AAT1154 1MHz 3A Step-Down DC/DC Converter General Description Features The AAT1154 SwitchReg is a step-down switching converter 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 parts count. • • • • • • • • The AAT1154 is available in a Pb-free SOP-8 package and is rated over the -40°C to +85°C temperature range. • • • • • • SwitchReg™ VIN Range: 2.7V to 5.5V Fixed or Adjustable VOUT: 1.0V to 4.2V 3A Output Current Up to 95% Efficiency Integrated Low On Resistance Power Switch Internally Compensated Current Mode Control 1MHz Switching Frequency Constant Pulse Width Modulation (PWM) Mode Low Output Ripple With Light Load Internal Soft Start Current Limit Protection Over-Temperature Protection SOP-8 Package -40°C to +85°C Temperature Range Applications • • • • • Cable/DSL Modems Computer Peripherals High Efficiency Conversion from 5V or 3.3V Supply Network Cards Set-Top Boxes Typical Application INPUT VP 10μF 100Ω FB AAT1154 VCC 1.5μH LX EN 0.1μF OUTPUT GND 1154.2006.09.1.6 120μF 1 AAT1154 1MHz 3A Step-Down 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 and 7 are connected to the drain of the P-channel switch. Feedback input pin. This pin must be connected to the converter output. It is used to set the converter output to regulate to the desired value. Ground connection. Enable input pin. When connected high, the AAT1154 is in normal operation; when connected low, it is powered down. This pin should not be left floating. Power supply: supplies power for the internal circuitry. Pin Configuration SOP-8 VP 7 LX 3 6 LX 4 5 VP GND 2 EN VCC 2 1 1 2 8 FB 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Absolute Maximum Ratings1 TA = 25°C, unless otherwise noted. Symbol VCC, VP VLX VFB VEN TJ VESD Description VCC, VP to GND LX to GND FB to GND EN to GND Operating Junction Temperature Range ESD Rating2 - 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 Value Units 110 909 °C/W mW Rating Units -40 to +85 °C Thermal Characteristics3 Symbol ΘJA PD Description Thermal Resistance Maximum Power Dissipation (TA = 25°C)4 Recommended Operating Conditions Symbol T Description Ambient Temperature Range 1. 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. 2. Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. 3. Mounted on a demo board (FR4, in still air). 4. Derate 9.1mW/°C above 25°C. 1154.2006.09.1.6 3 AAT1154 1MHz 3A Step-Down DC/DC Converter Electrical Characteristics VIN = VCC = VP = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol VIN Output Voltage Tolerance VUVLO Under-Voltage Lockout TSD THYS Conditions Input Voltage Range VOUT VUVLO(HYS) IQ ISHDN ILIM RDS(ON)H η ΔVOUT (VOUT*ΔVIN) ΔVOUT/VOUT FOSC VEN(L) VEN(H) 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-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis VIN = VOUT + 0.2V to 5.5V, IOUT = 0A to 3A VIN Rising VIN Falling No Load, VFB = 0V VEN = 0V, VIN = 5.5V TA = 25°C TA = 25°C IOUT = 1A ILOAD = 0A to 3A VIN = 2.7V to 5.5V TA = 25°C Min Typ Max Units 2.7 5.5 V -5.0 5.0 % 2.5 1.2 250 630 1000 1.0 4.4 60 92 ±2.6 0.75 1 0.6 1.4 V mV µA µA A mΩ % % %/V MHz V V 140 °C 15 °C 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Typical Characteristics Efficiency vs. Load Current RDS(ON) vs. Temperature (VIN = 5V; VOUT = 3.3V) 100 90 90 VIN = 2.7V 80 85 RDS(ON) (mΩ) Efficiency (%) 95 80 75 70 65 VIN = 4.2V VIN = 3.6V 70 60 VIN = 5.5V 50 60 0.01 0.1 1 10 VIN = 5V 40 -20 Output Current (A) 0 20 40 60 80 100 120 Temperature (°C) RDS(ON) vs. VIN Oscillator Frequency Variation vs. Supply Voltage (IDS = 1A) 70 0.5 RDS(ON) (mΩ Ω) Variation (%) 65 0.25 0 -0.25 60 55 50 45 40 -0.5 3.5 4 4.5 5 2.5 5.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Input Voltage (V) Enable Threshold vs. Input Voltage Oscillator Frequency Variation vs. Temperature (VIN = 5V) 1.2 Enable Threshold (V) 1 Variation (%) 0 -1 -2 -3 1.1 EN(H) 1 0.9 0.8 EN(L) 0.7 0.6 -4 -20 0 20 40 60 Temperature (°C) 1154.2006.09.1.6 80 100 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) 5 AAT1154 1MHz 3A Step-Down DC/DC Converter Typical Characteristics Output Voltage vs. Temperature Line Regulation (IOUT = 2A) (VOUT = 3.3V) 0.4 1 Output Voltge Error (%) Variation (%) 0.2 0 -0.2 -0.4 -0.6 -0.8 -20 0 20 40 60 80 100 IO = 0.3A 0 -1 -2 IO = 3.0A -3 -4 -5 3 3.5 4 Temperature (°°C) Over-Temperature Current vs. Input Voltage Load Regulation (VOUT = 3.3V) (VIN = 5.0V; VIN = 3.3V) 6 -1.0 70°C 3.2 Output Error (%) Output Current (A) 5.5 0.0 3.4 3 2.8 85°C 2.6 2.4 100°C 2.2 -2.0 -3.0 -4.0 -5.0 -6.0 -7.0 -8.0 -9.0 2 -10.0 3.5 3.75 4 4.25 4.5 4.75 5 5.25 0.01 5.5 0.1 Input Voltage (V) 1 10 Load Current (A) Non-Switching Operating Current vs. Temperature Over-Temperature Shutdown Current vs. Temperature (FB = 0V) (VOUT = 3.3V; VIN = 5.0V; L = 1.5μH) 0.8 VIN = 5.5V 6 VIN = 5.0V Output Current (A) Operating Current (mA) 5 Input Voltage (V) 3.6 0.7 0.6 0.5 VIN = 2.7V VIN = 3.6V VIN = 4.2V 5.5 5 4.5 4 3.5 3 2.5 2 0.4 -20 0 20 40 60 Temperature (°C) 6 4.5 80 100 120 10 20 30 40 50 60 70 80 90 100 Temperature (°C) 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Typical Characteristics Inrush and Output Overshoot Characteristics Inrush and Output Overshoot Characteristics (3A Load) (No Load) Voltage (V) (bottom traces) 14 4 12 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 6 Inductor Current 2 8 0 6 -2 Input 4 -4 2 -6 Output 0 -8 -2 2 -10 0 0.4 0.8 Time (ms) 1.2 1.6 2 Time (ms) Output Ripple Output Ripple (IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V) (IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V) 4 7 6 2 6 0 5 0 5 -2 4 -2 4 -4 3 -4 3 -6 2 -6 2 -8 1 300µF 6.3VCeramic TDK P/N C3325X5R0J107M -10 0 -12 AC Output Ripple (top) (mV) 7 2 -1 0 1 2 3 4 -8 1 200μF 6.3V Ceramic TDK P/N C3325X5R0J107M -10 Inductor Current (bottom) (A) 4 Inductor Current (bottom) (A) AC Output Ripple top (mV) 4 10 Inductor Current (A) (top trace) 6 Inductor Current (A) (top trace) Inductor Current 12 Voltage (V) (bottom traces) 14 0 -12 -1 5 0 Time (μ μs) 1 2 3 4 5 Time (μ μs) Loop Crossover Gain and Phase Tantalum Output Ripple 20 6 0 5 -20 4 -40 3 -60 2 -80 1 120μF 6.3V Tantalum Vishay P/N 594D127X96R3C2T -100 -120 0 1 2 3 Time (μ μs) 1154.2006.09.1.6 4 5 16 180 12 135 8 Gain (dB) 7 Phase 4 45 3x 100μF 0 -4 -8 90 2x 100μF 100μF 6.3V Ceramic TDK P/N C3225X5R0J107M 0 -12 -1 -16 10000 0 -45 -90 Phase (degrees) 40 Inductor Current (bottom) (A) AC Output Ripple (top) (mV) (IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V) -135 -180 100000 Frequency (Hz) 7 AAT1154 1MHz 3A Step-Down DC/DC Converter Typical Characteristics Loop Crossover Gain and Phase Transient Response (IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V) 180 120μF 6.3V Tantalum Vishay P/N 594D127X96R3C2T 12 Gain (dB) Phase 45 0 0 -4 -45 Gain 5 -200 4 -300 3 -400 2 -500 1 0 -90 -12 -135 -600 -180 100000 -700 -1 0 100 Frequency (Hz) Tantalum Transient Response 100 7 6 0 6 -100 5 -200 4 -300 3 -400 2 5 -200 4 -300 3 -400 2 -500 1 -600 0 -600 -700 -1 -700 100 200 300 400 500 -500 1 0 120μF 6.3V Tantalum Vishay P/N 594D127X96R3C2T 0 100 200 300 Inductor Current (bottom) (A) 7 Inductor Current (bottom) (A) Output Voltage (top) (mV) 500 (IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V) Time (μ μs) 8 400 Transient Response -100 0 300 (IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V) 2x 100μF 6.3V Ceramic TDK P/N C3325X5R0J107M 0 200 Time (μ μs) Output Voltage (top) (mV) 100 6 -100 -8 -16 10000 7 3x 100μF 6.3V Ceramic TDK P/N C3325X5R0J107M 0 Inductor Current (bottom) (A) 90 Phase (degrees) 8 4 100 135 Output Voltage (top) (mV) 16 -1 400 500 Time (μ μs) 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Functional Block Diagram VCC VP = 2.7V to 5.5V REF FB OP. AMP CMP DH LOGIC OSC Temp. Sensing GND Applications Information Main Control Loop The AAT1154 is a peak current mode step-down 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 1V. 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. The crossover frequency and phase margin are set by the output capacitor value. 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. 1154.2006.09.1.6 LX EN 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. When pulled low, the enable input 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 (shown in Figure 1) filters noise associated with the power switching. Current Limit and Over-Temperature Protection Over-temperature and current limit circuitry protects the AAT1154 and the external Schottky diode during overload, short-circuit, and excessive ambient temperature conditions. The junction over-temperature threshold is 140°C nominal and has 15°C of hysteresis. Typical graphs of the over-temperature load current vs. input voltage and ambient temperature are shown in the Typical Characteristics section of this document. 9 AAT1154 1MHz 3A Step-Down DC/DC Converter VIN 3.5V to 5.5V VOUT 3.3V @ 3A R1 100 C4 100µF R2 100k U1 AAT1154-3.3 FB VP L1 1.5µH GND LX EN C1 10µF LX VCC VP C3 0.1µF rtn C2 120µF D1 B340LA + - 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 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 1: 3.3V, 3A Output. Inductor The output inductor is selected to limit the ripple current to 20% to 40% of 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 normal load conditions. During overload and short-circuit conditions, the inductor can exceed its peak current rating without affecting 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 effect on the total converter efficiency must be considered. For a 3A load and the ripple current set to 30% at the maximum input voltage, the maximum peak-to-peak ripple current is 0.9A. Assuming a 5V ±5% input voltage and 30% ripple, the output inductance required is: 10 L =I = OUT VOUT ⎞ VOUT ⎛ · k · FS · ⎝1 - VIN(MAX)⎠ 3.3V ⎞ ⎛ ⎞ ⎛ · 1 - 3.3V ⎝ 3A · 0.3 · 1MHz ⎠ ⎝ 5.25V⎠ = 1.36μH 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 ΔI 2 ⎞ I + ≈ I O = 3A ⎝ O 12 ⎠ ΔI 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 4.0A DC current rating with a height of 4mm. At full load, the inductor DC loss is 99mW for a 1% loss in efficiency. 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Schottky Freewheeling Diode The Schottky average current is the load current multiplied by one minus the duty cycle. For VIN at 5V and VOUT at 3.3V, 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 θJA · VFWD = 125°C - 70°C = 1.14A 120 °C/ W · 0.4V For overload, short-circuit, and excessive ambient temperature conditions, the AAT1154 enters overtemperature shutdown mode, protecting the AAT1154 and the output Schottky. In this mode, the output current is limited internally until the junction temperature reaches the temperature limit (see over-temperature characteristics graphs). The diode reverse voltage must be rated to withstand 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 · A high ESR tantalum capacitor 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 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 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: 3A Surface Mount Schottky Diodes Diodes Inc. ROHM Micro Semi B340LA RB050L-40 5820SM 0.45V @ 3A 0.45V @ 3A 0.46V @ 3A 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 stray inductance, the capacitor should be placed as closely 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. Proper placement of the input capacitor C1 is shown in the layout in Figure 2. 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 10µF. The input capacitor RMS current varies with the input voltage 1154.2006.09.1.6 VO ⎛ V · 1- O ⎞ VIN ⎝ VIN ⎠ IRMS = 1 (VOUT + VFWD) · (VIN - VOUT) L · FS · VIN 2· 3 · For a ceramic output capacitor, the dissipation due to the RMS current and associated output ripple 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 ΔI where ΔI 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 with a greater loop crossover frequency. 11 AAT1154 1MHz 3A Step-Down DC/DC Converter Figure 2: AAT1154 Fixed Output Top Side Layout. Layout Figures 2 and 3 display the suggested PCB layout for the fixed output AAT1154. The following guidelines should be used to help ensure 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 VP (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 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 return. 6. R1 and C3 are required in order to provide a cleaner power source for the AAT1154 control circuitry. 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: 12 Figure 3: AAT1154 Fixed Output Bottom Side Layout. PON = I RMS2 · RDS(ON) RDS(ON) losses IRMS = 2 ⎛ 2 ΔI ⎞ IO + ·D ⎝ 12 ⎠ Internal switch RMS current D is the duty cycle and VF is the forward drop of the Schottky diode. D= VO + VF VIN + VF ΔI is the peak-to-peak inductor ripple current. A simplified form of calculating the RDS(ON) and switching losses is given by: P= I O 2 · R DS(ON) VO + tSW · FS · IO + IQ · VIN VIN where IQ is the AAT1154 quiescent current. Once the total losses have been determined, the junction temperature can be derived. The thermal resistance (ΘJA) for the SOP-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. 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Design Example AAT1154 Junction Temperature (See Figures 1 and 4 for reference) PON = IOUT 3A IRIPPLE 30% of Full Load at Max VIN VOUT 3.3V VIN 5V ±5% FS 1MHz TMAX 70°C = IO2 · RDS(ON) · VO ⎛ tSW · FS · IO + IQ⎞ · VIN = + VIN 2 ⎝ ⎠ ⎞ 32 · 65mΩ · 3.3V ⎛ 20ns · 1MHz · 3A + + 750 μA ⎝ ⎠ 5V 2 = 0.539 Watts TJ(MAX)= TAMB + ΘJA · P = 70°C + 110°C / W · 0.54W = 129°C Inductor Selection L= = VOUT V · ⎛1 - OUT ⎞ IO · k · FS ⎝ VIN ⎠ Diode ⎛ V ⎞ IDIODE= IO · 1 - O ⎝ VIN ⎠ 3.3V ⎛ 3.3 V ⎞ · 1= 1.25μH 3A · 0.3 ·1MHz ⎝ 5V ⎠ ⎛ 3.3V ⎞ = 3A · 1 = 1.02A ⎝ 5V ⎠ Use standard value of 1.5µH Sumida Inductor Series CDRH6D38. ΔI = = VF = 0.35 V VO ⎛ V ⎞ 1- O ⎝ L · FS VIN ⎠ PDIODE · VF · IDIODE 0.35V · 1.01A = 0.354W 3.3V 3.3V ⎞ ⎛ 1= 0.82A 1.5μH · 1MHz ⎝ 5.25V⎠ I PK = IOUT + Given an ambient thermal resistance of 120°C/W from the manufacturer's data sheet, TJ(MAX) of the diode is: ΔI 2 = 3A + 0.41A = 3.41A TJ(MAX) = TAMB + ΘJA · P = 70°C + 120°C / W · 0.354W = 112°C Efficiency vs. Load Current (VIN = 5V; VOUT = 3.3V) 100 Efficiency (%) 95 Output Capacitor 90 85 80 75 70 65 60 0.01 0.1 1 Output Current (A) 10 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 dampened transient response, the output voltage ripple will be higher. Figure 4: 5V Input, 3.3V Output. 1154.2006.09.1.6 13 AAT1154 1MHz 3A Step-Down DC/DC Converter The 120µF Vishay 594D tantalum capacitor has an ESR of 85mΩ and a ripple current rating of 1.48Arms 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. In the examples shown, C1 is a ceramic capacitor located as closely 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 AAT1154 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. The ESR requirement for a tantalum capacitor can be estimated by: ESR ≤ IRMS = = VRIPPLE 100 mV = = 121 mΩ ΔI 0.82A (VOUT + VF) · (VIN - VOUT) L · FS · VIN 2· 3 1 · 3.65V ·1.7 V = 240mArms 2 · 3 1.5μH · 1MHz · 5V 1 · Adjustable Output 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. For applications requiring an output other than the fixed outputs available, the 1V version can be externally programmed. Resistors R3 and R4 of Figure 5 force the output to regulate higher than 1V. For 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 1.25V output with R4 set to 10kΩ, R3 is 2.5kΩ. Input Capacitor R3 = (VO - 1) · R4 = 0.25 · 10kΩ = 2.5kΩ The input capacitor ripple is: IRMS = I O · Figures 6 and 7 display the suggested PCB layout for the adjustable output AAT1154. VO ⎛ V ⎞ · 1 - O = 1.42 Arms VIN ⎝ VIN ⎠ VIN 2.7V to 5.5V VOUT 1.25V @3A R1 100 C4 100µF R2 100k R3 2.55k U1 AAT1154-1.0 FB VP L1 1.5µH GND LX EN C1 10µF VCC VP C3 0.1µF rtn LX 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. 14 1154.2006.09.1.6 AAT1154 1MHz 3A Step-Down DC/DC Converter Figure 6: Evaluation Board Adjustable Output Top Side Layout. Figure 7: Evaluation Board Adjustable Output Bottom Side Layout. 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 16.0 Temp Co. Case X5R X5R X5R X5R 1812 1812 1812 1206 C C 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 0.014 0.025 0.022 0.022 0.016 4.0 2.8 3.2 4.7 4.7 Type Shielded Non-Shielded Shielded Non-Shielded Shielded Diodes Manufacturer Part Number VF Diodes Inc. ROHM Micro Semi B340LA RB050L-40 5820SM 0.45V @ 3A 0.45V @ 3A 0.46V @ 3A 1154.2006.09.1.6 15 AAT1154 1MHz 3A Step-Down DC/DC Converter Ordering Information Output Voltage Package Marking Part Number (Tape and Reel)1 1.0V (Adj. VOUT ≥ 1.0V) 1.8V 2.5V 3.3V SOP-8 SOP-8 SOP-8 SOP-8 115410 115418 115425 115433 AAT1154IAS-1.0-T1 AAT1154IAS-1.8-T1 AAT1154IAS-2.5-T1 AAT1154IAS-3.3-T1 All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree. Package Information 3.90 ± 0.10 6.00 ± 0.20 SOP-8 4.90 ± 0.10 1.27 BSC 45° 4° ± 4° 1.55 ± 0.20 0.42 ± 0.09 × 8 0.175 ± 0.075 0.375 ± 0.125 0.235 ± 0.045 0.825 ± 0.445 All dimensions in millimeters. 1. Sample stock is generally held on part numbers listed in BOLD. © Advanced Analogic Technologies, Inc. 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. Customers are advised 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. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 16 1154.2006.09.1.6