DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter General Description Features The AAT1155 is a step-down, SwitchReg™, switching converter ideal for applications where high efficiency, small size, and low ripple are critical. Able to deliver 2.5A with an internal power MOSFET, the current-mode controlled IC provides high efficiency. Fully internally compensated, the AAT1155 simplifies system design and lowers external parts count. • • • • • • • • • • • • • • The AAT1155 is available in a Pb-free, MSOP-8 package and is rated over the -40°C to +85°C temperature range. 5.5V Max Supply Input Adjustable VOUT: 1.0V to 4.2V 2.5A Output Current Up to 95% Efficiency Integrated Low On-Resistance Power Switches 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 MSOP-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 VOUT : 1.0V - 4.2V 100Ω VP AAT1155 FB VP LX VCC LX ENABLE 10μF GND 1.5μH 120μF 0.1μF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 1 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Pin Descriptions Pin # Symbol 1 FB 2 GND 3 EN 4 5, 8 6, 7 VCC VP LX Function Feedback input pin. This pin is connected to an external resistive divider for an adjustable output. Signal ground. Enable input pin. When connected high, the AAT1155 is in normal operation. When connected low, it is powered down. This pin should not be left floating. Small signal filtered bias supply. Input supply for converter power stage. Inductor connection pins. These pins should be connected to the output inductor. Pin Configuration MSOP-8 (Top View) VP 7 LX 3 6 LX 4 5 VP GND 2 EN VCC 2 1 1 2 8 FB Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Absolute Maximum Ratings1 Symbol VCC, VP VLX VFB VEN TJ TLEAD VESD Description VCC, VP to GND LX to GND FB to GND EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) 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 150 300 3 kV Value Units 150 833 °C/W mW V °C Thermal Characteristics3 Symbol JA PD Description Maximum Thermal Resistance Maximum Power Dissipation Recommended Operating Conditions Symbol T Description Ambient Temperature Range Rating Units -40 to +85 °C 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. 2. Human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin. 3. Mounted on a demo board (FR4, in still air). Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 3 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Electrical Characteristics VIN = VCC = VP = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol VIN VOUT VEN(L) VEN(H) VUVLO VUVLO(HYS) IQ ISHDN ILIM RDS(ON)H VOUT (VOUT*VIN) VOUT/VOUT fOSC TSD THYS 4 Description Input Voltage Range Output Voltage Tolerance Enable Low Voltage Enable High Voltage Under-Voltage Lockout Conditions Min VIN = VOUT + 0.2 to 5.5V, IOUT = 0.5A 2.7 -2.5 Typ Max Units 5.5 2.5 0.6 V % 1.4 VIN Rising VIN Falling 2.5 V 1.2 Under-Voltage Lockout Hysteresis Quiescent Supply Current Shutdown Current Current Limit High Side Switch On Resistance Efficiency No Load, VFB = 0V VEN = 0V, VIN = 5.5V TA = 25°C TA = 25°C IOUT = 1.0A 250 630 Load Regulation ILOAD = 0A to 2.5A 2.3 Line Regulation Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis VIN = 2.7V to 5.5V TA = 25°C 0.75 1 140 15 mV 1000 1.0 4.4 60 92 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 μA A m % %/V MHz °C DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Typical Characteristics Efficiency vs. Load Current Enable Threshold vs. Input Voltage (VIN = 5.0V; VOUT = 3.3V) 1.2 Enable Threshold (V) 100 Efficiency (%) 95 90 85 80 75 70 65 60 0.01 0.1 1 1.1 EN(H) 1 0.9 0.8 EN(L) 0.7 0.6 10 2.5 3 Output Current (A) 3.5 4 4.5 5 5.5 5 5.5 Input Voltage (V) RDS(ON) vs. Temperature RDS(ON) vs. Input Voltage (IDS = 1A) 80 90 3.6V RDS(ON) (mΩ) 80 4.2V 75 RDS(ON) (mΩ Ω) 2.7V 70 60 5.0V 5.5V 70 65 60 55 50 50 45 40 40 -20 0 20 40 60 80 100 2.5 120 3 3.5 4 4.5 Input Voltage (V) Temperature (°C) Oscillator Frequency Variation vs. Temperature Oscillator Frequency Variation vs. Input Voltage (VIN = 5V) (VOUT = 3.3V) 1 0 0.25 Variation (%) Variation (%) 0.5 0 -0.25 -1 -2 -3 -0.5 3.5 4 4.5 Input Voltage (V) 5 5.5 -4 -20 0 20 40 60 80 100 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 5 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Typical Characteristics Output Voltage Variation vs. Temperature Line Regulation (IOUT = 2A; VO = 3.3V) (VOUT = 3.3V) Output Voltage Error (%) 0.4 Variation (%) 0.2 0 -0.2 -0.4 -0.6 -0.8 -20 0 20 40 60 80 100 1 0 IO = 0.3A -1 -2 -3 -4 IO = 3.0A -5 3.4 3.7 4 0.0 3.4 -1.0 55°C Output Error (%) Output Current (A) (VOUT = 3.3V) 70°C 2.6 2.4 85°C 2.2 2 100°C 1.8 -2.0 -3.0 -4.0 -5.0 -6.0 -7.0 -8.0 3.75 4 4.25 4.5 4.75 5 5.25 -10.0 0.01 5.5 0.1 Input Voltage (V) (VOUT = 3.3V; VIN = 5.0V) 5 700 650 2.7V 3.6V Output Current (A) Operating Current (mA) 10 Over-Temperature Shutdown Current vs. Temperature (FB = 0V) 750 1 Load Current (A) Non-Switching Operating Current vs. Temperature 4.2V 600 550 500 5.0V 5.5V 60 80 4.5 4 3.5 3 2.5 2 450 -20 0 20 40 Temperature (°C) 6 5.5 -9.0 1.6 3.5 5.2 (VIN = 5.0V; VOUT = 3.3V) 3.6 2.8 4.9 Load Regulation AAT1155 Evaluation Board Over-Temperature Current vs. Input Voltage 3 4.6 Input Voltage (V) Temperature (°°C) 3.2 4.3 100 120 -20 -10 0 10 20 30 40 50 60 70 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 80 90 100 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Inrush and Output Overshoot Characteristics Tantalum Output Ripple 14 6 12 4 10 2 8 0 6 -2 4 -4 2 -6 0 -8 0.04 7 0.02 6 0.00 5 -0.02 4 -0.04 3 -0.06 2 -0.08 0.4 0.8 1.2 1.6 1 120μF 6.3V Tantalum Vishay P/N 594D127X96R3C2T -0.10 -2 0 2 0 -0.12 -1 0 Time (ms) Inductor Current (bottom) (A) 8 Output Ripple (top) (mV) (IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V) Inductor Current (A) (bottom trace) Enalbe and Output Voltage (V) (top trace) Typical Characteristics 1 2 3 4 5 Time (μ μs) Output Ripple Output Ripple (IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V) (IOUT = 3.0A; VOUT = 3.3V; VIN = 5.0V) 4 7 2 6 2 6 AC Output Ripple (top) (mV) 4 -4 3 -6 2 -8 1 200μF 6.3V Ceramic -10 TDK P/N C3325X5R0J107M Vishay GRM43SR60J107ME20L -12 0 1 2 3 4 0 5 -2 4 -4 3 -6 2 -8 0 -10 -1 -12 5 0 2 1 Time (μ μs) 12 -12 Gain (dB) 16 180 135 12 135 90 8 90 45 0 200μF gain 300μF gain 100μF 6.3 Ceramic TDK P/N C3225X5R0J107M Vishay GRM43SR60J107ME20L -16 10000 -45 -90 -135 -180 100000 Frequency (Hz) 5 4 45 Gain 0 0 -4 -45 -8 -90 -12 120μF 6.3V Tantalum Vishay P/N 594D127X96R3C2T -16 10000 100000 Phase (Degrees) Phase 0 -8 4 180 Phase (Degrees) 8 -4 -1 3 Loop Crossover Gain and Phase Gain (dB) L = 1.5μHy 4 0 Time (μ μs) Loop Crossover Gain and Phase 16 1 300μF 6.3VCeramic TDK P/N C3325X5R0J107M Vishay GRM43SR60J107ME20L Inductor Current (bottom) (A) 5 Inductor Current (bottom) (A) 0 -2 AC Output Ripple (top) (mV) 7 4 -135 -180 1000000 Frequency (Hz) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 7 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Tantalum Transient Response Transient Response (IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V) (IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V) 3.40 7 6 3.30 6 3.20 5 3.10 4 3.00 3 2.90 2 2.80 1 120μF 6.3V Tantalum Vishay P/N 594D127X96R3C2T 2.70 2.60 0 100 200 300 400 Output Voltage (top) (mV) 7 3.30 3.20 2x 100μF 6.3V Ceramic TDK P/N C3325X5R0J107M Vishay GRM43SR60J107ME20L 3.10 3 2.90 2 2.80 1 0 2.70 0 -1 2.60 500 -1 0 100 200 300 400 Time (μ μs) Transient Response 3.40 7 3.30 6 3.10 5 4 3.00 3 2.90 2 2.80 1 2.70 0 2.60 Inductor Current (bottom) (A) Output Voltage (top) (mV) (IOUT = 0 to 3.0A; VOUT = 3.3V; VIN = 5.0V) 3x 100μF 6.3V Ceramic TDK P/N C3325X5R0J107M Vishay GRM43SR60J107ME20L -1 0 100 200 300 400 500 Time (μ μs) 8 4 3.00 Time (μ μs) 3.20 5 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 500 Inductor Current (bottom) (A) 3.40 Inductor Current (bottom) (A) Output Voltage (top) (mV) Typical Characteristics DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Functional Block Diagram VCC VP = 2.5V to 5.5V REF FB OP. AMP CMP DH LOGIC OSC LX Temp. Sensing EN Applications Information Main Control Loop The AAT1155 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 external, 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. 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. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 9 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Power and Signal Source The corresponding inductor RMS current is: Current Limit and Over-Temperature Protection Over-temperature and current limit circuitry protects the AAT1155 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. 2 IRMS = ⎛⎝ IOUT2 + ∆I ≈ IOUT = 2.5A 12 ⎛ ⎝ 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. I is the peak-to-peak ripple current which is fixed by the inductor selection above. For a peak-to-peak current of 40% of the full load current, the peak current at full load will be 120% of the full load. The 1.5μH inductor selected from the Sumida CDRH6D38 series has a 11m DCR and a 4.0A DC current rating with a height of 4mm. At full load, the inductor DC loss is 70mW for a 0.84% loss in efficiency. Schottky Freewheeling Diode The Schottky average current is the load current multiplied by one minus the duty cycle. Inductor ⎛ ⎝ 3.3V · ⎛⎝1 - 3.3V 2.5A · 0.4 · 1MHz 5.25V ⎛ ⎝ = VOUT VOUT · ⎛1 IOUT ∙ k · fS ⎝ VIN(MAX) = 1.23μH The factor “k” is the fraction of the full load (40%) selected for the ripple current at the maximum input voltage. 10 VOUT 3.3V IAVG = IOUT ∙ ⎛1 = 2.5A ∙ ⎛1 ⎝ ⎝ VIN 5.0V ⎛ ⎝ L= For VIN at 5V and VOUT at 3.3V, the average diode current is: ⎛ ⎝ For a 2.5A load and the ripple current set to 40% at the maximum input voltage, the maximum peak-to-peak ripple current is 1A. Assuming a 5V ±5% input voltage and 40% ripple, the output inductance required is: VOUT ⎛ ⎝1 - VIN ⎛ ⎝ The output inductor is selected to limit the ripple current to 20% to 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 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 DCR. The losses associated with the DCR and its effect on the total converter efficiency must be considered. = 0.85A With a 125°C maximum junction temperature and a 120°C/W thermal resistance, the maximum average current is: IAVG = TJ(MAX) - TAMB θJA · VF = 125°C - 70°C = 1.14A 120°C / W ∙ 0.4V VF is the forward voltage drop of the Schottky diode. For overload, short-circuit, and excessive ambient temperature conditions, the AAT1155 enters over-temperature shutdown mode protecting the AAT1155 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-temperature characteristics graphs). The diode reverse voltage must be rated to withstand the input voltage. Input Capacitor Selection The primary function of the input capacitor is to provide a low impedance loop for the edges of pulsed current Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter VOUT VOUT ⎛ ∙ 1- V VIN ⎝ IN ⎛ ⎝ IRMS = IOUT ∙ 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. 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. Thermal Losses associated with the AAT1155 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) RDS(ON) losses 2 IRMS = ⎛⎝ IOUT2 + ∆I ∙ D 12 ⎛ ⎝ drawn by the AAT1155. 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 AAT1155. 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 10μF. 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. where, IRMS is internal switch RMS current. D is the duty cycle and VF is the forward voltage drop of the Schottky diode. D= 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: IRMS = (V - VF) · (VIN - VOUT) 1 · OUT 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 ≤ VOUT+ VF VIN + VF I is the peak-to-peak inductor ripple current. A simplified form of calculating the RDS(ON) and switching losses is given by: P= IOUT2 · RDS(ON) ∙ VOUT + (tSW · fS · IOUT + IQ) · VIN VIN where IQ is the AAT1155 quiescent current. Once the total losses have been determined, the junction temperature can be derived. The thermal resistance (JA) for the MSOP-8 package mounted on an FR4 printed circuit board in still air is 150°C/W. TJ = P · ΘJA + TAMB TAMB is the maximum ambient temperature and TJ is the resultant maximum junction temperature. VRIPPLE ΔI where I is the peak-to-peak inductor ripple current. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 11 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter 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 Capacitance (μF) Voltage (V) Temp Co. 100 Murata 47 10 120 100 Vishay X5R 6.3 Case 1812 1206 C 16 Table 1: AAT1155 Recommended Capacitors. Part Number Manufacturer CDRH6D38-4763-T055 N05D B1R5M NP06DB B1R5M LQH55DN1R5M03 LQH66SN1R5M03 Sumida Taiyo Yuden Inductance (μH) I (A) DCR (Ω) Height (mm) Type 0.014 0.025 1.5 4.0 3.2 3.0 3.7 3.8 4.0 2.8 3.2 Shielded Non-Shielded Shielded Non-Shielded Shielded Murata 0.022 0.016 4.7 Table 2: AAT1155 Recommended Inductors. Manufacturer Part Number VF Diodes Inc. ROHM Micro Semi B340LA RB050L-40 5820SM 0.45V @ 3A 0.45 @ 3A 0.46V @ 3A Table 3: AAT1155 Recommended Diodes. 12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Evaluation Board Description Layout The AAT1155 evaluation board demonstrates the performance, along with the suggested size and placement of external components for the AAT1155 integrated buck regulator. The external components are selected for minimum size and optimum operation up to 2.5A output current. Figure 1 shows the evaluation board schematic. Figures 2 and 3 display the suggested PCB layout for the AAT1155. The following guidelines should be used to help ensure a proper layout. Table 4 and 5 provide the AAT1155 evaluation board specifications and the component list respectively. 1. Components Summary Capacitor C4 is a high equivalent series resistance (ESR) tantalum capacitor for damping the high Q input network associated with the inductance of the leads feeding the input power to the evaluation board and the low ESR 10μF ceramic input capacitor (C1). R2 is a pull-up resistor to allow the enable pin to be used to enable and disable the IC by either shorting the enable pin to GND or leaving the pin open. Both R2 and C4 are for demonstration purposes only and are not necessary in the final solution. Resistors R3 and R4 are used with the 1V model to set the output voltage to any desired value from 1.0V to as high as 200mV below the minimum input voltage. They are not required for the fixed output voltage versions of the AAT1155. For fixed output voltage versions, R4 is omitted and R3 is replaced with a short. 2. 3. 4. 5. 6. The connection from the input capacitor to the Schottky anode should be as short as possible. The input capacitor should connect as closely as possible to VP (Pins 5 and 8) and GND (Pin 2). 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. 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. 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. R1 and C3 are required in order to provide a cleaner power source for the AAT1155 control circuitry. VIN+ VOUT+ R1 100 C4 100μF U1 AAT1155 R3 1 R2 100k Enable C1 10μF C3 0.1μF VP 8 2 GND LX 7 3 EN LX 6 4 VCC VP 5 FB R4 10.0k LX L1 1.5μH C2 CR1 B340LA 120μF GND Figure 1: AAT1155 Evaluation Board with Adjustable Output. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 13 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Specification Test Conditions Input Voltage Output Error Voltage Output Current Min Typ Max Units 2.7 3.6 ±3 5.5 V % A 0 2.5 Table 4: AAT1155 Evaluation Board Specifications. Figure 2: Evaluation Board Top Side. Component Part# U1 U1 U1 U1 CR1 C2 C4 C1 C3 R1 R2 L1 AAT1155IKS-1.0-T1 AAT1155IKS-1.8-T1 AAT1155IKS-2.5-T1 AAT1155IKS-3.3-T1 B340LA 594D127X96R6R3C2T 565D107X0016C GRM319R60J106KE01 GRM155R61A104KA01 Chip Resistor Chip Resistor CDRH6D28-1R5 R3 Chip Resistor R4 Chip Resistor Figure 3: Evaluation Board Bottom Side. Description 1.0V 850kHz 2.5A Buck Converter 1.8V 850kHz 2.5A Buck Converter 2.5V 850kHz 2.5A Buck Converter 3.3V 850kHz 2.5A Buck Converter Low VF 3A, 40V Schottky Diode 120μF, 6.3V, Tantalum 100μF, 16V, Tantalum 10μF, 6.3V, X5R, 10%, 1206 0.1μF, 25V, X5R, 10%, 0402 100kΩ, 5%, 1/16W, 0402 100kΩ, 5%, 1/16W, 0402 1.5μH Shielded AAT1155IKS-1.0-T1 see Table 6, 1%, 1/16W, 0402 AAT1155IKS-1.1-T1 thru 0Ω, 0402 AAT1155IKS-3.3 -T1 AAT1155IKS-1.0-T1 (when output is > 1.0V only, 10kΩ, 1%, 1/16W; 0402 otherwise not needed) AAT1155IKS-1.1-T1 thru AAT1155IKS-3.3 -T1 Manufacturer Skyworks Skyworks Skyworks Skyworks Diodes Inc. Vishay Vishay MuRata MuRata Vishay Vishay Sumida Vishay Vishay Vishay N/A Table 5: AAT1155 Evaluation Board Component Listing. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter For an adjustable output, set R4 to 10kΩ and select R3 according to table 6. Vo (V) R3 (kΩ) 1.0 1.1 1.2 1.25 1.3 1.4 1.5 1.6 1.7 1.8 1.85 1.9 2.0 2.1 2.2 2.3 2.4 2.5 3.3 0.00 (short) 1.00 2.00 2.55 3.01 4.02 4.99 6.04 6.98 8.06 8.45 9.09 10.0 11.0 12.1 13.0 14.0 15.0 23.2 Table 6. Resistor selection for adjustable output voltage (R4=10.0kΩ) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 15 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Design Example Efficiency vs. Load Current IOUT 2.5A IRIPPLE 40% of Full Load at Max VIN VOUT 2.5V VIN 5V 5% fS 1MHz TMAX 70°C (VIN = 5.0V; VOUT = 3.3V) 100 Efficiency (%) 95 Inductor Selection V VOUT · ⎛1 - OUT IOUT ∙ k · fS ⎝ VIN ⎛ ⎝ TJ(MAX) = TAMB + ΘJA · PON = 70°C + 150°C/W · 0.42W = 133°C Diode V IDIODE = IOUT ∙ ⎛⎝1 - OUT VIN V = 2.5A ∙ ⎛1 - OUT = 0.93A ⎝ VIN ⎛ ⎝ IPK is the peak current. (2.5A)2 · 70mΩ · 3.3V ⎛20ns · 1MHz · 2.5A + 690μA⎞ + · 5V ⎝ ⎠ 5V 2 ⎛ ⎝ = 2.91A IOUT2 · RDS(ON) · VOUT ⎛tSW · FS · IOUT + IQ⎞ · VIN + 2 ⎝ VIN ⎠ = 0.42 W ⎛ ⎝ = 2.5A +0.41A 10 Output Current (A) = ⎛ ⎝ 3.3V · ⎛1 - 3.3V 1.5μH · 1MHz ⎝ 5.25V ∆I IPK = IOUT + 12 1 Figure 4: 5V Input, 3.3V Output. PON = Sumida inductor Series CDRH6D38. = 0.82A 0.1 AAT1155 Junction Temperature Use standard value of 1.5μH = 70 65 = 1.23μH V VOUT ⎛ · 1 - OUT ⎝ L · fS VIN 75 60 0.01 3.3V = · ⎛⎝1 - 3.3V 2.5A · 0.4 · 1MHz 5.25V ∆I = 85 80 ⎛ ⎝ L= 90 PDIODE = VF · IDIODE = 0.35V · 0.93A = 0.33W Given an ambient thermal resistance of 120°C/W from the manufacturer’s datasheet, TJ(MAX) of the diode is: TJ(MAX) = TAMB + ΘJA · P = 70°C + 120°C / W · 0.33W = 109°C 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Input 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 dampened transient response, the output voltage ripple will be higher. The input capacitor ripple is: The 120μF Vishay 594D tantalum capacitor has an ESR of 85m 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. The ESR requirement for a tantalum capacitor can be estimated by : ESR ≤ IRMS = = VRIPPLE ∆I = 100 mV = 111mΩ 0.9A (VOUT + VF) · (VIN + VOUT) L · fS · VIN 2· 3 1 1 2 ∙ 3.65V ∙1.7 V = 240mArms 3 1.5μH· 1MHz ∙ 5V · Two or three 1812 X5R 100μF 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. IRMS = IOUT ∙ VOUT VOUT ⎛ ∙ 1- V VIN ⎝ IN ⎛ ⎝ Output Capacitor = 1.82Arms 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 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 AAT1155 through large PCB traces or planes, it is not required. When operating the AAT1155 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. Adjustable Output For applications requiring an output other than 1V, the AAT1155 can be externally programmed. Resistors R3 and R4 of Figure 1 force the output to regulate higher than 1V. For accurate results (less than 1% error for all outputs), select R4 to be 10k. Once R4 has been selected, R3 can be calculated. For a 1.25V output with R4 set to 10k, R3 is 2.5k. R3 = (VOUT - 1) · R4 = 0.25 · 10kΩ = 2.5kΩ Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013 17 DATA SHEET AAT1155 1MHz 2.5A Step-Down DC/DC Converter Ordering Information Output Voltage Package Marking1 Part Number (Tape & Reel)2 1.0V (Adj. VOUT ≥ 1.0V) MSOP-8 KXXYY AAT1155IKS-1.0-T1 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Package Information MSOP-8 4° ± 4° 4.90 ± 0.10 3.00 ± 0.10 1.95 BSC 0.95 REF 0.60 ± 0.20 PIN 1 3.00 ± 0.10 0.85 ± 0.10 0.95 ± 0.15 10° ± 5° GAUGE PLANE 0.254 BSC 0.155 ± 0.075 0.075 ± 0.075 0.65 BSC 0.30 ± 0.08 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. 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Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201994B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • February 7, 2013