AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n General Description The AME5253A is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. Capable of delivering 1A output current over a wide input voltage range from 2.5V to 5.5V. Supply current with no load is 400µA and drops to<1µA in shutdown. The 2.5V to 5.5V input Voltage range makes the AME5253A ideally suited for single Li-Ion batterypowered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. PWM pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. At very light load, the AME5253A will automatically skip pulses in pulse skip mode operation to maintain output regulation. The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. The AME5253A is available in SOT-25 packages. Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection. n Applications l l l l l Cellular Telephones Personal Information Appliances Wireless and DSL Modems MP3 Players Portable Instruments n Typical Application VIN = 2.5V to 5.5V VIN IN CIN 4.7µF CER 2.2µH AME5253A EN VOUT SW GND CFWD FB R1 150K R2 75K 1.8V 1000mA COUT 10µF CER VOUT=VFB (R1+R2)/R2 Figure 1: 1.8V at 1000mA Step-Down Requlator CFWD: 22pF~220pF n Features l l l l High Efficiency: Up to 95% Shutdown Mode Draws < 1µA Supply Current 2.5V to 5.5V Input Range Adjustable Output From 0.6V to VIN l l l l l l 1A Output Current Low Dropout Operation: 100% Duty Cycle No Schottky Diode Required 1.5MHz Constant Frequency PWM Operation SOT-25 Packages All AME’ s Lead Free Product Meet RoHS Standard Rev.A.03 1 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Function Block Diagram Constant Off-time Mode Select Slope COMP VIN IN 4 PWM COMP FB 5 0.6V 0.6V VREF SW LOGIC 3 0.55V UVDET Soft Start EN 1 NMOS COMP IRCOMP OSC GND 2 Figure 2: Founction Block Diagram 2 Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Pin Configuration SOT-25 Top View 5 AME5253A-AEVADJ 1. EN 2. GND 3. SW 4. IN 5. FB 4 AME5253A 1 2 3 Die Attach: Conductive Epoxy n Pin Description Pin Number Pin Name 1 EN 2 GND Ground. Tie directly to ground plane. 3 SW Switch Node Connection to Inductor. 4 IN Input Supply Voltage Pin. Bypass this pin with a capacitor as close to the device as possible. 5 FB Output voltage Feedback input. Rev.A.03 Pin Description No connection. Not internally connected. Can left floating or connected to GND. 3 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Ordering Information AME5253A - x x x xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration A (SOT-25) 4 1. EN 2. GND 3. SW 4. IN 5. FB Package Type Number of Pins E: SOT-2X V: 5 Output Voltage ADJ: Adjustable Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Absolute Maximum Ratings Parameter Symbol Maximum V IN -0.3 to 6.5 V EN , V OUT -0.3 to V IN V SW -0.3 to V IN Input Supply Voltage EN, V OUT Voltage SW Voltage Unit V B* ESD Classification Caution: Stress above the listed absolute maximum rating may cause permanent damage to the device. * HBM B: 2000V~3999V n Recommended Operating Conditions Parameter Symbol Rating Unit Supply Voltage Voltage V IN 2.5 to 5.5 V Ambient Temperature Range TA -40 to +85 o C Junction Temperature Range TJ -40 to +125 o C n Thermal Information Parameter Package Die Attach Thermal Resistance* (Junction to Case) Thermal Resistance (Junction to Ambient) Symbol Maximum θ JC 81 Unit o SOT-25 Conductive Epoxy Internal Power Dissipation Solder Iron (10Sec)** θJA 260 PD 400 350 C/W mW o C * Measure θJC on center of molding compound if IC has no tab. ** MIL-STD-202G 210F Rev.A.03 5 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Electrical Specifications VIN=3.6V, VOUT=2.5V, VFB=0.6V, L=2.2µH, CIN=4.7µF, COUT=10µF, TA=25oC, IMAX=1A unless otherwise specified. Parameter Test Condition Min Typ Max Units Input voltage VIN 2.5 5.5 V Adjustable Output Range Vout VFB VIN-0.2 V Feedback Voltage VFB 0.588 0.612 V Feedback Pin Bias Current IFB VFB=VIN 50 nA Quiescent Current IQ IOUT=0mA, VFB=1V 0.4 0.5 mA Shutdown Current ISHDN VEN=GND 0.1 1 µA Switch Frequency fOSC 1.5 1.8 MHz 0.6 -50 1.2 High-side Switch On-Resistance RDS,ON, LHI ISW=200mA, VIN=3.6V 0.28 Ω Low-side Switch On-Resistance RDS,ON, LO ISW=200mA, VIN=3.6V 0.25 Ω Switch Current Limit ISW,CL VIN=2.5 to 5.5V 1.4 1.6 A EN High (Enabled the Device) VEN,HI VIN=2.5 to 5.5V 1.5 EN Low (Shutdown the Device) VEN,LO VIN=2.5 to 5.5V Input Undervoltage Lockout VUVLO rising edge Input Undervoltage Lockout Hysteresis VUVLO,HYST Thermal Shutdown Temperature OTP Maximum Duty Cycle DMAX SW Leakage Current 6 Symbol V 0.4 Shutdown, temperature increasing 1.8 V 0.1 V o 160 100 EN=0V, VIN=5.0V VSW=0V or 5.0V -1 V C % 1 µA Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Detailed Description Main Control Loop AME5253A uses a constant frequency, current mode step-down architecture. Both the main (P-channel MOSFET) and synchronous (N-channel MOSFET) switches are intermal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator resets the RS latch. While the top MOSFET is off, the bottom MOSFET is turned on until either the inductor current starts to reverse as indicated by the current reversal comparator IRCMP. Pulse Skipping Mode Operation At light loads, the inductor current may reach zero or reverse on each pulse.The bottom MOSFET is turned off by the current reversal comparator, IRCMP, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. n Application Information The basic AME5253A application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and followed by CIN and COUT. Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current DIL increases with higher VIN and decreases with higher inductance. ∆I L = 1 ( f )(L ) VOUT 1 − VOUT VIN A reasonable starting point for setting ripple current is ∆IL=0.4(lmax). 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 DC-resistance inductor. Short-Circuit Protection When the output is shorted to ground, the frequency of the oscillator is reduced to about 180KHz. This frequency foldback ensures that the inductor current hsa more time do decay, thereby preventing runaway. The oscillator’ s frequency will progressively increase to 1.5MHz when VFB or VOUT rises above 0V. Dropout Operation 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 main switch to remain on for more than one cycle until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor. Rev.A.03 CIN and COUT Selection The input capacitance, CIN is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large voltage transients, a low ESR input capacitorsized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: I RMS = I OUT ( MAX ) VOUT VIN V IN −1 VOUT This formula has a maximum at VIN=2VOUT, where IRMS=IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that the capacitor manufacturer ripple current ratings are often based on 2000 hours of life. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. 7 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A The selection of COUT is determined by the effective series resistance(ESR) that is required to minimize voltage ripple and load step transients. The output ripple, VOUT, is determined by: ∆VOUT ≅ ∆I L ESR + Where VREF equals to 0.6V typical. The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 4. 0.6V ≤ VOUT ≤ 5.5V 1 8 fCOUT R1 Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Output Voltage Programming The output voltage is set by an external resistive divider according to the following equation : VOUT = V REF × 1 + R1 R2 FB AME5253 A R2 GND Figure 3: Setting the AME5253A Output Voltage Thermal Considerations In most applications the AME5253A does not dissipate much heat due to its high efficiency. But, in applications where the AME5253A 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 node will become high impedance. To avoid the AME5253A from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The temperature rise is given by: TR = (PD )(θ JA ) Where PD is the power dissipated by the regulator and θJA is the thermal resistance from the junction of the die to the ambient temperature. 8 Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A VIN 2.5V to 5.5V 2.2µH VIN 2.7V to 5.5V VOUT 1.2V SW IN AME5253 A EN FB GND CIN 4.7µF CER COUT 10µF CER AME5253 A EN 150K 2.2µH CIN 4.7µF CER EN FB GND CIN 4.7µF CER COUT 10µF CER EN FB GND CIN 4.7µF CER VOUT 3.3V SW AME5253 A 150K Figure 5: 1.5V Step-Down Regulator CFWD: 22pF~220pF CFWD COUT 10µF CER 150K 33.3K Figure 8: 3.3V Step-Down Regulator CFWD: 22pF~220pF VOUT 1.6V SW IN AME5253 A EN FB GND CIN 4.7µF CER COUT 10µF CER 150K 2.2µH IN CFWD 2.2µH CFWD 47.3K VIN 3.6V to 5.0V VOUT 1.5V 100K VIN 2.5V to 5.5V VOUT 2.5V Figure 7: 2.5V Step-Down Regulator CFWD: 22pF~220pF SW AME5253 A FB GND Figure 4: 1.2V Step-Down Regulator CFWD: 22pF~220pF IN SW IN CFWD 150K VIN 3.3V to 5.5V 2.2µH CFWD COUT 10µF CER 150K 90K Figure 6: 1.6V Step-Down Regulator CFWD: 22pF~220pF Rev.A.03 9 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the AME5253A. These items are also illustrated graphically in Figures 9. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 2. Does the VFB pin connect directly to the feedback resistors? The resistive divider R2/R1 must be connected between the (+) plate of COUT and ground. 3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the switching node, SW, away from the sensitive VFB node. 5. Keep the (-) plates of CIN and COUT as close as possible. L1 VIN IN CFWD AME5253 A CIN R2 GND - R1 CFWD: 22pF~220pF 10 + COUT FB EN + - VOUT SW Figure 9: AME5253A Adjustable Voltage Regulator Layout Diagram Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Application Information External components selection Supplier Inductance (µ H) Current Rating (mA) DCR (m Ω ) Dimensions (mm) Series TAIYO YUDEN 2.2 1480 60 3.00 x 3.00 x 1.50 NR 3015 GOTREND 2.2 1500 58 3.85 x 3.85 x 1.80 GTSD32 Sumida 2.2 1500 75 4.50 x 3.20 x 1.55 CDRH2D14 Sumida 4.7 1000 135 4.50 x 3.20 x 1.55 CDRH2D14 TAIYO YUDEN 4.7 1020 120 3.00 x 3.00 x 1.50 NR 3015 GOTREND 4.7 1100 146 3.85 x 3.85 x 1.80 GTSD32 Table 1. Recommended Inductors Table 2. Recommended Capacitors for CIN and COUT Rev.A.03 11 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Characterization Curve Efficiency vs. Output Current Efficiency vs. Output Current 100 100 90 80 VIN = 3.6V 80 70 Efficiency(%) Efficiency(%) 90 VIN = 2.7V 60 50 40 30 20 70 60 50 40 30 20 10 VOUT = 2.5V 0 1 10 10 COUT = 10µF L = 2.2µH 100 VOUT = 2.5V 0 1 1000 Output Current(mA) 100 90 90 70 Efficiency(%) Efficiency(%) 80 VIN = 2.7V 60 50 40 30 10 VOUT = 1.5V 0 60 50 40 30 1 10 10 COUT = 10µF L = 2.2µH 100 0 1 1000 Output Current(mA) 100 90 90 80 10 COUT = 10µF L = 2.2µH 100 Output Current(mA) 1000 80 Efficiency(%) VIN = 2.5V 70 VOUT = 1.5V Efficiency vs. Output Current Efficiency vs. Output Current 100 Efficiency(%) VIN = 3.6V 70 20 20 60 50 40 30 V IN = 5.5V 70 60 50 40 30 20 20 10 VOUT = 1.2V 1 10 100 V OUT = 1.2V 10 COUT = 10µF L = 2.2µH Output Current(mA) 12 1000 Efficiency vs. Output Current Efficiency vs. Output Current 0 100 Output Current(mA) 100 80 10 COUT = 10µF L = 2.2µH 1000 0 1 10 COUT = 10µF L = 2.2µH 100 1000 Output Current(mA) Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Characterization Curve Reference Voltage vs. Temperature Frequency vs. Temperature 0. 620 1.90 1.80 1.75 0. 610 1.70 1.65 Frequency(MHz) Reference Voltage(V) 1.85 0. 615 0. 605 0. 600 0. 595 0. 590 1.55 1.50 1.45 1.40 1.35 1.30 VIN = 3.6V 1.25 1.20 VIN = 3.6V 0. 585 1.60 1.15 0. 580 -50 -25 0 +25 +50 O +75 +100 1.10 +125 -50 -25 +0 Temperature( C) 1.90 1.65 1.89 1.60 1.88 1.55 1.87 1.50 1.45 1.40 1.35 1.30 1.25 VIN(V) 5. 0 1.82 1.81 1.80 1.77 0 5. 5 Current Limit(A) Current Limit(A) -10 +5 +20 +35 +50 +65 +80 +95 +110 +125 Temperature (oC) Rev.A.03 200 300 400 500 600 700 800 900 1000 Current Limit vs. Temperature VIN = 3.3V VOUT = 1.2V -25 100 Output Current(mA) Current Limit vs. Temperature 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 -40 VOUT = 1.8V VIN = 3.6V 1.83 1.78 4. 5 +125 1.84 1.79 4. 0 +100 1.85 1.15 3. 5 +75 1.86 1.20 3. 0 +50 Output Voltage vs. Output Current Output Voltage(V) Frequency(MHz) Frequency vs. Supply Voltage 1.70 1.10 2. 5 +25 Temperature(OC) 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 -40 VIN = 3.6V VOUT = 1.2V -25 -10 +5 +20 +35 +50 +65 +80 Temperature (oC) +95 +110 +125 13 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Characterization Curve Current Limit(A) Current Limit vs. Temperature 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 -40 Light Load Mode output voltage ripple VIN = 5.0V VOUT = 1.2V -25 -10 +5 +20 +35 +50 +65 +80 +95 +110 +125 Temperature (oC) VIN = 3.6V VOUT = 1.2V IOUT = 50mA 1) VSW= 2V/div 2) VOUT = 10mV/div 3) IL = 500mA/div Heavy Load Mode Output Voltage Ripple 14 Load Step VIN = 3.6V VOUT = 1.2V IOUT = 1A VIN = 3.6V VOUT = 1.8V IOUT = 0A~1A~0A 1) VSW= 2V/div 2) VOUT = 10mV/div 3) IL = 500mA/div 1) VOUT= 100mV/div 2) IOUT = 500mA/div Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Characterization Curve Load Step VIN = 3.6V VOUT = 1.8V IOUT = 50mA~1A~50mA VIN = 3.6V VOUT = 1.8V IOUT = 200mA~1A~200mA 1) VOUT= 100mV/div 2) IOUT = 500mA/div 1) VOUT= 100mV/div 2) IOUT = 500mA/div Power On from EN VOUT = 1.2V IOUT = 1A 1) EN= 2V/div 2) VOUT = 500mV/div 3) IL = 1A/div Rev.A.03 Load Step Power Off from EN VIN = 3.6V VOUT = 1.8V IOUT = 1A 1) EN = 2V/div 2) VOUT = 2V/div 3) IL = 500mA/div 15 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Tape and Reel Dimension SOT-25 P0 W AME AME PIN 1 P Carrier Tape, Number of Components Per Reel and Reel Size 16 Package Carrier Width (W) Pitch (P) Pitch (P0) Part Per Full Reel Reel Size SOT-25 8.0±0.1 mm 4.0±0.1 mm 4.0±0.1 mm 3000pcs 180±1 mm Rev. A.03 AME 1A, 1.5MHz Synchronous Step-Down Converter AME5253A n Package Dimension SOT-25 Top View Side View D E H L PIN 1 S1 e b A1 A Front View n Lead Pattern SOT-25 2.40 BSC 1.00 BSC 0.70 BSC 0.95 BSC 0.95 BSC 1.90 BSC Note: 1. Lead pattern unit description: BSC: Basic. Represents theoretical exact dimension or dimension target. 2. Dimensions in Millimeters. 3. General tolerance +0.05mm unless otherwise specified. Rev.A.03 17 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. , August 2014 Document: 1283-DS5253A-A.03 Corporate Headquarter AME, Inc. 2F, 302 Rui-Guang Road, Nei-Hu District Taipei 114, Taiwan. Tel: 886 2 2627-8687 Fax: 886 2 2659-2989