3.7 A 400 µA/V High-side Switch Current Limit VSW=0V, V EN =0V 0.1 20 µA High-side Switch On Resistance RDSON,HI 130 mΩ Low-side Switch On Resistance R DSON,LO 90 mΩ Thermal Shutdown Protection 6 Max OTP Rising 160 o C OTH Hysteresis 20 o C Rev. A.01 AME AME5287 n Detailed Description Normal Operation The AME5287 uses a user adjustable frequency, current mode step-down architecture with internal MOSFET switch. During normal operation, the internal high-side (PMOS) switch is turned on each cycle when the oscillator sets the SR latch, and turned off when the comparator resets the SR latch. The peak inductor current at which comparator resets the SR latch is controlled by the output of error amplifier EA. While the high-side switch is off, the low-side switch turns on until either the inductor current starts to reverse or the beginning of the next switching cycle. Dropout Operation The output voltage is dropped from the input supply for the voltage which across the high-side switch. As the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the high-side switch to remain on for more than one cycle until it reaches 100% duty cycle. Soft-Start The AME5287 has a built-in digital soft-start to control the output voltage rise and limit the current surge at the start-up. When the internal soft-start begins, and count 896 switching cycles, soft start is complete, the converter enters steady state operation. 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter Under Voltage Protection Under Voltage Protection will activate once the feedback voltage falls below 0.4V, the operating frequency is switched to 1/10 of normal switching frequency and after four-times hiccup mode counted, the internal high-side power switch will be turned off,and latched. Unless Restart the power supply. Over Temperature Protection In most applications the AME5287 does not dissipate much heat due to high efficiency. But, in applications where the AME5287 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 160oC, the internal high-side power switch will be turned off and the SW switch will become high impedance. Inductor Selection For most applications, the value of the inductor will fall in the range of 2.2µH to 4.7µH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or V OUT also increase the ripple current ∆IL: ∆I L = V 1 VOU T 1 − OUT f ×L VIN Hiccup Mode During hiccup mode, the AME5287 disables the highside MOSFET and begins a cool down period of 8320 switching cycles. At the conclusion of this cool down period, the regulator performs an internal 896 cycle soft start identical to the soft start at turn-on. Rev. A.01 7 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 A reasonable inductor current ripple is usually set as 1/ 3 to 1/5 of maximum out current. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. For better efficiency, choose a low DCR inductor. Output Voltage Programming The output voltage of the AME5287 is set by a resistive divider according to the following formula: R1 VOUT = 0.8 × 1 + Volt . R2 Capacitor Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low ESR input capacitor sized for maximum RMS current must be used. The maximum RMS capacitor current is given by: CIN requires IRMS ≅ I OMAX VOUT (VIN − VOUT ) VIN This formula has a maximum at V IN =2V OUT , whereIRMS=IOUT/2. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. The selection of COUT is driven by the required effective series resistance (ESR). Typically, once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. The output ripple ∆VOUT is determined by: ∆VOUT 1 ≅ ∆I L ESR + 8 fCOUT Loop Compensation The AME5287 employs peak current mode control for easy use and fast transient response. Peak current mode control eliminates the double pole effect of the output LC filter. It greatly simplifies the compensation loop design. With peak current mode control, the buck power stagecan be simplified to be a one-pole and one-zero system in frequency domain. The pole can be calculated by: f P1 = 1 2π × COUT × RL The zero is a ESR zero due to output capacitor and its ESR. It can be calculated by: f Z1 = 1 2π × COUT × ESRCOUT For a fixed output voltage, the output ripple is highestat maximum input voltage since ∆IL increases with input voltage. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for given value and size. 8 Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 Where COUT is the output capacitor, RL is load resistance; ESRCOUT is the equivalent series resistance of output capacitor. The compensation design is to shape the converter close loop transfer function to get desired gain and phase. For most cases, a series capacitor and resistor network connected to the COMP pin sets the pole-zero and is adequate for a stable high-bandwidth control loop. In the AME5287, FB pin and COMP pin are the inverting input and the output of internal transconductance error amplifier (EA). A series R3 and C1 compensation network connected to COMP pin provides one pole and one zero: for R3<<AEA/GEA, fP2 = fZ2 = 1 A 2π × C1 R3 + EA GEA ≈ G EA 2π × C1 × AEA 1 2π × C1 × R3 where GEA is the error amplifier transconductance AEA is the error amplifier voltage gain R3 is the compensation resistor C1 is the compensation capacitor The desired crossover frequency fc of the system is defined to be the frequency where the control loop has unity gain. It is also called the bandwidth of the converter. In general, a higher bandwidth means faster response to load transient. However, the bandwidth should not be too high because of system stability concern. When designing the compensation loop, converter stability under all line and load condition must be considered. Usually, it is recommended to set the bandwidth to be less than 1/10 of switching frequency. Using selected crossover frequency, fC, to calculate R3: V 2π × COUT R3 = f C × OUT × VFB G EA × GCS Rev. A.01 Where GCS is the current sense circuit transconductance. The compensation capacitor C1 and resistor R3 together make zero. This zero is put somewhere close to the pole fP1 of selected frequency. C1 is selected by: C1 = COUT × RL R3 Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to (∆ILOAD X ESR), where ESR is the effective series resistance of COUT. ∆ILOAD also begins to charge or discharge COUT, which generates a feedback error signal. The regulator loop then acts to return VOUT to its steadystate value. During this recovery time V OUT can be monitored for overshoot or ringing that would indicate a stability problem. Efficiency Considerations Although all dissipative elements in the circuit produce losses, one major source usually account for most of the losses in AME5287 circuits: I2R losses. The I2R loss dominates the efficiency loss at medium to high load currents. The I2R losses are calculated from the resistances of the internal switches, RSW, and external inductor RL. In continuous mode, the average output current flowing through inductor L is "chopped" between the main switch and the synchronous switch. Thus the series resistance looking into the SW pin is a function of both top and bottom MOSFET RDS(ON) and the duty cycle (D) as follows: RSW = (RDS(ON)TOP)(D) + (RDS(ON)BOTTOM )(1-D) The RDS(ON) for both the top and bottom MOSFETs can be obtained from Electrical Characteristics table. Thus, to obtained I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. 9 AME AME5287 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter Other losses including CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss. Thermal Considerations In most application the AME5287 does not dissipate much heat due to its high efficiency. But, in applications where the AME5287 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 160oC, both power switches will be turned off and the SW switch will become high impedance. 10 Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Typical Operating Circuit VIN 2.5V to 5V CIN 10µF L 4 3 Chip Enable 1 C2 Optional SW IN V OUT 5, 6 EN R1 AME5287 COMP FB C1 FREQ 8 7 R3 2 RFREQ GND GND COUT R2 9 (Exposed pad) VOUT(V) C IN (µF) R1(KΩ) R2(K Ω) R3(K Ω) C1(pF ) L( µH) COUT(µF ) 3.3 10 75 24 25 680 2.2 22 2.5 10 51 24 20 680 2.2 22 1.8 10 30 24 15 680 1.5 22 1.5 10 21 24 13 680 1.5 22 1.2 10 12 24 11 680 1.5 22 1 10 6 24 8.2 680 1.5 22 Table 1. Recommended Components Selectin for fsw = 2MHz The ground area must provide adequate heat dissipating area to the thermal pad andusing multiple vias to help thermal dissipation. R3 Connect the FB pin directly to feedback R2 resistors. C1 COMP 1 8 FB R1 GND 2 V OUT GND 7 FREQ RFREQ GND EN 3 6 SW V IN 4 5 SW SW VI N SW pad should be connected together to Inductor by wide and short trace, keep sensitive components away from this trace . L1 C IN must be placed between VI N and GND as close as CIN possible Place the input and output capacitors as close to the IC as possible C OUT V OUT Figure 3. AME5287 Regulators Layout Diagram Rev. A.01 11 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Characterization Curve Efficiency vs. Output Current Efficiency vs. Output Current 100 100 90 90 80 70 VOUT=3.3V V OUT =2.5V VOUT=1.8V Efficiency (%) Efficiency (%) 80 VOUT=1.2V 60 V OUT =1.0V 50 40 30 60 V OUT =1.2V 50 V OUT=1.0V 40 20 V IN = 5V R FREQ = 18K 10 0 500 1000 1500 2000 2500 V IN = 5V R FREQ = 30K 10 0 3000 0 500 Output Current (mA) 100 100 90 90 2000 2500 3000 80 V OUT=3.3V 70 VOUT=2.5V V OUT =1.8V 60 Efficiency (%) Efficiency (%) 1500 Efficiency vs. Output Current 80 V OUT=1.2V VOUT=1.0V 50 40 30 70 V OUT=3.3V VOUT=2.5V VOUT=1.8V 60 V OUT=1.2V 50 VOUT=1.0V 40 30 20 V IN = 5V R FREQ = 47K 10 0 500 1000 1500 2000 Output Current (mA) 12 1000 Output Current (mA) Efficiency vs. Output Current 0 VOUT=2.5V VOUT=1.8V 30 20 0 VOUT=3.3V 70 2500 3000 20 VIN = 5V R FREQ = NC 10 0 0 500 1000 1500 2000 2500 3000 Output Current (mA) Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Characterization Curve (Contd.) Load Step Load Step VIN = 3.3V VOUT= 1.8V IOUT= 1A to 3A VIN= 3.3V VOUT= 1.0V IOUT= 1A to 3A 1 1 2 2 Time (200µSec/DIV) Time (200µSec/DIV) 1) VOUT= 200mV/div 2) IL= 2A/div 1) VOUT= 200mV/div 2) IL= 2A/div Load Step Load Step VIN= 5.0V VOUT= 1.0V IOUT= 1A to 3A VIN = 5.0V VOUT = 3.3V I OUT = 1A to 3A 1 1 2 2 Time (200µSec/DIV) 1) VOUT= 200mV/div 2) IL= 2A/div Rev. A.01 Time (200µSec/DIV) 1) VOUT= 200mV/div 2) IL= 2A/div 13 AME AME5287 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter n Characterization Curve (Contd.) Power ON from VIN 1 Power off from VIN 1 2 2 3 3 4 4 2.0mS / div 2.0mS / div 1) VIN= 5V/div 2) Vsw= 5V/div 3) VOUT= 1V/div 4) IL= 2A/div 1) VIN= 5V/div 2) Vsw= 5V/div 3) VOUT= 1V/div 4) IL= 5A/div Start-Up from EN Power Off from EN 1 1 2 2 3 3 4 4 2.0mS / div 1) EN= 5V/div 2) VSW= 5V/div 3) VOUT= 1V/div 4) IL = 2A/div 14 1.0mS / div 1) EN= 5V/div 2) VSW= 5V/div 3) VOUT= 1V/div 4) IL = 5A/div Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Characterization Curve (Contd.) Steady State Test Steady State Test VIN = 5V VOUT= 3.3V IOUT= 3A VIN = 5V VOUT= 1.1V IOUT= 3A 1 1 2 2 400nS / DIV 400nS / DIV 1) VOUT= 10mV/div 2) VSW= 2V/div 1) VOUT= 10mV/div 2) VSW= 2V/div VFB vs. Temperature Frequency vs. Temperature 450 0.82 400 Frequency (KHz) VFB (V) 0.81 0.80 0.79 0.78 0.77 -40 V IN = 5V -25 -10 +5 +20 +35 +50 +65 +80 Temperature (°C) Rev. A.01 +95 +110 +125 350 300 250 VIN = 5V 200 150 -40 -25 -10 +5 +20 +35 +50 +65 +80 +95 +110 +125 Temperature ( °C) 15 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 Characterization Curve (Contd.) Frequency vs. Output Current Frequency vs. Supply Voltage 450 300 290 400 Frequency (KHz) Frequency (KHz) 280 350 300 250 VOUT = 3.3V 200 270 260 250 240 230 VIN=5.0V VOUT = 3.3V 220 210 150 3.5 4 4.5 5 5.5 Input Voltage (V) 200 200 400 600 800 1000 1200 1400 1600 1800 2000 Iout (mA) Short Circuit Test Short Circuit Test VIN =5V VOUT=1V VIN=5V VOUT=3.3V 1 1 2 2 Time (100ms/DIV) 1) VOUT= 1V/div 2) IOUT= 2A/div 16 Time (100ms/DIV) 1) VOUT= 2V/div 2) IOUT= 2A/div Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Tape and Reel Dimension SOP-8/PP P PIN 1 W AME AME Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size SOP-8/PP 12.0±0.1 mm 4.0±0.1 mm 2500pcs 330±1 mm DFN-8C (3mmx3mmx0.75mm) P PIN 1 W AME AME Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size DFN-8C (3x3x0.75mm) 12.0±0.1 mm 4.0±0.1 mm 3000pcs 330±1 mm Rev. A.01 17 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Package Dimension SOP-8/PP TOP VIEW SIDE VIEW D1 SYMBOLS ? E1 E2 E L1 C PIN 1 D e A1 FRONT VIEW 18 A A2 b MILLIMETERS INCHES MIN MAX MIN MAX A 1.350 1.750 0.053 0.069 A1 0.000 0.150 0.000 0.006 A2 1.350 1.600 0.053 0.063 C 0.100 0.250 0.004 0.010 E 3.750 4.150 0.148 0.163 E1 5.700 6.300 0.224 0.248 L1 0.300 1.270 0.012 0.050 b 0.310 0.510 0.012 0.020 D 4.720 5.120 0.186 0.202 1.270 BSC e 0.050 BSC θ 0 8 E2 2.150 2.513 0.085 0.099 D1 2.150 3.402 0.085 0.134 o o 0 o 8 o Rev. A.01 AME 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287 n Package Dimension (Contd.) DFN-8C (3mmx3mmx0.75mm) b D e L E E1 PIN 1 IDENTIFICATION TOP VIEW D1 BOTTOM VIEW A G1 G REAR VIEW SYMBOLS Rev. A.01 MILLIMETERS INCHES MIN MAX MIN MAX A 0.700 0.800 0.028 0.031 D 2.900 3.100 0.114 0.122 E 2.900 3.100 0.114 0.122 e 0.600 0.700 0.024 0.028 D1 2.200 2.400 0.087 0.094 E1 1.400 1.600 0.055 0.063 b 0.180 0.320 0.007 0.013 L 0.375 0.575 0.015 0.023 G 0.153 0.253 0.006 0.010 G1 0.000 0.050 0.000 0.002 19 www.ame.com.tw E-Mail: [email protected] Life Support Policy: These products of AME, Inc. are not authorized for use as critical components in life-support devices or systems, without the express written approval of the president of AME, Inc. AME, Inc. reserves the right to make changes in the circuitry and specifications of its devices and advises its customers to obtain the latest version of relevant information. © AME, Inc. , October 2012 Document: TU003-DS5287-A.01 Corporate Headquarter AME, Inc. 8F, 12, WenHu St., Nei-Hu Taipei 114, Taiwan . Tel: 886 2 2627-8687 Fax: 886 2 2659-2989