DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO General Description Features The AAT2749 is a two channel power regulator that operates from 2.3V to 5.5V. The AAT2749 contains a 3.0MHz, 600mA step-down converter and a low input voltage 300mA LDO regulator. • VIN Range: 2.3V to 5.5V • Two Outputs ▪ VOUT_BUCK = 1.8V ▪ VOUT_LDO = 1.0V, 1.2V • Step-Down Converter ▪ Ultra-Small 0603 Inductor (Height 1mm) ▪ Up to 92% Efficiency ▪ 3.0MHz Switching Frequency ▪ MODE Selection Pin to Select Forced PWM or PWM/ LL Operation Mode ▪ Current Limit Protection ▪ Automatic Soft Start • LDO Regulator ▪ VINL Range: 1.62V to VIN ▪ 300mA Output Current ▪ Current Limit Protection • 100μA No Load Quiescent Current • Over-Temperature Protection • -40°C to +85°C Temperature Range The step-down converter can deliver 600mA of load current. The 3.0MHz switching frequency minimizes the size of external components while keeping switching losses low. The AAT2749 step-down converter maintains high efficiency throughout the operating range, which is critical for portable applications. Fixed frequency, low noise operation can be forced by a logic signal on the MODE pin. The AAT2749 also contains a 300mA LDO regulator with input voltage capability as low as 1.62V. The LDO regulator power input can be tied directly to the output of the step-down regulator to increase efficiency. Total quiescent current for the step-down converter and LDO is a low 100μA under no load condition. The AAT2749 is available in a Pb-free, space-saving 9-pin chip scale package (CSP) (200μm bump in 400μm pitch) and is rated over the -40°C to +85°C temperature range. Applications • • • • • Battery-Powered Applications Cellular and Smart Phones Digital Still and Video Cameras PDAs, Palmtops Portable Instruments Typical Application 2.2μH (2.3V - 5.5V) IN_BUCK CIN_BUCK 4.7μF (1.62V - 5.5V) IN_LDO CIN_LDO 1.0μF 1.8V: 600mA LX OUT_BUCK OUT_LDO AAT2749 CBUCK 4.7μF 1.2V: 300mA CLDO 2.2μF CHIP_ENABLE MODE GND Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 1 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Pin Descriptions Pin # Symbol 1 2 3 4 5, 9 6 7 IN_LDO OUT_LDO OUT_BUCK MODE GND CE IN_BUCK 8 LX Description Input supply voltage for the LDO regulator. May be connected to output of step-down regulator. LDO power output. Step-down converter output voltage feedback pin. Mode pin. To force the buck converter into fixed frequency, PWM mode pull the MODE pin high. Ground pin. Chip enable; Logic High enables step-down converter and LDO. Input supply voltage for the step-down converter. Switching node. Connect the inductor to this pin. It is internally connected to the drain of both highand low-side MOSFETs. Pin Configuration LX WLCSP-9 (Top View) GND 9 8 7 IN_BUCK CE 6 5 4 MODE 1 IN_LDO GND 3 2 OUT_LDO OUT_BUCK 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Absolute Maximum Ratings1 TA = 25OC unless otherwise noted. Symbol VIN_BUCK, VIN_LDO VLX VOUT_BUCK VOUT_LDO VCE, VMODE TJ TLEAD Description Value Input Voltage LX to GND OUT_BUCK to GND OUT_LDO to GND CE to GND Maximum Junction Operating temperature Maximum Soldering Temperature (at leads, 10 sec) Units -0.3 to 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -40 to +150 300 V O C Thermal Information3 Symbol JA PD Description Value Thermal Resistance Maximum Power Dissipation 4 284 352 Units C/W mW O 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. Based on long-term current density limitation. 3. Mounted on an FR4 board. 4. Derate 20mW/°C above 25°C. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 3 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Electrical Characteristics1 VIN = 3.6V; CIN = COUT_BUCK = 4.7μF; CIN_LDO = 1.0μF; COUT_LDO = 2.2μF; TA = -40oC to 85oC unless otherwise noted. Typical values are at TA = 25oC. Symbol Description Conditions Step-Down Converter VIN_BUCK Input Voltage VOUT_BUCK_ACC Output Voltage Accuracy VOUT_BUCK_TOL Output Voltage Tolerance VOUTB/VIN Line Regulation ILIM P-Channel Current Limit High Side Switch On Resistance RDS(ON)H RDS(ON)L Low Side Switch On Resistance IOUT_BUCK Out_BUCK Leakage Current TS Start-Up Time FOSC Oscillator Frequency LDO Regulator VIN_LDO Input Voltage VOUT_LDO_ACC Output Voltage Accuracy VOUT_LDO_TOL Output Voltage Tolerance VOUT/VIN Line Regulation ΔVOUT/IOUT Load Regulation IOUT(MAX) Maximum Output Current ILIM Output Current Limit VDO Dropout Voltage System Quiescent Curent IQ ISHDN Logic VCE(L) VCE(H) ICE Thermal TSD THYS 4 System Quiescent Current Shutdown Current Enable Threshold Low Enable Threshold High Input Low Current Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Min Typ 2.3 VIN = 3.6V, 1mA Load, TA = 25°C, PWM Mode 0mA to 600mA load, VIN = 2.5V to 5.5V VIN = 2.5V to 5.5V 591 600 -3.0 Max Units 5.5 V 609 mV 3.0 % %/V mA mΩ mΩ μA μs MHz 0.1 1000 360 200 Vout_BUCK = 1.8V From Enable to Output Regulation TA = 25°C VIN_BUCK = 3.6V, VIN_LDO = 1.8V, 1mA Load, TA = 25°C 0mA to 300mA load; VIN_LDO = 2.5V to 5.5V VINL = 2.5V to 5.5V 0mA to 300mA load 20 50 3.0 1.62 VIN_BUCK V -2 +2 % +3 % %/V % mA A mV -3 0.6 1.2 300 1 300 VIN_BUCK = 3.6V, VIN_LDO = 1.8V, 200mA load VOUT_BUCK = 1.8V, No load on LDO, LL Mode PWM Mode VCE = GND 100 7 1 0.4 VIN = VOUT = 5.5V 1.4 -1.0 1.0 140 15 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 μA mA μA V V μA °C °C DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Typical Characteristics No Load Quiescent Current vs. Input Voltage (EN_BUCK = EN_LDO = VIN; LL Mode) (EN_BUCK = EN_LDO = VIN; PWM Mode) 150 14 130 12 110 90 70 T = 85°C T = 25°C T = -40°C 50 Input Current (μA) Input Current (μA) No Load Quiescent Current vs. Input Voltage 10 8 6 4 T = 85°C T = 25°C T = -40°C 2 0 30 2.3 2.8 3.3 3.8 4.3 4.8 5.3 2.3 Input Voltage (V) 3.8 4.3 4.8 5.3 LDO Turn-Off Response Time (VOUT = 1.2V; VIN = 5V; IOUT = 400mA) (VOUT = 1.2V; VIN = 5V; IOUT = 400mA) 3.5 6 4 3 4 3 2 2.5 2 2.5 0 2 0 2 -2 1.5 -4 1 1.5 -4 1 -6 0.5 -8 0 -10 3.5 -6 0.5 -8 0 -10 -0.5 Time (50μs/div) -0.5 Time (10μs/div) LDO Line Transient Response LDO Line Transient Response (VOUT = 1.2V; VIN = 4V to 5V; IOUT = 400mA) (VOUT = 1.2V; VIN = 4V to 5V; IOUT = 400mA) 1.8 5 1.7 4 1.6 4 1.6 3 1.5 2 1.4 1 1.3 0 1.2 -1 1.1 -2 1 Enable Voltage (top) (1V/div) 6 1.7 3 1.5 2 1.4 1 1.3 0 1.2 -1 1.1 -2 1 Output Voltage (bottom) (100mV/div) 1.8 5 Output Voltage (bottom) (100mV/div) 6 Time (50μs/div) Output Voltage (bottom) (500mV/div) -2 Enable Voltage (top) (2V/div) 6 Output Voltage (bottom) (500mV/div) Enable Voltage (top) (2V/div) 3.3 Input Voltage (V) LDO Turn-On Response Time Enable Voltage (top) (1V/div) 2.8 Time (50μs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 5 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Typical Characteristics Step-Down Converter Switching Frequency vs. Input Voltage Step-Down Converter Switching Frequency vs. Temperature Switching Frequency (MHz) Frequency Variation (%) (VOUT = 1.8V; IOUT = 100mA) 3 2 1 0 -1 -2 -3 -4 -5 2.3 2.8 3.3 3.8 4.3 4.8 (VOUT = 1.8V; IOUT = 100mA) 3.02 3 2.98 2.96 2.94 2.92 2.9 2.88 2.86 2.84 2.82 5.3 -40 -15 10 Input Voltage (V) Step-Down Converter Efficiency vs. Load 90 0.8 Efficiency (%) 80 70 60 50 40 VIN = 5.5V VIN = 4.2V VIN = 3.3V VIN = 2.7V VIN = 2.3V 30 20 10 0 100 Output Error (%) 1 10 VIN = 5.5V VIN = 4.2V VIN = 3.3V VIN = 2.7V VIN = 2.3V 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 1000 0.1 1 Output Current (mA) 90 0.8 80 0.6 70 60 50 40 VIN = 5.5V VIN = 4.2V VIN = 3.3V VIN = 2.7V VIN = 2.3V 30 20 10 6 100 1000 Output Error (%) Efficiency (%) 1 Output Current (mA) 1000 (VOUT = 1.8V; L = 2.2μH; PWM Mode) 100 10 100 Step-Down Converter DC Regulation (VOUT = 1.8V; L = 2.2μH; PWM Mode) 1 10 Output Current (mA) Step-Down Converter Efficiency vs. Load 0 0.1 85 (VOUT = 1.8V; L = 2.2μH; LL Mode) 100 1 60 Step-Down Converter DC Regulation (VOUT = 1.8V; L = 2.2μH; LL Mode) 0.1 35 Temperature (°C) VIN = 5.5V VIN = 4.2V VIN = 3.3V VIN = 2.7V VIN = 2.3V 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0.1 1 10 100 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 1000 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Step-Down Converter Output Ripple Step-Down Converter Output Ripple (VOUT = 1.8V; VIN = 5V; IOUT = 1mA) (VOUT = 1.8V; VIN = 5V; IOUT = 600mA) 1.84 0.5 1.82 1.8 0.4 1.78 0.3 1.76 0.2 1.74 0.1 1.72 0 1.7 -0.1 1.68 -0.2 Output Voltage (top) (20mV/div) 0.6 1.82 3.5 3 1.8 2.5 1.78 2 1.76 1.5 1.74 1 1.72 0.5 0 1.7 -0.5 1.68 Time (20μs/div) Time (200ns/div) Step-Down Converter N-Channel RDS(ON) vs. Input Voltage 700 400 600 350 500 300 RDS(ON)L (mΩ) RDS(ON)H (mΩ) Step-Down Converter P-Channel RDS(ON) vs. Input Voltage 400 300 T = 120°C T = 100°C T = 85°C T = 25°C 200 100 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 250 200 150 50 0 2.7 5.5 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Step-Down Converter Soft Start Step-Down Converter Line Transient Response (VOUT = 1.8V; VIN = 5V; IOUT = 600mA) (VOUT = 1.2V; VIN = 4V to 5V; IOUT = 600mA) 6 2.4 4 3 5 2.3 2 2.5 4 2.2 0 2 3 2.1 -2 1.5 -4 1 -6 0.5 -8 0 -0.5 Time (50μs/div) Enable Voltage (top) (1V/div) 3.5 2 2 1 1.9 0 1.8 -1 1.7 -2 1.6 Output Voltage (bottom) (100mV/div) 6 Inductor Current (bottom) (500mV/div) Enable Voltage (top) (2V/div) Output Voltage (middle) (2V/div) T = 120°C T = 100°C T = 85°C T = 25°C 100 Input Voltage (V) -10 Inductor Current (bottom) (500mA/div) 1.84 Inductor Current (bottom) (100mA/div) Output Voltage (top) (20mV/div) Typical Characteristics Time (200μs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 7 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Typical Characteristics Step-Down Converter Load Transient Response Step-Down Converter Line Regulation (VOUT = 1.8V; VIN = 5V; IOUT = 1mA to 600mA; CFF = 0pF) (VOUT = 1.8V; L = 2.2μH) 1.9 3 1.8 2.5 1.7 2 1.6 1.5 1.5 1 1.4 0.5 1.3 0 1.2 -0.5 1 IOUT = 600mA IOUT = 300mA IOUT = 100mA IOUT = 10mA IOUT = 0.1mA 0.8 0.6 Accuracy (%) Output Voltage (top) (100mV/div) 3.5 Output Current (middle) Inductor Current (bottom) (500mA/div) 2 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 2.3 2.7 3.1 3.5 3.9 4.3 4.7 Input Voltage (V) Time (100μs/div) LDO Power Supply Rejection Ratio, PSRR (IOUT2 = 1.8V; BW = 100Hz to 300Hz) 100 Magnitude (dB) 90 80 70 60 50 40 30 20 10 0 102 103 104 105 Frequency (Hz) 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 5.1 5.5 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Functional Block Diagram IN_BUCK VP EN REF DC-DC Converter LX CE Control GND MODE OUT_BUCK VP REF EN IN_LDO LDO OUT_LDO GND Functional Description The AAT2749 is a two channel power converter that operates from a 2.3V to 5.5V power supply. The AAT2749 step-down converters can deliver up to 600mA while the LDO regulator can deliver up to 300mA. The typical no load quiescent current is 100μA for both the step-down converter and LDO regulator. Step-Down Regulator The AAT2749 contains a high performance 600mA, 3.0MHz monolithic step-down converter. Typically, a 2.2μH inductor and a 4.7μF ceramic capacitor are recommended (see table of values). At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the RDS(ON) drop of the P-channel high-side MOSFET. The input voltage range is 2.3V to 5.5V. The converter efficiency has been optimized for all load conditions, ranging from no load to 600mA. The internal error amplifier and compensation provides excellent transient response, load, and line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. Mode Pin To ensure high efficiency across the load range, the AAT2749 will automatically shift out of PWM mode in light load conditions. This mode of operation maintains high efficiency under light load conditions (typically <150mA). The MODE pin allows optional fixed frequency PWM mode for improved noise performance. This maintains constant frequency and low output ripple across all load conditions. Control Loop The AAT2749 step down converter 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 9 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO 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 trans-conductance voltage error amplifier output. Soft Start / Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When disabled, the AAT2749 is in a low-power, non-switching state. The total input current during shutdown is less than 1μA. Current Limit For overload conditions, the peak input current is limited. To minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. Switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. Applications Information Step-Down Converter 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 channel 1 is 0.75A/μs. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 2.2μH inductor. m= L= 0.75 · VO 0.75 · 1.8V A = = 0.75 L 1.8μH μs 0.75 · VO 0.75 · 1.8V = = 1.8μH m A 0.75 μs The 300mA LDO regulator is stable with a 2.2μF ceramic output capacitor. The LDO regulator has a current limit to protect against short circuit conditions. The inductor should be set equal to the output voltage numeric value in micro henries (μH). This guarantees that there is sufficient internal slope compensation. 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. Over-Temperature Protection Step-Down Converter Input Capacitor Thermal protection completely disables the converters when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. Select a 2.2μF to 4.7μF 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 CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. LDO Regulator The AAT2749 includes a low-dropout (LDO) linear regulator. The LDO regulator operates from 1.62V to 5.5V; however, VIN_LDO cannot exceed the input voltage to the step-down regulator (VIN_BUCK). The linear regulator output voltage is set by internal resistive voltage dividers. The LDO regulator consumes about 50μA of quiescent current. Chip Enable Pin (CE) Logic High at CE pin enables step-down converter and LDO. CIN = V VO · 1- O VIN VIN VPP - ESR · FS IO VO V · 1- O VIN VIN 10 = 1 for VIN = 2 · VO 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO 1 CIN(MIN) = VPP - ESR · 4 · FS IO Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6μF. The maximum input capacitor RMS current is: VO V · 1- O VIN VIN IRMS = IO · = D · (1 - D) = 0.52 = 1 2 For VIN = 2 · VO IRMS(MAX) = VO · 1- 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 capacitor. This dampens the high Q network and stabilizes the system. Step-Down Converter Output Capacitor The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current. VO V · 1- O VIN VIN 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. IO 2 VO VIN The term VIN appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2749. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C1) can be seen in the evaluation board layout in the Layout section of this datasheet. 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 output capacitor limits the output ripple and provides holdup during large load transitions. A 2.2μF to 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 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. IRMS(MAX) = 1 VOUT · (VIN(MAX) - VOUT) L · FS · VIN(MAX) 2· 3 · 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 11 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO The maximum output capacitor RMS ripple current is given by: IRMS(MAX) = 1 VOUT · (VIN(MAX) - VOUT) L · FS · VIN(MAX) 2· 3 · Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. LDO Input Capacitor Typically, a 1μF or larger capacitor is recommended for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation. However, if the AAT2749 is physically located more than three centimeters from an input power source, a CIN capacitor will be needed for stable operation. CIN should be located as close to the device VIN pin as possible. CIN values greater than 1μF will offer superior input line transient response and will assist in maximizing the highest possible power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN. There is no specific capacitor ESR requirement for CIN. However, for 300mA LDO regulator output operation, 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. LDO Output Capacitor For proper load voltage regulation and operational stability, a capacitor is required between the VOUT and GND pins. The COUT capacitor connection to the LDO regulator ground pin should be as close as possible for maximum device performance. The AAT2749 LDO has been specifically designed to function with very low ESR ceramic capacitors. For best performance, ceramic capacitors are recommended. Typical output capacitor values for maximum output current conditions range from 1μF to 10μF. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of the channel 2 should use 2.2μF or greater for COUT. If desired, COUT may be increased without limit. In low output current applications where output load is less than 10mA, the minimum value for COUT can be as low as 0.47μF. 12 LDO Enable Function The AAT2749 features an LDO regulator enable/disable function. This pin (EN) is active high and is 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. When the LDO regulator is in shutdown mode, an internal 1.5kΩ resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulator is disabled. The internal 1.5kΩ has no adverse effect on device turn-on time. LDO Short-Circuit Protection The AAT2749 LDO contains an internal short-circuit protection circuit that will trigger when the output load current exceeds the internal threshold limit. Under shortcircuit conditions, the output of the LDO regulator will be current limited until the short-circuit condition is removed from the output or LDO regulator package power dissipation exceeds the device thermal limit. LDO Thermal Protection The AAT2749 LDO has an internal thermal protection circuit which will turn on when the device die temperature exceeds 150°C. 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 150°C trip point. The combination and interaction between the short circuit and thermal protection systems allows the LDO regulator to withstand indefinite short-circuit conditions without sustaining permanent damage. Thermal Calculations There are three types of losses associated with the AAT2749 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 synchro- Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO nous step-down converter and LDO losses is given by: PTOTAL = IOUT12 · (RDS()ON)H · VOUT1 + RDS(ON)L · [VIN1 -VOUT1]) VIN1 + (tSW · FS · IOUT1 + IQ1) · VIN1 + (VIN2 - VOUT2 ) · IOUT2 IQ1 is the step-down converter and LDO quiescent current respectively. The term tSW is used to estimate the full load step-down converter switching losses. 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 θJA for the CSP-9 package, which is 284°C/W. Layout Considerations The suggested PCB layout for the AAT2749 is shown in Figures 2 and 3. The following guidelines should be used to help ensure a proper layout. 1. 2. 3. 4. TJ(MAX) = PTOTAL · θJA + TA 5. The bypass capacitors (C1, C2 and C4) should connect as closely as possible to input and output pin (Pins 1, 2, and 7) and PGND (Pin 9). C3 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. The feedback trace or OUT-BUCK pin (Pin 3) should be separated from any power trace and connected as closely as possible to the load point. Sensing along a high current load trace will degrade DC load regulation. The resistance of the trace from the load return to PGND (Pin 9) 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. The pad on the PCB for the CSP-9 package should use NSMD (non-solder mask defined) configuration due to its tighter control on the copper etch process. A pad thickness of less than 1 oz. is recommended to achieve higher stand-off. A high-density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 13 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO JP2 1 IN_LDO OUT_LDO OUT-LDO 2 C2 1μF VIN-BUCK 7 IN_BUCK 2.3V-5.5V LX 8 2.2μH AAT2749 EN 6 CE 4 MODE L1 1.2V/300mA C4 2.2μF OUT_BUCK 3 PGND 9 OUT-BUCK 1.8V/600mA C3 4.7μF C1 4.7μF MODE U1 C1, C3 C2 C3 L1 U1 5 AAT2749 Skyworks, 300mA LDO and 600mA Buck Converter, CSP-9 Cap, MLC, 4.7μF/10V, 0805 Cap, MLC, 1μF/10V, 0805 Cap, MLC, 2.2μF/6.3V, 0805 LQM2MPN2R2NGO, Murata, 2.2μH, ISAT = 1.2A, DCR = 0.11Ω Figure 2: AAT2749-IUR Evaluation Board Schematic and Bill of Materials (BOM). Figure 3: AAT2749-IUR Evaluation Board Top Layer. 14 Figure 4: AAT2749-IUR Evaluation Board Bottom Layer. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO AAT2749 Design Example Specifications VO1 = 1.8V @ 600mA, Pulsed Load ILOAD = 600mA VO2 = 1.2V @ 300mA VIN1 = 5V FS = 3MHz TAMB = 85°C in CSP-9 Package Step-Down Converter Output Inductor For Murata chip inductor LQM2MPN2R2NG0, 2.2μH, DCR = 0.11Ω. ΔI = VOUT1 V 1.8V 1.8V · 1 - OUT1 = · 1= 174mA L · FS VIN1 2.2μH · 3MHz 5V IPK1 = IOUT1 + ΔI = 600mA + 87mA = 687mA 2 PL1 = IOUT12 · DCR = 600mA2 · 111mΩ = 40mW Step-Down Converter Output Capacitor VDROOP = 0.18V (10% Output Voltage) COUT = 3 · ΔILOAD 3 · 600mA = = 3μF; use 4.7μF 0.18V · 3MHz VDROOP · FS IRMS(MAX) = VOUT1 · (VIN(MAX) - VOUT1) 1 1.8V · (5.5V - 2.3V) · = 46mArms = L · FS · VIN1(MAX) 2 · 3 2.2μH · 3MHz · 5.5V 2· 3 1 · PRMS = ESR · IRMS2 = 5mΩ · (46mA)2 = 11μW Step-Down Converter Input Capacitor Input Ripple VPP = 10mV CIN1 = IRMS = 1 VPP - ESR · 4 · FS IOUT1 = 1 10mV - 5mΩ · 4 · 3MHz 600mA = 7μF; use 4.7μF IOUT1 = 300mA 2 P = ESR · (IRMS2) = 5mΩ · (300mA)2 = 0.31mW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 15 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO AAT2749 Losses All values assume 25°C ambient temperature and thermal resistance of 284°C/W in the CSP-9 package. PTOTAL = IOUT12 · (RDS(ON)H · VOUT1 + RDS(ON)L · [VIN1 - VOUT1]) VIN1 + (tSW · FS · IOUT1 + IQ1) · VIN + (VIN2 - VOUT2) · IOUT2 = 600mA2 · (360mΩ · 1.8V + 200mΩ · [5V - 1.8V]) 5V + (5ns · 3MHz · 600mA + 100μA) · 5V + (1.8V - 1.2V) · 300mA PTOTAL = 318mW TJ(MAX) = TAMB + ΘJA · PLOSS = 25°C + (284°C/W) · 318mW = 115°C 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2749 3.0MHz Step-Down Converter and Low-VIN LDO Ordering Information Output Voltages VOUT_BUCK VOUT_LDO Package Part Marking Part Number (Tape and Reel) 1.8V 1.8V 1.2V 1.0V WLCSP-9 WLCSP-9 6QXY 7UXY AAT2749IUR-IE-T1 AAT2749IUR-ID-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 WLCSP-9 0.300 0.100 0.100 Line 2 Top View 0.500 ± 0.050 0.205 ± 0.025 0.300 1.360 ± 0.035 0.2 (Ref.) Pin 1 Indication 0.400 BSC 0.800 1.350 ± 0.035 0.170 ± 0.025 0.330 ± 0.025 Line 1 Bottom View Side View Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes. No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale. THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or environmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper use or sale. Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters. Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202037A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 17