DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter General Description Features The AAT1161 is an 800kHz high efficiency step down DC-DC converter with wide input voltage range. With 4.0V to 13.2V input rating, the AAT1161 is the perfect choice for 2-cell Li+ battery powered devices and mid power range regulated 12V powered applications. The internal power switch is capable of delivering up to 3A load current. Input Voltage Range: 4.0V to 13.2V Up to 3A Load Current Fixed or Adjustable Output: ▪ Output Voltage: 0.6V to VIN Less than 1μA Shutdown Current Up to 95% Efficiency Integrated High-Side Power Switch External Schottky Rectifier 800kHz Switching Frequency Soft Start Function Short-Circuit and Over-Temperature Protection Minimum External Components Tiny 14-pin 3x3mm TDFN Package Temperature Range: -40°C to +85°C The AAT1161 is a highly integrated device in order to simplify system level design for the users. It is a nonsynchronous converter that is used with an external Schottky diode rectifier for low-cost applications. Minimum external components are required for the converter. All the control circuits are integrated in the IC. The AAT1161 optimizes efficiency throughout the entire load range. It operates in a combination PWM/Light Load mode for improved light-load efficiency. It can also operate in a forced Pulse Width Modulation (PWM) mode for easy control of the switching noise as well as faster transient response. The high switching frequency allows the use of small external components. The low current shutdown feature disconnects the load from VIN and drops shutdown current to less than 1μA. Applications Digital Camcorders Industrial Applications Portable DVD Players Rack Mounted Systems Set Top Boxes The AAT1161 is available in a Pb-free, space-saving, thermally-enhanced 14-pin TDFN33 package and is rated over an operating temperature range of -40°C to +85°C. Typical Application L1 3.8μH VIN 4.5V- 13.2V 6 C6 10μF R4 10Ω C8 1μF EN LX 8 IN LX 9 10 C2 0.1μF 11 IN AAT1161 FB VOUT 5V, 3A C1 D1 100pF 1 R3 432 kΩ C3, 4, 5 66μF 13 AIN 4, 5 7 PGND 12 DGND COMP 2 AGND 3 N/C PGND EP1 LDO R6 59kΩ R5 51kΩ 14 C9 1μF C7 150pF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 1 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Pin Descriptions Pin # Symbol 1 FB 2 COMP 3 AGND 4, 5 DGND 6 EN 7 N/C 8, 9 LX 10, 11 IN 12, EP PGND 13 AIN 14 LDO Function Output voltage feedback input. FB senses the output voltage for regulation control. For fixed output versions, connect FB to the output voltage. For adjustable versions, drive FB from the output voltage through a resistive voltage divider. The FB regulation threshold is 0.6V. Control compensation node. In most configurations external compensation is not required. If external compensation is required, connect a series RC network from COMP to AGND. See Compensation section. Analog signal ground. Used for the Compensation, LDO bypass and feedback divider ground. Connect AGND to DGND/PGND at a single point as close to the IC as possible or directly under the package exposed thermal pad (EP). Digital/Power Ground. Used for the input and enable ground. Connect DGND to AGND/PGND at a single point as close to the IC as possible or directly under the package exposed thermal pad (EP). Active high enable input. Drive EN high to turn on the AAT1161; drive it low to turn it off. For automatic startup, connect EN to IN through a 4.7kΩ resistor. EN must be biased high, biased low, or driven to a logic level by an external source. Do not let the EN pin float when the device is powered. No Connect. Leave floating; do not connect anything to this pin. Power switching node. LX is the drain of the internal P-channel switch. Connect the external rectifier from LX to PGND and the external LC output filter from LX to the load. Power source input. Connect IN to the input power source. Bypass IN to DGND with a 10μF or greater capacitor. Connect both IN pins together as close to the IC as possible. An additional 100nF ceramic capacitor should also be connected between the two IN pins and DGND. Power Ground. The exposed thermal pad (EP) should be connected to board ground plane and pins 3, 4, 5 and 12 directly under the package. The ground plane should include a large exposed copper pad under the package for thermal dissipation (see package outline). Internal analog bias input. AIN supplies internal power to the AAT1161. Connect AIN to the input source voltage and bypass to AGND with a 0.1μF or greater capacitor. For additional noise rejection, connect to the input power source through a 10Ω or lower value resistor. Internal LDO bypass node. The output voltage of the internal LDO is bypassed at LDO. The internal circuitry of the AAT1161 is powered from LDO. Do not draw external power from LDO. Bypass LDO to AGND with a 1μF or greater capacitor. Pin Configuration TDFN33-14 (Top View) FB COMP AGND DGND DGND EN N/C 2 1 14 2 13 3 12 4 11 5 10 6 9 7 8 LDO AIN PGND IN IN LX LX Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Absolute Maximum Ratings1 Symbol VIN, VAIN VLX VFB VEN TJ Description Input Voltage LX to GND Voltage FB to GND Voltage EN to GND Voltage Operating Junction Temperature Range Value Units -0.3 to 14 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -40 to 150 V V V V °C Value Units 2.0 50 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 20mW/°C above 25°C. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 3 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Electrical Characteristics 4.0V < VIN < 13.2V. CIN= 22μF, COUT= 66μF; L= 2.2μH or 3.8μH, TA= -40 to +85C unless otherwise noted. Typical values are at TA= 25C. Symbol VIN Description Input Under-Voltage Lockout IQ ISHDN Supply Current Shutdown Current VOUT Output Voltage Range VFB IFBLEAK FOSC TS DC TON TSS RDS(ON)H ILIM ILXLEAK TSD THYS VILEN VIHEN IEN Min Input Voltage Range VUVLO VOUT VLINEREG/ VIN VLOADREG Conditions VIN = 4.5V to 13.2V Load Regulation Feedback Reference Voltage (adjustable version) VIN = 12V, VOUT = 5V, IOUT = 0A to 3A Efficiency PMOS Current Limit LX Leakage Current Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis EN Logic Low Input Threshold EN Logic High Input Threshold EN Input Current 13.2 4.0 V 0.6 Line Regulation P-Channel On Resistance Units 0.3 150 IOUT = 0A to 3A Oscillator Frequency Start-Up Time Foldback Frequency Maximum Duty Cycle Minimum Turn-On Time Soft-Start Time Max 4.0 Rising Hysteresis No Load VEN = GND Output Voltage Accuracy FB Leakage Current Typ -2.5 No Load, TA = 25°C VOUT = 1.2V 0.59 Adjustable Version Fixed Version 300 1 0.94 VIN 2.5 0.6 4.0 % 0.4 % 0.60 2 0.8 2 200 0.61 1 100 2 0.12 0.15 90 6.0 VIN = 13.2V, VLX = 0 to VIN 1 0.4 1.4 -1.0 V μA MHz ms kHz % ns ms 140 25 VEN = 0V, VEN = 13.2V V %/V 94 VIN = 12V VIN = 6V VIN = 12V, VOUT = 5V, IOUT = 3A μA μA 0.023 0.2 IOUT = 3A, VOUT = 5V V 1.0 % A μA °C °C V V μA 1. The AAT1161 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 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Efficiency vs. Load Current Efficiency vs. Load Current (VOUT = 5V) (VOUT = 3.3V) 100 100 90 90 80 80 Efficiency (%) Efficiency (%) Typical Characteristics 70 60 50 VIN = 6V VIN = 7V VIN = 10V VIN = 12V VIN = 13.2V 40 30 20 10 0 0.0001 0.001 0.01 0.1 1 70 60 50 VIN = 5V VIN = 7V VIN = 10V VIN = 12V VIN = 13.2V 40 30 20 10 0 0.0001 10 0.001 0.01 Load Current (A) Load Current (A) Load Regulation Load Regulation 0.75 0.5 0.25 0 VIN = 13.2V VIN = 12V VIN = 10V VIN = 7V VIN = 6V -0.25 -0.5 -0.75 0.001 0.01 0.1 1 10 1.5 1 0.75 0.4 0.2 0 -0.5 0.0001 0.001 0.01 Line Regulation (VOUT = 3.3V) -0.4 -0.6 -0.8 6 7 0.1 Line Regulation -0.2 -1 8 9 10 0 -0.25 Load Current (A) 3A 1.5A 1A 100mA 10mA 0.6 1 0.5 0.25 Load Current (A) 10 Input Voltage (V) 11 12 Output Voltage Difference (%) Output Voltage Difference (%) 1 10 VIN = 13.2V VIN = 12V VIN = 10V VIN = 7V VIN = 6V 1.25 (VOUT = 5V) 0.8 1 (VOUT = 3.3V) 1 Output Voltage Difference (%) Output Voltage Difference (%) (VOUT = 5V) -1 0.0001 0.1 1 0.8 0.6 0.4 0.2 0 -0.2 3A 1.5A 1A 100mA 10mA -0.4 -0.6 -0.8 -1 5 6 7 8 9 10 11 12 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 5 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Typical Characteristics P-Channel RDS(ON) vs. Temperature (VIN = 6V) 180 200 85°C 25°C -40°C 170 160 180 Resistance (mΩ Ω) Non Switching Supply Current (µA) Non Switching Supply Current vs. Input Voltage 150 140 130 120 160 6V 140 120 12V 100 80 60 40 110 20 0 -40 100 5 6 7 8 9 10 11 12 -15 VOUT Tolerance vs. Temperature (VOUT = 3.3V; ILOAD = 3A) 805 800 795 790 785 780 VIN = 12V VIN = 6V 775 770 -40 -15 10 35 60 85 Output Voltage Difference (%) Switching Frequency (kHz) 60 (VIN = 6V) 810 85 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -40 -15 10 35 60 85 Temperature (°C) Load Transient (VOUT = 5.0V; CFF = 100pF; IOUT = 1A to 3A; COUT = 66µF) 20 5.1 18 16 5.0 14 4.9 12 4.8 10 4.7 8 5.6 8 5.4 7 5.2 6 5.0 5 4.8 4 4.6 3 4.4 2 4.6 6 4.2 1 4.5 4 4.0 0 Time (200ms/div) Time (200ms/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 Load Current (bottom) (A) 5.2 Output Voltage (top) (V) Line Transient (VOUT = 5.0V; CFF = 100pF; VIN = 6V to 11V; IOUT = 3A; CIN = 10µF; COUT = 66µF; L = 3.8µH) Input Voltage (bottom) (V) Output Voltage (top) (V) 35 Switching Frequency vs. Temperature Temperature (°C) 6 10 Temperature (°C) Input Voltage (V) DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Typical Characteristics Load Transient Start-Up Time 5.4 7 5.2 6 5.0 5 4.8 4 4.6 3 4.4 2 4.2 1 4.0 0 Time (200ms/div) Enable and Input Voltage (top) (V) 8 9 (VOUT = 5.0V; CFF = 100pF; RLOAD = 1.67Ω Ω; CIN = 10µF; COUT = 22µF; L = 3.8µH) 7 7 6 5 5 3 4 1 3 2 -1 VENABLE VOUT ILOAD -3 -5 -7 1 Load Current (bottom) (A) 5.6 Load Current (bottom) (A) Output Voltage (top) (V) (VOUT = 5.0V; CFF = 100pF; IOUT = 50mA to 3A; COUT = 66µF) 0 -1 Time (1ms/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 7 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Functional Block Diagram LDO Internal Power * FB AIN IN LDO Current Sense Amp Err Amp DH Comp Voltage Reference Control Logic LX PGND EN Input DGND AGND COMP * For fixed output voltage versions, FB is connected to the error amplifier through the resistive voltage divider shown. Functional Description Control Loop The AAT1161 is a current-mode step-down DC/DC converter that operates over a wide 4V to 13.2V input voltage range and is capable of supplying up to 3A to the load with the output voltage regulated as low as 0.6V. The P-channel power switch is internal, reducing the number of external components required. An external Schottky diode is used for the low side rectifier. The output voltage is adjusted by an external resistor divider; fixed output voltage versions are available upon request. The regulation system is externally compensated, allowing the circuit to be optimized for each application. The AAT1161 includes cycle-by-cycle current limiting, frequency foldback for improved short-circuit performance, and thermal overload protection to prevent damage in the event of an external fault condition. The AAT1161 regulates the output voltage using constant frequency current mode control. The AAT1161 monitors current through the high-side P-channel MOSFET and uses that signal to regulate the output voltage. This provides improved transient response and eases compensation. Internal slope compensation is included to ensure the current “inside loop” stability. High efficiency is maintained under light load conditions by automatically switching to variable frequency Light Load control. In this condition, transition losses are reduced by operating at a lower frequency at light loads. The AAT1161 uses an external Schottky rectifier diode to minimize cost. 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Low Dropout Operation Applications Information The AAT1161 operates with duty cycle up to 100% to minimize the dropout voltage, increasing the available input voltage range for a given output voltage. As the input voltage decreases toward the output voltage, the duty cycle increases until it reaches the maximum ontime. Further reduction of the supply voltage forces the PMOS on 100%; the output voltage is determined by the p-channel MOSFET switch and inductor voltage drops. Setting the Output Voltage Figure 1 shows the basic application circuit for the AAT1161 and output setting resistors. Resistors R3 and R6 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 R6 is 5.9kΩ. 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 1 summarizes the resistor values for various output voltages with R6 set to either 5.9kΩ for good noise immunity or 59kΩ for reduced no load input current. The external resistors set the output voltage according to the following equation: Short-Circuit Protection The AAT1161 uses a cycle-by-cycle current limit to protect itself and the load from an external fault condition. When the inductor current reaches the internally set 6.0A current limit, the P-channel MOSFET switch turns off, limiting the inductor and the load current. During an overload condition, when the output voltage drops below 25% of the regulation voltage (0.15V at FB), the AAT1161 switching frequency drops by a factor of 4. This gives the inductor current ample time to reset during the off time to prevent the inductor current from rising uncontrolled in a short-circuit condition. ⎛ R3 ⎞ VOUT = 0.6V 1 + ⎝ R6 ⎠ or ⎛ VOUT ⎞ R3 = V -1 · R6 ⎝ REF ⎠ Thermal Protection The adjustable feedback resistors, combined with an external feed forward capacitor (C1 in Figure 1), deliver enhanced transient response for extreme pulsed load applications. The addition of the feed forward capacitor typically requires a larger output capacitor C3/C4/C5 for stability. Larger C3/C4/C5 values reduce overshoot and undershoot during startup and load changes. However, do not exceed 470pF to maintain stable operation. The AAT1161 includes thermal protection that disables the regulator when the die temperature reaches 140ºC. It automatically restarts when the temperature decreases by 25ºC or more. L1 3.8μH VIN 4.5V- 13.2V 6 C6 10μF R4 10Ω C8 1μ F EN LX 8 IN LX 9 10 C2 0.1μ F 11 IN AAT1161 FB VOUT 5V, 3A C1 D1 100pF 1 R3 432 kΩ C3, 4, 5 66μF 13 AIN 4, 5 7 PGND 12 DGND COMP 2 AGND 3 N/C PGND EP1 LDO R6 59kΩ R5 51kΩ 14 C9 1μ F C7 150pF Figure 1: Typical Application Circuit. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 9 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Table 1 shows the resistor selection for different output voltage settings. VOUT (V) R6 = 5.9kΩ R3 (kΩ) R6 = 59kΩ R3 (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 5.0 1.96 2.94 3.92 4.99 5.90 6.81 7.87 8.87 11.8 12.4 13.7 18.7 26.7 43.2 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 432 Table 1: Resistor Selection for Different Output Voltage Settings. Standard 1% Resistors are Substituted for Calculated Values. Inductor Selection For most designs, the AAT1161 operates with inductors of 2μH to 4.7μH. Low inductance values are physically smaller, but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation: L1 = VOUT · (VIN - VOUT) VIN · ΔIL · FOSC Where ∆IL is inductor ripple current. Large value inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current approximately 32% of the maximum load current 3A, or ∆IL = 959mA. For output voltages above 3.3V, the mini- Manufacturer Part Number mum recommended inductor is 3.8μH. For 3.3V and below, use a 2 to 2.2μH inductor. For optimum voltagepositioning load transients, choose an inductor with DC series resistance in the 15mΩ to 20mΩ range. For higher efficiency at heavy loads (above 1A), or minimal load regulation (but some transient overshoot), the resistance should be kept below 18mΩ. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (3A + 526mA). Table 2 lists some typical surface mount inductors that meet target applications for the AAT1161. 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. For example, the 3.7μH CDR7D43 series inductor selected from Sumida has an 18.9mΩ DCR and a 4.3ADC current rating. At full load, the inductor DC loss is 170mW which gives only a 1.13% loss in efficiency for a 3A, 5V output. Input Capacitor Selection The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than the input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 22μF ceramic capacitor is sufficient for most applications. L (μH) Max DCR (mΩ) Rated DC Current (A) Size WxLxH (mm) Sumida CDRH103RNP-2R2N 2.2 16.9 5.10 10.3x10.5x3.1 Sumida Coilcraft CDR7D43MNNP-3R7NC MSS1038-382NL 3.7 3.8 18.9 13 4.3 4.25 7.6x7.6x4.5 10.2x7.7x3.8 Table 2: Typical Surface Mount Inductors. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter 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 · FOSC ⎝ IO ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 1 ⎛ VPP ⎞ - ESR · 4 · FOSC ⎝ IO ⎠ Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 16V, X5R ceramic capacitor with 12V DC applied is actually about 8.5μF. The maximum input capacitor RMS current is: IRMS = IO · VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ D · (1 - D) = 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. Output Capacitor Selection 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⎠ minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C6) can be seen in the evaluation board layout in Figure 3. Additional noise filtering for proper operation is accomplished by adding a small 0.1μF capacitor on the IN pins (C2). 0.52 = 1 2 for VIN = 2 · VO The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current. The output ripple VOUT is determined by: ΔVOUT ≤ IRMS(MAX) = VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ IO 2 The term appears in both the input voltage ripple and input capacitor RMS current equations and is at 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. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1161. 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, ⎞ VOUT · (VIN - VOUT) ⎛ 1 · ESR + ⎝ VIN · FOSC · L 8 · FOSC · COUT⎠ The output capacitor limits the output ripple and provides holdup during large load transitions. A 10μF to 47μF 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 11 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter voltage droop during the three switching cycles to the output capacitance can be estimated by: COUT = 3 · ΔILOAD VDROOP · FOSC 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 22μF. 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 FOSC is the switching frequency and COUT is based on the output capacitor calculation. The CCOMP value can be determined from the following equation: VOUT · (VIN(MAX) - VOUT) L · FOSC · VIN(MAX) 2· 3 · CCOMP (C) = 2πRCOMP (R5) · FOSC 10 Schottky Diode Selection Power dissipation is the limiting factor when choosing a diode. The worst-case average power can be calculated as follows: ⎛ V ⎞ PDIODE = 1 - OUT ⋅ IOUT ⋅ VF VIN ⎠ ⎝ where VF is the voltage drop across the diode at the given output current IOUTMAX. The total power dissipation of the diode is the combined totaI of forward power dissipation, reverse power dissipation and switching loss. Ensure that the selected diode will be able to dissipate the power based on the equation: 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. TJ(MAX) = TAMB + ΘJA · PDIODE Where: Compensation The AAT1161 step-down converter uses peak current mode control with slope compensation scheme to maintain stability with lower value inductors for duty cycles greater than 50%. The regulation feedback loop in the IC is stabilized by the components connected to the COMP pin, as shown in Figure 1. To optimize the compensation components, the following equations can be used. The compensation resistor RCOMP (R5) is calculated using the following equation: RCOMP (R5)= 4 θJA = Package Thermal Resistance (°C/W) TJ(MAX) = Maximum Device Junction Temperature (°C) TA = Ambient Temperature (°C) For reliable operation over the input voltage range, ensure that the reverse-repetitive maximum voltage is greater than the maximum input voltage (VRRM>VINMAX). The diode’s forward-current specification must meet or exceed the maximum output current (IF(AV)>=IOUTMAX). See Table 3 for recommended diodes for different IOUT conditions. 2πVOUT · COUT · FOSC 10GEA · GCOMP · VFB Where VFB = 0.6V, GCOMP = 40.1734 and GEA = 9.091 · 10-5. 12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Part Number VF IF(AV) VRRM θJA TJ(MAX) Manufacturer Dimensions (mm) M1FM3 D1FH3 SK32 SS5820 30BQ040/LSM345 B220/A SDM100K30L B0520WS 0.46V 0.36V 0.5V 0.475A 0.43 0.5V 0.485V 0.43V 3A 3A 3A 3A 3A 2A 1A 0.5A 30V 30V 20V 20V 40V 20V 30V 20V 80°C/W 65°C/W 60°C/W 55°C/W 46°C/W 25°C/W 426°C/W 426°C/W 150°C 125°C 150°C 125°C 150°C 150°C 125°C 125°C Shindengen Shindengen MCC Jinan Jingheng IR/Microsemi Diodes Inc. Diodes Inc. Diodes Inc. 2.8x1.8 4.4x2.5 7x6 4.3x3.6 7x6 4.3x3.6 1.7x1.3 1.7x1.3 Table 3: Recommended Schottky Diodes for Different Output Current Requirements. Layout Guidance 4. Figure 2 is the schematic for the evaluation board. When laying out the PC board, the following layout guideline should be followed to ensure proper operation of the AAT1161: 5. 1. 2. 3. Exposed pad EP1 must be reliably soldered to PGND/ DGND/AGND. The exposed thermal pad should be connected to board ground plane and pins 6, 11, 13, and 16. The ground plane should include a large exposed copper pad under the package for thermal dissipation. The power traces, including GND traces, the LX traces and the VIN trace should be kept short, direct and wide to allow large current flow. The L1 connection to the LX pins should be as short as possible. Use several via pads when routing between layers. Exposed pad pin EP2 must be reliably soldered to the LX pins 1 and 2. The exposed thermal pad should be connected to the board LX connection and the inductor L1 and also pins 1 and 2. The LX plane should include a large exposed copper pad under the package for thermal dissipation. 6. 7. 8. The input capacitors (C2 and C6) should be connected as close as possible to IN (Pins 4 and 5) and DGND (Pin 6) to get good power filtering. Keep the switching node LX away from the sensitive FB node. The feedback trace for the FB pin should be separate from any power trace and connected as closely as possible to the load point. Sensing along a highcurrent load trace will degrade DC load regulation. The feedback resistors should be placed as close as possible to the FB pin (Pin 9) to minimize the length of the high impedance feedback trace. The output capacitors C3, 4, and 5 and L1 should be connected as close as possible and there should not be any signal lines under the inductor. The resistance of the trace from the load return to the PGND (Pin 16) 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 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 13 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter JP1 EN R1 R2 4.75K NP D1 Schottky TP1 LX DGND U1 TP3 VIN VIN R3 10 TB2 VIN TB3 C1 0.1μF 6 10 11 13 4 12 C7 22μF 5 AAT1161 EN IN IN LX LX FB COMP AIN AGND DGND PGND DGND C8 0.1μF N/C EP LDO VOUT C2 100pF 3 7 14 TP4 C6 150pF NP R4 43.2K R5 51.0K LDO C9 150pF TB1 C3 22μF C4 22μF R6 5.90K C5 22μF VOUT TB4 GND TP5 GND TP2 3.3μH C10 0.1μF GND VOUT L1 9 8 1 2 TP7 DGND PGND PGND GND AGND Note: Connect GND, DGND, PGND, and AGND at IC C2 - Increase C2 to reduce overshoot Figure 2: AAT1161 Evaluation Board Schematic. Figure 3: AAT1161 Evaluation Board Top Side Layout. 14 Figure 4: AAT1161 Evaluation Board Bottom Side Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Design Example Specifications VOUT VIN FOSC TAMB 5V @ 3A, Pulsed Load ILOAD = 3A 12V nominal 800kHz 85°C in TDFN34-16 Package Output Inductor L1 = VOUT · (VIN - VOUT) = 3.8µH; see Table 2. VIN · ΔIL · FOSC ΔIL = 0.32 · ILOAD For Coilcraft inductor MSS1038 3.8μH DCR = 13m max. ΔI1 = ⎛ VOUT 5V 5V ⎞ ⎛ V ⎞ ⋅ 1 - O1 = ⋅ 1= 959mA L1 ⋅ FOSC ⎝ VIN ⎠ 3.8µH ⋅ 800kHz ⎝ 12V⎠ IPK1 = ILOAD + ΔI1 = 3A + 0.479A = 3.48A 2 PL1 = ILOAD2 ⋅ DCR = 3A2 ⋅ 13mΩ = 117mW Output Capacitor VDROOP = 0.2V COUT = 3 · ΔILOAD 3 · 3A = = 56µF; use three 22µF VDROOP · FOSC 0.2V · 800kHz IRMS(MAX) = (VOUT) · (VIN(MAX) - VOUT) 1 5V · (12V - 5V) · = 277mArms = L · FOSC · VIN(MAX) 2 · 3 3.8µH · 800kHz · 12V 2· 3 1 · Pesr = esr · IRMS2 = 5mΩ · (277mA)2 = 384µW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 15 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Input Capacitor Input Ripple VPP = 50mV CIN = ⎛ VPP ⎝ ILOAD IRMS(MAX) = 1 1 = = 26µF; use 22µF ⎞ ⎛ 50mV ⎞ - 5mΩ · 4 · 800kHz - ESR · 4 · FOSC ⎠ ⎝ 3A ⎠ ILOAD = 1.5Arms 2 P = esr · IRMS2 = 5mΩ · (1.5A)2 = 11.25mW AAT1161 Losses Total losses can be estimated by calculating at the nominal input voltage (12V). All values assume an 85°C ambient temperature and a 140°C junction temperature with the TDFN 50°C/W package. RDS(ON) = 0.18 tSW = 5ms IQ = 300μA PLOSS = ILOAD2 · (RDS(ON) · VOUT) VIN + [(tsw · FOSC · ILOAD + IQ) · VIN] PLOSS = 823mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 0.823W = 126°C 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Ordering Information Package Marking1 Part Number (Tape and Reel)2 TDFN33-14 1HXYY AAT1161IWO-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 TDFN33-143 Detail "A" 3.000 ± 0.050 2.500 ± 0.050 Index Area 3.000 ± 0.050 1.650 ± 0.050 Top View Bottom View + 0.100 - 0.000 Pin 1 Indicator (Optional) 0.180 ± 0.050 Side View 0.400 BSC 0.000 0.203 REF 0.750 ± 0.050 0.425 ± 0.050 Detail "A" All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012 17 DATA SHEET AAT1161 13.2V Input, 3A Step-Down Converter Copyright © 2012 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 201997A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012