DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter General Description Features The AAT2512 is a member of Skyworks' Total Power Management IC (TPMIC™) product family. It is a dual channel synchronous buck converter operating with an input voltage range of 2.7V to 5.5V, making it ideal for applications with single-cell lithium-ion/polymer batteries. • VIN Range: 2.7V to 5.5V • Output Current: ▪ Channel 1: 400mA ▪ Channel 2: 400mA • 98% Efficient Step-Down Converter • Integrated Power Switches • 100% Duty Cycle • 1.4MHz Switching Frequency • Internal Soft Start • 150μs Typical Turn-On Time • Over-Temperature Protection • Current Limit Protection • Available in TDFN33-12 Package • -40°C to +85°C Temperature Range Both regulators have independent input and enable pins. Offered with fixed or adjustable output voltages, each channel is designed to operate with 27μA (typical) of quiescent current, allowing for high efficiency under light load conditions. The AAT2512 requires only three external components (CIN, COUT, and LX) for each converter, minimizing cost and real estate. Both channels are designed to deliver 400mA of load current and operate with a switching frequency of 1.4MHz, reducing the size of external components. The AAT2512 is available in a Pb-free, 12-pin TDFN33 package and is rated over the -40°C to +85°C temperature range. Applications • • • • • Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core/ IO Power PDAs and Handheld Computers Typical Application V OUT1 V BAT C IN VIN1 LX1 VIN2 FB1 L1 4.7μH AAT2512 EN1 VOUT2 LX2 L2 4.7μH EN2 COUT 4.7μF FB2 GND 4.7μF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 1 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Pin Descriptions Pin # Symbol 1 EN1 2 FB1 3, 6, 7, 10 GND 4 EN2 5 FB2 8 9 11 12 LX2 VIN2 LX1 VIN1 Function Enable pin for Channel 1. When connected low, it disables the channel and consumes less than 1μA of current. When connected high, normal operation. Feedback input pin for Channel 1. This pin is connected to the converter output. It is used to see the output of the converter to regulate to the desired value via an external resistor divider. Ground. Enable pin for Channel 2. When connected low, it disables the channel and consumes less than 1μA of current. When connected high, normal operation. Feedback input pin for Channel 2. This pin is connected to the converter output. It is used to see the output of the converter to regulate to the desired value via an external resistor divider. Power switching node for Channel 2. Output switching node that connects to the output inductor. Input supply voltage for Channel 2. Must be closely decoupled. Power switching node for Channel 2. Output switching node that connects to the output inductor. Input supply voltage for Channel 1. Must be closely decoupled. Pin Configuration TDFN33-12 (Top View) EN1 FB1 GND EN2 FB2 GND 2 1 12 2 11 3 10 4 9 5 8 6 7 VIN1 LX1 GND VIN2 LX2 GND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Absolute Maximum Ratings1 Symbol VIN VLX VFB VEN TJ TLEAD Description Input Voltages to GND LX to GND FB1 and FB2 to GND EN1 and EN2 to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec.) Value Units 6.0 -0.3 to VP + 0.3 -0.3 to VP + 0.3 -0.3 to 6.0 -40 to 150 300 V V V V °C °C Value Units 2.0 50 W °C/W Thermal Information Symbol PD JA Description Maximum Power Dissipation Thermal Resistance2 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 3 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Electrical Characteristics1 VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol VIN VOUT VOUT IQ ISHDN ILX_LEAK IFB ILIM RDS(ON)H RDS(ON)L VLINE FOSC TS TSD THYS VEN(L) VEN(H) IEN Description Input Voltage Output Voltage Tolerance Output Voltage Range Quiescent Current Shutdown Current LX Leakage Current Feedback Leakage P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance Line Regulation Oscillator Frequency Start-Up Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current Conditions Min IOUT = 0 to 400mA; VIN = 2.7V to 5.5V 2.7 -3.0 0.6 Per Channel EN1 = EN2 = GND VIN = 5.5V, VLX = 0 to VIN VFB = 1.0V Both Channels VIN = 2.7V to 5.5V From Enable to Output Regulation; Both Channels Typ Max Units 27 5.5 3.0 VIN 70 1.0 1.0 0.2 1.2 0.45 0.40 0.2 1.4 150 V % V μA μA μA μA A % MHz μs 140 °C 15 °C 0.6 VIN = VFB = 5.5V 1.4 -1.0 1.0 V V μA 1. The AAT2512 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 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Typical Characteristics EN1 = VIN; EN2 = GND. Efficiency vs. Load DC Regulation (VOUT = 1.8V; L = 4.7μ μH) (VOUT = 1.8V) 1.0 100 Efficiency (%) 90 80 Output Error (%) VIN = 2.7V VIN = 4.2V VIN = 3.6V 70 60 50 0.1 1 10 100 0.5 VIN = 4.2V 0.0 -1.0 0.1 1000 VIN = 3.6V -0.5 VIN = 2.7V 1 10 Output Current (mA) Output Current (mA) Efficiency vs. Load DC Regulation (VOUT = 2.5V; L = 6.8μ μH) 100 (VOUT = 2.5V) VIN = 2.7V Output Error (%) Efficiency (%) VIN = 5.0V 80 VIN = 4.2V VIN = 3.6V 60 VIN = 4.2V 0.5 VIN = 5.0V 0.0 VIN = 3.6V -0.5 VIN = 3.0V 50 0.1 1 10 100 -1.0 1000 0.1 1 Output Current (mA) 1.0 Output Error (%) 90 Efficiency (%) 1000 (VOUT = 3.3V; L = 6.8µH) VIN = 3.6V VIN = 4.2V 80 VIN = 5.0V 60 50 0.1 100 DC Regulation (VOUT = 3.3V; L = 6.8μ μH) 70 10 Output Current (mA) Efficiency vs. Load 100 1000 1.0 90 70 100 1 10 Output Current (mA) 100 1000 VIN = 5.0V 0.5 VIN = 4.2V 0.0 -0.5 -1.0 VIN = 3.6V 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 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 5 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Typical Characteristics 5.0 Soft Start Line Regulation (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) (VOUT = 1.8V) 0.40 1.6 0.30 3.0 1.2 0.20 2.0 1.0 1.0 0.8 0.0 0.6 VEN VO -1.0 0.4 -2.0 0.2 IL -3.0 0.0 -4.0 -0.2 -5.0 -0.4 Accuracy (%) 1.4 4.0 Inductor Current (bottom) (A) Enable and Output Voltage (top) (V) EN1 = VIN; EN2 = GND. IOUT = 10mA 0.10 0.00 -0.10 IOUT = 1mA IOUT = 400mA -0.20 -0.30 -0.40 2.5 3.0 3.5 μs/div) Time (100μ 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) Output Voltage Error vs. Temperature Switching Frequency vs. Temperature (VIN = 3.6V; VO = 1.8V; IOUT = 400mA) (VIN = 3.6V; VOUT = 1.8V) 2.0 15.0 9.0 1.0 Variation (%) Output Error (%) 12.0 0.0 -1.0 6.0 3.0 0.0 -3.0 -6.0 -9.0 -12.0 -2.0 -40 -20 0 20 40 60 80 -15.0 -40 100 -20 0 Temperature (°°C) 80 100 50 VOUT = 1.8V 1.0 Supply Current (μ μA) Frequency Variation (%) 60 No Load Quiescent Current vs. Input Voltage 2.0 0.0 -1.0 VOUT = 2.5V -2.0 VOUT = 3.3V -3.0 2.7 3.1 3.5 3.9 4.3 Input Voltage (V) 6 40 Temperature (°°C) Frequency vs. Input Voltage -4.0 20 4.7 5.1 5.5 45 40 35 25°C 85°C 30 25 20 15 10 -40°C 2.7 3.1 3.5 3.9 4.3 4.7 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 5.1 5.5 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Typical Characteristics EN1 = VIN; EN2 = GND. P-Channel RDS(ON) vs. Input Voltage 750 750 700 700 120°C 650 100°C RDS(ON) (mΩ Ω) 650 RDS(ON) (mΩ Ω) N-Channel RDS(ON) vs. Input Voltage 600 550 85°C 500 450 25°C 400 120°C 600 550 500 85°C 450 400 25°C 350 350 300 300 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 6.0 3.0 Input Voltage (V) (300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7μ μF) 300mA 1mA 1.90 1.85 Output Voltage (top) (V) Output Voltage (top) (V) IO 1.80 1.75 VO IO 0.4 0.3 IL 0.2 0.1 Load Transient Response Load Transient Response (300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μ μF) (300mA to 400mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μ μF; C4 = 100pF) 0.4 0.3 0.2 0.1 Time (50μs/div) 1.825 Output Voltage (top) (V) 300mA 1.850 1.800 1.775 VO IO 400mA 300mA 0.4 0.3 IL 0.2 0.1 Load and Inductor Current (200mA/div) (bottom) 400mA Load and Inductor Current (200mA/div) (bottom) VO IL 6.0 Time (50μs/div) 1.90 IO 400mA 300mA Time (50μs/div) 1.75 5.5 Load and Inductor Current (200mA/div) (bottom) VO 0 1.80 5.0 Load Transient Response IL 1.85 4.5 Load Transient Response 1.8 1.7 4.0 Input Voltage (V) Load and Inductor Current (200mA/div) (bottom) 1.9 3.5 (1mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μ μF; CFF = 100pF) 2.0 Output Voltage (top) (V) 100°C Time (50μs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 7 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Typical Characteristics EN1 = VIN; EN2 = GND. Output Ripple (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA) 1.82 6.0 1.80 5.0 1.79 4.5 1.78 4.0 1.77 3.5 1.76 3.0 Input Voltage (bottom) (V) Output Voltage (top) (V) 5.5 Time (25μ μs/div) 0.30 40 20 0.25 VO 0 0.20 -20 0.15 -40 0.10 -60 -80 0.05 IL 0.00 -100 -0.05 -120 -0.10 Time (10µs/div) Output Ripple 0.9 40 20 0.8 VO 0 0.7 -20 0.6 -40 0.5 -60 0.4 0.3 -80 -100 IL Inductor Current (bottom) (A) Output Voltage (AC coupled) (top) (mV) (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) 0.2 0.1 -120 Time (500ns/div) 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 Inductor Current (bottom) (A) 1.81 Output Voltage (AC coupled) (top) (mV) Line Response (VOUT = 1.8V @ 400mA) DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Functional Block Diagram FB1 VIN1 Err. Amp. DH Comp. LX1 Logic Voltage Reference DL Control Logic EN1 GND1 VIN2 See Note SGND1 FB2 Err. Amp. DH Comp. LX2 Logic Voltage Reference Control Logic EN2 DL GND2 See Note SGND2 Note: Internal resistor divider included for ≥1.2V versions. For low voltage versions, the feedback pin is tied directly to the error amplifier input. Functional Description The AAT2512 is a high performance power management IC comprised of two buck converters. Each channel has independent input voltages and enable/disable pins. Designed to operate at 1.4MHz of switching frequency, the converters require only three external components (CIN, COUT, and LX), minimizing cost and size of external components. Both converters are designed to operate with an input voltage range of 2.7V to 5.5V. Typical values of the output filter are 4.7μH and 4.7μF ceramic capacitor. The output voltage operates to as low as 0.6V and is offered as both fixed and adjustable. Power devices are sized for 400mA current capability while maintaining over 90% efficiency at full load. Light load efficiency is maintained at greater than 80% down to 500μA of load current. Both channels have excellent transient response, load, and line regulation. Transient response time is typically less than 20μs. The AAT2512 also features soft-start control to limit inrush current. Soft start increases the inductor current limit point in discrete steps when power is applied to the input or when the enable pins are pulled high. It limits the current surge seen at the input and eliminates output voltage overshoot. The enable input, when pulled low, forces the converter into a low power, non-switching state consuming less than 1μA of current. For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140°C with 15°C of hysteresis. The under-voltage lockout guarantees sufficient VIN bias and proper operation of all internal circuits prior to activation. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 9 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Applications Information 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. Inductor Selection The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the adjustable and low-voltage fixed versions of the AAT2512 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. Input Capacitor Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. 0.75 ⋅ VO 0.75 ⋅ 1.5V A m= = = 0.24 L 4.7μH μsec This is the internal slope compensation for the adjustable (0.6V) version or low-voltage fixed version. When externally programming the 0.6V version to a 2.5V output, the calculated inductance would be 7.5μH. 0.75V 0.75 ⋅ VO μsec ≈ 3 A ⋅ VO L= = m 0.24A /μsec =3 μsec ⋅ 2.5V = 7.5μH A 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. 0.6V Adjustable With External Feedback Fixed Output ⎛ VPP ⎞ - ESR ⋅ FS ⎝ IO ⎠ This equation provides an estimate for the input capacitor required for a single channel. The equation below solves for input capacitor size for both channels. It makes the worst-case assumptions that both converters are operating at 50% duty cycle and are synchronized. CIN = In this case, a standard 6.8μH value is selected. For highvoltage fixed versions (2.5V and above), m = 0.48A/μsec. Table 1 displays inductor values for the AAT2512 fixed and adjustable options. Configuration CIN = V ⎞ VO ⎛ ⋅ 1- O VIN ⎝ VIN ⎠ 1 ⎛ VPP ⎞ - ESR • 4 • FS ⎝ IO1 + IO2 ⎠ Because the AAT2512 channels will generally operate at different duty cycles and are not synchronized, the actual ripple will vary and be less than the ripple (VPP) used to solve for the input capacitor in the equation above. 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 5V DC applied is actually about 6μF. The maximum input capacitor RMS current is: IRMS = IO1 · ⎛ ⎝ VO1 ⎛ V ⎞ · 1 - O1 ⎞ + IO2 · ⎛ VIN ⎝ VIN ⎠ ⎠ ⎝ VO2 ⎛ V ⎞ · 1 - O2 VIN ⎝ VIN ⎠ Output Voltage Inductor 1V, 1.2V 1.5V, 1.8V 2.5V, 3.3V 0.6V to 3.3V 2.2μH 4.7μH 6.8μH 4.7μH Table 1: Inductor Values. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter 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 of both converters combined. IRMS(MAX) = IO1(MAX) + IO2(MAX) 2 This equation also makes the worst-case assumption that both converters are operating at 50% duty cycle and are synchronized. Since the converters are not synchronized and are not both operating at 50% duty cycle, the actual RMS current will always be less than this. Losses associated with the input ceramic capacitor are typically minimal. VO ⎛ V ⎞ · 1- O The term VIN ⎝ VIN ⎠ appears in both the input voltage ripple and input capacitor RMS current equations. It 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. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2512. Low ESR/ ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize the 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 (C3 and C8) can be seen in the evaluation board layout in Figure 4. Since decoupling must be as close to the input pins as possible, it is necessary to use two decoupling capacitors. C3 provides the bulk capacitance required for both converters, while C8 is a high frequency bypass capacitor for the second channel (see C3 and C8 placement in Figure 4). 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 printed circuit board 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 converter performance, a high ESR tantalum or aluminum electrolytic capacitor should be placed in parallel with the low ESR, ESL bypass ceramic capacitor. 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. As the loop responds, the inductor current increases to match the load current demand. This typically takes two to three switching cycles and can be estimated by: VO ⎛ V ⎞ · 1 - O = D ⋅ (1 - D) = 0.52 = 0.25 VIN ⎝ VIN ⎠ 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: COUT = 3 · ΔILOAD VDROOP · FS Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot spot temperature. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 11 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Adjustable Output Resistor Selection Thermal Calculations For applications requiring an adjustable output voltage, the 0.6V version can be programmed externally. Resistors R1 through R4 of Figure 2 program the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string, the minimum suggested value for R2 and R4 is 59k. Although a larger value will reduce the 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 and R4 set to either 59k for good noise immunity or 221k for reduced no load input current. There are three types of losses associated with the AAT2512 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 dual converter losses is given by: 1 V · (VIN(MAX) - VOUT) IRMS(MAX) = · OUT L · F · VIN(MAX) 2· 3 The adjustable version of the AAT2512 in combination with an external feedforward capacitor (C4 and C5 of Figure 2) delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor (C1 and C2) for stability. VOUT (V) R2, R4 = 59k R1, R3 (k) R2, R4 = 221k R1, R3 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75K 113K 150K 187K 221K 261K 301K 332K 442K 464K 523K 715K 1.00M ⎛ VOUT ⎞ ⎛ 1.5V ⎞ R1 = V -1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ ⎝ REF ⎠ ⎝ ⎠ IQ is the AAT2512 quiescent current for one channel and tsw is used to estimate the full load switching losses. For the condition where channel one is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = + IO12 · (RDSON(HS) · VO1 + RDSON(LS) · [VIN -VO1]) VIN IO22 · (RDSON(HS) · VO2 + RDSON(LS) · [VIN -VO2]) VIN + (tsw · F · [IO1 + IO2] + 2 · 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 TDFN33-12 package which is 50°C/W. TJ(MAX) = PTOTAL • ΘJA + TAMB Table 2: Adjustable Resistor Values For Use With 0.6V Version. 12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter PCB Layout 3. The following guidelines should be used to insure a proper layout. 1. Due to the pin placement of VIN for both converters, proper decoupling is not possible with just one input capacitor. The large input capacitor C3 should connect as closely as possible to VP and GND, as shown in Figure 4. The additional input bypass capacitor C8 is necessary for proper high frequency decoupling of the second converter. 2. The output capacitor and inductor should be connected as closely as possible. The connection of the inductor to the LX pin should also be as short as possible. 4. 5. The feedback trace 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. This prevents noise from being coupled into the high impedance feedback node. The resistance of the trace from the load return to GND 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. For good thermal coupling, PCB vias are required from the pad for the TDFN paddle to the ground plane. The via diameter should be 0.3mm to 0.33mm and positioned on a 1.2mm grid. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 13 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Design Example Specifications VO1 = 2.5V @ 400mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA VO2 = 1.8V @ 400mA (adjustable using 0.6V version), pulsed load ILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 1.4 MHz TAMB = 85°C 2.5V VO1 Output Inductor L1 = 3 μsec μsec ⋅ VO1 = 3 ⋅ 2.5V = 7.5μH (see Table 1) A A For Sumida inductor CDRH3D16, 10μH, DCR = 210m. ΔI1 = ⎛ 2.5V⎞ VO ⎛ V ⎞ 2.5V ⋅ 1 - O1 = ⋅ 1= 72.3mA L1 ⋅ F ⎝ VIN ⎠ 10μH ⋅ 1.4MHz ⎝ 4.2V⎠ IPK1 = IO1 + ΔI1 = 0.4A + 0.036A = 0.44A 2 PL1 = IO12 ⋅ DCR = 0.4A2 ⋅ 210mΩ = 34mW 1.8V VO2 Output Inductor L2 = 3 μsec μsec ⋅ VO2 = 3 ⋅ 1.8V = 5.4μH (see Table 1) A A For Sumida inductor CDRH3D16, 4.7μH, DCR = 105m. ΔI2 = ⎛ 1.8V ⎞ VO2 ⎛ V ⎞ 1.8V ⋅ 1 - O2 = ⋅ 1= 156mA L⋅F ⎝ VIN ⎠ 4.7μH ⋅ 1.4MHz ⎝ 4.2V⎠ IPK2 = IO2 + ΔI2 = 0.4A + 0.078A = 0.48A 2 PL2 = IO22 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW 2.5V Output Capacitor COUT = 3 · ΔILOAD 3 · 0.3A = = 3.2μF VDROOP · FS 0.2V · 1.4MHz IRMS(MAX) = (VOUT) · (VIN(MAX) - VOUT) 1 2.5V · (4.2V - 2.5V) · = 21mArms = L · F · VIN(MAX) 2 · 3 10μH · 1.4MHz · 4.2V 2· 3 1 · Pesr = esr · IRMS2 = 5mΩ · (21mA)2 = 2.2μW 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter 1.8V Output Capacitor COUT = 3 · ΔILOAD 3 · 0.3A = = 3.2μF 0.2V · 1.4MHz VDROOP · FS IRMS(MAX) = (VOUT) · (VIN(MAX) - VOUT) 1 1.8V · (4.2V - 1.8V) · = 45mArms = L · F · VIN(MAX) 2 · 3 4.7μH · 1.4MHz · 4.2V 2· 3 1 · Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW Input Capacitor Input Ripple VPP = 25mV. CIN = 1 1 = = 6.8μF ⎛ VPP ⎞ ⎛ 25mV ⎞ - ESR • 4 • FS - 5mΩ • 4 • 1.4MHz ⎝ IO1 + IO2 ⎠ ⎝ 0.8A ⎠ IRMS(MAX) = IO1 + IO2 = 0.4Arms 2 P = esr · IRMS2 = 5mΩ · (0.4A)2 = 0.8mW AAT2512 Losses The maximum dissipation occurs at dropout where VIN = 2.7V. All values assume an ambient temperature of 85°C and a junction temperature of 120°C. PTOTAL = IO12 · (RDSON(HS) · VO1 + RDSON(LS) · (VIN -VO1)) + IO22 · (RDSON(HS) · VO2 + RDSON(LS) · (VIN -VO2)) VIN + (tsw · F · IO2 + 2 · IQ) · VIN = 0.42 · (0.725Ω · 2.5V + 0.7Ω · (2.7V - 2.5V)) + 0.42 · (0.725Ω · 1.8V + 0.7Ω · (2.7V - 1.8V)) 2.7V + 5ns · 1.4MHz · 0.4A + 60μA) · 2.7V = 239mW TJ(MAX) = TAMB + ΘJA • PLOSS = 85°C + (50°C/W) • 239mW = 97°C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 15 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Output 1 Enable VIN 1 2 3 C41 R1 see Table 3 U1 AAT2512 1 2 3 C51 R3 see Table 3 4 5 6 R4 59.0k EN1 FB1 SGND1 VIN1 LX1 GND1 EN2 VIN2 FB2 LX2 SGND2 R2 59.0k GND2 LX1 12 L1 see Table 3 11 10 VO1 C3 LX2 9 10μF 8 VO2 L2 see Table 3 C11 4.7μF 7 C8 C7 0.01μF C6 0.01μF C21 4.7μF 0.1μF GND GND 3 2 1 Output 2 Enable Figure 3: AAT2512 Evaluation Board Schematic. Figure 4: AAT2512 Evaluation Board Top Side. Figure 5: AAT2512 Evaluation Board Bottom Side. 1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10μF. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Adjustable Version (0.6V device) R2, R4 = 59k R2, R4 = 221k1 VOUT (V) R1, R3 (k) R1, R3 (k) L1, L2 (μH) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75.0 113 150 187 221 261 301 332 442 464 523 715 1000 2.2 2.2 2.2 2.2 2.2 2.2 4.7 4.7 4.7 4.7 6.8 6.8 6.8 Fixed Version R2, R4 Not Used VOUT (V) R1, R3 (k) L1, L2 (μH) 0.6-3.3V 0 4.7 Table 3: Evaluation Board Component Values. Manufacturer Part Number Inductance (μH) Max DC Current (A) DCR () 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 10uF 22uF 10V 6.3V 6.3V X5R X5R X5R 0805 0805 0805 Table 5: Surface Mount Capacitors. 1. For reduced quiescent current, R2 and R4 = 221kΩ. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 17 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Ordering Information Voltage Package Channel 1 Channel 2 Marking1 Part Number (Tape and Reel)2 TDFN33-12 0.6V 0.6V QKXYY AAT2512IWP-AA-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. Legend Voltage Code Adjustable (0.6V) 0.9 1.2 1.5 1.8 1.9 2.5 2.6 2.7 2.8 2.85 2.9 3.0 3.3 4.2 A B E G I Y N O P Q R S T W C 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 DATA SHEET AAT2512 Dual 1.4MHz, 400mA Synchronous Buck DC/DC Converter Package Information TDFN33-121 Index Area 0.43 ± 0.05 0.1 REF C0.3 0.45 ± 0.05 2.40 ± 0.05 3.00 ± 0.05 Detail "A" 3.00 ± 0.05 1.70 ± 0.05 Top View Bottom View 0.23 ± 0.05 Pin 1 Indicator (optional) 0.05 ± 0.05 0.23 ± 0.05 0.75 ± 0.05 Detail "A" Side View All dimensions in millimeters. 1. 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. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202022B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013 19