PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package General Description Features The AAT2113A SwitchReg™ is a 1.5A step-down converter with a typical input voltage of 3.3V and a fixed output voltage of 1.2V or an adjustable output. The 3MHz switching frequency enables the use of small external components. The ultra-small 2mm x 2mm footprint and high efficiency make the AAT2113A an ideal choice for portable applications. • • • • • • The AAT2113A delivers 1.5A maximum output current while consuming only 55μA no-load quiescent current. Low RDS(ON) integrated MOSFETs and 100% duty cycle operation make the AAT2113A the ideal choice for high output voltage, high current applications which require a low dropout threshold. The AAT2113A provides excellent transient response and output accuracy across the operating range. No external compensation is required. The AAT2113A maintains high efficiency throughout the load range. The unique low-noise architecture reduces ripple and spectral noise. The AAT2113A automatically optimizes efficiency during Light Load mode (LL) and maintains constant frequency and low output ripple during PWM mode. Over-temperature and short circuit protection safeguard the AAT2113A and system components from damage. The AAT2113A is available in a Pb-free, ultra-small, low profile, 8-pin 2mm x 2mm FTDFN package. The product is rated over a temperature range of -40°C to 85°C. • • • • • • • • • • 5mm x 5mm Total Solution Size 1.5A Maximum Output Current Tiny 0.47μH Chip Inductor Excellent Transient Response Input Voltage: 2.7V to 5.5V Ultra-small, Low Profile 8-pin 2mm x 2mm FTDFN Package Fixed or Adjustable Output Voltage Options: ▪ Fixed Output Voltage: 1.2V ▪ Adjustable Output Voltage: 1.0V to 1.8V High Efficiency, Low Noise Architecture 3MHz Switching Frequency No External Compensation Required 55μA No Load Quiescent Current 100% Duty Cycle Low-Dropout Operation Internal Soft Start Over-Temperature and Current Limit Protection <1μA Shutdown Current -40°C to 85°C Temperature Range Applications • • • • • • • • Cellular Phones Digital Cameras Hard Disk Drives MP3 Players PDAs and Handheld Computers Portable Media Players USB Devices Wireless Network Cards Typical Application Load Transient Response VIN 2.7V to 5.5V (VIN = 5V; VOUT = 1.2V; IOUT = 10% to 100%; COUT = 10µF, 6.3V, 0603) U1 1.3V 1.25V 1.2V 100mV 1.15V 1.1V 1.5A C1 4.7µF 6.3V 0603 C3 1.0µF 6.3V 0402 L1 VP LX EN LX AAT2113A VCC AGND FB VOUT 1.2V/1.5A 0.47µH C3 10µF 6.3V 0603 PGND FTDFN 22-8 150mA Time (20µs/div) 2113A.2009.06.1.1 www.analogictech.com 1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Pin Descriptions Pin # Symbol 1 2 3 PGND VP VCC 4 FB 5 AGND 6 EN 7, 8 LX Function Main power ground return pin. Connect to the output and input capacitor return. Input power supply tied to the source of the high side P-channel MOSFET. Power supply; supplies power for the internal circuitry. Feedback input pin. This pin is connected directly to the converter output for the 1.2V fixed output version, or connected to an external resistor divider for the adjustable output version. Analog Ground. This pin is internally connected to the analog ground of the control circuitry. Enable pin. A logic low disables the converter and it consumes less than 1μA of current. When connected high, it resumes normal operation. Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high and low side MOSFETs. Pin Configuration FTDFN22-8 (Top View) PGND VP VCC FB 2 1 8 2 7 3 6 4 5 LX LX EN AGND www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Absolute Maximum Ratings1 TA = 25°C unless otherwise noted. Symbol VCC, VP VLX VFB EN TJ TLEAD Description VP, VCC 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 VP + 0.3 -0.3 to VP + 0.3 -0.3 to VCC + 0.3 -40 to 150 300 V V V V °C °C Value Units 70 1.4 °C/W W Thermal Characteristics Symbol ΘJA PD Description Maximum Thermal Resistance Maximum Power Dissipation2, 3 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. 3. Derate 14mW/°C above 25°C. 2113A.2009.06.1.1 www.analogictech.com 3 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Electrical Characteristics1 VIN = 3.3V, TA = -40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C. Symbol Description VIN VOUT Input Voltage Output Voltage Range VUVLO UVLO Threshold VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L ΔVLOADREG ΔVLINEREG/ ΔVIN VFB ILXLEAK,R IFBLEAK FOSC TS TSD THYS EN Logic VIL VIH ILEAK Conditions Typ Max Units 2.7 1 3.3 1.2 5.5 1.8 2.4 V V V mV V +3.0 % 90 1.0 ILOAD = 0A to 1.5A 3 140 100 0.5 μA μA A mΩ mΩ % VIN = 3.3V to 4.0V 0.3 %/V VIN rising Hysteresis VIN falling IOUT = 0A to 1.5A, VIN = 3.3V, VOUT = 1.2V fixed No Load EN = GND Output Voltage Tolerance Quiescent Current Shutdown Current Current Limit High Side Switch On-Resistance Low Side Switch On-Resistance Load Regulation 180 1.6 -3.0 55 2 Line Regulation Feedback Threshold Voltage Accuracy (Adjustable Version) LX Reverse Leakage Current FB Leakage Current Internal Oscillator Frequency Start-up Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis EN Threshold Low EN Threshold High EN Leakage Current Min No load, TA = 25°C 0.0591 0.60 VIN unconnected, VLX = 5.5V, EN = GND VOUT = 1.2V 2.6 Enable to Output Regulation VEN = 5.5V 1.4 -1.0 3 60 140 25 0.609 V 1.0 0.2 3.4 μA μA MHz μs °C °C 0.4 V V μA 1.0 1. The AAT2113A is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Efficiency vs. Output Current Efficiency vs. Output Current (VOUT = 1.2V; L = 0.47µH) (VOUT = 1.8V; L = 0.47µH) 100 100 90 90 80 80 Efficiency (%) Efficiency (%) Typical Characteristics 70 60 50 VIN = 5.5V VIN = 5.0V VIN = 4.2V VIN = 3.6V VIN = 3.0V VIN = 2.7V 40 30 20 10 0 0.1 1 10 100 1000 70 60 50 VIN = 5.5V VIN = 5.0V VIN = 4.2V VIN = 3.6V VIN = 3.0V VIN = 2.7V 40 30 20 10 0 0.1 10000 1 10 Load Regulation Load Regulation (VOUT = 1.2V; L = 0.47µH) (VOUT = 1.8V; L = 0.47µH) 1.0 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 10 100 1000 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.1 10000 1 10 Line Regulation Line Regulation (VOUT = 1.2V; L = 0.47µF) (VOUT = 1.8V; L = 0.47µF) 1000 1.0 1.0 IOUT = 1500mA IOUT = 1000mA IOUT = 500mA IOUT = 1mA 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 2.7 Input Voltage (V) 2113A.2009.06.1.1 10000 IOUT = 1500mA IOUT = 1000mA IOUT = 500mA IOUT = 1mA 0.8 Line Regulation (%) Line Regulation (%) 100 Output Current (mA) Output Current (mA) 0.8 10000 VIN = 5.5V VIN = 5.0V VIN = 4.2V VIN = 3.6V VIN = 3.0V VIN = 2.7V 0.8 Load Regulation (%) Load Regulation (%) 0.6 1 1000 1.0 VIN = 5.5V VIN = 5.0V VIN = 4.2V VIN = 3.6V VIN = 3.0V VIN = 2.7V 0.8 -1.0 0.1 100 Output Current (mA) Output Current (mA) 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) www.analogictech.com 5 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Typical Characteristics Output Voltage vs. Input Voltage Output Voltage vs. Input Voltage (VOUT = 1.8V; IOUT = 1A) 1.25 1.85 1.24 1.84 1.23 1.83 Output Voltage (V) Output Voltage (V) (VOUT = 1.2V; IOUT = 1A) 1.22 1.21 1.20 1.19 1.18 T = 85°C T = 25°C T = -40°C 1.17 1.16 1.15 2.7 3.1 3.5 3.9 4.3 4.7 5.1 1.82 1.81 1.80 1.79 1.78 1.77 1.76 1.75 2.7 5.5 T = 85°C T = 25°C T = -40°C 3.1 3.5 Input Voltage (V) Output Voltage Error vs. Temperature 5.1 5.5 1.5 Output Voltage Error (%) Output Voltage Error (%) 4.7 (VOUT = 1.8V; VIN = 3.3V; IOUT = 1A) 1.0 0.5 0.0 -0.5 -1.0 -1.5 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 1.0 0.5 0.0 -0.5 -1.0 -1.5 -40 -30 -20 -10 90 10 20 30 40 50 60 70 80 90 Quiescent Current vs. Input Voltage Switching Frequency vs. Temperature (No Load) (VOUT = 1.2V; IOUT = 1A) 3.04 80 Supply Current (µA) 3.02 3.00 2.98 2.96 2.94 2.92 2.90 2.88 2.86 2.84 -40 -30 -20 -10 0 Temperature (°C) Temperature (°C) Switching Frequency (MHz) 4.3 Output Voltage Error vs. Temperature (VOUT = 1.2V; VIN = 3.3V; IOUT = 1A) 70 60 50 40 30 20 T = 85°C T = 25°C T = -40°C 10 0 0 10 20 30 40 50 60 70 80 90 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Temperature (°C) 6 3.9 Input Voltage (V) www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Typical Characteristics Load Transient (VOUT = 1.8V; VIN = 3.3V; IOUT = 0A to 1.5A; COUT = 10µF) 1.90 1.25 1.85 1.10 1.5 1.0 0.5 0.0 1.80 Output Voltage (top) (50mV/div) 1.20 1.15 1.75 1.70 1.5 1.0 0.5 0.0 Output Current (bottom) (500mA/div) 1.30 Output Current (bottom) (500mA/div) Output Voltage (top) (50mV/div) Load Transient (VOUT = 1.2V; VIN = 3.3V; IOUT = 0A to 1.5A; COUT = 10µF) -0.5 Time (20µs/div) Time (20µs/div) Load Transient (VOUT = 1.8V; VIN = 3.3V; IOUT = 75mA to 1350mA; COUT = 10µF) 1.85 1.20 1.15 1.5 1.10 1.0 0.5 0.0 Output Voltage (top) (50mV/div) 1.90 1.25 1.80 1.75 1.5 1.70 1.0 0.5 0.0 Output Current (bottom) (500mA/div) 1.30 Output Current (bottom) (500mA/div) Output Voltage (top) (50mV/div) Load Transient (VOUT = 1.2V; VIN = 3.3V; IOUT = 75mA to 1350mA; COUT = 10µF) -0.5 Time (20µs/div) Line Transient Line Transient (VOUT = 1.2V; VIN = 3.3V to 3.6V; IOUT = 1A) (VOUT = 1.8V; VIN = 3.3V to 3.6V; IOUT = 1A) 4.0 3.5 3.5 1.210 1.205 1.200 1.195 1.190 Time (50µs/div) 2113A.2009.06.1.1 3.0 1.815 1.810 1.805 1.800 1.795 Output Voltage (bottom) (5mV/div) 3.0 Input Voltage (top) (500mV/div) 4.0 Output Voltage (bottom) (5mV/div) Input Voltage (top) (500mV/div) Time (20µs/div) Time (20µs/div) www.analogictech.com 7 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Soft Start (VOUT = 1.8V; VIN = 3.3V; IOUT = 1A) 4 3 1 0 2 1 0 -1 4 3 2 1 0 2 1 0 -1 Time (100µs/div) Time (2ms/div) Output Voltage Ripple Output Voltage Ripple (VOUT = 1.2V; VIN = 3.3V; IOUT = 1mA) (VOUT = 1.8V; VIN = 3.3V; IOUT = 1mA) 0.2 0.1 0 -0.1 Output Voltage (top) (10mV/div) Output Voltage (top) (10mV/div) 0.3 1.81 1.80 0.3 1.79 0.2 0.1 0 -0.1 -0.2 -0.2 Time (10µs/div) Time (10µs/div) Output Voltage Ripple Output Voltage Ripple (VOUT = 1.2V; VIN = 3.3V; IOUT = 1.5A) (VOUT = 1.8V; VIN = 3.3V; IOUT = 1.5A) 2.0 1.5 1.0 0.5 Output Voltage (top) (20mV/div) Output Voltage (top) (20mV/div) 1.18 1.82 Time (200ns/div) 1.80 1.78 2.0 1.5 1.0 Inductor Current (bottom) (500mA/div) 1.20 Inductor Current (bottom) (500mA/div) 1.22 8 Inductor Current (bottom) (100mA/div) 1.20 Inductor Current (bottom) (100mA/div) 1.21 1.19 Inductor Current (bottom) (1A/div) 2 Enable Voltage (top) (1V/div) Output Voltage (middle) (1V/div) Soft Start (VOUT = 1.2V; VIN = 3.3V; IOUT = 1A) Inductor Current (bottom) (1A/div) Enable Voltage (top) (1V/div) Output Voltage (middle) (1V/div) Typical Characteristics Time (200ns/div) www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Functional Block Diagram FB VCC VP AAT2113A-1.2V Only Err Amp VREF = 0.6V DH Comp LX Logic DL EN Input PGND AGND Functional Description The AAT2113A SwitchReg is a 1.5A step-down converter with a typical input voltage of 3.3V and a fixed output voltage of 1.2V. The 3MHz switching frequency enables the use of small external components. The ultra-small, 2mm x 2mm footprint and high efficiency make the AAT2113A an ideal choice for portable applications. Typically, a 0.47μH inductor and a 10μF ceramic capacitor are recommended for a 1.2V output (see Figure 2 for recommended 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 (plus the DC drop of the external inductor). The device integrates extremely low RDS(ON) MOSFETs to achieve low dropout voltage during 100% duty cycle operation. The integrated low-loss MOSFET switches can provide excellent efficiency at heavy loads. Light load operation maintains high efficiency, low ripple and low spectral noise even at lower currents (typically <150mA). PWM mode operation maintains constant frequency and low output ripple at output loads greater than 200mA. 2113A.2009.06.1.1 In battery-powered applications, as VIN decreases, the converter dynamically adjusts the operating frequency prior to dropout to maintain the required duty cycle and provide accurate output regulation. Output regulation is maintained until the dropout voltage, or minimum input voltage, is reached. At 1.5A output load, dropout voltage headroom is approximately 200mV. The AAT2113A typically achieves better than ±0.5% output regulation across the input voltage and output load range. A current limit of 3.0A (typical) protects the IC and system components from short-circuit damage. Typical no load quiescent current is 55μA. Thermal protection completely disables switching when the maximum junction temperature is detected. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault condition is removed, the output voltage automatically recovers. Peak current mode control and optimized internal compensation provide high loop bandwidth and excellent response to input voltage and fast load transient events. Soft start eliminates output voltage overshoot when the enable or the input voltage is applied. Under-voltage lockout prevents spurious start-up events. www.analogictech.com 9 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Control Loop The AAT2113A 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 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 reference voltage is internally set to program the converter output voltage greater than or equal to 0.6V. Soft Start/Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. The enable input, when pulled low, forces the AAT2113A into a low-power, non-switching state. The total input current during shutdown is less than 1μA. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited. To 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. Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hys- teresis. Once an over-temperature or over-current fault condition is removed, the output voltage automatically recovers. Under-Voltage Lockout Internal bias of all circuits is controlled via the VCC input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. Component Selection 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. For applications where the duty cycle is less than 50%, the inductor values can be chosen freely. 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. For low cost application and a sufficiently small footprint in a 5x5mm area, the LQM2HPNR47MG0 shielded chip inductor, which has 40mΩ DCR and 1.8A DC current rating, is selected for 1.2V output. The inductors listed in Table 1 have been used with the AAT2113A. Manufacturer Part Number Value (μH) DC Resistance (Ω) Size (mm) Murata LQM2HPNR47MG0 EPL2010-421ML EPL2010-681ML 0.47 ± 20% 0.42 ± 20% 0.68 ± 20% 0.04 ± 25% 0.04 ± 25% 0.058 ± 25% 2.5x2.0x1.0 2.0x2.0x1.0 2.0x2.0x1.0 Coilcraft Table 1: AAT2113A List of Inductors. 10 www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Input Capacitor Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ Capacitance (µF) 12 0603 Package 0805 Package 10 8 6 4 2 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 DC Bias Voltage (V) Figure 1: 10μF Capacitor Value vs. DC Bias Voltage for Different Package Sizes. The maximum input capacitor RMS current is: IRMS = IO · 2113A.2009.06.1.1 VO V · 1- O VIN VIN = D · (1 - D) = IRMS(MAX) = 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 3.5V DC applied is actually about 5μF. Some examples of DC bias voltage versus capacitance for different package sizes are shown in Figure 1. 0 VO V · 1- O VIN VIN for VIN = 2 · VO V ⎞ VO ⎛ · 1- O VIN ⎝ VIN ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 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. 0.52 = 1 2 IO 2 ⎛ V ⎞ · 1- O VIN ⎠ appears in both the input voltage The term VIN ⎝ 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 AAT2113A. 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 (see Figure 3). 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 capacitor. This dampens the high Q network and stabilizes the system. www.analogictech.com 11 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Output Capacitor The output capacitor limits the output ripple and prevents the output voltage droop during large load transitions. A 10μF to 22μF 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 The AAT2113A adjustable version, combined with an external feed forward capacitor (C2 in Figure 5), delivers enhanced transient response for extreme pulsed load applications. The suggested value for C2 is in the range of 22pF to 100pF. VOUT (V) R2 = 59kΩ R1 (kΩ) R2 = 200kΩ R1 (kΩ) 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 39.2 49.9 59 68.1 78.7 88.7 97.6 107 118 133 165 200 232 267 301 332 365 400 Table 2: Feedback Resistor Selection for Adjustable Output Voltage Version. Thermal Calculations 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 10μF. 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. Feedback Resistor Selection There are three types of losses associated with the AAT2113A 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: PTOTAL = Resistors R1 and R2 of Figure 5 program the output to regulate at a voltage higher than 0.6V for the AAT2113A adjustable version. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the suggested value for R2 is 200kΩ. Table 1 summarizes the resistor values for various output voltages with R2 set to either 59kΩ or 200kΩ. Alternately, the feedback resistor may be calculated using the following equation: VIN + (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: 1.8V VOUT R1 = V -1 · R2 = 0.6V - 1 · 200kΩ = 400kΩ REF 12 IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) www.analogictech.com PTOTAL= IO2 · RDS(ON)H + IQ · VIN 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package 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. 3. Given the total losses, the maximum junction temperature can be derived from the θJA for the FTDFN22-8 package, which is 70°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB PCB Layout Considerations The suggested PCB layout for the AAT2113A is shown in Figures 3 and 4 (fixed version) or Figures 6 and 7 (adjustable version). The following guidelines should be used to help ensure a proper layout: 1. 2. The input capacitor (C1) should be connected as close as possible to VP and PGND. The output capacitor and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. 2113A.2009.06.1.1 4. 5. For the fixed version, the feedback trace or FB pin 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. For the adjustable version, the trace connecting the FB pin to resistors R1 and R2 should be as short as possible by placing R1 and R2 immediately next to the AAT2113A. The sense trace connection from R1 to the output voltage should be separate from any power trace and connect as closely as possible to the load point. The external feed-forward capacitor C2 should be connected as close as possible in parallel with R1 for enhanced transient response. The resistance of the trace from the load return to PGND should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. Connect unused signal pins to ground to avoid unwanted noise coupling. www.analogictech.com 13 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package VIN 2.7V to 5.5V U1 2 VP LX 8 L1 VOUT 1.2V/1.5A 0.47μH 6 EN EN LX 7 AAT2113A C1 4.7μF 3 C3 1μF 5 VCC AGND FB PGND 4 C2 10μF 1 FTDFN22-8 U1 C1 L1 C2 C3 AAT2113AIXS-1.2V-T1 AnalogicTech, 3MHz Fast Transient, 1.5A Step-Down Converter , FTDFN22-8, 2x2mm GRM188R60J475KE19D, Murata, Cap, MLC, 4.7μF/6.3V, 0603 (HMAX = 0.9mm) LQM2HPNR47MGO, Murata, 0.47μH, ISAT = 1800mA, DCR = 40mΩ, 2.5 x 2 x 0.9 mm, shielded chip inductor GRM188R60J106ME47D, Murata, Cap, MLC, 10μF/6.3V, 0603 (HMAX = 0.9mm) GRM155R60J105KE19D, Murata, Cap, MLC, 1μF/6.3V, 0402 Figure 2: AAT2113A Evaluation Board Schematic For 1.2V Fixed Output Voltage Version. Figure 3: AAT2113A Evaluation Board Top Side Layout for 1.2V Fixed Output Voltage Version. 14 Figure 4: AAT2113A Evaluation Board Bottom Side Layout for 1.2V Fixed Output Voltage Version. www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package VIN 2.7V–5.5V U1 2 6 EN LX EN LX L1 8 0.47μH 7 C2 22pF AAT2113A C1 4.7μF U1 C1 C2 L1 R1, R2 C3 C4 VP 3 C4 1μF 5 VCC AGND FB PGND VOUT 1.2V/1.5A R1 200k C3 10μF 4 R2 200k 1 AAT2113AIXS-0.6-T1 AnalogicTech, 3MHz Fast Transient, 1.5A Step-Down Converter, FTDFN22-8, 2x2mm GRM188R60J475KE19D, Murata, Cap, MLC, 4.7μF/6.3V, 0603 (HMAX = 0.8mm) Optional, 22pF, 0201 LQM2HPNR47MGO, Murata, 0.47μH, ISAT =1.8A, DCR = 0.04Ω, 2.5 x 2 x 1mm, shielded chip inductor Carbon film resistor, 200kΩ, 1%, 0201 GRM188R60J106ME47D, Murata, Cap, MLC, 10μF/6.3V, 0603 (HMAX = 0.8mm) GRM155R60J105KE19D, Murata, Cap, MLC, 1μF/6.3V, 0402 Figure 5: AAT2113A Evaluation Board Schematic For Adjustable Output Voltage Version. Figure 6: AAT2113A Evaluation Board Top Side Layout for Adjustable Output Voltage Version. 2113A.2009.06.1.1 Figure 7: AAT2113A Evaluation Board Bottom Side Layout for Adjustable Output Voltage Version. www.analogictech.com 15 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package AAT2113A Design Example Specifications VOUT = 1.2V @ 1.5A, Pulsed Load ΔILOAD = 1.5A VIN = 3.3V FS = 3MHz TAMB = 85°C in 8-pin 2x2mm DFN low profile package Output Inductor For Murata, 0.47μH LQM2HPNNR47MG0 shielded chip inductor has a 40mΩ DCR. ΔI = VO V 1.2V 1.2V · 1- O = · 1= 542mA L1 · FS VIN 0.47μH · 3MHz 3.3V IPK = IOUT + ΔI = 1.5A + 0.271A = 1.8A 2 PL1 = IOUT2 · DCR = 1.5A2 · 40mΩ = 90mW Output Capacitor For VDROOP = 0.12V (10% Output Voltage) COUT = 3 · ΔILOAD 3 · 1.5A = = 12.5μF; use 10μF 0.12V · 3MHz VDROOP · FS For VDROOP = 0.06V (5% Output Voltage) COUT = 3 · ΔILOAD 3 · 1.5A = = 25μF; use 22μF VDROOP · FS 0.06V · 3MHz IRMS(MAX) = VOUT · (VIN(MAX) - VOUT) 1 1.2V · (5V - 1.2V) · = 58.5mArms = 1.5μH · 3MHz · 5V · V L · F 2· 3 2· 3 S IN(MAX) 1 · PRMS = ESR · IRMS2 = 5mΩ · (58.5mA)2 = 17μW 16 www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Input Capacitor For Input Ripple VPP = 30mV CIN = IRMS = 1 VPP - ESR · 4 · FS IO = 1 30mV - 5mΩ · 4 · 3MHz 1.5A = 5.6μF; use 4.7μF IOUT1 = 0.75A 2 P = ESR · (IRMS)2 = 5mΩ · (0.75A)2 = 2.8mW AAT2113A Losses All values assume 85°C ambient temperature and thermal resistance of 70°C/W in the 8-pin 2x2mm DFN low profile package. PTOTAL = IOUT2 · RDS(ON)H + (tSW · FSW · IOUT + IQ) · VIN = 1.5A2 · 152mΩ + (5ns · 3MHz · 1.5A + 50μA) · 3.3V = 416mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (70°C/W) · 416mW = 114°C 2113A.2009.06.1.1 www.analogictech.com 17 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Ordering Information Output Voltage Package Marking1 Part Number (Tape and Reel)2 1.2V Adjustable (0.6V) FTDFN22-8 FTDFN22-8 8BXYY 8AXYY AAT2113AIXS-1.2-T1 AAT2113AIXS-0.6-T1 All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/about/quality.aspx. Package Information FTDFN22-83 0.400 ± 0.050 Detail "A" 2.000 ± 0.050 Index Area Bottom View 2.000 ± 0.050 Top View + 0.100 - 0.000 Pin 1 Identification 0.250 ± 0.050 Side View 0.450 ± 0.050 0.000 0.230 ± 0.050 0.750 ± 0.050 0.500 ± 0.050 Detail "A" 1. XYY = assembly and date code. 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. 18 www.analogictech.com 2113A.2009.06.1.1 PRODUCT DATASHEET AAT2113A SwitchRegTM 3MHz, Fast Transient 1.5A Step-Down Converter in 2mm x 2mm Package Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © Advanced Analogic Technologies, Inc. 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Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 2113A.2009.06.1.1 www.analogictech.com 19