DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs General Description Features The AAT2612 is a multiple rail power management IC. It integrates a 600mA high-frequency switching-converter and three 300mA linear regulators. The switching power supply is a highly-integrated monolithic step-down converter operating at 1.5MHz, achieving high efficiency with small external components. The three linear regulators are high PSRR low dropout regulators (LDOs) providing accurate regulation and excellent transient response. • Current Mode Control DC/DC Converter: ▪ Programmable Output Up to 600mA ▪ 1.5MHz Switching Frequency ▪ Up to 90% Efficiency ▪ Integrated Switching Power FETS ▪ Integrated Compensation Network ▪ Internal Current Limit •3 Low Dropout Regulators with Separate Enable Pins: ▪ 300mA per Channel ▪ High PSRR ▪ Factory Programmable Output •Integrated Soft-Start •Over-Current Protection •Over-Thermal Protection •TQFN33-20 Package The step down converter is programmable with external feedback resistors, and the three LDOs are fixed voltage outputs of six combinations for 1.8V, 2.8V, 3.0V and 3.3V. Integrated over-current or over-temperature protection circuitry becomes active as appropriate, when either fault occurs, and the AAT2612 recovers automatically when the fault is removed. The AAT2612 is available in a Pb-free, thermally enhanced 20-pin TQFN33 package. Applications • • • • • Cellular Phones I/O Power Memory Power Processor Core Power Smart Handheld Devices Typical Application 2.5V to 5.5V INL1 OUTL1 2.2μF 2.5V to 5.5V 1μF INL2 OUTL2 1μF 2.2μF ENL1 ENL2 ENL3 2.8 V 300mA 2.8V 300mA 1.8V 300mA OUTL3 1μF AAT2612 2.2μH ENBK 2.5V to 5.5V 4.7μF INBK LX 1.2V , 600mA 10μF FB AGND PGND R1 59k R2 59k Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 1 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Pin Descriptions Pin # Symbol Function 1 2, 8, 10, 18, 19 INL1 I 3 ENL1 I 4 INBK I 5 6 7 LX PGND ENBK I/O 9 FB I 11 ENL2 I 12 ENL3 I 13,17 14 15 16 20 EP AGND OUTL3 OUTL2 INL2 OUTL1 GND O O I O N/C Description Power input for LDO1. Connect a 2.2μF capacitor between this pin and ground. Not Connected I Active high enable pin. When pulled high, LDO1 regulates its output to the programmed voltage value. Power input pin for the switching converter. Connect a 4.7μF capacitor between ground and INBK. DC/DC step-down converter switching node. Connect LX to the terminal of the inductor. DC/DC converter power ground. Active high step-down DC/DC converter enable pin. DC/DC converter output feedback pin. Connect to a resistor divider for an adjustable output voltage. Active high enable pin. When pulled high, LDO2 regulates its output to the programmed voltage value. Active high enable pin. When pulled high, LDO3 regulates its output to the programmed voltage value. Analog ground. LDO3 output. Connect a 1μF capacitor between the pin and ground. LDO2 output. Connect a 1μF capacitor between the pin and ground. Power input for LDO2/3. Connect a 2.2μF capacitor between the pin and ground. LDO1 output. Connect a 1μF capacitor between the pin and ground. Exposed pad. Pin Configuration 2 OUTL1 N/C N/C AGND INL2 TQFN33-20 (Top View) 20 19 18 17 16 2 14 OUTL3 ENL1 3 13 AGND INBK 4 12 ENL3 LX 5 11 ENL2 6 7 8 9 10 N/C N/C FB OUTL2 N/C 15 ENBK 1 PGND INL1 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Absolute Maximum Ratings1 Symbol Description Value INL1, INL2, INBK, OUTL1, OUTL2, OUTL3 ENL1, ENL2, ENL3 ENBK, FB LX to PGND PGND to AGND, AGND to AGND Operating Ambient Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec.) TA TS TLEAD -0.3 to 6.0 -0.3 to 6.0 -0.3 to VINBK -0.3 to VINBK -0.3 to +0.3 -40 to 85 -65 to 150 300 Units V °C Thermal Information2 Symbol θJA PD Description Thermal Resistance Maximum Power Dissipation 3 Value Units 50 2 °C/W W 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. 2. Mounted on an FR4 board. 3. Thermal Resistance measured with the device on multi-layer evaluation board in a thermal oven. The amount of power dissipation which will cause the thermal shutdown to activate will depend on the ambient temperature and the PC board layout ability to dissipate the heat. De-rate 30mW/°C above 70°C. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 3 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Electrical Characteristics1 VINBK = VINL1 = VINL2 = 3.6V, L = 2.2μH, CINL1, 2 = 2.2μF, CINBK = 4.7μF, COUTBK = 10μF, COUTL1, 2, 3 = 1μF, TA= 25°C unless otherwise noted. Symbol Description PMU Operation VIN Input Voltage Under-Voltage UVLO Lockout TSD Thermal Shutdown Quiescent Current IQ Logic Control Input Logic High VIH Threshold Input Logic Low VIL Threshold DC-DC Step-Down Converter Shutdown Current ISHDN from INBK Pin IQ Quiescent Current P-Channel Current ILIM Limit Output Voltage VOUT Range Feedback Voltage VFB_ACC Accuracy Operating SwitchfSW ing Frequency High-Side Switch RDS(ON)H On Resistance RDS(ON)L LDO ISHDN ILIM VDROP VOUTL_ACC ΔVOUTL/ IOUTL VOUTL/ VINL Low-Side Switch On Resistance Shutdown Current Output Current Limit Dropout Voltage Output Voltage Accuracy Conditions Min 2.5 Rising Hysteresis Threshold Hysteresis VENBK > 1.5V, VENL1,2,3 >1.5V, no load 1.5 ENL1, ENL2, ENL3, ENBK 4 5.5 420 V V mV °C °C μA VINBK V 0.4 V 1 μA VENL 1, 2, 3 < 0.4V , VENBK >1.5V , IOUTB = 0mA 120 280 μA VINBK = 2.7V to 5.5V 800 mA 0.9 TA = -40°C to 85°C 0.585 0.600 85%∙VINBK V 0.615 V 1.5 IOUTB IOUTB IOUTB IOUTB = = = = 200mA 200mA, VINBK = 2.5V 200mA 200mA, VINBK = 2.5V RLOAD = 1Ω 450 IOUTL = 300mA TA = -40°C to 85°C, 1mA load Line Regulation VINL1 = VINL2 = 2.7V to 5.5V COUT1,2,3 = 1μF, VINL = VOUTL1,2,3 + 1V -3 0.3 f = 1kHz MHz 230 280 180 220 VENBK = VENL < 0.4V 1mA < IOUTL < 300mA Output Voltage Temperature Coefficient Units 0.1 f = 10kHz VOUTL_TC Max VENBK < 0.4V, VENL 1, 2, 3 < 0.4V Load Regulation Power Supply Rejection Ratio 1.9 150 140 15 220 ENL1, ENL2, ENL3, ENBK f = 100Hz PSRR Typ IOUT = 10mA IOUT = 150mA IOUT = 10mA IOUT = 150mA IOUT = 10mA IOUT = 150mA mΩ mΩ 1 μA 600 mA 500 mV 3 % 0.6 % 0.2 %/V 75 75 70 70 50 50 dB 100 ppm/°C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 DATA SHEET PRODUCT DATASHEET AAT2612 AAT2612 SwitchRegTM Step-Down DC/DC DC/DC Converter Converter With WithThree Three High High PSRR PSRR LDOs LDOs Step-Down Supply Current vs Supply Voltage Buck Quiescent Current vs Supply Voltage (VOUT= 1.2V, VENB> 1.5V,VENL< 0.4V) 250 140.00 230 130.00 IQ (μA) Supply Current (μA) (VENB, VENL> 1.5V) 120.00 210 110.00 190 85°C 170 100.00 85°C 25°C -40°C 25°C -40°C 150 2.5 3.0 3.5 4.0 4.5 5.0 90.00 2.5 5.5 3.0 3.5 Switching Frequency vs Temperature Switching Frequency (MHz) Switching Frequency (MHz) 5.5 (VOUTB = 1.2V, IOUTB = 600mA) 1.60 1.55 1.50 1.45 1.40 1.35 10 5.0 Switching Frequency vs Input Voltage (VINB = 3.6V, IOUT = 600mA) -15 4.5 Supply Voltage (V) Supply Voltage (V) -40 4.0 35 60 1.54 1.52 1.50 1.48 1.46 1.44 85 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Temperature (°C) Buck Efficiency vs Output Current UVLO Volatge vs Temperature (VOUT = 1.2V; L = 2.2μH) 1.950 100 90 1.910 VEOC (V) Efficiency (%) 80 70 60 50 1.870 1.830 40 VIN = 2.5V 30 VIN = 3.6V 1.790 VIN = 4.2V 20 VIN = 5.0V 10 UVLO_H VIN = 5.5V UVLO_L 0 0.1 1 10 Output Current (mA) 100 1000 1.750 -40 -15 10 35 60 85 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 5 DATA SHEET PRODUCT DATASHEET AAT2612 AAT2612 SwitchRegTM Step-Down DC/DC DC/DC Converter Converter With WithThree Three High High PSRR PSRR LDOs LDOs Step-Down Buck Output Voltage vs Temperature Buck Line Regulation (VINB= 3.6V; VOUTB = 1.2V; L = 2.2μH) (VOUT = 1.2V; L = 2.2μH) 1 1.000 0.8 VOUT Error (%) Output Error (%) 0.600 0.200 -0.200 -0.600 0.6 0.4 0.2 0 -0.2 -0.4 IOUT = 10mA -0.6 IOUT = 100mA IOUT = 300mA -0.8 IOUT = 600mA -1 -1.000 -40 -15 10 35 60 2.5 85 3 Temperature (°C) 3.5 4 4.5 5 5.5 Input Voltage (V) Buck Load Regulation EN VIH vs Supply Voltage (VOUT = 1.2V; L = 2.2μH) 1.20 1 EN VIH (V) Output Error (%) 0.8 0.6 0.4 0.2 0 1.10 1.00 0.90 -0.2 -0.4 VIN = 2.5V VIN = 3.6V -0.6 0.80 VIN = 4.2V -40°C VIN = 5.0V -0.8 25°C VIN = 5.5V 85°C 0.70 -1 10 70 130 190 250 310 370 430 490 550 610 2.5 Output Current (mA) 3.0 3.5 4.0 4.5 Supply Voltage (V) EN VIL vs Supply Voltage Softstart (VIN = 3.6V; VOUTB = 1.2V; IOUTB = 600mA) 1.20 EN VIL (V) 1.10 VIN 2V/div 1.00 0.90 VOUT 1V/div 0 0 0.80 0.70 IIN -40°C 0.2A/div 0 25°C 85°C 0.60 2.5 3.0 3.5 4.0 4.5 Supply Voltage (V) 6 5.0 5.5 Time 40 μS/div Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 5.0 5.5 DATA SHEET PRODUCT DATASHEET AAT2612 AAT2612 SwitchRegTM Step-Down DC/DC DC/DC Converter Converter With WithThree Three High High PSRR PSRR LDOs LDOs Step-Down Buck Load Transient Buck Line Transient (VIN = 3.6V, VOUTB = 1.2V, CINB = 10μF, COUTB = 10μF) (VINB = 4V to 5V, IOUTB = 600mA) VOUTB 1.2 200mV/div VIN 1V/div 4 600mA IOUTB 400mA 0.2A/div VOUT 50mV/div 1.2 0A Time 40 μS/div Output Ripple LDO Output Voltage vs Temperature (VIN = 3.6V; VOUT = 1.2V; IOUT = 600mA; CINB = 4.7μF) (VIN = 3.6V) 0.600 LDO1 0.400 VOUT 20mv/div 1.2 LDO2 VOUT Error (%) LDO3 0.200 0.000 -0.200 VLX 2V/div 0 -0.400 -0.600 -40 -15 Time 0.4 μS/div 10 35 60 85 Temperature (°C) LDO Quiescent Current vs Supply Voltage LDO Line Regulation (Single Channel) (VOUTL = 1.8V) 34.00 0.1 0.08 Output Error (%/V) IQ (μA) 32.00 30.00 28.00 85°C 25°C 26.00 -40°C 0.06 0.04 0.02 0 -0.02 -0.04 IOUTB = 10mA -0.06 IOUTB = 100mA -0.08 IOUTB = 200mA IOUTB =300mA 24.00 2.5 3.0 3.5 4.0 4.5 Supply Voltage (V) 5.0 5.5 -0.1 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 7 DATA SHEET PRODUCT DATASHEET AAT2612 AAT2612 SwitchRegTM Step-Down DC/DC DC/DC Converter Converter With WithThree Three High High PSRR PSRR LDOs LDOs Step-Down Dropout Voltage vs Load Current LDO Load Transient (VOUT = 2.8V) (VIN = 3.6V, VOUTL = 1.8V, CINL = 2.2μF, COUTL = 1μF) Dropout Voltage(mV) 350 300 250 VOUTL 1.8 200mV/div 200 150 300mA 100 85°C 25°C 50 IOUTL -40°C 0.2A/div 0A 0 20 60 100 140 180 220 260 300 Load Current (mA) Time 100 μS/div LDO Line Transient LDO1 Power Supply Rejection Ratio, PSRR (VINB = 4V to 5V, IOUTL = 300mA) (IOUT1 = 10mA, BW = 100~100KHz) 100 90 VIN 1V/div Magnitude (dB) 80 4 VOUT 20mV/div 2.8 70 60 50 40 30 20 10mA 10 0 100 Time 20 μs/div 8 1000 10000 Frequency (Hz) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 100000 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Block Diagram INBK 4.7uF Buck ENBK INL2 LX 2.2uH 1.2V, 600mA Control 4.7uF PGND 1uF FB INL1 R2 59k Bias, Control, and OTP, Thermal Shutdownd 1uF R1 59k ENL3 LDO 3 OUTL3 1.8V. 300mA 1uF ENL2 LDO 2 LDO 1 ENL1 OUTL2 2.8V, 300mA 1uF OUTL1 2.8V. 300mA 1 uF AGND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 9 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Functional Description The AAT2612 is a compact power management solution. It integrates a step-down converter with three high PSRR low-dropout regulators to provide power from a wall adapter, USB port, or a single-cell Lithium Ion/Polymer battery or dual cell alkaline battery. The AAT2612 uses fixed-frequency peak current control architecture. Light load mode is used to enhance light load efficiency. Compensation is integrated to reduce the number of external components and achieve excellent transient response and load/line regulation. The ideal 1.5MHz switching frequency allows the use of smaller output filter components for improved power density, reduced external component size, and optimized output voltage ripple. The AAT2612 has four separate enable pins to control buck converter and three LDO regulator outputs’ startup. Also see the “Enable Function” section in the Applications Information section of this datasheet. Synchronous Step-Down Converter The AAT2612 contains one high performance 600mA, 1.5MHz synchronous step-down converter. The stepdown converter operates to ensure high efficiency performance over all load conditions. The input voltage range is from 2.5V to 5.5V, and the output voltage is programmable from 85% of VIN to as low as 0.9V with external resistor divider. Power devices are sized for 600mA current capability while maintaining over 85% efficiency at full load. High efficiency is maintained at lower currents A high DC gain error amplifier with internal compensation controls the output. It provides excellent transient response and load/line regulation. The converter has soft start control to limit inrush current. Apart from the resistor divider and input capacitor, only a small L-C filter is required at the output side for the step-down converter to operate properly. Typically, a 2.2μH inductor and a 10μF ceramic capacitor are recommended for low output voltage ripple and small component size. Control Loop The converter is a peak current mode step-down converter. The inner, wide bandwidth loop controls the inductor peak current. The inductor current is sensed through the P-channel MOSFET (high side) and is also 10 used for short circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage programmed current source in parallel with the output capacitor. The output of the voltage error amplifier programs the current mode loop for the necessary peak inductor current to force a constant output voltage for all load and line conditions. The voltage feedback resistive divider is external and the error amplifier reference voltage is 0.6V. The voltage loop has a high DC gain making for excellent DC load and line regulation. The internal voltage loop compensation is located at the output of the transconductance voltage error amplifier. Soft-Start Soft start increases the inductor current limit point linearly when the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. Current Limit and Over-Temperature Protection 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. LDO Regulator The advanced circuit design of the linear regulator is specifically optimized for very fast start-up and shutdown timing. This proprietary LDO is also tailored for superior transient response characteristics. These traits are particularly important for applications which require fast power supply timing. The high-speed turn-on capability is enabled through the implementation of a fast start control circuit, which accelerates the power up behavior of fundamental control and feedback circuits within the LDO regulator. Fast turn-off time response is achieved by an active output pull down circuit, which is enabled when the LDO regulator is placed in the shutdown mode. This active fast shutdown circuit has no adverse effect on normal device operation. The LDO regulator output has been specifically optimized to function with low cost, low ESR ceram- Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs ic capacitors. However, the design will allow for operation over a wide range of capacitor types. The regulator comes with complete short circuit and thermal protection. The combination of these two internal protection circuits gives a comprehensive safety system to guard against extreme adverse operating conditions. Application Information The proper placement of the input capacitors (C1, C2, and C3) is shown in the evaluation board layout in Figure 2. Step-down Converter Input Capacitor Select a 4.7uF to 10uF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor value and size, determine the acceptable input ripple voltage level (Vpp) and solve for CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = V VO · 1- O VIN VIN VPP - ESR · fS IO 1 VPP - ESR · 4 · fS IO Where CIN is the input capacitance, VIN is age, VO is the output voltage, fS is the quency, IO is the output current, ESR is series resistor of output capacitor, and cycle. Output Capacitor the input voltswitching frethe equivalent D is the duty 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 = 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 can also result in the loop phase and gain measurements. 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 capacitor should be placed in parallel with the low ESR/ESL bypass ceramic capacitor. This dampens the high Q network and stabilizes the system. VO D= V IN CIN(MIN) = The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2612. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize parasitic inductances, 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. IO 2 The maximum input voltage ripple also appears at 50% duty cycle. The output capacitor limits the output ripple and provides holdup during large load transitions. A typical 4.7μF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output voltage droop during the three switching cycles to the output capacitance can be estimated by: COUT = 3 · ΔILOAD VDROOP · FS Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 11 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs 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. Output Inductor For most designs, the AAT2612 operates with inductor values of 2.2μH to 4.7μH. Inductors with low inductance values are physically smaller but generate higher inductor current ripple leading to higher output voltage ripple. The inductor value can be derived from the following equation: L= VOUT · (VIN - VOUT) VIN · ∆IL · fOSC Where ΔIL is inductor ripple current. Large value inductors result in lower ripple current and small value inductors result in high ripple current. Choose inductor ripple current approximately 30% of the maximum load current 0.6A, or ∆IL = 180mA 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. The DC current rating of the inductor should be at least equal to the maximum load current plus half the inductor ripple current to prevent core saturation (0.6A + 180mA). 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. Feedback Resistor Selection The Buck output voltage on the AAT2612 is adjustable with external resistors R1 and R2 which program the output to regulate at a voltage in the range of 0.9V to 0.85 ∙ VINBK. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R2 is 59kΩ. 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. The maximum value of R1 should be below 1Mohm to keep reference voltage normal and avoid noise coupling. 12 R1 = VOUT VOUT - 1 · R2 = - 1 · R2 VREF 0.6V Table 1 shows the standard 1% metal film resistor values for different step-down output voltages VOUT (V) R2 = 59kΩ, R1 (kΩ) 1.2 2.8 3.3 3.6 4.2 59 216 265.5 259 354 Table 1: VOUT Resistor Selection Enable Function The AAT2612 features one buck output enable/disable function for buck converter. This pin (ENBK) is active high and is compatible with CMOS logic. To assure the buck output will switch on, the ENBK turn-on control level must be greater than 1.5V. The buck converter will go into the disable shutdown mode when the voltage on the ENBK pin falls below 0.6V. If the enable function is not needed in a specific application, it may be tied to VIN to keep the buck output in a continuously on state. Low Dropout Regulator Input Capacitor Typically, a 2.2μF or larger capacitor is recommended for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation. However, if the LDO is physically located any distance more than one or two centimeters from the input power source, a CIN capacitor will be needed for stable operation. CIN should be located as closely to the device VINL pin as practically possible. CIN values greater than 1μF will offer superior input line transient response and will assist in maximizing the power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN as there is no specific capacitor ESR requirement. For better performance, ceramic capacitors are recommended for CIN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources such as batteries in portable devices. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Output Capacitor For proper load voltage regulation and operational stability, a capacitor is required between pins VOUT and GND. The COUT capacitor connection to the LDO regulator ground pin should be made as direct as practically possible for maximum device performance. The AAT2612 LDOs have been specifically designed to function with very low ESR ceramic capacitors. Although the device is intended to operate with these low ESR capacitors, it is stable over a very wide range of capacitor ESR, thus it will also work with some higher ESR tantalum or aluminum electrolytic capacitors. For best performance, ceramic capacitors are recommended. The value of COUT typically ranges from 1μF to 10μF. 1μF is sufficient for most operating conditions. Enable Function stand indefinite short-circuit conditions without sustaining permanent damage. No-Load Stability The AAT2612 LDO is designed to maintain output voltage regulation and stability under operational no-load conditions. This is an important characteristic for applications where the output current may drop to zero. An output capacitor is required for stability under no-load operating conditions. Refer to the Output Capacitor section of this datasheet for recommended typical output capacitor values. Internal Power Supply The AAT2612 internal circuitry uses INL1 as the internal power supply. The buck output will have no output when INL1 is not connected to power. Thermal Calculations The AAT2612 features three LDO regulator enable/disable function for LDO1/2/3 respectively. These pins (ENL1, ENL2, and ENL3) are active high and are compatible with CMOS logic. To assure the LDO regulator will switch on, the EN turn-on control level must be greater than 1.5V. The LDO regulator will go into the disable shutdown mode when the voltage on the EN pin falls below 0.6V. If the enable function is not needed in a specific application, it may be tied to VIN to keep the LDO regulator in a continuously on state. There are three types of losses associated with the AAT2612 step-down converters: 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, with continuous conduction mode (CCM), a simplified form of the losses is given by: Short-circuit and Thermal Protection VO VO PBUCK = IO2 · RDS(ON)P · V + RDS(ON)N · 1 - V IN IN The AAT2612 LDOs are protected by both current-limiting and over-temperature protection circuitry. The internal short-circuit current limiting circuit is designed to activate when the output load demand exceeds the maximum rated output. If a short-circuit condition were to continually draw more than the current limit threshold, the LDO regulator’s output voltage would drop to a level necessary to supply the current demanded by the load. Under shortcircuit or other over-current operating conditions, the output voltage would drop and the AAT2612’s die temperature would rapidly increase. Once the regulator’s power dissipation capacity has been exceeded and the internal die temperature reaches approximately 140°C, the system thermal protection circuit will become active. The internal thermal protection circuit will actively turn off the LDO regulator output pass device to prevent the possibility of over-temperature damage. The LDO regulator output will remain in a shutdown state until the internal die temperature falls back below the 140°C trip point. The interaction between the short-circuit and thermal protection systems allows the LDO regulator to with- + tSW · fS · IO · VIN + IQ · VIN Where IQ is the step-down converter quiescent current, tsw is the switching time, RDS(ON)P and RDS(ON)N are the high side and low side switching MOSFETs’ on-resistance. VIN, VO and IO are the input voltage, the output voltage and the load current. 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. For all the LDOs, PD(MAX) = (VIN – VOUT) · IOUT(MAX). The total power losses of both step-down converter and LDOs can be expressed as PTOTAL = PBUCK + PD(MAX). Given the total losses, the maximum junction temperature can be derived from the θJA for the package. TJ(MAX) = PTOTAL · θJA + TA Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 13 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Layout Considerations The suggested PCB layout for the AAT2612 is shown in Figures 2(a) - 2(d). The following guidelines are recommended to ensure a proper layout: 1. 2. 3. of L1 to the LX pins as short as possible and route no signal lines under the inductor. Separate the feedback traces or FB pin (Pin 9) from any power trace and connect as close as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. Keep the resistance of the trace from the load returns to PGND 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. Connect the ground pin of the exposed pad to AGND internal plane with multiple vias to decrease the effect of large power ground PGND noise on the analog ground. Connect the ground pins of LDO output capacitors to AGND. 4. Connect the input capacitors (C1, C2, C3) and output capacitors (C5, C6, C7, C8 ) as close as possible to the pins (INL1, INL2, INBK, VOUT) and power ground (AGND, PGND) to minimize any parasitic inductance in the switched current path which generates a large voltage spike during the switching interval. Keep the power traces (GND, LX, and INBK) short, direct, and wide to allow large current flow. Place sufficient multiple-layer pads when needed to change the trace layer. Connect the output capacitor C8 and inductor L1 as close as possible to the device. Keep the connection 5. 6. 7. U1 AAT2612 INL1 2.5V to 5.5V 1 INL1 C1 2.2μF J_IN1 INL2 2.5V to 5.5V 16 INL2 OUTL1 20 LDO1 LDO1 LDO2 LDO2 LDO3 LDO3 L1 BO1 1.2V 600mA C5 1μF C2 2.2μF J_IN2 INBK 2.5V to 5.5V 4 INBK OUTL2 C3 4.7μF C6 1μF 2 ENL1 3 ENL2 ENL2 11 ENL3 ENL3 12 13 17 OUTL3 14 C7 1μF ENL1 ENL2 LX ENL3 AGND AGND FB PGND 5 LX 2.2μH 9 FB 6 PGND R1 C4 59k N/C C8 10μF 0 AGND ENBK N/C EP ENBK 7 ENBK ENL1 15 R2 59k GND Figure 1: AAT2612IDG Evaluation Board Schematic. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs a: Top Side b: Internal Plane 1 (AGND) c: Internal Plane 2 (PGND) d: Bottom Side Figure 2: AAT2612IDG Evaluation Board Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 15 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Component Part Number Description Manufacturer U1 C1, C2 C3 C8 C4, C5, C6, C7 L1 R1, R2 AAT2612 GRM188R71A225KE15 GRM188R60J475KE19 GRM188R60J106ME47 GRM188R71C105KA12 LQH3NPN2R2MM0 RC0603FR-0759KL Step-Down DC/DC Converter with Three High PSRR LDOs Cap Ceramic 2.2μF 0603 X7R 10V 10% Cap Ceramic 4.7μF 0603 X5R 6.3V 10% Cap Ceramic 10μF 0603 X5R 6.3V 10% Cap Ceramic 1μF 0603 X7R 6.3V 10% 2.2μH, 73mΩ, 1.25A, 20% Res, 59kΩ, 1/10W, 1%, 0603, SMD Skyworks Murata Yageo Table 2: AAT2612IDG Evaluation Board Bill of Materials (BOM). Manufacturer Murata Coilcraft Part Number L (μH) Max DCR (mΩ) Saturation Current (A) LQH3NP2R2NG0 LQH3NP3R3NG0 LQH3NP4R7NG0 LPA3015-222MLC LPA3015-332MLC LPA3015-472MLC 2.2 3.3 4.7 2.2 3.3 4.7 140 180 260 110 130 200 1.27 0.85 0.8 1.1 1.1 0.9 Size WxLxH (mm) 3.0x3.0x0.9 3.1x3.1x1.5 Table 3: Surface Mount Inductors. Manufacturer Murata AVX KEMET Part Number Value (μF) Voltage (V) Tolerance Temp. Co. Case GRM188R70J105K GRM188R70J106K GRM188R71A225K GRM188R71A475K 06036C105KAT 06036C106KAT 0603ZC225KAT 0603ZC475KAT C0603C105K9RAC C0603C106K9RAC C0603C225K8RAC C0603C475K8RAC 1 10 2.2 4.7 1 10 2.2 4.7 1 10 2.2 4.7 6.3 6.3 10 10 6.3 6.3 10 10 6.3 6.3 10 10 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% 10% X7R X7R X7R X7R X7R X7R X7R X7R X7R X7R X7R X7R 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 Table 4: Surface Mount Capacitors. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs Ordering Information DC-DC Step-Down (V) LDO1 (V) LDO2 (V) LDO3 (V) Part Marking1 Part Number (Tape and Reel)2 Adj Adj Adj Adj Adj Adj 2.8 2.8 2.8 2.8 2.8 3.0 2.8 1.8 2.8 1.8 1.8 1.8 1.8 1.8 2.8 3.0 3.3 3.3 S2XYY TBD TBD TBD T5XYY T6XYY AAT2612IDG-1-T1 AAT2612IDG-2-T1 AAT2612IDG-3-T1 AAT2612IDG-4-T1 AAT2612IDG-5-T1 AAT2612IDG-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 TQFN33-203 3.00 ± 0.05 1.700 ± 0.050 Index Area 0.400 BSC 1.700 ± 0.050 Detail "A" 0.400 ± 0.050 3.00 ± 0.05 R(5x) Top View (Saw Type) Bottom View 0.210 ± 0.040 0.75 ± 0.05 Detail "A" 0 + 0.10 -0.00 0.203 REF Side View (Saw Type) All dimensions in millimeters. 1. A = assembly house code, Y = year, W = week. 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 202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013 17 DATA SHEET AAT2612 Step-Down DC/DC Converter With Three High PSRR LDOs 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. 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. 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