DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter General Description Features The AAT1147 SwitchReg is a member of Skyworks' Total Power Management IC™ (TPMIC™) product family. It is a fixed frequency 1.4MHz step-down converter with an input voltage range of 2.7V to 5.5V and output voltage as low as 0.6V. • • • • • • • • • • • • The AAT1147 is optimized for low noise portable applications, reacts quickly to load variations, and reaches peak efficiency at heavy load. The AAT1147 output voltage is programmable with external feedback resistors. It can deliver 400mA of load current while maintaining high power efficiency. The 1.4MHz switching frequency minimizes the size of external components while keeping switching losses low. The AAT1147 is available in a Pb-free, space-saving 2.0x2.1mm SC70JW-8 package and is rated over the -40°C to +85°C temperature range. VIN Range: 2.7V to 5.5V VOUT Adjustable from 0.6V to VIN 400mA Output Current Up to 98% Efficiency Low Noise, 1.4MHz Fixed Frequency PWM Operation Fast Load Transient 150μs Soft Start Over-Temperature and Current Limit Protection 100% Duty Cycle Low Dropout Operation <1μA Shutdown Current 8-Pin SC70JW 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 VIN 3 1 C2 4.7µF VO = 1.8V U1 AAT1147 5 8 VIN LX EN OUT AGND PGND PGND PGND 4 2 L1 4.7µH 118k 7 6 R1 R2 59k C1 4.7µF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 1 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Pin Descriptions Pin # Symbol 1 2 3 EN OUT VIN 4 LX 5 6, 7, 8 AGND PGND Function Enable pin. Feedback input pin. This pin is connected to an external resistive divider for an adjustable output. Input supply voltage for the converter. Switching node. Connect the inductor to this pin. It is connected internally to the drain of both highand low-side MOSFETs. Non-power signal ground pin. Main power ground return pins. Connect to the output and input capacitor return. Pin Configuration SC70JW-8 (Top View) EN OUT VIN LX 2 1 8 2 7 3 6 4 5 PGND PGND PGND AGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VOUT VEN TJ TLEAD Description Input Voltage to 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 6.0 -40 to 150 300 V V V V °C °C Value Units 0.625 160 W °C/W Thermal Information2 Symbol PD JA Description Maximum Power Dissipation3 Thermal Resistance 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 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 3 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA 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 ILXLEAK VLINEREG VOUT IOUT 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 LX Leakage Current Line Regulation Out Threshold Voltage Accuracy Out 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 VIN Falling IOUT = 0 to 400mA, VIN = 2.7V to 5.5V Max Units 5.5 2.7 V V mV V % V μA μA mA μA %/V mV μA μs MHz °C °C 100 1.8 -3.0 0.6 No Load EN = AGND = PGND 160 3.0 VIN 300 1.0 600 0.45 0.40 VIN = 5.5V, VLX = 0 to VIN, EN = GND VIN = 2.7V to 5.5V 0.6V Output, No Load, TA = 25°C 0.6V Output From Enable to Output Regulation 1 591 1.0 0.1 600 150 1.4 140 15 609 0.2 2.0 0.6 VIN = VOUT = 5.5V 1.4 -1.0 1.0 V V μA 1. The AAT1147 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 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Typical Characteristics Efficiency vs. Load DC Regulation (VOUT = 3.3V; L = 6.8µH) (VOUT = 3.3V) 100 2.0 VIN = 3.6V 1.5 Output Error (%) Efficiency (%) 80 60 VIN = 4.2V 40 VIN = 5.0V 20 1.0 VIN = 4.2V 0.5 0.0 -0.5 VIN = 3.6V -1.0 VIN = 5.0V -1.5 -2.0 0 1 10 100 1000 0.1 1 Output Current (mA) 100 1000 Output Current (mA) Efficiency vs. Load DC Regulation (VOUT = 2.5V; L = 6.8µH) (VOUT = 2.5V) 100 2.0 1.5 Output Error (%) VIN = 3.6V 80 Efficiency (%) 10 60 VIN = 4.2V 40 VIN = 5.0V 20 1.0 VIN = 4.2V 0.5 0.0 -0.5 VIN = 5.0V -1.0 VIN = 3.6V -1.5 0 1 10 100 -2.0 0.1 1000 1 Output Current (mA) 100 1000 Output Current (mA) Efficiency vs. Load DC Regulation (VOUT = 1.8V; L = 4.7µH) (VOUT = 1.8V) 100 2.0 1.5 Output Error (%) VIN = 3.0V 80 Efficiency (%) 10 60 VIN = 3.6V 40 VIN = 4.2V 20 1.0 VIN = 4.2V 0.5 0.0 VIN = 3.6V -0.5 -1.0 VIN = 3.0V -1.5 0 1 10 100 Output Current (mA) 1000 -2.0 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 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 5 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Typical Characteristics Line Regulation Line Regulation (VOUT = 3.3V) 0.5 0.4 0.4 0.3 0.3 IOUT = 10mA IOUT = 1mA 0.2 Accuracy (%) Accuracy (%) (VOUT = 2.5V) 0.5 0.1 0 -0.1 -0.2 IOUT = 400mA -0.3 IOUT = 10mA IOUT = 1mA 0.2 0.1 0.0 -0.1 -0.2 IOUT = 400mA -0.3 -0.4 -0.4 -0.5 -0.5 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 3.0 3.2 3.4 3.6 Input Voltage (V) 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Input Voltage (V) Line Regulation Frequency vs. Input Voltage (VOUT = 1.8V) 0.5 Frequency Variation (%) 2.0 0.4 Accuracy (%) 0.3 0.2 0.1 IOUT = 10mA 0.0 IOUT = 1mA -0.1 -0.2 -0.3 IOUT = 400mA -0.4 -0.5 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 1.0 VOUT = 1.8V 0.0 -1.0 -2.0 VOUT = 2.5V -3.0 -4.0 2.5 5.0 2.9 3.3 4.5 4.9 Output Voltage Error vs. Temperature Switching Frequency vs. Temperature (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) (VIN = 3.6V; VOUT = 1.8V) 2.0 15 1.5 12 0.5 0.0 -0.5 -1.0 -2.0 -40 5.3 9 1.0 6 3 0 -3 -6 -9 -1.5 -12 -15 -25 -10 5 20 35 50 Temperature (°°C) 6 4.1 Input Voltage (V) Variation (%) Output Error (%) Input Voltage (V) 3.7 VOUT = 3.3V 65 80 95 -40 -25 -10 5 20 35 50 65 Temperature (°°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 80 95 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Typical Characteristics No-Load Quiescent Current vs. Input Voltage Line Transient Response (40mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7µF; CFF = 100pF) 220 190 85°C 180 25°C Output Voltage (top) (V) Supply Current (µA) 200 170 160 -40°C 150 140 130 120 2.0 1.4 1.9 1.2 1.8 1.0 1.7 0.8 1.6 0.6 1.5 0.4 1.4 0.2 400 mA 1.3 1.2 40 mA 1.1 2.5 3.0 3.5 4.0 4.5 5.0 1.0 5.5 1.4 1.9 1.2 1.8 1.0 1.7 0.8 1.6 0.6 1.5 0.4 1.4 0.2 0.0 400mA 40mA 1.0 -0.2 -0.4 -0.6 5.6 3.6 4.8 3.2 4.0 2.8 3.2 2.4 2.4 2.0 1.6 1.6 0.8 1.2 0.0 0.8 -0.8 0.4 -1.6 0.0 -2.4 -0.4 Time (25µs/div) Output Ripple (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) 5.2 1.85 5.0 1.80 4.8 1.75 4.6 1.70 4.4 1.65 4.2 1.60 4.0 1.55 3.8 1.50 3.6 1.45 3.4 1.40 3.2 Time (25µs/div) 40 0.9 20 0.8 0 0.7 -20 0.6 -40 0.5 -60 0.4 -80 0.3 -100 0.2 -120 0.1 Inductor Current (bottom) (A) 1.90 Output Voltage (AC Coupled) (top) (mV) Line Response (VOUT = 1.8V @ 400mA) Input Voltage (bottom) (V) Output Voltage (top) (V) Time (25µs/div) Inductor Current (bottom) (A) 2.0 Enable and Output Voltage (top) (V) (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) Load and Inductor Current (bottom) (200mA/div) Output Voltage (top) (V) Soft Start (40mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7µF) 1.1 -0.4 -0.6 Line Transient Response 1.2 -0.2 Time (25µs/div) Input Voltage (V) 1.3 0.0 Load and Inductor Current (bottom) (200mA/div) 210 Time (500ns/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 7 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Functional Block Diagram VIN OUT Err Amp . DH Voltage Reference EN INPUT LX Logic DL PGND AGND Functional Description The AAT1147 is a high performance 400mA 1.4MHz monolithic step-down converter. It has been designed with the goal of minimizing external component size and optimizing efficiency at heavy load. 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). Only three external power components (CIN, COUT, and L) are required. Output voltage is programmed with external resistors and ranges from 0.6V to the input voltage. An additional feed-forward capacitor can also be added 8 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 RDS(ON) drop of the P-channel high-side MOSFET. The input voltage range is 2.7V to 5.5V. The converter efficiency has been optimized for heavy load conditions up to 400mA. The internal error amplifier and compensation provide excellent transient response, load, and line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter 1 2 3 Enable VIN C4 100pF U1 AAT1147 1 VOUT =1.8V R1 2 L1 118k 4.7μH 3 4 C1 10μF C3 n/a R2 59k EN PGND OUT PGND VIN PGND LX AGND 8 7 6 5 C2 4.7μF GND LX GND2 U1 AAT1147 SC70JW-8 L1 CDRH3D16-4R7 C2 4.7μF 10V 0805 X5R C1 10μF 6.3V 0805 X5R Figure 1: Enhanced Transient Response Schematic. Control Loop The AAT1147 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. Current Limit and Over-Temperature Protection 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. 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. The error amplifier reference is 0.6V. 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 / Enable Under-Voltage Lockout Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT1147 into a low-power, non-switching state. The total input current during shutdown is less than 1μA. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 9 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Applications Information for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. 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 AAT1147 is 0.24A/μsec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7μH inductor. 0.75 ⋅ VO 0.75 ⋅ 1.5V A m= = = 0.24 L 4.7μH μsec This is the internal slope compensation. When externally programming the 0.6V version to 2.5V, the calculated inductance is 7.5μH. L= 0.75 ⋅ VO = m =3 μsec 0.75 ⋅ VO ≈ 3 A ⋅ VO A 0.24A μsec μsec ⋅ 2.5V = 7.5μH A In this case, a standard 6.8μH value is selected. 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. Configuration Output Voltage Inductor 0.6V Adjustable With External Feedback 1V, 1.2V 1.5V, 1.8V 2.5V, 3.3V 2.2μH 4.7μH 6.8μH Table 1: Inductor Values. The maximum input capacitor RMS current is: Table 1 displays inductor values for the AAT1147. 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 CDRH3D16 series inductor selected from Sumida has a 105m DCR and a 900mA DC current rating. At full load, the inductor DC loss is 17mW which gives a 2.8% loss in efficiency for a 400mA, 1.5V output. IRMS = IO · 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 ⎠ 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 10 D · (1 - D) = 0.52 = 1 2 for VIN = 2 · VO IRMS(MAX) = VO Input Capacitor VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ IO 2 ⎛ V ⎞ · 1- O The term VIN ⎝ VIN ⎠ 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1147. 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 proper placement of the input capacitor (C2) can be seen in the evaluation board layout in Figure 2. Figure 2: AAT1147 Evaluation Board Top Side. 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. Figure 3: Exploded View of Evaluation Board Top Side Layout. Figure 4: AAT1147 Evaluation Board Bottom Side. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 11 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter 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. Output Capacitor 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: 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) = 12 1 VOUT · (VIN(MAX) - VOUT) L · FS · 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. Output Resistor Selection The output voltage of the AAT1147 0.6V version can be externally programmed. Resistors R1 and R2 of Figure 5 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 voltages with R2 set to either 59k for good noise immunity or 221k for reduced no load input current. ⎛ VOUT ⎞ ⎛ 1.5V ⎞ R1 = V -1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ ⎝ REF ⎠ ⎝ ⎠ The AAT1147, combined with an external feedforward capacitor (C4 in Figure 1), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor C1 for stability. VOUT (V) R2 = 59kΩ R1 (kΩ) R2 = 221kΩ R1 (kΩ) 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 75 113 150 187 221 261 301 332 442 464 523 715 1000 Table 2: Resistor Values For Use With 0.6V Step-Down Converter. · Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter 1 2 3 Enable VIN U1 AAT1147 1 R1 VOUT C1 10μF 2 118k 3 L1 4.7μH 4 EN PGND OUT PGND VIN PGND LX AGND 8 7 6 5 C2 4.7μF R2 59k GND GND2 LX U1 AAT1147 SC70JW-8 L1 CDRH3D16-4R7 C1 10μF 10V 0805 X5R C2 4.7μF 10V 0805 X5R Figure 5: AAT1147 Evaluation Board Schematic. Thermal Calculations For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: There are three types of losses associated with the AAT1147 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: 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. IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. Given the total losses, the maximum junction temperature can be derived from the JA for the SC70JW-8 package which is 160°C/W. PTOTAL = IO2 · (RDSON(H) · VO + RDSON(L) · [VIN - VO]) PTOTAL = IO2 · RDSON(H) + IQ · VIN TJ(MAX) = PTOTAL · ΘJA + TAMB VIN + (tsw · FS · IO + IQ) · VIN Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 13 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Layout The suggested PCB layout for the AAT1147 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 1. 2. 3. 4. 14 The input capacitor (C2) should connect as closely as possible to VIN (Pin 3) and PGND (Pins 6-8). C1 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 OUT pin (Pin 2) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. External feedback resistors should be placed as closely as possible to the OUT pin (Pin 2) to minimize the length of the high impedance feedback trace. The resistance of the trace from the load return to the PGND (Pins 6-8) 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. A high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor. An evaluation board is available with this inductor and is shown in Figure 6. The total solution footprint area is 40mm2. Figure 6: Minimum Footprint Evaluation Board Using 2.0mm x 1.6mm x 0.95mm Inductor. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 1.4MHz TAMB = 85°C 1.8V Output Inductor L1 = 3 μsec μsec ⋅ VO2 = 3 ⋅ 1.8V = 5.4μH (use 4.7μH; see Table 1) A A For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m. ΔIL1 = ⎛ VO V ⎞ 1.8V 1.8V ⎞ ⎛ ⋅ 1- O = ⋅ 1= 156mA L1 ⋅ FS ⎝ VIN⎠ 4.7μH ⋅ 1.4MHz ⎝ 4.2V ⎠ IPKL1 = IO + ΔIL1 = 0.4A + 0.068A = 0.468A 2 PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW 1.8V Output Capacitor VDROOP = 0.1V COUT = 3 · ΔILOAD 3 · 0.3A = = 6.4μF; use 10µF 0.1V · 1.4MHz VDROOP · FS IRMS = (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 45mArms = L1 · FS · VIN(MAX) 2 · 3 4.7μH · 1.4MHz · 4.2V 2· 3 1 · Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 15 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Input Capacitor Input Ripple VPP = 25mV CIN = IRMS = ⎛ VPP ⎝ IO 1 1 = = 3.11μF; use 4.7μF ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 1.4MHz - ESR · 4 · FS ⎠ ⎝ 0.4A ⎠ IO = 0.2Arms 2 P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW AAT1147 Losses PTOTAL = IO2 · (RDSON(H) · VO + RDSON(L) · [VIN -VO]) VIN + (tsw · FS · IO + IQ) · VIN TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 126mW = 105.1°C 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Adjustable Version (0.6V device) VOUT (V) R2 = 59kΩ R1 (kΩ) R2 = 221kΩ1 R1 (kΩ) 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 Table 3: Evaluation Board Component Values. Manufacturer Part Number Inductance (μH) Max DC Current (A) DCR (Ω) Size (mm) LxWxH Type Sumida Sumida Sumida Murata Murata Coilcraft Coiltronics Coiltronics Coiltronics CDRH3D16-2R2 CDRH3D16-4R7 CDRH3D16-6R8 LQH2MCN4R7M02 LQH32CN4R7M23 LPO3310-472 SD3118-4R7 SD3118-6R8 SDRC10-4R7 2.2 4.7 6.8 4.7 4.7 4.7 4.7 6.8 4.7 1.20 0.90 0.73 0.40 0.45 0.80 0.98 0.82 1.30 0.072 0.105 0.170 0.80 0.20 0.27 0.122 0.175 0.122 3.8x3.8x1.8 3.8x3.8x1.8 3.8x3.8x1.8 2.0x1.6x0.95 2.5x3.2x2.0 3.2x3.2x1.0 3.1x3.1x1.85 3.1x3.1x1.85 5.7x4.4x1.0 Shielded Shielded Shielded Non-Shielded Non-Shielded 1mm Shielded Shielded 1mm Shielded Table 4: Typical Surface Mount Inductors. Manufacturer Part Number Value Voltage Temp. Co. Case Murata Murata 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 = 221kW. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012 17 DATA SHEET AAT1147 High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter Ordering Information Package Marking1 Part Number (Tape and Reel)2 SC70JW-8 SCXYY AAT1147IJS-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 SC70JW-8 2.20 ± 0.20 1.75 ± 0.10 0.50 BSC 0.50 BSC 0.50 BSC 0.225 ± 0.075 2.00 ± 0.20 0.100 7° ± 3° 0.45 ± 0.10 4° ± 4° 0.05 ± 0.05 0.15 ± 0.05 1.10 MAX 0.85 ± 0.15 0.048REF 2.10 ± 0.30 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. Copyright © 2012 Skyworks Solutions, Inc. 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