AAT1154 1MHz 3A Buck DC/DC Converter General Description Features The AAT1154 SwitchReg™ is a member of AnalogicTech™'s Total Power Management™ IC product family. The Step-down switching converter is ideal for applications where high efficiency, small size, and low ripple are critical. Able to deliver 3A with an internal power MOSFET, the current-mode controlled IC provides high efficiency. Fully internally compensated, the AAT1154 simplifies system design and lowers external part count. • • • • • • • • • • • • • • VIN Range: 2.7-5.5Volts Fixed or adjustable VOUT: 1.0V - 4.2V 3A output current Up to 95% efficiency Integrated low on resistance power switch Internally compensated current mode control 1MHz switching frequency Constant PWM mode Low output ripple with light load Internal softstart Current limit protection Over-Temperature protection SOP-8 package -40 to 85°C Temperature Range Preliminary Information The AAT1154 is available in an SOP-8 package, rated over -40 to 85°C. SwitchReg™ Applications • • • • • Computer Peripherals Set Top Boxes Network Cards Cable/DSL Modems High efficiency conversion from 5V or 3.3V supply Typical Application INPUT VP 10µF 100Ω FB AAT1154 VCC 1.5µH LX ENABLE 0.1µF OUTPUT GND 1154.2003.08.0.91 120µF 1 AAT1154 1MHz 3A Buck DC/DC Converter Pin Descriptions Pin # Symbol Function 1 FB 2 GND 3 EN 4 VCC 5, 8 VP Input Supply Voltage for converter power stage. 6, 7 LX Inductor connection pins. These pins should be connected to the output inductor. Internally, pins 6 & 7 are connected to the drain of the P-channel switch. Feedback input pin. This pin must be connected to the converter’s output. It is used to set the output of the converter to regulate to the desired value. Ground connection. Enable input pin. When connected high, AAT1154 is in normal operation. When connected low, it is powered down. This pin should not be left floating. Power supply. It supplies power for the internal circuitry. Pin Configuration SO-8 2 8 7 2 2 1 1 FB GND EN VCC 3 6 4 5 VP LX LX VP 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Absolute Maximum Ratings Symbol VCC, VP VLX VFB VEN TJ VESD (TA=25°C unless otherwise noted) Description VCC, VP to GND LX to GND FB to GND EN to GND Operating Junction Temperature Range ESD Rating 1 - HBM Value Units 6 -0.3 to VP+0.3 -0.3 to VCC+0.3 -0.3 to VCC+0.3 -40 to 150 3000 V V V V °C V Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time. Note 1: Human body model is a 100pF capacitor discharged through a 1.5K resistor into each pin. Thermal Characteristics Symbol ΘJA PD Description Thermal Resistance 2 Maximum Power Dissipation (TA = 25°C) 2, 3 Value Units 110 909 °C/W mW Rating Units -40 to +85 °C Note 2: Mounted on a demo board (FR4, in still air). Note 3: Derate 9.1mW/°C above 25°C. Recommended Operating Conditions Symbol T 1154.2003.08.0.91 Description Ambient Temperature Range 3 AAT1154 1MHz 3A Buck DC/DC Converter Electrical Characteristics (VIN = VCC = VP = 5V, TA= -40 to 85°C unless otherwise noted. Typical values are at TA = 25°C) Symbol VIN VOUT Input Voltage Range Output Voltage Tolerance VUVLO Under Voltage Lockout VUVLO(HYS) IQ ISHDN ILIM RDS(ON)L η ∆VOUT (VOUT*∆VIN) ∆VOUT/VOUT FOSC VEN(L) VEN(H) TSD THYS 4 Description Under Voltage Lockout Hysteresis Quiescent Supply Current Shutdown Current Current Limit High Side Switch On Resistance Efficiency Load Regulation Line Regulation Oscillator Frequency Enable Threshold Low Enable Threshold High Over Temp Shutdown Threshold Over Temp Shutdown Hysteresis Conditions VIN = VOUT + 0.2 to 5.5V, IOUT = 0 to 3A VIN Rising VIN Falling No Load, VFB= 0 V VEN = 0 V, VIN= 5.5V TA = 25°C TA = 25°C IOUT = 1.0 A ILOAD = 0 - 3A VIN= 2.7 to 5.5V TA = 25°C Min Typ Max Units 2.7 -5.0 5.5 5.0 V % 2.5 V V mV µA µA A mΩ 1.2 250 630 1000 1.0 4.4 60 92 ±2.6 0.75 1 0.6 1.4 140 15 % %/V MHz V V °C °C 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Typical Characteristics Oscillator Frequency Variation vs. Supply Voltage RDS(ON) vs. Temperature 90 0.5 VIN = 2.7V VIN = 4.2V VIN = 3.6V Variation (%) RDS(ON) (mΩ) 80 70 60 VIN = 5.5V 50 VIN = 5V 0.25 0 -0.25 40 -20 0 20 40 60 80 100 -0.5 120 3.5 4 4.5 Temperature (°C) 5 5.5 Input Voltage (V) RDS(ON) vs. VIN, IDS = 1A Oscillator Frequency Variation vs. Temperature VIN = 5V 70 1 65 Variation (%) RDS(ON) (mΩ Ω) 0 60 55 50 45 -1 -2 -3 40 2.5 3 3.5 4 4.5 5 -4 5.5 -20 0 20 Input Voltage (V) 60 80 100 Temperature (°C) Enable Threshold vs. Input Voltage Output Voltage vs. Temperature IOUT=2A 1.2 0.4 1.1 0.2 EN(H) 1 Variation (%) Enable Threshold (V) 40 0.9 0.8 EN(L) 0.7 0 -0.2 -0.4 -0.6 0.6 -0.8 2.5 3 3.5 4 Input Voltage (V) 1154.2003.08.0.91 4.5 5 5.5 -20 0 20 40 60 80 100 Temperature (°°C) 5 AAT1154 1MHz 3A Buck DC/DC Converter Typical Characteristics Over Temp Current vs. Input Voltage VOUT = 3.3V Line Regulation VOUT=3.3V 3.6 Output Current (A) Output Voltge Error (%) 1 IO = 0.3A 0 -1 -2 IO = 3.0A -3 3.4 70°C 3.2 3 2.8 85°C 2.6 2.4 -4 100°C 2.2 2 -5 3 3.5 4 4.5 5 5.5 3.5 6 3.75 4 4.25 Input Voltage (V) Load Regulation VIN = 5.0V, VIN = 3.3V 0.0 Operating Current (mA) Output Error (%) 5 5.25 5.5 0.8 -2.0 -3.0 -4.0 -5.0 -6.0 -7.0 -8.0 -9.0 -10.0 0.01 0.1 1 10 VIN = 5.5V 0.6 VIN = 4.2V VIN = 3.6V 0.5 VIN = 2.7V 0.4 -20 0 20 14 6 Voltage (V) (bottom traces) 4.5 4 3.5 3 4 2 8 0 6 Temperature (°C) 80 90 100 -4 2 -2 70 -2 Input 4 2 60 120 6 Inductor Current 10 0 50 100 12 2.5 40 80 Current (A) (top trace) 5 30 60 Inrush and Output Overshoot Characteristic 3A Load 5.5 20 40 Temperature (°C) Over Temp Shutdown Current vs. Temperature VOUT = 3.3V, VIN = 5.0V, L = 1.5µH 10 VIN = 5.0V 0.7 Load Current (A) Output Current (A) 4.75 Non-Switching Operating Current vs. Temperature FB = 0V -1.0 6 4.5 Input Voltage (V) -6 Output -8 -10 0 0.4 0.8 1.2 1.6 2 Time (millisec) 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Typical Characteristics Inrush and Output Overshoot Characteristic No Load Inductor Current 4 7 4 2 6 0 5 -2 4 -4 3 -6 2 10 2 8 0 6 -2 Input 4 -4 2 -6 Output 0 -8 -2 -10 0 0.4 0.8 1.2 1.6 -8 2 -1 0 1 2 5 -2 4 -4 3 -6 2 -8 1 200 uF 6.3V Ceramic TDK P/N C3325X5R0J107M 0 -12 AC Output Ripple (top) (mV) AC Output Ripple (top) (mV) 6 0 -1 3 4 40 7 20 6 0 5 -20 4 -40 3 -60 2 -80 5 16 135 12 100µF 6.3V Ceramic TDK P/N C3225X5R0J107M -16 10000 1154.2003.08.0.91 0 -45 -90 -135 -180 100000 Frequency (Hz) 4 5 120 µF 6.3V Tantalum Vishay P/N 594D127X96R3C2T 8 Gain (dB) Gain (dB) -12 90 45 2x 100µF 3 135 90 Phase 4 0 -4 180 45 0 Gain -45 -8 -90 -12 -135 -16 10000 Phase (Degrees) Phase Phase (Degrees) -8 2 Loop Crossover Gain and Phase 180 3x 100µF 1 Time (µ µsec) 12 0 -1 0 16 -4 0 -120 Loop Crossover Gain and Phase 4 1 120 µF 6.3V Tantalum Vishay P/N 594D127X96R3C2T -100 Time (µ µsec) 8 5 Inductor Current (bottom) (A) 2 Inductor Current (bottom) (A) 7 2 4 Tantalum Output Ripple IOUT = 3.0A, VOUT = 3.3V, VIN = 5.0V 4 1 3 Time (µ µsec) Output Ripple IOUT = 3.0A, VOUT = 3.3V, VIN = 5.0V 0 0 -12 Time (millisec) -10 1 300 µF 6.3VCeramic TDK P/N C3325X5R0J107M -10 Inductor Current bottom (A) 6 Current (A) (top trace) Voltage (V) (bottom traces) 12 AC Output Ripple top (mV) 14 Output Ripple IOUT = 3.0A, VOUT = 3.3V, VIN = 5.0V -180 100000 Frequency (Hz) 7 AAT1154 1MHz 3A Buck DC/DC Converter Typical Characteristics Transient Response IOUT = 0 to 3.0A, VOUT = 3.3V, VIN = 5.0V 100 3x 100µF 6.3V Ceramic TDK P/N C3325X5R0J107M 7 100 6 0 5 -200 4 -300 3 -400 2 -500 1 -600 0 -700 -1 -700 0 100 200 300 400 500 Output Voltage (top) (mV) -100 6 -100 5 -200 4 -300 3 -400 2 -500 1 -600 0 -1 0 Time (µ µs) 7 2x 100 uF 6.3V Ceramic TDK P/N C3325X5R0J107M Inductor Current (bottom) (A) Inductor Current (bottom) (A) Output Voltage (top) (mV) 0 Transient Response IOUT = 0 to 3.0A, VOUT = 3.3V, VIN = 5.0V 100 200 300 400 500 Time (µ µs) 100 7 0 6 -100 5 -200 4 -300 3 -400 2 -500 1 -600 0 120µF 6.3V Tantalum Vishay P/N 594D127X96R3C2T -700 0 100 200 300 Inductor Current (bottom) (A) Output Voltage (top) (mV) Tantalum Transient Response IOUT = 0 to 3.0A, VOUT = 3.3V, VIN = 5.0V -1 400 500 Time (µ µs) 8 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Functional Block Diagram VCC VP= 2.7V- 5.5V REF FB OP. AMP CMP DH LOGIC OSC LX Temp. Sensing GND EN Applications Information The crossover frequency and phase margin are set by the output capacitor value. Main Control Loop Duty cycle extends to 100% as the input voltage approaches the output voltage. Thermal shutdown protection disables the device in the event of a short circuit or overload condition. The AAT1154 is a peak current mode buck converter. The inner wide bandwidth loop controls the inductor peak current. The inductor current is sensed as it flows through the internal P-Channel MOSFET. A fixed slope compensation signal is then added to the sensed current to maintain stability for duty cycles greater than 50%. The inner loop appears as a voltage programmed current source in parallel with the output capacitor. The voltage error amplifier output programs the current loop for the necessary inductor current to force a constant output voltage for all load and line conditions. The feedback resistive divider is internal, dividing the output voltage to the error amplifier reference voltage of 1.0V. The error amplifier has a limited DC gain. This eliminates the need for external compensation components while still providing sufficient DC loop gain for good load regulation. 1154.2003.08.0.91 Soft Start/Enable Soft-start controls the current limit when the input voltage or enable is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. The enable input, when pulled low, forces the device into a low power non-switching state. The total input current during shutdown is less than 1µA. Power and Signal Source Separate small signal ground and power supply pins isolate the internal control circuitry from switching noise. In addition, the low pass filter R1 and C3 in figure 3 filters noise associated with the power switching. 9 AAT1154 1MHz 3A Buck DC/DC Converter Current Limit and Over Temp Protection The AAT1154 over temp and current limit circuitry protects the AAT1154 as well as the external Schottky diode during overload, short circuit and excessive ambient temperature conditions. The junction over temp threshold is 140°C nominal and has 15°C of hysteresis. Typical graphs of the over temp load current vs. input voltage and ambient temperature are shown in the Typical Characteristics section. Inductor The output inductor is selected to limit the ripple current to 20-40% of the full load current at the maximum input voltage. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the inductor saturation characteristics. The inductor should not show any appreciable saturation under all normal load conditions. During overload and short circuit conditions the inductor can exceed its peak current rating without affecting the converter performance. Some inductors may have sufficient peak and average current ratings yet result in excessive losses due to a high DC resistance (DCR). The losses associated with the DCR and its affect on the total converter efficiency must be considered. For a 3 Amp load and the ripple current set to 30% at the maximum input voltage, the maximum peak to peak ripple current is 0.9Amp. Assuming a 5V ± 5% input voltage and 30% ripple the output inductance required is L =I OUT = VOUT VOUT · k · FSW · 1 - VIN(MAX) 3.3V · 1 - 3.3V 3.0A · 0.3 · 1MHz 5.25V = 1.36µH 10 The factor "k" is the fraction of the full load (30%) selected for the ripple current at the maximum input voltage. The corresponding inductor RMS current is: IRMS = 2 ∆I 2 I + ≈ I O = 3A O 12 ∆I is the peak to peak ripple current which is fixed by the inductor selection above. For a peak to peak current of 30% of the full load current the peak current at full load will be 115% of the full load. The 1.5µH inductor selected from the Sumida CDRH6D38 series has a 11mΩ DCR and a 4.0 Amp DC current rating with a height of 4 mm. At full load the inductor DC loss is 99 mW for a 1 % loss in efficiency. Schottky Freewheeling Diode The Schottky average current is the load current times one minus the duty cycle. For VIN at 5 Volts and Vout at 3.3 Volts the average diode current is V 3.3V = 1A I AVG = IO · 1 - O = 3A · 1 VIN 5.0V With a 125°C maximum junction temperature and a 120°C/W thermal resistance the maximum average current is IAVG = TJ(MAX)- TAMB θJ-A · VFWD = 125°C - 70°C = 1.14A 120 °C/ W · 0.4V For overload, short circuit, and excessive ambient conditions the AAT1154 enters the over-temperature shutdown mode protecting the AAT1154 as well as the output Schottky. In this mode the output current is limited internally until the junction temperature reaches the temperature limit (see over temp characteristics graphs). The diode reverse voltage must be rated to withstand the input voltage. 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Diodes Inc. ROHM Micro Semi B340LA RB050L-40 5820SM 0.45V@3A 0.45@3A 0.46V@3A 3 Amp Surface Mount Schottky Diodes Input Capacitor Selection The primary function of the input capacitor is to provide a low impedance loop for the edges of pulsed current drawn by the AAT1154. A low ESR/ESL ceramic capacitor is ideal for this function. To minimize the stray inductance the capacitor should be placed as close as possible to the IC. This also keeps the high frequency content of the input current localized, minimizing the radiated and conducted EMI while facilitating optimum performance of the AAT1154. The proper placement of the input capacitor C1 is shown in the layout in figure 1. Ceramic X5R or X7R capacitors are ideal. The size required will vary depending on the load, output voltage, and input voltage source impedance characteristics. Typical values range from 1µF to 10 µF. The input capacitor RMS current varies with the input voltage and the output voltage. It is highest when the input voltage is double the output voltage where it is one half of the load current. IRMS = IO · VO V · 1- O VIN VIN A high ESR tantalum with a value about 10 times the input ceramic capacitor may also be required when using a 10µF or smaller ceramic input bypass capacitor. This dampens out any input oscillations that may occur due to the source inductance resonating with the converter input impedance Output Capacitor With no external compensation components, the output capacitor has a strong effect on the loop stability. Larger output capacitance will reduce the crossover frequency with greater phase margin. A 200µF ceramic capacitor provides sufficient bulk capacitance to stabilize the output during large load transitions and has ESR and ESL characteristics necessary for very low output ripple. The RMS ripple current is given by 1154.2003.08.0.91 IRMS = 1 2· 3 · ( VOUT+ VFWD) · (VIN - VOUT) L · F · VIN For a ceramic output capacitor the dissipation due to the RMS current and output ripple associated with are negligible. Tantalum capacitors, with sufficiently low ESR to meet output ripple requirements, generally have an RMS current rating much greater than that actually seen in this application. The maximum tantalum output capacitor ESR is ESR ≤ VRIPPLE ∆I Where ∆I is the peak to peak inductor ripple current. Due to the ESR zero associated with the tantalum capacitor, smaller values than those required with ceramic capacitors provide more phase margin a with greater loop crossover frequency. Layout Figures 1 and 2 display the suggested PCB layout for the AAT1154. The following guidelines should be used to help insure a proper layout. 1. The connection from the input capacitor to the Schottky anode should be as short as possible. 2. The input capacitor should connect as closely as possible to VPOWER (pins 5 and 8) and GND (pin 2). 3. C1, L1, and CR1 should be connected as closely as possible. The connection from the cathode of the Schottky to the LX node should be as short as possible. 4. The feedback trace (pin 1) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high current load trace can degrade DC load regulation. 5. The resistance of the trace from the load return to the gnd (pin 2) should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal reference ground and the load rtn. 6. R1 and C3 are required in order to provide a cleaner power source for the AAT1154 control circuitry. 11 AAT1154 1MHz 3A Buck DC/DC Converter Figure 1. AAT1154 Fixed Output Top Side Layout Thermal The losses associated with the AAT1154 output switching MOSFET are due to switching losses and conduction losses. The conduction losses are associated with the RDS(ON) characteristics of the output switching device. At the full load condition, assuming continuous conduction mode (CCM), an accurate calculation of the RDS(ON) losses can be derived from the following equations. PON = I RMS2 · RDS(ON) Figure 2. AAT1154 Fixed Output Bottom Side Layout Once the total losses have been determined the junction temperature can be derived. The thermal resistance (ΘJA) for the SO-8 package mounted on an FR4 printed circuit board in still air is 110°C/W. TJ = P · ΘJA + TAMB TAMB is the maximum ambient temperature and TJ is the resultant maximum junction temperature. Design Example IOUT 3A RDS(ON) losses ∆I 2 ·D IRMS = I O2 + 12 Internal switch RMS current D is the duty cycle and VF is the forward drop of the Schottky diode. D= IRIPPLE 30% of full load at max Vin VOUT 3.3V VIN 5V ± 5% FS 1MHz TMAX = 70°C Inductor Selection VO + VF VIN + VF IQ is the peak to peak inductor ripple current. A simplified form of calculating the RDS(ON) and switching losses is given by P= L= = VOUT VOUT · 1IO · k · F VIN 3.3V 3.3 V · 1= 1.25µH 3A · 0.3 ·1MHz 5V Use standard value of 1.5 µH I O 2 · R DS(ON) Vo + tSW ·F · I O + I Q · VIN VIN where IQ is the AAT1154 quiescent current. 12 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Sumida inductor Series CDRH6D38. ∆I = VO V 1- O = L · F VIN 3.3V 3.3V 1= 0.82A 1.5µH · 1MHz 5.25V I PK = IOUT + AAT1154 Junction Temperature IO2 · RDS(ON) · VO tSW · F · IO + IQ · VIN = + VIN 2 32 · 65mΩ · 3.3V 20ns · 1MHz · 3A + + 750µA · 5V = 5V 2 0.539 Watts TJ(MAX)= TAMB + ΘJA · P = 70°C + 110°C / W · 0.54W = 129°C Diode V IDIODE= IO · 1 - O = VIN 3.3V = 1.02A 3A · 1 5V VFW = 0.35V PDIODE =VFW · IDIODE = 0.35V · 1.01A = .354W 1154.2003.08.0.91 TJ(MAX) = TAMB + ΘJA · P = 70°C + 120°C / W · 0.354W = 112°C ∆I = 2 3A + 0.41A = 3.41A PON = Given a case to ambient thermal resistance of 120°C/W from the manufacturer's data sheet, TJ(MAX) of the diode is Output Capacitor The output capacitor value required for sufficient loop phase margin depends on the type of capacitor selected. For a low ESR ceramic capacitor a minimum value of 200µF is required. For a low ESR tantalum capacitor lower values are acceptable. While the relatively higher ESR associated with the tantalum capacitor will give more phase margin and a more damped transient response, the output voltage ripple will be higher. The 120µF Vishay 594D tantalum capacitor has an ESR of 85 mΩ and a ripple current rating of 1.48 Arms in a C case size. Although smaller case sizes are sufficiently rated for this ripple current, their ESR level would result in excessive output ripple. The ESR requirement for a tantalum capacitor can be estimated by ESR ≤ IRMS = VRIPPLE 100 mV = = 121 mΩ ∆I 0.82A 1 2· 3 · (VOUT+ VFWD) · (VIN - VOUT) L · F · VIN = 1 3.65V ·1.7 V · = 240mArms 2 · 3 1.5µH · 1MHz · 5V Two or three 1812 X5R 100uF 6.3V ceramic capacitors in parallel also provide sufficient phase margin. The low ESR and ESL associated with ceramic capacitors also reduces output ripple significantly over that seen with tantalum capacitors. Temperature rise due to ESR ripple current dissipation is also reduced. 13 AAT1154 1MHz 3A Buck DC/DC Converter Input Capacitor The input capacitor ripple is: IRMS = I O · VO V · 1 - O = 1.42 Arms VIN VIN In the examples shown C1 is a ceramic capacitor located as close to the IC as possible. C1 provides the low impedance path for the sharp edges associated with the input current. C4 may or may not be required depending upon the impedance characteristics looking back into the source. It serves to dampen out any input oscillations that may arise from a source that is highly inductive. For most applications where the source has sufficient bulk capacitance and is fed directly to the AA1154 through large PCB traces or planes it is not required. When operating the AAT1154 evaluation board on the bench C4 is required due to the inductance of the wires running from the laboratory power supply to the evaluation board. Vin 3.5V-5.5V Efficiency vs. Load Current VIN = 5.0V, VOUT = 3.3V Vout 3.3V @ 3A R2 100k C4 100µF U1 AAT1154-3. 3 FB 100 VP 95 L1 1.5µH GND LX EN C1 10µF C3 0.1µF rtn LX VCC VP D1 B340LA C2 120µF + - C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3 C2 Vishay120µF 6.3V 594D127X96R6R3C2T C3 0.1µF 0603ZD104M AVX C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V D1 B340LA Diodes Inc. L1 CDRH6D28-1.5µH Sumida Efficiency (%) R1 100 90 85 80 75 70 65 60 0.01 0.1 1 10 Output Current (A) Options C2 MuRata 100µF 6.3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel) Figure 3. 3.3 Volt 3 Amp Output Adjustable Output For applications requiring an output other than the fixed outputs available, the 1V version can be programmed externally. Resistors R3 and R4 of figure 5 force the output to regulate higher than 1 Volt. For 14 Figure 4. 5 Volt Input 3.3 Volt Output accurate results (less than 1% error for all outputs) select R4 to be 10kΩ. Once R4 has been selected R3 can be calculated. For a 1.25 Volt output with R4 set to 10k R3 is 2.5kΩ. R3 = (VO - 1) · R4 = 0.25 · 10kΩ = 2.5kΩ 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Vin 2.7V-5.5V VOUT 1.25V @ 3A R1 100 R2 100k R3 2.55k U1 AAT1154-1.0 FB C4 100µF VP L1 1.5µH GND LX EN C1 10µF C3 0.1µF rtn LX VCC VP R4 10.0k D1 B340LA C2 120µF C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3 C2 Vishay 120µF 6.3V 594D127X96R6R3C2T C3 0.1µF 0603ZD104M AVX C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V D1 B340LA Diodes Inc. L1 CDRH6D28-1.5µH Sumida Options C2 MuRata 100uF 6.3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel) C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel) Figure 5. AAT1154 Evaluation Board with adjustable output Figure 6. Evaluation Board Top Side 1154.2003.08.0.91 Figure 7. Evaluation Board Bottom Side 15 AAT1154 1MHz 3A Buck DC/DC Converter Capacitors Part Number Manufacturer C4532X5ROJ107M GRM43-2 X5R 107M 6.3 GRM43-2 X5R 476K 6.3 GRM42-6 X5R 106K 6.3 594D127X_6R3C2T 595D107X0016C TDK MuRata MuRata MuRata Vishay Vishay Capacitance (µF) Voltage (V) 100 100 47 10 120 100 6.3 6.3 6.3 6.3 6.3 16 Temp Co. Case X5R X5R X5R X5R 1812 1812 1812 1206 C case C case Inductors Part Number Manufacturer CDRH6D38-4763-T055 N05D B1R5M NP06DB B1R5M LQH55DN1R5M03 LQH66SN1R5M03 Sumida Taiyo Yuden Taiyo Yuden MuRata MuRata Inductance (µH) I (Amps) DCR Ω) (Ω Height (mm) 1.5 1.5 1.5 1.5 1.5 4.0 3.2 3.0 3.7 3.8 .014 .025 .022 .022 .016 4.0 2.8 3.2 4.7 4.7 shielded Non shielded shielded Non shielded shielded Diodes 16 Manufacturer Part Number Vfwd Diodes Inc. ROHM Micro Semi B340LA RB050L-40 5820SM 0.45V @ 3A 0.45 @ 3A 0.46V @ 3A 1154.2003.08.0.91 AAT1154 1MHz 3A Buck DC/DC Converter Ordering Information Output Voltage Package Marking Part Number (Tape and Reel) 1.0V SO-8 AAT1154IAS-1.0-T1 1.8V SO-8 AAT1154IAS-1.8-T1 2.5V SO-8 AAT1154IAS-2.5-T1 3.3V SO-8 AAT1154IAS-3.3-T1 Package Information 6.00 ± 0.20 3.90 ± 0.10 SO-8 4.90 ± 0.10 0.42 ± 0.09 × 8 1.27 BSC 45° 4° ± 4° 0.175 ± 0.075 1.55 ± 0.20 0.375 ± 0.125 0.235 ± 0.045 0.825 ± 0.445 All dimensions in millimeters. 1154.2003.08.0.91 17 AAT1154 1MHz 3A Buck DC/DC Converter AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18 1154.2003.08.0.91