DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator General Description Features The AAT2522 is a SwitchReg, dual, high-current, stepdown converter with an input voltage range of 2.7V to 5.5V and an adjustable output voltage from 0.6V to VIN. The 1.4MHz switching frequency enables the use of small external components. The compact footprint and high efficiency make the AAT2522 an ideal choice for portable applications. • • • • • • • • • • • • • • • • • The AAT2522 delivers load currents up to 3.0A maximum output current per regulator. Ultra-low RDS(ON) integrated MOSFETs and 100% duty cycle operation make the AAT2522 an ideal choice for high output-voltage, high current applications which require a low dropout threshold. The AAT2522 provides excellent transient response and high output accuracy across the operating range. The AAT2522’s unique architecture requires no external compensation components, and produces reduced ripple and spectral noise. Over-temperature and short-circuit protection safeguard the AAT2522 and system components from damage. Dual 3.0A Peak Output Current Regulators 2.7V to 5.5V Input Voltage Range Adjustable Output Voltage (0.6V to VIN) 100% Duty-Cycle, Low-Dropout Operation Integrated 120mΩ High-Side Power MOSFET Integrated 85mΩ Low-Side Power MOSFET Low Noise Light Load Mode No External Compensation Required Very Low 90μA No-Load Operating Current <1μA Shutdown Current Up to 95% Efficiency 1.4MHz Switching Frequency Overload and Short-Circuit Protection Over-Temperature Protection Internal Voltage Ramped Soft-Start Temperature Range: -40°C to +85°C 16-pin 3mm x 4mm TDFN Package Applications • • • • • The AAT2522 is available in a Pb-free, space-saving 16-pin 3mm x 4mm TDFN package. The product is rated over an operating temperature range of -40°C to +85°C. Digital Cameras and Camcorders Netbooks and Nettops Portable DVD and Media Devices Power-Over-Ethernet Set-Top Boxes Typical Application VIN 2.7V to 5.5V VOUT1 0.6V to VIN IN1 VCC1 LX1 FB1 PGND1 ON/OFF EN1 AGND1 AAT2522 IN2 VCC2 LX2 FB2 PGND2 ON/OFF EN2 VOUT2 0.6V to VIN AGND2 EP Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 1 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Pin Descriptions Pin # Name 1 VCC2 2 EN2 3 IN2 4 EN1 5 6-7 VCC1 IN1 8 LX1 9-10 PGND1 11 FB1 12 AGND1 13 LX2 14 PGND2 15 FB2 16 AGND2 EP AGND Function Bias supply input for regulator #2. Enable input for regulator #2. A logic high enables the second regulator of the AAT2522. A logic low forces regulator #2 into shutdown mode, placing the second output into a high-impedance state and reducing the VCC2 quiescent current to less than 1μA. Power supply input for regulator #2. Enable input for regulator #1. A logic high enables the primary regulator of the AAT2522. A logic low forces regulator #1 into shutdown mode, placing the primary output into a high-impedance state and reducing the VCC1 quiescent current to less than 1μA. Bias supply input for regulator #1. Power supply input for regulator #1. Inductor switching node for regulator #1. LX1 is the drain of the internal high-side P-channel and low-side N-channel MOSFETs. Externally connected to the power inductor as shown in the "Typical Application" drawing on page 1 of this datasheet. Power ground for regulator #1. PGND1 is internally connected to the source of the internal low-side N-channel MOSFET. Feedback input for regulator #1. FB1 senses the output voltage for regulation control. Connect a resistive divider network from the output to FB1 to AGND1 to set the output voltage accordingly. The FB1 regulation threshold is 0.8V. Analog ground for regulator #1. AGND1 is internally connected to the analog ground of the control circuitry. Inductor switching node for regulator #2. LX2 is the drain of the internal high-side P-channel and low-side N-channel MOSFETs. Externally connected to the power inductor as shown in the "Typical Application" drawing on page 1 of this datasheet. Power ground for regulator #2. PGND2 is internally connected to the source of the internal low-side N-channel MOSFET. Feedback input for regulator #2. FB2 senses the output voltage for regulation control. Connect a resistive divider network from the output to FB2 to AGND2 to set the output voltage accordingly. The FB2 regulation threshold is 0.6V. Analog ground for regulator #2. AGND2 is internally connected to the analog ground of the control circuitry. Substrate analog ground. Pin Configuration TDFN34-16 (Top View) VCC2 EN2 IN2 EN1 VCC1 IN1 IN1 LX1 2 1 16 2 15 3 14 4 5 AGND 13 12 6 11 7 10 8 9 AGND2 FB2 PGND2 LX2 AGND1 FB1 PGND1 PGND1 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Absolute Maximum Ratings Symbol Description VIN1, VIN2 VCC1, VCC2 IINP1, IINP2 VLX1 VLX2 ILX1, ILX2 VEN1, VEN2 VFB1 VFB2 VGND IN1 to PGND1, IN2 to PGND2 VCC1 to AGND1, VCC2 to AGND2 INPx RMS Current Capability LX1 to PGND1 LX2 to PGND2 LX RMS Current Capability EN1 to AGND1, EN2 to AGND2 FB1 to AGND1 FB2 to AGND2 AGND1 to PGND1, AGND2 to PGND2 Value -0.3 to +6 -0.3 to +6 ±3.0 -0.3 to (VIN1 + 0.3) -0.3 to (VIN2 + 0.3) ±5.0 -0.3 to VIN -0.3 to (VFB1 + 0.3) -0.3 to (VFB2 + 0.3) -0.3 to +0.3 Units V A V A V Thermal Characteristics Symbol TA TJ Description Ambient Temperature Range Operating Junction Temperature Range TSTORAGE Storage Temperature Range TLEAD Maximum Soldering Temperature (at leads, 10 sec.) Power SO-10 Thermal Impedance θJA Maximum Junction-to-Ambient Thermal Resistance PD Maximum Power Dissipation Value Units -40 to +85 -40 to +150 -65 to +150 300 °C 50 2 °C/W W Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 3 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Electrical Characteristics CIN = 10μF, COUT = 22μF, L = 1.5μH. VIN1 = VIN2 = 3.6V, IN1 = VCC1 = EN1, IN2 = VCC2 = EN2, AGND = PGND. TA = -40°C to 85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol VIN VOUT Description VFB Input Voltage Range Output Voltage Range Output Voltage Tolerance FB Regulation Threshold IQ No Load Supply Current ISHDN IFB ΔVOUT(LOAD) ΔVOUT/VIN fOSC tSS Protection VUVLO TSHDN Shutdown Current FB Leakage Current Load Regulation Line Regulation Oscillator Frequency Soft-Start Period Features Input Under-Voltage Lockout Over-Temperature Shutdown Threshold Conditions IOUT = 0 to 3A, VIN = 2.7V to 5.5V No Load, TA = 25°C Including IN1, VCC1, IN2, and VCC2 supply currents; No Load Current; not switching EN = GND VFB = 1.0V 0A to 3A Load VIN = 2.7V to 5.5V Min 2.7 0.6 -3.0 591 Typ Max Units 600 5.5 VIN +3.0 609 V V % mV 90 180 μA 1.0 200 μA nA % %/V MHz μs 2.7 V 0.5 0.2 1.40 150 VIN Rising, Hysteresis = 0.25V Hysteresis = 15°C 140 °C 120 mΩ MOSFETs High-Side P-Channel MOSFET On-Resistance High-Side P-Channel MOSFET ILIMPK Current Limit RDS(ON)LO Low-Side N-Channel On-Resistance Logic Input/Output Pins VEN EN Input Logic Threshold IEN EN Input Current RDS(ON)HI 3.61 A 85 0V, VIN 0.6 -1.0 mΩ 1.4 +1.0 1. Specified by design. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 V μA DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Step-Down Converter Efficiency vs. Load Step-Down Converter DC Regulation (VOUT = 1.2V; L = 1.2µH) (VOUT = 1.2V; L = 1.2µH) 100 2.0 90 1.5 Output Error (%) Efficiency (%) Typical Characteristics 80 70 VIN = 2.7V VIN = 3.0V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 60 50 40 30 20 0.1 1 10 100 1000 VIN = 2.7V VIN = 3.0V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1 10000 1 Output Current (mA) 90 1.5 80 70 VIN = 2.7V VIN = 3.0V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 20 0.1 1 10 100 1000 Output Error (%) Efficiency (%) 2.0 30 VIN = 2.7V VIN = 3.0V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1 10000 1 Output Current (mA) 10 100 1000 Step-Down Converter Efficiency vs. Load Step-Down Converter DC Regulation (VOUT = 2.5V; L = 2.5µH) (VOUT = 2.5V; L = 2.5µH) 100 2.0 90 1.5 80 70 60 VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 50 40 30 20 0.1 1 10 100 Output Current (mA) 10000 Output Current (mA) 1000 10000 Output Error (%) Efficiency (%) 10000 (VOUT = 1.8V; L = 1.8µH) 100 40 1000 Step-Down Converter DC Regulation (VOUT = 1.8V; L = 1.8µH) 50 100 Output Current (mA) Step-Down Converter Efficiency vs. Load 60 10 VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1 1 10 100 1000 10000 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 5 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Step-Down Converter Efficiency vs. Load Step-Down Converter DC Regulation (VOUT = 3.3V; L = 3.3µH) (VOUT = 3.3V; L = 3.3µH) 100 2.0 90 1.5 Output Error (%) Efficiency (%) Typical Characteristics 80 70 60 50 VIN = 3.6V VIN = 4.2V VIN = 5.0V VIN = 5.5V 40 30 20 0.1 1 10 100 1000 1.0 0.5 0.0 -0.5 -1.0 VIN = 4.2V VIN = 5.0V VIN = 5.5V -1.5 -2.0 0.1 10000 1 (VOUT = 1.8V; L = 1.8µH) 1.5 1.5 1.0 1.0 0.5 0.0 IOUT = 0.10mA IOUT = 100mA IOUT = 1A IOUT = 1.5A IOUT = 2A IOUT = 3A -0.5 -1.0 3.1 3.5 3.9 4.3 4.7 5.1 Accuracy (%) 2.0 -2.0 2.7 IOUT = 0.10mA IOUT = 100mA IOUT = 1A IOUT = 1.5A IOUT = 2A IOUT = 3A 0.5 0.0 -0.5 -1.0 -1.5 -2.0 2.7 5.5 3.1 3.5 Input Voltage (V) 0.0 -0.5 -1.0 -1.5 -25 0 25 50 Temperature (°C) 75 100 Output Voltage Error (%) 1.0 4.7 5.1 5.5 (VIN = 3.6V; VOUT = 1.8V) IOUT = 1A IOUT = 1.5A IOUT = 2A IOUT = 3A 0.5 4.3 Step-Down Converter Output Voltage Error vs. Temperature (VIN = 3.6V; VOUT = 1.2V) 2.0 1.5 3.9 Input Voltage (V) Step-Down Converter Output Voltage Error vs. Temperature Output Voltage Error (%) 10000 Step-Down Converter Line Regulation -1.5 6 1000 Step-Down Converter Line Regulation 2.0 -2.0 -50 100 Output Current (mA) (VOUT = 1.2V; L = 1.2µH) Accuracy (%) 10 Output Current (mA) 2.0 IOUT = 1A IOUT = 1.5A IOUT = 3A 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -50 -25 0 25 50 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 75 100 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Typical Characteristics Step-Down Converter Output Voltage Error vs. Temperature Step-Down Converter Output Voltage Error vs. Temperature (VIN = 4.2V; VOUT = 3.3V) 1.5 1.0 0.5 0.0 -0.5 IOUT = 1A IOUT = 1.5A IOUT = 3A -1.0 -1.5 -2.0 -50 -25 0 25 50 75 Output Voltage Error (%) Output Voltage Error (%) (VIN = 3.6V; VOUT = 2.5V) 2.0 2.0 IOUT = 1A IOUT = 1.5A IOUT = 2A IOUT = 3A 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -50 100 -25 0 Temperature (°C) No Load Input Current vs. Input Voltage 110 100 90 80 70 85°C 25°C -40°C 60 50 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Frequency Variation (%) 120 Input Current (µA) 75 100 (VOUT = 1.8V; IOUT = 1.5A) 130 5 4 3 2 1 0 -1 -2 -3 -4 -5 2.7 Input Voltage (V) 1.50 1.45 1.40 1.35 1.30 1.25 20 40 Temperature (°°C) 3.9 4.3 4.7 5.1 5.5 Step-Down Converter Soft Start 60 80 (VIN = 3.6V; VOUT = 1.8V; IOUT = 1.5A; CFF = 100pF) Enable Voltage (top) (V) Output Voltage (middle) (V) 1.55 0 3.5 4 3 2 1 0 2 1 0 Inductor Current (bottom) (A) (VIN = 3.6V; VOUT = 1.8V; IOUT = 1.5A) 1.60 -20 3.1 Input Voltage (V) Step-Down Converter Switching Frequency vs. Temperature Switching Frequency (MHz) 50 Step-Down Converter Switching Frequency vs. Input Voltage (VEN1 = VEN2 = VIN) 1.20 -40 25 Temperature (°C) 100 Time (100µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 7 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Typical Characteristics (IOUT = 2.25A to 3.0A; VIN = 3.6V; VOUT = 1.2V; COUT = 22µF) 4 1 0.3A 0 1.4 1.2 1.0 0.8 5 3.0A 4 3 2.25A 2 1.4 1.2 1.0 Output Current (top) (A) 2 Output Current (top) (A) 3.0A 3 Output Voltage (bottom) (V) Step-Down Converter Load Transient Response (IOUT = 0.3A to 3.0A; VIN = 3.6V; VOUT = 1.2V; COUT = 22µF) Output Voltage (bottom) (V) Step-Down Converter Load Transient Response 0.8 Time (100µs/div) Time (100µs/div) (IOUT = 2.25A to 3.0A; VIN = 4.2V; VOUT = 3.3V; COUT = 22µF) 4 2 1 0.3A 3.7 0 3.5 3.3 3.1 2.9 5 3.0A 2.25A 2 3.5 3.3 3.1 2.9 Time (100µs/div) Time (100µs/div) Step-Down Converter Line Transient Response Step-Down Converter Line Transient Response (VIN = 3.6V to 4.3V; VOUT = 1.2V; IOUT = 3A) (VIN = 3.6V to 4.3V; VOUT = 1.8V; IOUT = 3A) 2 1.3 1.2 1.1 1.0 Time (200µs/div) 8 Input Voltage (top) (V) Input Voltage (top) (V) 3.6V 5 4 3 4.3V 3.6V 2 2.0 1.9 1.8 1.7 1.6 Time (100µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 Output Voltage (bottom) (V) 3 4.3V Output Voltage (bottom) (V) 5 4 4 3 Output Current (top) (A) 3.0A Output Current (top) (A) 3 Output Voltage (bottom) (V) Step-Down Converter Load Transient Response (IOUT = 0.3A to 3.0A; VIN = 4.2V; VOUT = 3.3V; COUT = 22µF) Output Voltage (bottom) (V) Step-Down Converter Load Transient Response DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Typical Characteristics Step-Down Converter Output Ripple (VIN = 3.6V to 4.3V; VOUT = 2.5V; IOUT = 3A) (VIN = 3.6V; VOUT = 1.2V; IOUT = 1mA) Input Voltage (top) (V) 3 4.3V 3.6V 2 2.9 2.7 2.5 2.3 2.1 3.6V 0V 1.22 1.20 0.4 1.18 0.2 0.0 Time (100µs/div) Step-Down Converter Output Ripple (VIN = 3.6V; VOUT = 1.2V; IOUT = 3A) (VIN = 4.2V; VOUT = 3.3V; IOUT = 1mA) 0V 1.22 1.20 1.18 3.5 3.0 2.5 4.2V 0V 3.35 3.30 3.25 0.2 0.0 Time (500ns/div) Step-Down Converter Short Circuit Protection (VIN = 4.2V; VOUT = 3.3V; IOUT = 3A) (VIN = 5V; VOUT = 1.8V; CFF = 100pF) 0V 3.35 3.30 3.25 3.1 3.0 2.9 Time (500ns/div) 5 3 1 1.8V 0V 4 2 0 Inductor Current (bottom) (A) 4.2V LX Voltage (top) (V) Output Voltage (middle) (V) Step-Down Converter Output Ripple LX Voltage (top) (V) Inductor Current (bottom) (A) Output Voltage (middle) (V) Time (500ns/div) LX Voltage (top) (V) Inductor Current (bottom) (A) 3.6V Output Voltage (middle) (V) Step-Down Converter Output Ripple LX Voltage (top) (V) Inductor Current (bottom) (A) Output Voltage (middle) (V) Time (200µs/div) LX Voltage (top) (V) Inductor Current (bottom) (A) 4 Output Voltage (bottom) (V) 5 Output Voltage (middle) (V) Step-Down Converter Line Transient Response Time (100µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 9 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Functional Block Diagram IN1 Slope Comp VCC1 FB1 AGND1 0.6V REF Osc Control Logic INP LX1 PGND1 TSHDN EN1 IN2 Slope Comp VCC2 FB2 AGND2 0.6V REF Osc Control Logic INP LX2 PGND2 TSHDN EN2 Functional Description The AAT2522 dual step-down regulators provide highperformance operation with a 1.4MHz switching frequency. The AAT2522 regulators are completely independent, including separate power supply inputs and enable signals. The highly integrated controller minimizes the external component requirements, optimizes efficiency over the complete load range, and produces reduced ripple and spectral noise. Apart from the small bypass input capacitor, only a small LC filter is required at the output. Typically, a 3.3μH inductor and a 22μF ceramic capacitor are recommended for a 3.3V output (see table of 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 high-side P-channel MOSFET (plus the DC drop of the external inductor and PCB layout). The device integrates extremely low RDS(ON) MOSFETs to achieve low dropout voltage during 100% duty cycle operation. 10 This is advantageous in applications requiring high output voltages (typically > 2.5V) at low input voltages. The integrated low-loss MOSFET switches can provide greater than 85% efficiency at full load (5V Input to 3.3V Output). Light-load, low-noise operation maintains high efficiency, low ripple and low spectral noise with low current conditions (typically < 150mA). In battery-powered applications, as VIN decreases, the converter dynamically adjusts the operating frequency prior to dropout to maintain the required high duty-cycle and maintain accurate output regulation. The regulators will maintain output regulation until either the dropout voltage limit is exceeded, or the input under-voltage threshold is reached. The AAT2522 typically achieves better than ±0.5% output regulation across the input voltage and output load range. A current limit of 4.0A (typical) protects the IC and system components from short-circuit damage. Typical no load quiescent current is 90μA. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator 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. 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. 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. 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. Control Scheme Inductor Selection The AAT2522 regulators are peak current-mode, stepdown converters. The controller senses the current through the high-side P-channel MOSFET for current loop control, as well as short-circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The resulting peak current-mode loop appears as a voltage-programmed current source in parallel with the output capacitor. 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. Therefore, the inductor should be set equal to the output voltage numeric value in μH. This guarantees that there is sufficient internal slope compensation. 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. When pulled low, the enable input forces the AAT2522 into a low-power non-switching state. The total input current during shutdown is less than 1μA. Protection Circuitry 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 Input Under-Voltage Lockout Component Selection 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. The 3.3μH CDRH6D38NP series Sumida inductor has a 15mΩ worst case DCR and a 3.5A DC current rating. With a 3A load, the inductor DCR conduction loss is 135mW, which gives less than 1.4% loss in efficiency for a 3A, 3.3V output. Output Capacitor Selection The output capacitor limits the output ripple and provides holdup 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 11 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The first-order relationship of the output voltage droop during the three switching cycles to the output capacitance can be estimated by: COUT = 3 · ΔIO VDROOP · fSW 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. Input Capacitor Selection Select a 10μF to 22μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPK-PK) and solve for CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage (VIN = 2x VO): CIN = D · (1 - D) VPKPK - ESR · fSW IO and D = VO VIN The peak ripple voltage occurs when VIN = 2x VO (50% duty cycle), resulting in a minimum output capacitance recommendation: CIN(MIN) = 1 VPKPK - ESR · 4 · fSW IO Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the derated 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 · IRMS = IO · 12 D · (1 - D) VO V · 1- O VIN VIN The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current: IRMS(MAX) = IO occurs when VIN = 2 · VO 2 The term D (1-D) 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 AAT2522. 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 alu¬minum electrolytic should be placed in parallel with the low ESR/ESL bypass ceramic capacitor. This dampens the high Q network and stabilizes the system. Adjustable Feedback Network The output voltage on the AAT2522 is programmed with external resistors ROUT-FB and RFB-GND. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, mak- Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator ing it more sensitive to external noise and interference. Therefore, the recommended value range for RFB-GND (R3 and R5 in Figure 2) is 100kΩ for good noise immunity or 221kΩ for reduced no load input current. The external resistor ROUT-FB (R2 and R4 in Figure 2), combined with an external 100pF feed forward capacitor (C5 and C6 in Figure 2), delivers enhanced transient response for extreme pulsed load applications and reduces ripple in light load conditions. The addition of the feed forward capacitor typically requires a larger output capacitor (COUT) for stability. The external resistors set the output voltage according to the following equation: Thermal Calculations There are three types of losses associated with the AAT2522 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: PLOSS(RES) = IO2 · RDS(ON)H · VO VIN - VO + RDS(ON)L · VIN VIN 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 switching losses is given by: R VO = 0.6V · 1 + OUT-FB RFB-GND or solving for ROUT-FB ROUT-FB = Applications Information VO - 1 · RFB-GND 0.6V R3 = R5= 100kΩ VOUT (V) R2 = R4 (kΩ) 1.0 1.2 1.5 1.8 2.2 2.5 3.3 4.2 4.6 5 65.5 100 150 200 267 316 453 604 655 806 Table 1: Step-Down Converter Feedback Resistor Selection for Different Output Voltages. The typical circuit shown in the AAT2522 evaluation schematic is intended to be general purpose and suitable for most applications. In applications where transient load steps are more severe and the restriction on output voltage deviation is more stringent. To handle these cases some simple adjustments can be made. The schematic in Figure 2 shows the configuration for improved transient response in an application where the output is stepped down to 1.2V. The adjustments consist of adding an additional 22μF output capacitor, increasing the value of the feed forward capacitor C6 to 1nF, and adding the bias RC filter networks R1, C3 and R6, C4 in Figure 2. PLOSS(SW) = tSW · fSW · IO · VIN The term tSW is used to estimate the full load step-down converter switching losses. Finally, the losses associated with the controller bias requirements are based the regulator’s quiescent current (IQ): PLOSS(BIAS) = IQ · VIN Summing the three power loss terms together provides the total power loss that the AAT2522 package must dissipate: PTOTAL = PLOSS(RES) + PLOSS(SW) + PLOSS(BIAS) For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = IO2 · RDS(ON)H = VO + IQ · VIN 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 13 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Given the total losses, the maximum junction temperature can be derived from the θJA for the TDFN34-16 package, which is 50°C/W. TJ(MAX) = PTOTAL · θJA + TAMB Assuming the operating ambient temperature is 85°C (the worst case), the maximum power dissipation for the TDFN34-16 package is determined in the following equation: PMAX = TJ(MAX) - TAMB θJA 140°C - 85°C = 1.1W 50°C/W The power dissipation varies with the duty cycle and the output current of the converters. Given the maximum power dissipation of the TDFN34-16 package at 25°C and 85°C, the relationship between the maximum allowable load for each channel and percent duty cycle are expressed in Figure 1. As illustrated in Figure 1, the load limitation varies with the percentage of duty cycle and the operating ambient temperature. The total maximum load for both channels running at the same time in an 85°C ambient is about 4A (2A per channel). Therefore, if channel 1 is running at 1A, the maximum allowable load for channel 2 is no more than 3A to prevent the thermal shutdown. However, the maximum allowable load for each channel running at room temperature can increase up to 3A. In high current applications, the exposed pad needs to be connected to a thick power ground plane through vias for thermal dissipation. Layout Recommendations The suggested PCB layout for the AAT2522 is shown in Figures 3 and 4. The following guidelines should be used to help ensure a proper layout. 1. Maximum Output Current vs. Duty Cycle Maximum Output Current (A) (VIN = 3.6V) 4 85°C 25°C 3.5 2. 3 3. 2.5 2 1.5 4. 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) 5. Figure 1: Maximum Allowable Current for AAT2522 Step-Down Converters. 14 Place the input capacitor (CIN) as closely as possible to VIN and PGND. Split the input supply tray to separate the two input capacitors in order to prevent noise coupling between two channels at heavy load. The output capacitor and inductor should be connected as closely as possible. The inductor connection to the LX pin should be as short as possible. 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 highcurrent load trace will degrade DC load regulation. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator VIN 3 R1 0Ω 2.7V-5.5V C1 10μF EN2 C3 0.1μF 3 2 1 2 U1 AAT2522 IRN IN2 LX2 VCC2 FB2 AGND2 EN2 VOUT2 L2 13 3.3μH 15 C5 opt R2 453kΩ R3 100kΩ 16 3.3V/3A C7 22μF C8 opt 1 6 IN1 LX1 1.5μH R6 100Ω 7 5 EN1 C2 10μF 3 2 IN1 FB1 VCC1 AGND1 C4 0.1μF 4 EN1 PGND1 PGND2 PGND1 VOUT1 L1 8 11 C6 opt R5 100kΩ 12 1.2V/3A R4 100kΩ C9 22μF C10 opt 10 1 14 9 EP U1 C1, C2 C3, C4 C5, C6 C7-C9 L1 L2 R1-R6 AAT2522IRN, Skyworks, TDFN34-16 Ceramic cap, MLC, 10μF/10V, 0803 Ceramic cap, MLC, 0.1μF/10V, 0402 Ceramic cap, MLC, 100pF/10V, 0402, optional Ceramic cap, MLC, 22μF/10V, 0805 1.5μH, Sumida, CDRH4D22HPNP-1R5NC, 3.9A, 25mΩ 3.3μH, Sumida, CDRH6D38NP-3R3N, 3.5A, 15mΩ Carbon film resistor, 0402 Figure 2: AAT2522 Evaluation Board Schematic and Bill of Materials. Figure 3: AAT2522 Evaluation Board Top Side Layout. Figure 4: AAT2522 Evaluation Board Bottom Side Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 15 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator AAT2522 Design Example Specifications VOUT1 = 3.3V @ 1A, Pulsed Load ILOAD = 1A VOUT2 = 1.2V @ 2A, Pulsed Load ILOAD = 2A VIN1 = 3.6V FS = 1.4MHz TAMB = 85°C in TDFN34-16 Package Step-Down Converter Output Inductor The internal slope compensation for the AAT2522 is set to 75% of the inductor current down slope for a 1.8V output and 1.8μH inductor: 0.75 · VO 0.75 · 1.8V A = = 0.75 L 1.8μH μs m= For 3.3V and 1.2V outputs, the inductor values are given in the following equations: L= L= 0.75 · VO 0.75 · 3.3V = = 3.3μH; use 3.3μH m A 0.75A μs 0.75 · VO 0.75 · 1.2V = = 1.2μH; use 1.5μH m A 0.75A μs For Sumida inductor, CDRH6D38NP-3R3N, 3.3μH, ISAT = 3.5A, DCR = 15mΩ. For Sumida inductor, CDRH4D22HPNP-1R5NC, ISAT = 3.9A, 1.5μH, DCR = 25mΩ. ΔI1 = VOUT1 V 3.3V 3.3V · 1 - OUT1 = · 1= 0.06A VIN 3.3μH · 1.4MHz 3.6V L1 · FS ΔI2 = VOUT2 V 1.2V 1.2V · 1 - OUT2 = · 1= 0.476A L1 · FS VIN 1.2μH · 1.4MHz 3.6V IPK1 = IOUT1 + ΔI1 = 1A + 0.03A = 1.03A 2 IPK2 = IOUT2 + ΔI2 = 2A + 0.476A = 2.5A 2 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Step-Down Converter Output Capacitor VDROOP = 0.2V COUT = 3 · ΔILOAD 3 · 2A = = 21.4μF; use 22μF 0.2V · 1.4MHz VDROOP · FS IRMS(MAX) = VOUT2 · (VIN(MAX) - VOUT2) 1 1.2V · (5.5V - 1.2V) · = 129mARMS = L · FS · VIN(MAX) 2 · 3 1.5μH · 1.4MHz · 5.5V 2· 3 1 · PRMS = ESR · IRMS2 = 5mΩ · (129mA)2 = 83μW Step-Down Converter Input Capacitor Input Ripple VPP = 50mV CIN = IRMS = 1 VPP - ESR · 4 · FS IO = 1 50mV - 5mΩ · 4 · 1.4MHz 0.2A = 9μF; use 10μF IOUT = 1A 2 P = ESR · (IRMS2) = 5mΩ · (1A)2 = 5mW AAT2522 Losses All values assume at 85°C ambient temperature and thermal resistance of 50°C/W in the TDFN34-16 package. PTOTAL = IOUT12 · (RDS(ON)H · VOUT1 + RDS(ON)L · [VIN -VOUT1]) + (tsw · FS · IOUT1 + IQ1) · VIN VIN + IOUT22 · (RDS(ON)H · VOUT2 + RDS(ON)L · [VIN -VOUT2]) + (tsw · FS · IOUT2 + IQ2) · VIN VIN 2 PTOTAL = 1A · (0.12Ω · 3.3V + 0.085Ω · [3.6V - 3.3V]) + (5ns · 1.4MHz · 1A + 84μA) · 3.6V 3.6V + 2A2 · (0.12Ω · 1.2V + 0.085Ω · [3.6V - 1.2V]) + (5ns · 1.4MHz · 2A + 84μA) · 3.6V 3.6V PTOTAL = 0.58W TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 0.58mW = 114°C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 17 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator Ordering Information Package Marking Part Number (Tape and Reel)1 TDFN34-16 9BXYY AAT2522IRN-1-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 TDFN34-162 3.000 ± 0.050 1.600 ± 0.050 Detail "A" 3.300 ± 0.050 4.000 ± 0.050 Index Area 0.350 ± 0.100 Top View 0.230 ± 0.050 Bottom View C0.3 (4x) 0.050 ± 0.050 0.450 ± 0.050 0.850 MAX Pin 1 Indicator (optional) 0.229 ± 0.051 Side View Detail "A" All dimensions in millimeters. 1. Sample stock is generally held on part numbers listed in BOLD. 2. 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 202032A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012 DATA SHEET AAT2522 Dual High-Current, Low-Noise, Step-Down Regulator 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. 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