DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter General Description Features The AAT2148 SwitchReg is a 2MHz step-down converter with an input voltage range of 2.7V to 5.5V and output voltage as low as 0.6V. It is optimized to react quickly to a load variation. The AAT2148 incorporates a unique low noise architecture which reduces ripple and spectral noise. • • • • • • • • • • • • • • • • The AAT2148 is available in fixed voltage versions with internal feedback and a programmable version with external feedback resistors. It can deliver 1A of load current while maintaining a low 37μA no load quiescent current. The 2MHz switching frequency minimizes the size of external components while keeping switching losses low. The AAT2148 is designed to maintain high efficiency throughout the operating range, which is critical for portable applications. The AAT2148 is available in the Pb-free, thermally enhanced 3x3mm QFN-16 package and is rated over the -40°C to +85°C temperature range. VIN Range: 2.7V to 5.5V Low Noise Light Load Mode Low Ripple PWM Mode VOUT Fixed or Adjustable from 0.6V to VIN 37μA No Load Quiescent Current Up to 98% Efficiency 1A Max Output Current 2MHz Switching Frequency 150μs Soft Start Fast Load Transient Over-Temperature Protection Current Limit Protection 100% Duty Cycle Low-Dropout Operation <1μA Shutdown Current QFN33-16 Package Temperature Range: -40°C to +85°C Applications • • • • • • Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core / IO Power PDAs and Handheld Computers USB Devices Typical Application (Adjustable Output Voltage) VIN 2.7V - 5.5V U1 AAT2148 C1 4.7μF L1 4.7μH 12 VP LX 13 11 VP LX 14 10 VP LX 15 9 VCC FB 4 7 EN PGND 2 3 PGND PGND 1 R1 118k VO 1.8V, 1A C2 4.7μF R2 59k Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 1 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Pin Descriptions Pin # Symbol 1, 2, 3 PGND 4 FB 5, 6, 8, 16 9 10, 11, 12 N/C VCC VP 13, 14, 15 LX EP Function Power ground pin Feedback input. This pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. Not internally connected. Bias supply. Supplies power for the internal circuitry. Connect to input power. Input supply voltage for the converter power stage. Must be closely decoupled to GND. Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high- and low-side MOSFETs. Exposed paddle (bottom); connect to PGND directly beneath package. Pin Configuration QFN33-16 (Top View) LX LX LX N/C 13 14 15 16 PGND PGND PGND FB 1 12 2 11 3 10 4 9 VP VP VP VCC 8 7 6 5 N/C EN N/C N/C 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VOUT VEN TJ TLEAD Description Input Voltage GND LX to GND OUT to GND EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -40 to 150 300 V V V V °C °C Value Units 2 50 W °C/W Thermal Information Symbol PD JA Description Maximum Power Dissipation Thermal Resistance2 2, 3 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. Mounted on an FR4 board. 3. Derate 6.25mW/°C above 25°C. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 3 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Electrical Characteristics1 TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V. Symbol Description Conditions Step-Down Converter VIN Input Voltage VUVLO VOUT VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L VLinereg VFB IFB TS FOSC TSD THYS EN VEN(L) VEN(H) IEN UVLO Threshold Output Voltage Tolerance Output Voltage Range Quiescent Current Shutdown Current P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance Line Regulation Feedback Threshold Voltage Accuracy Feedback Leakage Current Start-Up Time Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current Min Typ 2.7 VIN Rising Hysteresis IOUT = 0mA to 1A, VIN = 2.7V to 5.5V 1.8 100 -3.0 0.6 No Load, 0.6V Adjustable Version EN = AGND = PGND 37 1300 VIN = 2.7V to 5.5V; IOUT = 1A 0.6V Output, No Load; TA = 25°C 0.6V Output From Enable to Output Regulation TA = 25°C 591 0.9 1700 0.35 0.30 0.1 600 150 2.0 140 15 Max Units 5.5 2.7 V V mV % V μA μA mA %/V mV μA μs MHz °C °C +3.0 VIN 70 1.0 609 1 2.6 0.6 VIN = VOUT = 5.5V 1.4 -1.0 1.0 V V μA 1. The AAT2148 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Efficiency vs. Output Current Load Regulation (VOUT = 1.2V; L = 2.2μH; COUT = 10μF) (VOUT = 1.2V; L = 2.2μH; COUT = 10μF) 100 1 90 0.8 80 0.6 70 60 50 40 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.0V 30 20 10 0 0.1 1 10 100 Output Error (%) Efficiency (%) Typical Characteristics VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.0V 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 1000 0.1 1 Load Regulation (VOUT = 1.8V; L = 4.7μH; COUT = 4.7μF) 1 0.8 80 0.6 70 60 50 40 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.0V 30 20 10 0 1 10 100 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.0V 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 1000 0.1 1 Output Current (mA) 10 100 1000 Output Current (mA) Efficiency vs. Output Current Load Regulation (VOUT = 3.3V; L = 6.8μH; COUT = 4.7μF) (VOUT = 3.3V; L = 6.8μH; COUT = 4.7μF) 100 1 90 0.8 80 0.6 70 60 50 40 30 VIN = 3.6V VIN = 4.2V VIN = 5.0V 20 10 0 1 10 Output Current (mA) 100 1000 Output Error (%) Efficiency (%) 1000 Efficiency vs. Output Current 90 0.1 100 (VOUT = 1.8V; L = 4.7μH; COUT = 4.7μF) 100 0.1 10 Output Current (mA) Output Error (%) Efficiency (%) Output Current (mA) VIN = 3.6V VIN = 4.2V VIN = 5.0V 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0.1 1 10 100 1000 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 5 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Typical Characteristics Line Regulation Switching Frequency vs. Temperature 1.00 IOUT = 1A IOUT = 500mA IOUT = 1mA Output Error (%) 0.75 0.50 0.25 0.00 -0.25 -0.50 -0.75 -1.00 2.7 3.1 3.5 3.9 4.3 4.7 5.1 Switching Frequency (MHz) (VOUT = 1.8V; COUT = 10μF; CFF = 100pF) 2.2 2.15 2.1 2.05 2 1.95 1.9 1.85 1.8 5.5 -40 -20 0 Input Voltage (V) 20 40 60 80 100 Temperature (°C) Output Error vs. Temperature Quiescent Current vs. Input Voltage (IOUT = 500mA) 60 Quiescent Current (μA) Output Error (%) 0.005 0.000 -0.005 -0.010 -0.015 -40 -20 0 20 40 60 80 55 50 45 40 30 2.7 100 VOUT = 3.3V VOUT = 1.8V VOUT = 1.2V 35 3.1 3.5 Temperature (°C) 3.9 4.3 4.7 5.1 Input Voltage (V) P-Channel RDS(ON) vs. Input Voltage Quiescent Current vs. Temperature (VIN = 3.6V) 500 50 40 30 20 -40 VOUT = 3.3V VOUT = 1.8V VOUT = 1.2V -20 0 20 40 Temperature (°C) 6 85°C 25°C -40°C 450 60 80 100 RDS(ON)_P (mΩ) Quiescent Current (μA) 60 400 350 300 250 200 2.7 3.3 3.9 4.5 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 5.1 5.5 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Typical Characteristics N-Channel RDS(ON) vs. Input Voltage Load Transient (VIN = 3.6V; VOUT = 1.8V; COUT = 10μF; CFF = 100pF) 450 85°C 25°C -40°C RDS(ON)_N (mΩ) 390 VOUT (100mV/div) 330 1.8 270 500mA IOUT (0.25A/div) 210 0A 150 2.7 3.3 3.9 4.5 5.1 Input Voltage (V) Time (40μs/div) Load Transient Load Transient (VIN = 3.6V; VOUT = 1.8V; COUT = 10μF; CFF = 100pF) (VIN = 3.6V; VOUT = 1.8V; COUT = 4.7μF; CFF = 0pF) VOUT (100mV/div) VOUT (200mV/div) 1.8 1.8 1A IOUT (0.5A/div) 300mA 500mA IOUT (0.25A/div) 0A 0A Time (16μs/div) VOUT (200mV/div) Time (40μs/div) Load Transient Line Transient (VIN = 3.6V; VOUT = 1.8V; COUT = 4.7μF; CFF = 0pF) (VOUT = 1.8V; VIN = 3.6V to 4.2V; IOUT = 500mA; CFF = 100pF) VIN (0.5V/div) 1.8 3.6 1A IOUT (0.5A/div) VOUT (20mV/div) 300mA 0A Time (16μs/div) 1.8 Time (200μs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 7 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Typical Characteristics LX (2V/div) Output Ripple Output Ripple (VIN = 3.6V; VOUT = 1.2V; IOUT = 10mA; L = 2.2μH; COUT = 10μF; CFF = 100pF) (VIN = 3.6V; VOUT = 1.2V; IOUT = 1A; L = 2.2μH; COUT = 10μF; CFF = 100pF) LX (2V/div) 0 0 ILX (0.1A/div) 0A ILX (0.2A/div) 1A VOUT (20mV/div) 1.2 VOUT (10mV/div) 1.2 Time (1μs/div) LX (2V/div) ILX (0.1A/div) VOUT (10mV/div) Output Ripple Soft Startup (VIN = 3.6V; VOUT = 1.8V; IOUT = 1A; L = 4.7μH; COUT = 10μF; CFF = 100pF) (VIN = 3.6V; VOUT = 1.8V; IOUT = 1A) VEN (2V/div) 0 1A 1.8 Time (0.2μs/div) 8 Time (0.2μs/div) 0 IIN (0.5A/div) 0 VOUT (1V/div) 0 Time (100μs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Functional Block Diagram VCC VP 0.6V REF FB OP. AMP CMP DH LOGIC 1MΩ LX DL Temp. Sensing OSC PGND EN Functional Description The AAT2148 is a high performance 1A 2MHz monolithic step-down converter. It has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range, and produces reduced ripple and spectral noise. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 4.7μH inductor and a 4.7μF ceramic capacitor are recommended (see table of values). The fixed output version requires only three external power components (CIN, COUT, and L). The adjustable version can be programmed with external feedback to any voltage, ranging from 0.6V to the input voltage. An additional feed-forward capacitor can also be added to the external feedback to provide improved transient response (see Figure 1). At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the RDSON drop of the P-channel high-side MOSFET. PGND The input voltage range is 2.7V to 5.5V. The converter efficiency has been optimized for all load conditions, ranging from no load to 1A. The internal error amplifier and compensation provides excellent transient response, load, and line regulation. Soft start eliminates any output voltage overshoot and input inrush current when the enable or the input voltage is applied. Control Loop The AAT2148 is a peak current mode step-down converter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as short circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 9 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter VIN U1 AAT2148 VIN 12 VP LX 13 C1 4.7μF 11 VP LX 14 LX 15 FB N/C N/C 4 VIN 10 EN 9 VCC 7 EN N/C N/C EP PGND 5 JP1 6 0 3 1 2 3 VP 8 16 PGND 2 PGND 1 L1 4.7μH R1 118k VOUT 1.8V C3 100pF C2 10μF R2 59k Figure 1: Enhanced Transient Response Schematic. The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. For fixed voltage versions, the error amplifier reference voltage is internally set to program the converter output voltage. For the adjustable output, the error amplifier reference is fixed at 0.6V. Current Limit and Over-Temperature Protection Soft Start / Enable Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT2148 into a low-power, non-switching state. The total input current during shutdown is less than 1μA. For overload conditions, the peak input current is limited. To minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. Switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Applications Information Inductor Selection The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the adjustable and low-voltage fixed versions of the AAT2148 is 0.24A/μs. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7μH inductor. m= 0.75 ⋅ VO 0.75 ⋅ 1.5V A = = 0.24 L 4.7µH µs This is the internal slope compensation for the adjustable (0.6V) version or low-voltage fixed versions. When externally programming the 0.6V version to 2.5V, the calculated inductance is 7.5μH. L= 0.75 ⋅ VO µs 0.75 ⋅ VO ≈ 3 A ⋅ VO = m A 0.24A µs µs = 3 ⋅ 2.5V = 7.5µH A In this case, a standard 6.8μH value is selected. For high-voltage fixed versions (2.5V), m = 0.48A/μs. Table 1 displays inductor values for the AAT2148 fixed and adjustable options. 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 saturation characteristics. The inductor should not show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. The 4.7μH SD3118 series inductor selected from Coilcraft has a 162m typical DCR and a 1.31A saturation current. At full load, the inductor DC loss is 162mW which gives a 9% loss in efficiency for a 1A, 1.8V output. Input Capacitor Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = V ⎞ VO ⎛ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6μF. Output Voltage (V) Inductor (μH) Output Capacitor (μF) 1, 1.2 1.5, 1.8 2.5, 3.3 2.2 4.7 6.8 10 4.7 4.7 Table 1: Inductor and Output Capacitor Values. The maximum input capacitor RMS current is: IRMS = IO · VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current. VO ⎛ V ⎞ · 1- O = VIN ⎝ VIN ⎠ D · (1 - D) = 0.52 = Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 1 2 11 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Output Capacitor for VIN = 2 · VO I IRMS(MAX) = O 2 VO ⎛ V ⎞ · 1- O The term V ⎝ V ⎠ appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. IN IN The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2148. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7μF to 10μF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output voltage droop during the three switching cycles to the output capacitance can be estimated by: The proper placement of the input capacitor (C1) can be seen in the evaluation board layout in Figure 2. A laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. 12 COUT = 3 · ΔILOAD VDROOP · FS Once the average inductor current increases to the DC load level, the output voltage recovers. The above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation also limits the minimum output capacitor value to 4.7μF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater phase margin. The maximum output capacitor RMS ripple current is given by: IRMS(MAX) = 1 VOUT · (VIN(MAX) - VOUT) L · F · VIN(MAX) 2· 3 · Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Figure 2: AAT2148 Evaluation Board Top Layer. 12 C1 4.7µF 11 10 VIN JP1 1 2 3 U1 AAT2148 VIN VIN Figure 3: AAT2148 Evaluation Board Bottom Layer. EN LX 13 VP LX 14 VP LX 15 FB N/C N/C 4 VP 9 VCC 7 EN N/C N/C EP PGND 5 6 0 3 8 16 PGND 2 PGND 1 L1 4.7µH R1 267k VOUT C3 100pF C2 10µF R2 59k Figure 4: AAT2148 Evaluation Board Schematic. Adjustable Output Resistor Selection For applications requiring an adjustable output voltage, the 0.6V version can be externally programmed. Resistors R1 and R2 of Figure 4 program the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R2 is 59k. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 2 summarizes the resistor values for various output volt- ages with R2 set to either 59k for good noise immunity or 221k for reduced no load input current. 1.5V VOUT R3 = V -1 · R4 = 0.6V - 1 · 59kΩ = 88.5kΩ REF The adjustable version of the AAT2148, combined with an external feedforward capacitor (C3 in Figure 1), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor C2 for stability. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 13 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter R2 = 59k R2 = 221k VOUT (V) R1 (k) R1 () 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75K 113K 150K 187K 221K 261K 301K 332K 442K 464K 523K 715K 1.00M Table 2: Adjustable Resistor Values For Use With 0.6V Step-Down Converter. Thermal Calculations There are three types of losses associated with the AAT2148 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the losses is given by: PTOTAL = PTOTAL = IO2 · RDSON(HS) + IQ · VIN Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. Given the total losses, the maximum junction temperature can be derived from the JA for the QFN33-16 package which is 50°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB Layout The suggested PCB layout for the AAT2148 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 1. 2. 3. IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO]) VIN + (tsw · F · IO + IQ) · VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. 14 For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: 4. The input capacitor (C1) should connect as closely as possible to VIN (Pins 9-12) and PGND (Pins 1-3). C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. The feedback trace or FB pin (Pin 4) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a highcurrent load trace will degrade DC load regulation. The external feedback resistors should be placed as closely as possible to the FB pin (Pin 4) to minimize the length of the high impedance feedback trace. The resistance of the trace from the load return to PGND (Pins 1-3) 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 signal ground and the power ground. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 1A (adjustable using 0.6V version), Pulsed Load ILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 2MHz TAMB = 85°C 1.8V Output Inductor L1 = 3 µs µs · VO1 = 3 · 1.8V = 5.4µH (use 4.7μH; see Table 1) A A For Coilcraft inductor SD3118, 4.7μH, DCR = 162m. ΔIL1 = VO V 1.8V 1.8V · 1- O = · 1L1 · FS VIN 4.7µH · 2.0MHz 4.2V IPKL1 = IO + = 109mA ΔIL1 = 1A + 0.055A = 1.055A 2 PL1 = IO2 · DCR = 1A2 · 162mΩ = 162mW 1.8V Output Capacitor VDROOP = 0.1V COUT = 3 · ΔILOAD 3 · 0.3A = = 4.5µF; use 4.7µF VDROOP · FS 0.1V · 2.0MHz IRMS = (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 32mArms = 4.7µH · 2.0MHz · 4.2V L1 · F · V 2· 3 2· 3 IN(MAX) 1 · Pesr = esr · IRMS2 = 5mΩ · (32mA)2 = 6µW Input Capacitor Input Ripple VPP = 30mV CIN = IRMS = 1 = VPP - ESR · 4 · FS IO 1 = 5μF; use 4.7μF 30mV - 5mW · 4 · 2.0MHz 1A IO = 0.5Arms 2 P = ESR · IRMS2 = 5mΩ · (0.5A)2 = 1.25mW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 15 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter AAT2148 Losses PTOTAL = IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO]) VIN + (tsw · F · IO + IQ) · VIN = 12 · (0.35Ω · 1.8V + 0.3Ω · [4.2V - 1.8V]) 4.2V + (5ns · 2.0MHz · 1A + 70μA) · 4.2V = 363mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 363mW = 103.2°C 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Adjustable Version (0.6V device) VOUT (V) R2 = 59k R1 (k) R2 = 221k1 R1 (k) L1 (μH) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75.0 113 150 187 221 261 301 332 442 464 523 715 1000 2.2 2.2 2.2 2.2 2.2 2.2 4.7 4.7 4.7 4.7 6.8 6.8 6.8 Fixed Version VOUT (V) R2, R4 Not Used R1 (k) L1 (μH) 0.6-3.3V 0 4.7 Table 3: Evaluation Board Component Values. Manufacturer Sumida Murata Coilcraft Part Number Inductance (μH) Saturation Current (A) DCR () Size (mm) LxWxH Type CDRH3D16/HP-2R2 CDRH5D16-4R7 CDRH5D16-6R8 LQH3NPN2R2NG0 LQH32PN2R2NN0 LQH32PN4R7NN0 SD3118-2R2-R SD3118-4R7-R SD3118-6R8-R 2.2 4.7 6.8 2.2 2.2 4.7 2.2 4.7 6.8 1.75 2.15 1.8 1.25 1.55 1.0 2.0 1.31 1.12 47 51.3 64.7 73 76 180 74 162 232 4.0x4.0x1.8 5.8x5.8x1.8 5.8x5.8x1.8 3.0x3.0x1.4 3.2x2.7x1.55 3.2x2.7x1.55 3.1x3.1x1.8 3.1x3.1x1.8 3.1x3.1x1.8 Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Table 4: Typical Surface Mount Inductors. Manufacturer Part Number Value Voltage Temp. Co. Case Murata GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39 4.7μF 10μF 22μF 10V 6.3V 6.3V X5R X5R X5R 0805 0805 0805 Table 5: Surface Mount Capacitors. 1. For reduced quiescent current, R2 and R4 = 221k. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 17 DATA SHEET AAT2148 Low-Noise, Fast Transient 1A Step-Down Converter Ordering Information Output Voltage1 Package Marking2 Part Number (Tape and Reel)3 Adj 0.6 QFN33-16 6VXYY AAT2148IVN-0.6-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 QFN33-16 Pin 1 Dot By Marking 0.230 ± 0.050 Pin 1 Identification 0.500 ± 0.050 1.250 ± 0.050 5 C0.3 13 9 1.250 ± 0.050 Top View 0.025 ± 0.025 Bottom View 0.214 ± 0.036 0.900 ± 0.100 3.000 ± 0.050 0.400 ± 0.100 3.000 ± 0.050 1 Side View All dimensions in millimeters. 1. Contact Sales for other voltage options. 2. XYY = assembly and date code. 3. 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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 202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012