AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n General Description n Features The AME5251A is a high efficiency monolithic synchronous dual buck regulator using a constant frequency, current mode architecture. Capable of delivering 1A output cur-rent each channel over a wide input voltage range from 2.5V to 5.5V. l High Efficiency: Up to 95% l Shutdown Mode Draws <1µA Supply Current l 2.5V to 5.5V Input Range l Adjustable Output From 0.6V to VIN 1A Output Current Per Channel Low Dropout Operation: 100% Duty Cycle No Schottky Diode Required 1.5MHz Constant Frequency PWM Opera tion l Small DFN-12A Packages l Green Products Meet RoHS Standard l l l l Supply current with no load is 400µA and drops to<1µA in shutdown.The 2.5V to 5.5V input Voltage range makes the AME5251A 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 AME5251A will automatically skip pulses in pulse skip mode operation to maintain output regulation. n Applications l l l l l 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 AME5251A is available in small DFN-12A packages. Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection. Cellular Telephones Personal Information Appliances Wireless and DSL Modems MPS Players Portable Instruments n Typical Application COUT2 VOUT2 L2 ON AME5251A VIN1 CIN2 R2 C1 R1 OFF EN2 SW2 NC2 GND FB2 FB1 GND NC1 SW1 EN1 IN1 ON VOUT1 COUT1 Rev.A.04 IN2 OFF R3 CIN1 C2 R4 VIN1 L1 1 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Function Block Diagram Constant Off-time Mode Select Slope COMP VIN 7 IN1 PWM COMP FB1 4 0.6V 0.6V VREF LOGIC 8 SW1 0.55V UVDET NMOS COMP Soft Start EN1 6 IRCOMP OSC 9 GND Constant Off-time Mode Select Slope COMP VIN 1 IN2 PWM COMP FB2 10 0.6V 0.6V VREF LOGIC 2 SW2 0.55V UVDET Soft Start EN2 12 OSC NMOS COMP IRCOMP 3 GND 2 Rev. A.04 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Pin Configuration DFN-12A (3mmx3mmx0.75mm) Top View 12 11 10 9 8 7 AME5251A 1 2 3 4 5 6 AME5251A-AVCxxxxxx 1. IN2 2. SW2 3. GND 4. FB1 5. NC1 6. EN1 7. IN1 8. SW1 9. GND 10. FB2 11. NC2 12. EN2 * Die Attach: Conductive Epoxy Note: Connect exposed pad (heat sink on the back) to GND. n Pin Description Pin Name NC No connection. Not internally connected. Can left floating or connected to GND. EN Enable Control Input, active high. IN Input Supply Voltage Pin. Bypass this pin with a capacitor as close to the device as possible. SW Switch Node Connection to Inductor. GND Ground. Tie directly to ground plane. FB Rev.A.04 Pin Description Output voltage Feedback input. 3 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Ordering Information AME5251A - x x x xxx xxx Output Voltage 2 Output Voltage 1 Number of Pins Package Type Pin Configuration & Special Feature Pin Configuration & Special Feature A (DFN-12A) 4 1 IN2 2. SW2 3. GND 4. FB1 5. NC1 6. EN1 7. IN1 8. SW1 9. GND 10. FB2 11. NC2 12. EN2 Package Type V: DFN Number of Pins C: 12 Output Voltage1 ADJ: Adjustable Output Voltage2 ADJ: Adjustable Rev. A.04 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Absolute Maximum Ratings Parameter Symbol Maximum VIN -0.3 to 6.5 VEN, V OUT -0.3 to VIN VSW -0.3 to VIN Input Supply Voltage EN, VOUT 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 VIN 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 θJC 8.5 Unit o C/W DFN-12A Internal Power Dissipation Solder Iron (10Sec)** Conductive Epoxy θJA 65 PD 1.54 W 350 o C * Measure θJC on backside center of Exposed Pad. ** MIL-STD-202G 210F Rev.A.04 5 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A 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 Symbol 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 For Adjustable OutputVoltage 0.588 0.612 V Feedback Pin Bias Current IFB VFB=VIN -50 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 1.2 0.6 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 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 Note 1. Spec. for per channel 6 Rev. A.04 AME AME5251A n Detailed Description Main Control Loop AME5251A 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. 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 abole 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.04 Dual 1A, 1.5MHz Synchronous Step-Down Converter n Applincation Information The basic AME5251A 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. 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 7 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A 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. 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 + 1 8 fCOUT 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 0.6V V OUT 5.5V R1 FB AME5251 A R2 GND Figure 1: Setting the AME5251A Output Voltage Thermal Considerations In most applications the AME5251A does not dissipate much heat due to its high efficiency. But, in applications where the AME5251A 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 AME5251A 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. The output voltage is set by an external resistive divider according to the following equation: VOUT = V REF × 1 + R1 R2 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 1. 8 Rev. A.04 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A VIN 2.5V to 5.5V 2.2µH SW IN AME5251A EN CFWD FB VIN 2.7V to 5.5V 2.2µH IN SW AME5251A COUT 10µF CER 150K GND CIN 4.7µF CER VOUT 1.2V GND CIN 4.7µF CER 150K FB EN CFWD 150K VOUT 2.5V COUT 10µF CER 47.3K Figure 2: 1.2V Step-Down Regulator Figure 5: 2.5V Step-Down Regulator CFWD: 22pF~220pF CFWD: 22pF~220pF VIN 3.3 to 5.5V 2.2µH IN SW AME5251A EN CFWD FB VIN 3.6 to 5.5V SW EN CIN 4.7µF CER 100K 2.2µH IN AME5251A COUT 10µF CER 150K GND CIN 4.7µF CER VOUT 1.5V FB GND CFWD 150K VOUT 3.3V COUT 10µF CER 33.3K Figure 3: 1.5V Step-Down Regulator Figure 6: 3.3V Step-Down Regulator CFWD: 22pF~220pF CFWD: 22pF~220pF VIN 2.5 to 5.5V 2.2µH IN SW AME5251A EN CIN 4.7µF CER VOUT 1.6V CFWD FB GND 150K COUT 10µF CER 90K Figure 4: 1.6V Step-Down Regulator CFWD: 22pF~220pF Rev.A.04 9 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the AME5251A. 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. SW1, SW2 should be connected to inductor by wide and short trace Keep sensitive components away from this trace . VIN2 1 12 EN2 SW2 2 11 NC2 GND 3 10 FB2 FB1 4 9 GND NC1 5 8 SW1 EN1 6 7 VIN1 VOUT2 L2 VOUT2 R12 C11 R11, R12, R21, R22 and C 11, C21 must be kept close to the ICs FB pin to prevent noise injection on the FB pin trace and keeping far away from SW node. AME5251A CIN 2 COUT2 . R11 VOUT1 NC 1, NC2 pin no connect or connect to GND. R21 R22 L1 GND The ground area must provide adequate heat dissipating area to the thermal pad and using multiple vias to help thermal dissipation . C21 VOUT 1 COUT1 CIN1 C IN1, CIN2 should be placed between V IN and GND as close as possible . Figure 7: AME5251A Adjustable Voltage Regulator Layout Diagram 10 Rev. A.04 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A 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.04 11 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Characterization Curve Efficiency vs. Output Current 100 100 90 90 80 VIN = 2.7V VIN = 3.6V 80 70 Efficiency(%) Efficiency(%) Efficiency vs. Output Current 60 50 40 30 20 70 60 50 40 30 20 10 VOUT = 2.5V 0 1 10 100 Output Current(mA) VOUT = 2.5V 10 COUT = 10µF L = 2.2µH 0 1000 1 Efficiency vs. Output Current Efficiency(%) Efficiency(%) 80 70 60 50 40 60 50 40 30 20 20 VOUT = 1.5V 1 10 VOUT = 1.5V 10 COUT = 10µF L = 2.2µH 100 VIN = 3.6V 70 30 10 0 1000 1 Output Current(mA) 100 100 90 90 80 Efficiency(%) 60 50 40 30 VOUT = 1.2V 100 Output Current(mA) 1000 60 50 40 30 VOUT = 1.2V 10 10 100 VIN = 5.5V 70 20 COUT = 10µF L = 2.2µH 10 1 10 Output Current(mA) 80 VIN = 2.5V 70 20 COUT = 10µF L = 2.2µH Efficiency vs. Output Current Efficiency vs. Output Current Efficiency(%) 1000 90 VIN = 2.7V 80 12 100 100 90 0 10 Output Current(mA) Efficiency vs. Output Current 100 0 COUT = 10µF L = 2.2µH 1000 0 1 10 COUT = 10µF L = 2.2µH 100 Output Current(mA) 1000 Rev. A.04 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Characterization Curve (Contd.) Reference Voltage vs. Temperature Frequency vs. Temperature 1.90 1.85 1.80 1.75 0.620 0.610 Frequency(MHz) Reference Voltage(V) 0.615 0.605 0.600 0.595 0.590 VIN = 3.6V -25 0 +25 +50 +75 Temperature(OC) +100 1.45 1.40 1.35 1.30 1.25 1.20 1.15 1.10 0.585 0.580 -50 1.70 1.65 1.60 1.55 1.50 +125 VIN = 3.6V -50 1.70 1.90 1.65 1.89 +75 +100 +125 VOUT = 1.8V VIN = 3.6V 1.88 1.87 1.55 Output Voltage(V) Frequency(MHz) +50 Output Voltage vs. Output Current 1.50 1.45 1.40 1.35 1.30 1.25 1.86 1.85 1.84 1.83 1.82 1.81 1.80 1.79 1.20 1.78 1.15 1.10 2.5 3.0 3.5 4.0 VIN(V) 4.5 5.0 1.77 0 5.5 Current Limit(A) VIN = 3.3V VOUT = 1.2V -25 -10 +5 +20 +35 +50 +65 +80 +95 +110 +125 Temperature (oC) 100 200 300 400 500 600 700 Output Current(mA) 800 900 1000 Current Limit vs. Temperature Current Limit vs. Temperature Current Limit(A) +25 O 1.60 Rev.A.04 +0 Temperature( C) Frequency vs. Supply Voltage 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 -25 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 o +95 +110 +125 Temperature ( C) 13 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Characterization Curve (Contd.) 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 1 2 -25 -10 +5 +20 +35 +50 +65 +80 +95 +110 +125 o 3 Temperature ( C) 400nS / div 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 Load Step 1 2 3 400nS / div 14 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.04 AME AME5251A Dual 1A, 1.5MHz Synchronous Step-Down Converter n Characterization Curve (Contd.) Load Step 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.04 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 Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Tape and Reel Dimension DFN-12A (3mmx3mmx0.75mm) P PIN 1 W AME AME Carrier Tape, Number of Components Per Reel and Reel Size 16 Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size DFN-12A (3x3x0.75mm) 12.0±0.1 mm 4.0±0.1 mm 5000pcs 330±1 mm Rev. A.04 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Package Dimension DFN-12A (3mmx3mmx0.75mm) e D L k E1 E D1 PIN 1 IDENTIFICATION b TOP VIEW P IN 1 BOTTOM VIEW A1 A3 A REAR VIEW SYMBOLS INCHES MIN MAX MIN MAX A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.203REF. 0.008REF. D 2.924 3.076 0.115 0.121 E 2.924 3.076 0.115 0.121 D1 2.450 2.650 0.096 0.104 E1 1.500 1.700 0.059 0.067 k b e L Rev.A.04 MILLIMETERS 0.200MIN. 0.150 0.250 0.450TYP. 0.324 0.476 0.008MIN 0.006 0.010 0.018TYP. 0.013 0.019 17 AME Dual 1A, 1.5MHz Synchronous Step-Down Converter AME5251A n Lead Pattern 0.000 BSC DFN-12A (3mmx3mmx0.75mm) 1.050 BSC 1.800 BSC 2.750 BSC 0.000 BSC 1.375 BSC PIN1 [1] 0.450 BSC 0.250 BSC 3 X 3 PKG REF. 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. 18 Rev. A.04 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. , January 2014 Document: 1283-DS5251A-A.04 Corporate Headquarter AME, Inc. 8F, 12, WenHu St., Nei-Hu Taipei 114, Taiwan. Tel: 886 2 2627-8687 Fax: 886 2 2659-2989