DATA SHEET AAT1153 2A Step-Down Converter General Description Features The AAT1153 SwitchReg™ is a 1.2MHz constant frequency current mode PWM step-down converter. It is ideal for portable equipment requiring very high current up to 2A from single-cell Lithium-ion batteries while still achieving over 90% efficiency during peak load conditions. The AAT1153 also can run at 100% duty cycle for low dropout operation, extending battery life in portable systems while light load operation provides very low output ripple for noise sensitive applications. • • • • • • • • The AAT1153 can supply up to 2A output load current from a 2.5V to 5.5V input voltage and the output voltage can be regulated as low as 0.6V. The high switching frequency minimizes the size of external components while keeping switching losses low. The internal slope compensation setting allows the device to operate with smaller inductor values to optimize size and provide efficient operation. The AAT1153 is available with adjustable (0.6V to VIN) output voltage. The device is available in a Pb-free, 3mm x 3mm 10-lead TDFN package and is rated over the -40°C to +85°C temperature range. • • • • • • Input Voltage Range: 2.5V to 5.5V Output Voltages from 0.6V to VIN 2A Output Current High Efficiency: Up to 95% 1.2MHz Constant Switching Frequency Low RDS(ON) Internal Switches: 0.15Ω Allows Use of Ceramic Capacitors Current Mode Operation for Excellent Line and Load Transient Response Short-Circuit and Thermal Fault Protection Soft Start Low Dropout Operation: 100% Duty Cycle Low Shutdown Current: ISHUTDOWN < 1μA TDFN33-10 Package -40°C to +85°C Temperature Range Applications • • • • • • Cellular Phones Digital Cameras DSP Core Supplies PDAs Portable Instruments Smart Phones Typical Application VIN 2.5V-5.5V 1 2 C1 22μF 3 EN LX IN LX AIN 6 AGND 4 AGND AAT1153 FB PGND PGND 8 7 5 10 9 L1 2.2μH R1 634kΩ VOUT 1.8V, 2A C2 22μF R2 316kΩ Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 1 DATA SHEET AAT1153 2A Step-Down Converter Pin Descriptions Pin # Symbol 1 EN 2 3 4, 6 IN AIN AGND 5 FB 7, 8 9, 10 LX PGND EP Function Enable pin. Active high. In shutdown, all functions are disabled drawing <1μA supply current. Do not leave EN floating. Power supply input pin. Must be closely decoupled to AGND with a 2.2μF or greater ceramic capacitor. Analog supply input pin. Provides bias for internal circuitry. Analog ground pin Feedback input. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V. Switching node pin. Connect the output inductor to this pin. Power ground pin Power ground exposed pad. Must be connected to bare copper ground plane. Pin Configuration TDFN-10 (Top View) EN 1 10 PGND IN 2 9 PGND AIN 3 8 LX AGND 4 7 LX FB/OUT 5 6 AGND 1. FB pin for the adjustable voltage version (AAT1153IDE-0.6), OUT pin for the fixed voltage version (AAT1153IDE-1.8). 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter Absolute Maximum Ratings1 Symbol Description IN, AIN VFB, VLX VEN PGND, AGND TA TSTORAGE TLEAD Input Supply Voltages FB, LX Voltages EN Voltage Ground Voltages Operating Temperature Range Storage Temperature Lead Temperature (Soldering, 10s) Value Units -0.3 to 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -40 to +85 -65 to 150 300 V V V V °C °C °C Value Units 45 2.2 °C/W W Thermal Information2 Symbol JA PD Description Thermal Resistance3 Maximum Thermal Dissipation at TA = 25°C 1. Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 2. TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + PD x JA. 3. Thermal Resistance is specified with approximately 1 square inch of 1 oz. copper. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 3 DATA SHEET AAT1153 2A Step-Down Converter Electrical Characteristics1 VIN = 3.6V, TA = -40°C to +85°C unless otherwise noted; typical values are TA = 25°C. Symbol VIN VOUT Description IQ Input DC Supply Current IFB Feedback Input Bias Current VFB Regulated Feedback Voltage3 VLINEREG/ VIN VLOADREG/ IOUT VFB FOSC TS TSD THYS ILIM RDS(ON) VEN(L) VEN(H) IEN Conditions Input Voltage Range2 Output Voltage Range Min Typ Max Units V V μA μA nA 0.6000 0.6000 0.6000 5.5 VIN 500 1 30 0.6120 0.6135 0.6150 0.20 %/V 2.5 0.6 Active Mode: VFB = 0.5V Shutdown Mode: VEN = 0V, VAIN = 5.5V VFB = 0.65V TA = 25°C 0°C ≤ TA ≤ 85°C -40°C ≤ TA ≤ 85°C 300 0.1 0.5880 0.5865 0.5850 Line Regulation VIN = 2.5V to 5.5V, IOUT = 10mA 0.10 Load Regulation IOUT = 10mA to 2000mA 0.20 Output Voltage Accuracy Oscillator Frequency Startup Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Peak Switch Current P-CH MOSFET N-CH MOSFET Enable Threshold Low Enable Threshold High Input Low Current VIN = 2.5 to 5.5V, IOUT = 10 to 2000mA VFB = 0.6V From Enable to Output Regulation -3 0.96 2.5 VIN = 3.6V VIN = 3.6V VIN = VEN = 5.5V 1.2 1.3 170 10 3.5 135 95 1.5 -1.0 V %/A +3 1.44 200 150 0.3 1.0 % VOUT MHz ms °C °C A mΩ V V μA 1. The AAT1153 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. 2. VIN should be not less than VOUT + VDROPOUT, where VDROPOUT = IOUT x (RDS(ON)PMOS + ESRINDUCTOR), typically VDROPOUT = 0.3V. 3. The regulated feedback voltage is tested in an internal test mode that connects VFB to the output of the error amplifier. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter Typical Characteristics Efficiency vs. Output Current DC Regulation (VOUT = 3.3V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) (VOUT = 3.3V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) 100 VIN = 3.7V 70 Output Voltage (V) 80 Efficiency (%) 3.399 VIN = 4.2V 90 VIN = 5.5V VIN = 5.0V 60 50 40 30 20 10 0 0.1 1 10 100 1000 3.366 VIN = 3.7V 3.267 VIN = 4.2V 3.234 0 200 400 Output Current (mA) 600 800 1000 1200 1400 1600 1800 2000 Output Current (mA) Efficiency vs. Output Current DC Regulation (VOUT = 1.8V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) (VOUT = 1.8V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) 100 1.854 80 70 60 VIN = 5.0V 50 Output Voltage (V) VIN = 4.2V VIN = 3.6V VIN = 2.5V 90 Efficiency (%) VIN = 5.0V 3.300 3.201 10000 VIN = 5.5V 3.333 VIN = 5.5V 40 30 20 1.836 VIN = 4.2V 1.818 VIN = 5.0V VIN = 5.5V 1.800 1.782 VIN = 3.6V 1.764 VIN = 2.5V 10 0 0.1 1.746 1 10 100 1000 0 10000 200 400 Output Current (mA) 800 1000 1200 1400 1600 1800 2000 Output Current (mA) Efficiency vs. Output Current DC Regulation (VOUT = 1.5V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) (VOUT = 1.5V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) 100 1.545 90 70 60 VIN = 4.2V Output Voltage (V) 80 Efficiency (%) 600 VIN = 3.6V VIN = 2.5V VIN = 5.5V 50 40 VIN = 5.0V 30 20 10 0 0.1 1 10 100 Output Current (mA) 1000 10000 1.530 VIN = 4.2V 1.515 VIN = 5.0V VIN = 5.5V 1.500 1.485 VIN = 3.6V VIN = 2.5V 1.470 1.455 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 5 DATA SHEET AAT1153 2A Step-Down Converter Typical Characteristics Efficiency vs. Output Current DC Regulation (VOUT = 1.2V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) (VOUT = 1.2V, TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) 100 1.236 Efficiency (%) 80 70 60 VIN = 3.6V VIN = 4.2V Output Voltage (V) 90 VIN = 2.5V 50 VIN = 5.5V VIN = 5.0V 40 30 20 10 0 0.1 1 10 100 1000 1.224 1.212 VIN = 3.6V VIN = 2.5V 1.188 1.176 200 400 600 Output Current (mA) 800 1000 1200 1400 1600 1800 2000 Output Current (mA) Quiescent Current vs. Input Voltage Quiescent Current vs. Temperature (TA = 25°C, L = 2.2µH, CIN = COUT = 22µF) (L = 2.2µH, CIN = COUT = 22µF) 0.38 Quiescent Current (µA) 400 0.36 Input Current (mA) VIN = 5.5V 1.200 1.164 0 10000 VIN = 5.0V VIN = 4.2V VOUT = 3.3V 0.34 0.32 0.30 VOUT = 1.8V 0.28 0.26 0.24 0.22 0.20 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Input Voltage (V) 350 VIN = 4.2V VOUT = 3.3V 300 VIN = 3.6V VOUT = 1.8V 250 200 -40 -20 0 20 40 60 Temperature (°C) Line Regulation (VOUT = 1.8V, L = 2.2µH, CIN = COUT = 22µF) Accuracy (%) 0.40 IOUT = 1A IOUT = 600mA 0.20 IOUT = 1mA IOUT = 1.5A 0.00 -0.20 -0.40 2.5 IOUT = 2A 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) 6 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 80 100 DATA SHEET AAT1153 2A Step-Down Converter Typical Characteristics P-Channel RDS(ON) vs. Input Voltage N-Channel RDS(ON) vs. Input Voltage 200 150 85°C 160 25°C 140 120 -40°C 110 3.5 4 4.5 5 -40°C 50 2.5 80 3 25°C 90 70 100 2.5 85°C 130 RDS(ON)_N (mΩ Ω) RDS(ON)_P (mΩ Ω) 180 5.5 3 3.5 4.5 5 5.5 Switching Frequency vs. Temperature Reference Voltage vs. Temperature (VIN = 3.6V; VOUT = 1.8V) (VIN = 3.6V) 1.4 0.609 1.3 1.2 1.1 1.0 -40 -20 0 20 40 60 80 0.607 0.605 0.603 0.601 0.599 0.597 0.595 0.593 0.591 -40 100 -20 Temperature (°C) 0 20 40 60 80 100 Temperature (°C) Soft Start Load Transient Response (VIN = 3.6V; VOUT = 1.8V; IOUT = 2A; CFF = 22pF) (VIN = 3.6V; VOUT = 1.8V; L = 2.2µH; CIN = COUT = 22µF) 2 0 -2 1.4 1.0 0.6 0.2 Output Voltage (top) (V) 4 2.2 2.0 1.8 1.6 2A 200mA -0.2 Time (400µs/div) 2.6 2.2 1.8 1.4 1.0 0.6 0.2 -0.2 Output Current (bottom) (A) 6 Input Current (bottom) (A) Enable Voltage (top) (V) Output Voltage (middle) (V) 4 Input Voltage (V) Reference Voltage (V) Switching Frequency (MHz) Input Voltage (V) Time (400µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 7 DATA SHEET AAT1153 2A Step-Down Converter Typical Characteristics Output Ripple Output Ripple (VIN = 3.6V; VOUT = 1.8V; IOUT = 0A; L = 2.2µH) (VIN = 3.6V; VOUT = 1.8V; IOUT = 2A; L = 2.2µH) 1.79 0.3 0.2 0.1 0.0 -0.1 Time (100µs/div) 8 Output Voltage (top) (V) Output Voltage (top) (V) 1.80 1.82 1.81 1.80 1.79 2.5 2.3 2.1 1.9 1.7 1.5 Time (400ns/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 Inductor Current (bottom) (A) 1.81 Inductor Current (bottom) (A) 1.82 DATA SHEET AAT1153 2A Step-Down Converter Functional Block Diagram OSC SLOPE COMP IN VIN 2.5V to 5.5V ISENSE AMP 0.6V Softstart SET I COMP RESET PWM LOGIC NON-OVERLAP CONTROL LX FB/OUT R1* R1* 0.65V Over-Temperature and Short-Circuit Protection COUT OVDET R2* R2* IZERO COMP 0.6V EN VOUT L1 REF PGND SHUTDOWN AIN AGND *The resistor divider R1 + R2 is internally set for the fixed output versions, and is externally set for the adjustable output versions. Functional Description The AAT1153 is a high output current monolithic switchmode step-down DC-DC converter. The device operates at a fixed 1.2MHz switching frequency, and uses a slope compensated current mode architecture. This step-down DC-DC converter can supply up to 2A output current at VIN = 3V and has an input voltage range from 2.5V to 5.5V. It minimizes external component size and optimizes efficiency at the heavy load range. The slope compensation allows the device to remain stable over a wider range of inductor values so that smaller values (1μH to 4.7μH) with lower DCR can be used to achieve higher efficiency. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. The device can be programmed with external feedback to any voltage, ranging from 0.6V to near the input voltage. It uses internal MOSFETs to achieve high efficiency and can generate very low output voltages by using an internal reference of 0.6V. At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the low RDS(ON) drop of the P-channel high-side MOSFET and the inductor DCR. The internal error amplifier and compensation provides excellent transient response, load and line regulation. Internal soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. Current Mode PWM Control Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line response with protection of the internal main switch (P-channel MOSFET) and synchronous rectifier (N-channel MOSFET). During normal operation, the internal P-channel MOSFET is turned on for a specified time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The current comparator, ICOMP, limits the peak inductor current. When the main switch is off, the synchronous rectifier turns on immediately and stays on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 9 DATA SHEET AAT1153 2A Step-Down Converter Control Loop The AAT1153 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 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. 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 fixed at 0.6V. Soft Start / Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. The enable pin is active high. When pulled low, the enable input (EN) forces the AAT1153 into a low-power, non-switching state. The total input current during shutdown is less than 1μA. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited to 3.5A. 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. The termination lasts for seven consecutive clock cycles after a current limit has been sensed during a series of four consecutive clock cycles. 10 Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 170°C with 10°C of hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. Dropout Operation When the battery input voltage decreases near the value of the output voltage, the AAT1153 allows the main switch to remain on for more than one switching cycle and increases the duty cycle until it reaches 100%. The duty cycle D of a step-down converter is defined as: D = TON · FOSC · 100% ≈ VOUT · 100% VIN Where TON is the main switch on time and FOSC is the oscillator frequency. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated does not exceed the maximum junction temperature of the IC. Maximum Load Current The AAT1153 will operate with an input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input voltages due to a large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely, the current limit increases as the duty cycle decreases. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter Applications Information VIN 2.5V-5.5V 1 2 C1 22μF 3 LX EN IN LX AIN AAT1153-0.6 6 AGND 4 AGND FB PGND PGND 8 L1 2.2μH 7 5 C3 22pF 10 9 VOUT 1.8V, 2A R1 634kΩ C2 22μF R2 316kΩ Figure 1: Basic Application Circuit. Setting the Output Voltage Figure 1 shows the basic application circuit for the AAT1153. The AAT1153 can be externally programmed. Resistors R1 and R2 in Figure 1 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 1 summarizes the resistor values for various output voltages with R2 set to either 59k for good noise immunity or 316k for reduced no load input current. The AAT1153, combined with an external feed forward capacitor (C3 in Figure 1), delivers enhanced transient response for extreme pulsed load applications. The addition of the feed forward capacitor typically requires a larger output capacitor C2 for stability. The external resistor sets the output voltage according to the following equation: ⎛ R1 ⎞ VOUT = 0.6V · 1 + ⎝ R2 ⎠ R1 = ⎛ VOUT ⎞ - 1 · R2 ⎝ 0.6V ⎠ Table 1 shows the resistor selection for different output voltage settings. VOUT (V) R2 = 59k R1 (k) R2 = 316k R1 (k) 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 88.7 118 124 137 187 267 105 158 210 261 316 365 422 475 634 655 732 1000 1430 Table 1: Resistor Selections for Different Output Voltage Settings (Standard 1% Resistors Substituted For Calculated Values). Inductor Selection For most designs, the AAT1153 operates with inductor values of 1μH 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: L= 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 30% of the maximum load current 2A, or ΔIL = 600mA For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.2μH. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 11 DATA SHEET AAT1153 2A Step-Down Converter Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 20m to 100m range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100m. 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 (2A + 600mA). Table 2 lists some typical surface mount inductors that meet target applications for the AAT1153. For example, the 2.2μH CDRH5D16-2R2 inductor selected from Sumida has a 28.7mΩ DCR and a 3.0ADC current rating. At full load, the inductor DC loss is 57mW which gives a 1.6% loss in efficiency for a 1200mA, 1.8V output. Slope Compensation The AAT1153 step-down converter uses peak current mode control with slope compensation for stability when duty cycles are greater than 50%. The slope compensation is set to maintain stability with lower value inductors which provide better overall efficiency. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. As an example, the value of the slope compensation is set to 1A/μs which is large enough to guarantee stability when using a 2.2μH inductor for all output voltage levels from 0.6V to 3.3V. The worst case external current slope (m) using the 2.2μH inductor is when VOUT = 3.3V and is: m= VOUT 3.3 = = 1.5A/µs L 2.2 To keep the power supply stable when the duty cycle is above 50%, the internal slope compensation (mA) should be: ma ≥ 1 · m = 0.75A/µs 2 Therefore, to guarantee current loop stability, the slope of the compensation ramp must be greater than one-half of the down slope of the current waveform. So the inter- 12 nal slope compensated value of 1A/μs will guarantee stability using a 2.2μH inductor value for all output voltages from 0.6V to 3.3V. 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 should be less than the input source impedance to prevent high frequency switching current passing to the input. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = CIN(MIN) = V ⎞ VO ⎛ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · fS ⎝ IO ⎠ 1 ⎛ VPP ⎞ - ESR · 4 · fS ⎝ IO ⎠ 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 for most applications is sufficient. A large value may be used for improved input voltage filtering. 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. IRMS(MAX) = 1 · IO 2 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 (C1) can be seen in the evaluation board layout in Figures 2 and 3. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter 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 In many practical designs, to get the required ESR, a capacitor with much more capacitance than is needed must be selected. For both continuous or discontinuous inductor current mode operation, the ESR of the COUT needed to limit the ripple to ∆VO, V peak-to-peak is: ESR ≤ Ripple current flowing through a capacitor’s ESR causes power dissipation in the capacitor. This power dissipation causes a temperature increase internal to the capacitor. Excessive temperature can seriously shorten the expected life of a capacitor. Capacitors have ripple current ratings that are dependent on ambient temperature and should not be exceeded. The output capacitor ripple current is the inductor current, IL, minus the output current, IO. The RMS value of the ripple current flowing in the output capacitance (continuous inductor current mode operation) is given by: The function of output capacitance is to store energy to attempt to maintain a constant voltage. The energy is stored in the capacitor’s electric field due to the voltage applied. The value of output capacitance is generally selected to limit output voltage ripple to the level required by the specification. Since the ripple current in the output inductor is usually determined by L, VOUT and VIN, the series impedance of the capacitor primarily determines the output voltage ripple. The three elements of the capacitor that contribute to its impedance (and output voltage ripple) are equivalent series resistance (ESR), equivalent series inductance (ESL), and capacitance (C). 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 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 = ΔVO ΔIL IRMS = ΔIL · 3 = ΔIL · 0.289 6 ESL can be a problem by causing ringing in the low megahertz region but can be controlled by choosing low ESL capacitors, limiting lead length (PCB and capacitor), and replacing one large device with several smaller ones connected in parallel. In conclusion, in order to meet the requirement of output voltage ripple small and regulation loop stability, ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current ratings. The output ripple VOUT is determined by: ΔVOUT ≤ 1 VOUT · (VIN - VOUT) ⎛ ⎞ · ⎝ESR + 8 · fOSC · COUT ⎠ VIN · fOSC · L A 22μF ceramic capacitor can satisfy most applications. 3 · ΔILOAD VDROOP · fS Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 13 DATA SHEET AAT1153 2A Step-Down Converter Thermal Calculations Layout Guidance There are three types of losses associated with the AAT1153 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: When laying out the PC board, the following layout guideline should be followed to ensure proper operation of the AAT1153: PTOTAL = 1. 2. 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. 3. 4. 5. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: 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 DFN-10 package which is 45°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB 14 6. 7. The exposed pad (EP) must be reliably soldered to the GND plane. A PGND pad below EP is strongly recommended. The power traces, including the GND trace, the LX trace and the IN 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. The input capacitor (C1) should connect as closely as possible to IN (Pin 2) and AGND (Pins 4 and 6) to get good power filtering. Keep the switching node, LX (Pins 7 and 8) away from the sensitive FB/OUT node. 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. If external feedback resistors are used, they should be placed as closely as possible to the FB pin (Pin 5) to minimize the length of the high impedance feedback trace. The output capacitor C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible and there should not be any signal lines under the inductor. The resistance of the trace from the load return to PGND 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. Figures 3, 4 and 5 show an example of a layout with 4 layers. The internal 2 layers are SGND and PGND. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter Manufacturer Part Number Sumida Sumida Sumida Coiltronics Coiltronics Coiltronics Inductance (μH) Max DC Current (A) DCR (m) 2.2 3.3 4.7 2.0 3.3 4.7 3.0 2.6 3.4 3.3 2.6 2.1 28.7 35.6 19 23 29 39 CDRH5D16 CDRH8D28 SD53 Size LxWxH (mm) Type 5.8x5.8x1.8 Shielded 8.3x8.3x3.0 Shielded 5.2x5.2x3.0 Shielded Manufacturer Part Number Value Voltage (V) Temp. Co. Case Murata Murata Murata GRM219R60J106KE19 GRM21BR60J226ME39 GRM1551X1E220JZ01B 10μF 22μF 22pF 6.3 6.3 25 X5R X5R JIS 0805 0805 0402 Table 2: Suggested Component Selection Information. JP1 SGND U1 AAT1153 1 JP3 EN PGND IN PGND 10 PGND 2.5V ~ 5.5V VIN 2 3 C1 22μF PGND 4 LX AIN LX AGND 9 SGND SW 8 L1 2.2μH 7 SGND 5 FB AGND EP 6 SGND 11 JP2 R2A 316k R2B 634k R2C 1M R2D 1.43M R1 316k SGND 1 2 3 4 5 6 7 8 1.2V, 1.8V, 2.5V, 3.3V VOUT C2 22μF C3 22pF JP2_1-2: JP2_3-4: JP2_5-6: JP2_7-8: 1.2V; 1.8V; 2.5V; 3.3V. L1: CDRH5D16-2R2NC C1, C2: GRM21BR60J226ME39 Figure 2: AAT1153 Recommended Evaluation Board Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 15 DATA SHEET AAT1153 2A Step-Down Converter Figure 4: AAT1153 Evaluation Board Component Side Layout. Figure 5: Exploded View of AAT1153 Evaluation Board Component Side Layout. Figure 6: AAT1153 Evaluation Board Solder Side Layout. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 2A VIN = 2.7V to 4.2V (3.6V nominal) fS = 1.2MHz Transient droop = 200mV ∆VO = 50mV 1.8V Output Inductor ΔIL = 30% ⋅ IO = 0.3 · 2 = 600mA L= VOUT · (VIN(MAX) - VOUT) 1.8 · (4.2 - 1.8) = = 1.4µH VIN(MAX) ⋅ ΔIL ⋅ fOSC 4.2 ⋅ 0.6 · 1.2 · 106 For Sumida 2.2μH inductor (CDRH2D14) with DCR 75m, the ∆IL should be: ΔIL = VO ⎛ VO ⎞ ⋅ 1· T = 395mA L ⎝ VIN ⎠ IPKL = IO + 0.395 ΔIL =2+ = 2.2A 2 2 PL = IO2 ⋅ DCR = 22 ⋅ 0.0287 = 114.8mW 1.8V Output Capacitor COUT = 3 · ΔILOAD 3 · 1.2 = = 25µF; use 22µF 0.2 · 1.2 · 106 VDROOP · fS ESR ≤ 0.05 ΔVO = = 0.13Ω ΔIL 0.395 Select a 22μF, 10m ESR ceramic capacitor to meet the ripple 50mV requirement. ΔVOUT ≤ = 1 VOUT · (VIN - VOUT) ⎛ ⎞ · ⎝ESR + 8 · fOSC · COUT ⎠ VIN · fOSC · L 1.8 · (4.2 - 1.8) 1 ⎛ ⎞ · ⎝ 0.01 + = 5.7mV 6 -6 6 -6 ⎠ 4.2 · 1.2 · 10 · 2.2 · 10 8 · 1.2 · 10 · 22 · 10 IRMS = IL ·0.289 = 0.395 · 0.289 = 114mArms PCOUT = ESR · IRMS2 = 0.01 · 12 = 10mW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 17 DATA SHEET AAT1153 2A Step-Down Converter Input Capacitor Input ripple VPP = 25mV CIN(MIN) = IRMS = 1 ⎛ VPP ⎞ - ESR · 4 · fS ⎝ IO ⎠ = 1 = 13.9µF; use 22µF ⎛ 0.025 ⎞ - 0.01 · 4 · 1.2 · 106 ⎝ 2 ⎠ IO 2 = = 1Arms 2 2 PCIN = ESR · IRMS2 = 0.01 · 12 = 10mW AAT1153 Losses PTOTAL = IO2 · RDS(ON)P · D + IO2 · RDS(ON)N · (1 - D) + (tSW · fS · IO) · VIN = 22 · 0.135 · 18 1.8 1.8⎞ ⎛ + 22 · 0.095 · 1 + (5 · 10-9 · 1.2 · 106 · 2) · 4.2 = 498.9mW ⎝ 4.2 4.2⎠ Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 DATA SHEET AAT1153 2A Step-Down Converter Ordering Information Output Voltage Package Marking1 Part Number (Tape and Reel)2 Adj. 0.6V to VIN TDFN33-10 ZSXYY AAT1153IDE-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 Information3 TDFN33-10 Pin 1 dot by marking 0.500 BSC 1.70 ± 0.05 3.00 ± 0.05 0.23 ± 0.05 Pin 1 identification R0.200 0.40 ± 0.05 3.00 ± 0.05 2.40 ± 0.05 Top View 0.05 ± 0.05 0.203 REF 0.75 ± 0.05 Bottom View Side View All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on all 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. Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 19