DATA SHEET AAT1120 500mA Step-Down Converter General Description Features The AAT1120 SwitchReg is a 1.5MHz step-down converter with an input voltage range of 2.7V to 5.5V and output as low as 0.6V. Its low supply current, small size, and high switching frequency make the AAT1120 the ideal choice for portable applications. • • • • • • • • • • • • • The AAT1120 delivers up to 500mA of load current, while maintaining a low 30μA no load quiescent current. The 1.5MHz switching frequency minimizes the size of external components, while keeping switching losses low. The AAT1120 feedback and control delivers excellent load regulation and transient response with a small output inductor and capacitor. The AAT1120 is available in a Pb-free, 8-pin, 2x2mm STDFN package and is rated over the -40°C to +85°C temperature range. VIN Range: 2.7V to 5.5V VOUT Range: 0.6V to VIN Up to 500mA Output Current Up to 96% Efficiency 30μA Typical Quiescent Current 1.5MHz Switching Frequency Soft-Start Control Over-Temperature and Current Limit Protection 100% Duty Cycle Low-Dropout Operation <1μA Shutdown Current Small External Components Ultra-Small STDFN22-8 Package Temperature Range: -40°C to +85°C Applications • • • • • • • Bluetooth® Headsets Cellular Phones Digital Cameras Handheld Instruments Micro Hard Disk Drive Portable Music Players USB Devices Typical Application VIN VO = 1.8V AAT1120 VP LX VIN C1 4.7µF EN GND FB PGND 500mA L1 3.0μH R1 118kΩ R2 59kΩ C2 4.7µF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 1 DATA SHEET AAT1120 500mA Step-Down Converter Pin Descriptions Pin # Symbol 1 2 3 4 5 6 VP VIN GND FB N/C EN 7 LX 8 PGND EP Function Input power pin; connected to the source of the P-channel MOSFET. Connect to the input capacitor. Input bias voltage for the converter. Non-power signal ground pin. Feedback input pin. Connect this pin to an external resistive divider for adjustable output. No connect. Enable pin. A logic high enables normal operation. A logic low shuts down the converter. Switching node. Connect the inductor to this pin. It is connected internally to the drain of both high- and low-side MOSFETs. Input power return pin; connected to the source of the N-channel MOSFET. Connect to the output and input capacitor return. Exposed paddle (bottom): connect to ground directly beneath the package. Pin Configuration STDFN22-8 (Top View) VP VIN GND FB 2 1 8 2 7 3 6 4 5 PGND LX EN N/C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VOUT VEN TJ TLEAD Description Input Voltage and Bias Power to GND LX to GND FB to GND EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -40 to 150 300 V V V V °C °C Value Units 2 50 W °C/W Thermal Information Symbol PD JA Description Maximum Power Dissipation (STDFN22-8) Thermal Resistance2 (STDFN22-8) 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 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 3 DATA SHEET AAT1120 500mA Step-Down Converter Electrical Characteristics1 VIN = 3.6V, TA = -40°C to +85°C, unless otherwise noted; typical values are TA = 25°C. Symbol Description VIN Input Voltage VUVLO VOUT VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L ILXLEAK VLinereg/ VIN VFB IFB FOSC TS TSD THYS VEN(L) VEN(H) IEN UVLO Threshold Output Voltage Tolerance2 Output Voltage Range Quiescent Current Shutdown Current P-Channel Current Limit High-Side Switch On Resistance Low-Side Switch On Resistance LX Leakage Current Conditions Min Typ 2.7 VIN Rising Hysteresis VIN Falling IOUT = 0 to 500mA, VIN = 2.7V to 5.5V Max Units 5.5 2.6 V V mV V % V μA μA mA μA 250 2.0 -3.0 0.6 No Load EN = GND 3.0 VIN 30 1.0 600 0.59 0.42 VIN = 5.5V, VLX = 0 to VIN Line Regulation VIN = 2.7V to 5.5V Feedback Threshold Voltage Accuracy FB Leakage Current Oscillator Frequency Startup Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current VIN = 3.6V VOUT = 1.0V 1.0 0.2 0.591 0.600 %/V 0.609 0.2 1.5 100 140 15 From Enable to Output Regulation 0.6 VIN = VEN = 5.5V 1.4 -1.0 1.0 V μA MHz μs °C °C V V μA 1. The AAT1120 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Output voltage tolerance is independent of feedback resistor network accuracy. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter Typical Characteristics Efficiency vs. Load Load Regulation (VOUT = 3.0V; L = 4.7µH) (VOUT = 3.0V; L = 4.7µH) 100 1.0 Efficiency (%) 90 Load Regulation (%) VIN = 3.6V VIN = 4.2V 80 VIN = 5.0V 70 60 50 0.8 0.6 0.4 0.0 -0.2 VIN = 4.2V -0.4 -0.6 -0.8 -1.0 40 0.1 1 10 100 0.1 1000 1 Output Current (mA) Efficiency vs. Load Load Regulation (VOUT = 1.8V; L = 3.3µH) (VOUT = 1.8V; L = 3.3µH) VIN = 3.6V VIN = 2.7V Load Regulation (%) Efficiency (%) 100 1000 2.0 90 80 VIN = 4.2V 70 60 50 40 0.1 1 10 100 1.5 1.0 VIN = 2.7V 0.0 -0.5 -1.0 VIN = 4.2V -1.5 -2.0 0.1 1000 VIN = 3.6V 0.5 1 Output Current (mA) 10 100 1000 100 1000 Output Current (mA) Efficiency vs. Load Load Regulation (VOUT = 1.2V; L = 1.5µH) (VOUT = 1.2V; L = 1.5µH) 2 90 Load Regulation (%) 100 Efficiency (%) 10 Output Current (mA) 100 80 VIN = 5.0V VIN = 3.6V 0.2 VIN = 2.7V VIN = 3.6V 70 VIN = 4.2V 60 50 40 0.1 VIN = 5.0V 1 0.5 10 Output Current (mA) 100 1000 VIN = 4.2V VIN = 3.6V 0 -0.5 -1 VIN = 5.0V -1.5 -2 1 VIN = 2.7V 1.5 0.1 1 10 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 5 DATA SHEET AAT1120 500mA Step-Down Converter Typical Characteristics Soft Start Line Regulation (VIN = 3.6V; VOUT = 1.8V; 500mA) (VOUT = 1.8V) 4.0 3.0 1.6 VO VEN 1.2 2.0 1.0 1.0 0.8 0.0 0.6 -1.0 0.4 -2.0 0.2 I LX -3.0 0.20 1.4 0.0 -4.0 Accuracy (%) 5.0 Inductor Current (bottom) (A) Enable and Output Voltage (top) (V) 0.30 IOUT = 10mA 0.00 IOUT = 250mA -0.10 IOUT = 0mA -0.20 -0.2 -5.0 IOUT = 50mA 0.10 IOUT = 150mA -0.30 2.5 -0.4 3.0 3.5 Time (100µs/div) 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) Output Voltage Error vs. Temperature Switching Frequency Variation vs. Temperature (VIN = 3.6V; VOUT = 1.8V; IOUT = 500mA) (VIN = 3.6V; VOUT = 1.8V) 3.0 2.0 8.0 Variation (%) Output Error (%) 10.0 1.0 0.0 -1.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -2.0 -8.0 -3.0 -40 -10.0 -20 0 20 40 60 80 100 -40 -20 0 Temperature (°°C) 80 100 50 VOUT = 1.8V 1.0 Supply Current (µA) Frequency Variation (%) 60 No Load Quiescent Current vs. Input Voltage 2.0 0.0 -1.0 -2.0 VOUT = 3.0V -3.0 2.7 3.1 3.5 3.9 4.3 Input Voltage (V) 6 40 Temperature (°°C) Frequency Variation vs. Input Voltage -4.0 20 4.7 5.1 5.5 45 40 35 85°C 30 25°C 25 -40°C 20 15 10 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 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 5.1 5.5 DATA SHEET AAT1120 500mA Step-Down Converter Typical Characteristics P-Channel RDS(ON) vs. Input Voltage N-Channel RDS(ON) vs. Input Voltage 750 1000 120°C 700 100°C 700 600 25°C 500 85°C 550 500 450 25°C 350 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 300 2.5 Input Voltage (V) 3.5 4.0 4.5 5.0 5.5 Load Transient Response Load Transient Response (1mA to 500mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7µF; CFF = 100pF) (350mA to 500mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7µF; CFF = 100pF) VO 1.6 1.4 IO 1.2 1.0 ILX 0.6 Time (25µs/div) 2.0 1.9 Output Voltage (top) (V) 1.8 6.0 1.8 VO 1.7 IO 1.6 1.5 1.4 1.3 1.2 1.1 ILX 1.0 Load and Inductor Current (bottom) (200mA/div) Load and Inductor Current (bottom) (400mA/div) 2.0 0.8 3.0 Input Voltage (V) 2.2 Output Voltage (top) (V) 100°C 600 400 400 300 120°C 650 85°C 800 RDS(ON)L (mΩ Ω) RDS(ON)H (mΩ Ω) 900 Time (25µs/div) Line Response (VOUT = 1.8V @ 500mA) 7.0 1.90 VO 6.5 1.80 6.0 1.75 5.5 5.0 1.70 1.65 VIN 4.5 1.60 4.0 1.55 3.5 1.50 3.0 Input Voltage (bottom) (V) Output Voltage (top) (V) 1.85 Time (25µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 7 DATA SHEET AAT1120 500mA Step-Down Converter Typical Characteristics Output Ripple Output Ripple (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA) (VIN = 3.6V; VOUT = 1.8V; IOUT = 500mA) VO -20 0.04 0.03 0.02 0.01 IL 0.00 -0.01 Time (2µs/div) 8 20 1.0 0.9 VO 0 0.8 -20 0.7 -40 0.6 ILX -60 0.5 -80 0.4 -100 0.3 -120 0.2 Time (200ns/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 Inductor Current (bottom) (A) 0 40 Output Voltage (AC Coupled) (top) (mV) 20 Inductor Current (bottom) (A) Output Voltage (AC Coupled) (top) (mV) 40 DATA SHEET AAT1120 500mA Step-Down Converter Functional Block Diagram FB VP VIN Err Amp DH Voltage Reference LX Logic EN INPUT DL PGND GND Functional Description The AAT1120 is a high performance 500mA, 1.5MHz monolithic step-down converter designed to operate with an input voltage range of 2.7V to 5.5V. The converter operates at 1.5MHz, which minimizes the size of external components. Typical values are 3.3μH for the output inductor and 4.7μF for the ceramic output capacitor. The device is designed to operate with an output voltage as low as 0.6V. Power devices are sized for 500mA current capability while maintaining over 90% efficiency at full load. Light load efficiency is maintained at greater than 80% down to 1mA of load current. 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 highside MOSFET. A high-DC gain error amplifier with internal compensation controls the output. It provides excellent transient response and load/line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 9 DATA SHEET AAT1120 500mA Step-Down Converter Control Loop The AAT1120 is a 500mA current mode step-down converter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as shortcircuit 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 switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. The error amplifier reference is fixed at 0.6V. Soft Start/Enable Soft start increases the inductor current limit point in discrete steps when the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT1120 into a low-power, non-switching state. The total input current during shutdown is less than 1μA. Applications Information 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 AAT1120 is 0.45A/μsec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 3.0μH inductor. m= 0.75 ⋅ VO 0.75 ⋅ 1.8V A = = 0.45 L 3.0µH µsec This is the internal slope compensation for the AAT1120. When externally programming to 3.0V, the calculated inductance is 5.0μH. L= 0.75 ⋅ VO = m = 1.67 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. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN power. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuits prior to activation. 10 µsec 0.75 ⋅ VO ≈ 1.67 A ⋅ VO A 0.45A µsec µsec ⋅ 3.0V = 5.0µH A In this case, a standard 4.7μH value is selected. For most designs, the AAT1120 operates with an inductor value of 1μH to 4.7μH. Table 1 displays inductor values for the AAT1120 with different output voltage options. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter Output Voltage (V) L1 (μH) 1.0 1.2 1.5 1.8 2.5 3.0 3.3 1.5 2.2 2.7 3.0 3.9 4.7 5.6 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 ⎠ 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 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 ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 1 ⎛ 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: IRMS = IO · VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ 0.52 = 1 2 for VIN = 2 · VO Table 1: Inductor Values. The 3.0μH CDRH2D09 series inductor selected from Sumida has a 150m DCR and a 470mA DC current rating. At full load, the inductor DC loss is 9.375mW which gives a 2.08% loss in efficiency for a 250mA, 1.8V output. D · (1 - D) = IRMS(MAX) = VO IO 2 ⎛ V ⎞ · 1- O The term VIN ⎝ 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 AAT1120. 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 Figure 2. A laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 11 DATA SHEET AAT1120 500mA Step-Down Converter 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. For enhanced transient response and low temperature operation application, a 10μF (X5R, X7R) ceramic capacitor is recommended to stabilize extreme pulsed load conditions. 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. 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: IRMS(MAX) = 12 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. Adjustable Output Resistor Selection Resistors R1 and R2 of Figure 1 program the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the suggested value for R2 is 59k. Decreased resistor values are necessary to maintain noise immunity on the FB pin, resulting in increased quiescent current. Table 2 summarizes the resistor values for various output voltages. ⎛ VOUT ⎞ ⎛ 3.3V ⎞ R1 = V -1 · R2 = 0.6V - 1 · 59kΩ = 267kΩ ⎝ REF ⎠ ⎝ ⎠ With enhanced transient response for extreme pulsed load application, an external feed-forward capacitor, (C3 in Figure 1), can be added. VOUT (V) R2 = 59k R1 (k) R2 = 221k R1 (k) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75 113 150 187 221 261 301 332 442 464 523 715 1000 Table 2: Adjustable Resistor Values For Step-Down Converter. · Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter Thermal Calculations Layout There are three types of losses associated with the AAT1120 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the losses is given by: The suggested PCB layout for the AAT1120 in an STDFN22-8 package is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. PTOTAL = 1. 2. IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) VIN 3. + (tsw · FS · IO + IQ) · VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: 4. PTOTAL = IO2 · RDS(ON)H + 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 STDFN22-8 package which is 50°C/W. 5. The input capacitor (C1) should connect as closely as possible to VP (Pin 1), PGND (Pin 8), and GND (Pin 3) C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin (Pin 7) should be as short as possible. Do not make the node small by using narrow trace. The trace should be kept wide, direct and short. The feedback pin (Pin 4) 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. Feedback resistors should be placed as closely as possible to the FB pin (Pin 4) to minimize the length of the high impedance feedback trace. If possible, they should also be placed away from the LX (switching node) and inductor to improve noise immunity. The resistance of the trace from the load return to PGND (Pin 8) and GND (Pin 3) 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. A high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor. TJ(MAX) = PTOTAL · ΘJA + TAMB Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 13 DATA SHEET AAT1120 500mA Step-Down Converter U1 1 VIN 2 3 4 C1 4.7μF VP PGND VIN LX GND EN FB N/C 8 7 LX L1 +VOUT 6 5 C2 4.7μF AAT1120 R1 Adj. C3 (optional) 100pF R2 59kΩ GND GND Figure 1: AAT1120 Schematic. Figure 2: AAT1120 Evaluation Board Top Side Layout. Figure 3: Exploded View of AAT1120 Evaluation Board Top Side Layout. Figure 4: AAT1120 Evaluation Board Bottom Side Layout. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 250mA, Pulsed Load ILOAD = 200mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 1.5MHz TAMB = 85°C 1.8V Output Inductor L1 = 1.67 µsec µsec ⋅ VO2 = 1.67 ⋅ 1.8V = 3µH (use 3.0μH; see Table 1) A A For Sumida inductor CDRH2D09-3R0, 3.0μH, DCR = 150m. ΔIL1 = ⎛ VO V ⎞ 1.8V 1.8V⎞ ⎛ ⋅ 1- O = ⋅ 1= 228mA L1 ⋅ FS ⎝ VIN⎠ 3.0µH ⋅ 1.5MHz ⎝ 4.2V⎠ IPKL1 = IO + ΔIL1 = 250mA + 114mA = 364mA 2 PL1 = IO2 ⋅ DCR = 250mA2 ⋅ 150mΩ = 9.375mW 1.8V Output Capacitor VDROOP = 0.1V COUT = 3 · ΔILOAD 3 · 0.2A = = 4µF (use 4.7µF) VDROOP · FS 0.1V · 1.5MHz IRMS = (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 66mArms = L1 · FS · VIN(MAX) 2 · 3 3.0µH · 1.5MHz · 4.2V 2· 3 1 · Pesr = esr · IRMS2 = 5mΩ · (66mA)2 = 21.8µW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 15 DATA SHEET AAT1120 500mA Step-Down Converter Input Capacitor Input Ripple VPP = 25mV CIN = IRMS = ⎛ VPP ⎝ IO 1 1 = = 1.38µF (use 4.7µF) ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 1.5MHz - ESR · 4 · FS ⎠ ⎝ 0.2A ⎠ IO = 0.1Arms 2 P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW AAT1120 Losses PTOTAL = IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO]) VIN + (tsw · FS · IO + IQ) · VIN = 0.22 · (0.59Ω · 1.8V + 0.42Ω · [4.2V - 1.8V]) 4.2V + (5ns · 1.5MHz · 0.2A + 30µA) · 4.2V = 26.14mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86.3°C 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter Output Voltage VOUT (V) R2 = 59k R1 (k) R2 = 221k1 R1 (k) L1 (μH) 0.62 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 — 75 113 150 187 221 261 301 332 442 464 523 715 1000 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2.2 2.7 3.0/3.3 3.0/3.3 3.0/3.3 3.9/4.2 5.6 Table 3: Evaluation Board Component Values. Manufacturer Part Number Inductance (μH) Max DC Current (mA) DCR (m) Size (mm) LxWxH Type Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden FDK FDK FDK FDK CDRH2D14-1R5 CDRH2D14-2R2 CDRH2D14-2R7 CDRH2D14-3R3 CDRH2D14-3R9 CDRH2D14-4R7 CDRH2D14-5R6 CDRH2D11-1R5 CDRH2D11-2R2 CDRH2D11-3R3 CDRH2D11-4R7 NR3010 NR3010 NR3010 NR3010 MIPWT3226D-1R5 MIPWT3226D-2R2 MIPWT3226D-3R0 MIPWT3226D-4R2 1.5 2.2 2.7 3.3 3.9 4.7 5.6 1.5 2.2 3.3 4.7 1.5 2.2 3.3 4.7 1.5 2.2 3 4.2 1800 1500 1350 1200 1100 1000 950 900 780 600 500 1200 1100 870 750 1200 1100 1000 900 50 75 85 100 110 135 150 54 78 98 135 80 95 140 190 90 100 120 140 3.0x3.0x1.55 3.0x3.0x1.55 3.0x3.0x1.55 3.0x3.0x1.55 3.0x3.0x1.55 3.0x3.0x1.55 3.0x3.0x1.55 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.2x2.6x0.8 3.2x2.6x0.8 3.2x2.6x0.8 3.2x2.6x0.8 Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Chip shielded Chip shielded Chip shielded Chip shielded Table 4: Suggested Inductors and Suppliers. Manufacturer Part Number Value (μF) Voltage Rating Temp. Co. Case Size Murata Murata GRM118R60J475KE19B GRM188R60J106ME47D 4.7 10 6.3 6.3 X5R X5R 0603 0603 Table 5: Surface Mount Capacitors. 1. For reduced quiescent current, R2 = 221k. 2. R2 is opened, R1 is shorted. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 17 DATA SHEET AAT1120 500mA Step-Down Converter Ordering Information Output Voltage Package Marking1 Part Number (Tape and Reel)2 0.6V STDFN22-8 VQXYY AAT1120IES-0.6-T1 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Package Information3 STDFN22-8 Index Area (D/2 x E/2) 0.80 ± 0.05 Detail "A" 1.45 ± 0.05 2.00 ± 0.05 2.00 ± 0.05 Top View Bottom View Side View Pin 1 Indicator (optional) 0.45 ± 0.05 0.23 ± 0.05 0.05 ± 0.05 0.15 ± 0.025 0.55 ± 0.05 0.35 ± 0.05 Detail "A" All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on all part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1120 500mA Step-Down Converter 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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