DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter General Description Features The AAT1112 SwitchReg is a 1.5A step-down converter with an input voltage range of 2.4V 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 small footprint and high efficiency make the AAT1112 an ideal choice for portable applications. • • • • • • • • • • • • • • • The AAT1112 delivers 1.5A maximum output current while consuming only 42μA of no-load quiescent current. Ultra-low RDS(ON) integrated MOSFETs and 100% duty cycle operation make the AAT1112 an ideal choice for high output voltage, high current applications which require a low dropout threshold. The AAT1112 provides excellent transient response and high output accuracy across the operating range. No external compensation components are required. The AAT1112 is designed to maintain high efficiency throughout the load range. Pulling the MODE/ SYNC pin high enables “PWM Only” mode, maintaining constant frequency and low output ripple across the operating range. Alternatively, the converter may be synchronized to an external clock input via the MODE/SYNC pin. Overtemperature and short-circuit protection safeguard the AAT1112 and system components from damage. 1.5A Maximum Output Current Input Voltage: 2.4V to 5.5V Output Voltage: 0.6V to VIN Up to 95% Efficiency 42μA No Load Quiescent Current No External Compensation Required 1.4MHz Switching Frequency Synchronizable to External Clock Optional “PWM Only” Low Noise Mode 100% Duty Cycle Low-Dropout Operation Internal Soft Start Over-Temperature and Current Limit Protection <1μA Shutdown Current TSOPJW-12 or TDFN33-12 Package Temperature Range: -40°C to +85°C Applications • • • • • • • Cellular Phones Digital Cameras Hard Disk Drives MP3 Players PDAs and Handheld Computers Portable Media Players USB Devices The AAT1112 is available in a Pb-free, space-saving TDFN33-12 or 2.85 x 3mm TSOPJW-12 package. The product is rated over an operating temperature range of -40°C to +85°C. Typical Application L1 3.3μH VIN VP LX AAT1112 R1 267kΩ VIN C2 10μF EN C1 22μF FB MODE/SYNC GND VOUT = 3.3V PGND R2 59kΩ Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 1 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Pin Descriptions Pin # TSOPJW-12 TDFN33-12 Symbol Function 1 12 LX 2 3 11 10 VP N/C 4 9 MODE/SYNC 5 8 EN 6 7 VIN 7 6 FB 8, 9, 10, 11 12 N/A 4, 5 1, 2, 3 EP GND PGND Switching node. Connect the output inductor to this pin. The switching node is internally connected to the drain of both high- and low-side MOSFETs. Input voltage for the power switches. Not connected. Connect to ground for PFM/PWM mode and optimized efficiency throughout the load range. Connect high for low noise PWM operation under all operating conditions. Connect to an external clock for synchronization (PWM only). Enable pin. A logic low disables the converter and it consumes less than 1μA of current. When connected high, it resumes normal operation. Power supply. Supplies power for the internal circuitry. Feedback input pin. This pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. Non-power signal ground pin. Main power ground return pin. Connect to the output and input capacitor return. Exposed paddle (bottom); connect to ground as closely as possible to the device. Pin Configuration TSOPJW-12 (Top View) LX 1 12 PGND VP 2 11 GND N/C 3 10 GND MODE/SYNC 4 9 GND EN 5 8 GND 7 FB VIN 2 TDFN33-12 (Top View) 6 PGND 1 12 LX PGND 2 11 VP PGND 3 10 N/C GND 4 9 MODE/SYNC GND 5 8 EN FB 6 7 VIN Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Absolute Maximum Ratings1 Symbol Description VIN VLX VFB VN TJ TLEAD VIN, VP to GND LX Pin to GND FB Pin to GND MODE/SYNC, 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 Thermal Information Symbol Description PD Maximum Power Dissipation JA Thermal Resistance2 Value TSOPJW-12 TDFN33-12 TSOPJW-12 TDFN33-12 0.625 2.0 160 50 Units W °C/W 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. 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 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 3 DATA SHEET AAT1112 1.5A, 1.4MHz 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 VOUT Input Voltage Output Voltage Range VUVLO UVLO Threshold VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L ILXLEAK ILXLK, R VLOADREG VLINEREG/ VIN VFB IFB FOSC TS TSD THYS Output Voltage Tolerance Quiescent Current Shutdown Current Current Limit High Side Switch On-Resistance Low Side Switch On-Resistance LX Leakage Current LX Reverse Leakage Current Load Regulation Line Regulation Feedback Threshold Voltage Accuracy (Adjustable Version) FB Leakage Current Internal Oscillator Frequency Synchronous Clock Start-Up Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Threshold Conditions Min Typ 2.4 0.6 Max Units 5.5 VIN 2.4 VIN = 5.5V, VLX = 0 to VIN VIN Unconnected, VLX = 5.5V, VEN = GND ILOAD = 0A to 1.5A 0.5 V V V mV V % μA μA A μA μA % VIN = 2.4V to 5.5V 0.2 %/V VIN Rising Hysteresis VIN Falling IOUT = 0A to 1.5A, VIN = 2.4V to 5.5V No Load VEN = GND 250 1.8 -3.0 42 3.0 90 1.0 1.8 0.120 0.085 No Load, TA = 25°C 1.0 1.0 0.591 0.60 0.609 V 1.4 0.2 1.68 3.0 μA 1.12 0.60 VOUT = 1.0V From Enable to Output Regulation 150 140 15 MHz μs °C °C EN VIL Enable VIH Enable IEN Enable MODE/SYNC VMODE/SYNC(L) Enable VMODE/SYNC(H) Enable IMODE/SYNC Enable Threshold Low Threshold High Leakage Current Threshold Low Threshold High Leakage Current 0.6 VIN = VEN = 5.5V 1.4 -1.0 VIN = VEN = 5.5V 1.4 -1.0 1.0 0.6 1.0 V V μA V V μA 1. The AAT1112 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Typical Characteristics Efficiency (%) 90 Load Regulation (PFM Mode; VOUT = 3.3V) (PFM Mode; VOUT = 3.3V) 0.50 VIN = 3.6V 80 VIN = 4.2V VOUT Error (%) 100 Efficiency vs. Output Current VIN = 5.0V 70 60 0.25 VIN = 3.6V VIN = 4.2V 0.00 -0.25 VIN = 5.0V 50 40 0.1 1 10 100 1000 -0.50 0.1 10000 1 Output Current (mA) 10 100 1000 10000 1000 10000 1000 10000 Output Current (mA) Efficiency vs. Output Current Load Regulation (PWM Mode; VOUT = 3.3V) (PWM Mode; VOUT = 3.3V) 100 0.50 VIN = 3.6V VOUT Error (%) Efficiency (%) 80 VIN = 5.0V 60 VIN = 4.2V 40 20 0 1.0 10 100 1000 0.25 0.00 VIN = 4.2V -0.25 -0.50 0.1 10000 1 Output Current (mA) 100 Load Regulation (PFM Mode; VOUT = 2.5V) (PFM Mode; VOUT = 2.5V) 0.50 80 VIN = 3.6V VOUT Error (%) Efficiency (%) 100 Efficiency vs. Output Current VIN = 2.7V VIN = 4.2V 70 60 0.1 10 Output Current (mA) 90 50 VIN = 5.0V VIN = 3.6V 1 10 100 Output Current (mA) 1000 10000 VIN = 2.7V 0.25 VIN = 3.6V 0.00 VIN = 4.2V -0.25 -0.50 0.1 1 10 100 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 5 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Typical Characteristics Efficiency vs. Output Current Load Regulation (PWM Mode; VOUT = 2.5V) (PWM Mode; VOUT = 2.5V) 0.50 100 90 VOUT Error (%) Efficiency (%) VIN = 3.6V VIN = 2.7V 80 70 60 VIN = 5.0V 50 40 30 VIN = 4.2V 20 10 0 VIN = 3.6V 1 10 100 1000 0.25 VIN = 5.0V 0.00 VIN = 4.2V -0.25 -0.50 0.1 10000 VIN = 2.7V 1 10 1000 10000 Output Current (mA) Output Current (mA) Efficiency vs. Output Current Load Regulation (PFM Mode; VOUT = 1.8V) (PFM Mode; VOUT = 1.8V) 100 0.50 VOUT Error (%) VIN = 2.7V 90 Efficiency (%) 100 80 70 VIN = 4.2V VIN = 3.6V 60 0.25 VIN = 2.7V VIN = 3.6V 0.00 -0.25 50 VIN = 4.2V 40 0.1 1 10 100 1000 -0.50 0.1 10000 1 Output Current (mA) 10 100 1000 Output Current (mA) Efficiency vs. Output Current Load Regulation (PWM Mode; VOUT = 1.8V) (PWM Mode; VOUT = 1.8V) 100 0.50 90 Efficiency (%) 70 VOUT Error (%) VIN = 2.7V 80 VIN = 4.2V 60 50 40 VIN = 3.6V 30 20 VIN = 2.7V 0.25 VIN = 3.6V 0.00 VIN = 4.2V -0.25 10 0 1 10 100 Output Current (mA) 6 1000 10000 -0.50 0.1 1 10 100 1000 Output Current (mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 10000 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Typical Characteristics Efficiency vs. Output Current Load Regulation (PFM Mode; VOUT = 1.2V) (PFM Mode; VOUT = 1.2V) 100 0.50 VIN = 2.7V 80 70 VIN = 4.2V VIN = 3.6V 60 VOUT Error (%) Efficiency (%) 90 50 VIN = 2.7V 0.25 VIN = 3.6V 0.00 VIN = 4.2V -0.25 40 30 0.1 1 10 100 1000 -0.50 0.1 10000 1 Output Current (mA) 10 100 1000 10000 Output Current (mA) Efficiency vs. Output Current Load Regulation (PWM Mode; VOUT = 1.2V) (PWM Mode; VOUT = 1.2V) 100 0.50 90 Efficiency (%) 70 VOUT Error (%) VIN = 2.7V 80 VIN = 4.2V 60 VIN = 3.6V 50 40 30 20 VIN = 2.7V 0.25 VIN = 3.6V 0.00 VIN = 4.2V -0.25 10 0 1 10 100 1000 -0.50 10000 0.1 1 10000 Supply Current vs. Supply Voltage (VIN = 3.6V; VOUT = 1.8V; IOUT = 1A) (VOUT = 1.8V; No Load; PFM Mode) 70 0.8 65 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -40 1000 Output Voltage vs. Temperature 1.0 -1.0 100 Output Current (mA) Supply Current (µA) Output Voltage Change (%) Output Current (mA) 10 -20 0 20 40 Temperature (°°C) 60 80 60 25°C 85°C 55 50 45 40 35 30 -40°C 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Supply Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 7 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Switching Frequency vs. Temperature Line Regulation (VIN = 3.6V; VOUT = 1.8V; IOUT = 1A) (VOUT = 1.8V; IOUT = 1A) 0.12 1.40 Output Voltage Error (%) Switching Frequency (MHz) Typical Characteristics 1.38 1.36 1.34 1.32 1.30 1.28 1.26 1.24 -40 -20 0 20 40 60 80 0.10 0.08 0.06 0.04 0.02 0.00 -0.02 -0.04 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 Switching Frequency (MHz) Temperature (°°C) Supply Voltage (V) Switching Frequency vs. Input Voltage Enable Soft Start (IOUT = 1A) (VOUT = 3.6V; IOUT = 1.5A) 1.40 1.39 1.38 EN (2V/div) VOUT = 1.8V VOUT = 2.5V 1.37 VOUT (1V/div) 1.36 1.35 VOUT = 3.3V 1.34 IIN (500mA/div) 1.33 1.32 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 Time (100µs/div) Input Voltage (V) P-Channel RDS(ON) vs. Input Voltage N-Channel RDS(ON) vs. Input Voltage 180 170 150 120°C 140 130 RDS(ON) (mΩ Ω) RDS(ON) (mΩ Ω) 160 150 140 85°C 130 120 110 25°C 110 100 85°C 90 80 70 90 60 Input Voltage (V) 8 120 100 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 5.5 120°C 25°C 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 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Light Load Switching Waveform (PWM Mode; VIN = 3.6V; VOUT = 1.8V; 1mA Load) 2.6 2.0 2.4 0.0 2.2 -2.0 2.0 -4.0 1.8 -6.0 1.6 -8.0 1.4 -10.0 1.2 -12.0 1.0 4.0 1200 2.0 1000 0.0 800 -2.0 600 -4.0 400 -6.0 200 -8.0 0 -10.0 -200 -12.0 -400 Time (2.5µs/div) Load Transient Response (VIN = 3.6V; VOUT = 1.8V; CFF = 100pF) 700 4.0 600 0.0 500 -4.0 400 -8.0 300 -12.0 200 -16.0 100 -20.0 0 -24.0 -100 2.0 2.4 1.9 2.2 1.8 2.0 1.7 1.8 1.6 1.6 1.5 1.4 1.4 1.2 1.3 1.0 1.2 0.8 Time (20µs/div) Load Transient Response Line Transient Response (VIN = 3.6V; VOUT = 1.8V; No CFF) (VOUT = 1.8V; 1.5A Load) 5.0 3.0 3.0 4.5 2.8 1.5 2.5 4.0 2.6 1.0 2.0 3.5 2.4 0.5 1.5 3.0 2.2 0.0 1.0 2.5 2.0 -0.5 0.5 2.0 1.8 -1.0 0.0 1.5 1.6 -1.5 -0.5 1.0 1.4 Time (50µs/div) Input Voltage (top) (V) 3.5 2.0 Output Voltage (bottom) (V) 2.5 Load Current (bottom) (A) Output Voltage (top) (V) Time (100µs/div) Load Current (bottom) (A) 8.0 Output Voltage (top) (V) Light Load Switching Waveform (PFM Mode; VIN = 3.6V; VOUT = 1.8V; 1mA Load) Inductor Ripple Current (bottom) (mA) Output Voltage (AC coupled) (top) (mV) Time (2.5µs/div) Inductor Ripple Current (bottom) (mA) 4.0 Output Voltage (AC coupled) (top) (mV) Heavy Load Switching Waveform (PWM Mode; VIN = 3.6V; VOUT = 1.8V; 1.5A Load) Inductor Ripple Current (bottom) (mA) Output Voltage (AC coupled) (top) (mV) Typical Characteristics Time (200µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 9 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Functional Block Diagram FB VP VIN Err. Amp DH VREF LX Logic EN Input DL MODE/SYNC PGND GND Functional Description The AAT1112 is a high performance 1.5A monolithic step-down converter operating at 1.4MHz switching frequency. It minimizes external component size and optimizes efficiency over the complete load range. Apart from the small bypass input capacitor, only a small L-C 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 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. 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 95% efficiency at full load. PFM operation 10 maintains high efficiency under light load conditions (typically <150mA). The MODE/ SYNC pin allows optional “PWM only” mode. This maintains constant frequency and low output ripple across all load conditions. Alternatively, the IC can be synchronized to an external clock via the MODE/ SYNC input. External synchronization is maintained between 0.6MHz and 3.0MHz. 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 AAT1112 typically achieves better than ±0.5% output regulation across the input voltage and output load range. A current limit of 2.0A (typical) protects the IC and system components from short-circuit damage. Typical no load quiescent current is 42μA. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Soft Start/Enable 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. Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT1112 into a low-power, non-switching state. The total input current during shutdown is less than 1μA. 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. 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. Control Loop The AAT1112 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. Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. 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. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. VIN U1 AAT1112 TDFN33-12 C1 10μF 11 7 3 2 1 8 9 Enable 10 5 3 2 1 VP VCC EN LX N/C FB SYNC PGND N/C PGND GND PGND 3.3V 12 L1 3.3μH 4 C3 (optional) R2 6 C2 22μF 3 2 R3 59K 1 SYNC Figure 1: AAT1112 Schematic. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 11 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter 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. The inductor should be set equal to the output voltage numeric value in μH. This guarantees that there is sufficient internal slope compensation. Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. The inductor should not show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. The 3.3μH CDRH4D28 series Sumida inductor has a 49.2m worst case DCR and a 1.57A DC current rating. At full 1.5A load, the inductor DC loss is 97mW which gives less than 1.5% loss in efficiency for a 1.5A, 3.3V output. Input Capacitor 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 (VPP) and solve for C. 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) = 12 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 ⎠ 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 ⎠ D · (1 - D) = 0.52 = 1 2 for VIN = 2 · VO IRMS(MAX) = VO IO 2 ⎛ V ⎞ · 1- O The term V ⎝ V ⎠ 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. IN IN The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1112. 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 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter 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. Output Capacitor 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 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: 3 · ΔILOAD COUT = 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 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. Adjustable Output Resistor Selection The output voltage on the AAT1112 is programmed with external resistors R1 and R2. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum sug- gested value for R2 is 59k. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 1 summarizes the resistor values for various output voltages with R2 set to either 59k for good noise immunity or 221k for reduced no load input current. 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 3.0 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 237 267 75 113 150 187 221 261 301 332 442 464 523 715 887 1000 Table 1: AAT1112 Resistor Values for Various Output Voltages. Thermal Calculations There are three types of losses associated with the AAT1112 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 = IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 13 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter 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 + 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 TDFN3-12 and TSOPJW-12 packages, which is 50°C/W and 160°C/W respectively. Layout The suggested PCB layout for the AAT1112 is shown in Figures 2 and 3. The following guidelines should be used to help ensure a proper layout. 1. 2. 3. 4. TJ(MAX) = PTOTAL · ΘJA + TAMB 5. The input capacitor (C1) should connect as closely as possible to VP and PGND. C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. The feedback trace or FB pin 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. 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. Figure 2: AAT1112 Evaluation Board Top Side Layout. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Figure 3: AAT1112 Evaluation Board Bottom Side Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 15 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Design Example Specifications VO 3.3V @ 1.5A, Pulsed Load ILOAD = 1.5A VIN 2.7V to 4.2V (3.6V nominal) FS 1.2MHz TAMB 85°C in TDFN33-12 Package Output Inductor L1 = VO(μH) = 3.3μH; see Table 2. For Sumida inductor CDRH4D28 3.3μH DCR = 49.2m max. ⎛ VO V ⎞ 3.3V 3.3V ⎞ ⎛ ⋅ 1 - O1 = ⋅ 1= 179mA L1 ⋅ FS ⎝ VIN ⎠ 3.3µH ⋅ 1.2MHz ⎝ 4.2V ⎠ ΔI1 = IPK1 = IO1 + ΔI1 = 1.5A + 0.089A = 1.59A 2 PL1 = IO12 ⋅ DCR = 1.5A2 ⋅ 49.2mΩ = 110mW Output Capacitor VDROOP = 0.2V COUT = 3 · ΔILOAD 3 · 1.5A = = 18.8µF; use 22µF VDROOP · FS 0.2V · 1.2MHz IRMS(MAX) = (VOUT) · (VIN(MAX) - VOUT) 1 3.3V · (4.2V - 3.3V) · = 52mArms = 3.3µH · 1.2MHz · 4.2V · V L · F · 2 3 2· 3 S IN(MAX) 1 · Pesr = esr · IRMS2 = 5mΩ · (52mA)2 = 13.3µW Input Capacitor Input Ripple VPP = 50mV CIN = 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO1 + IO2 ⎠ IRMS(MAX) = = 1 = 7.3µF; use 10µF ⎛ 50mV ⎞ - 5mΩ · 4 · 1.2MHz ⎝ 1.5A ⎠ IO = 0.75Arms 2 P = esr · IRMS2 = 5mΩ · (0.75A)2 = 3mW 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter AAT1112 Losses Total losses can be estimated by calculating the dropout (VIN = VO) losses where the power MOSFET RDS(ON) will be at the maximum value. All values assume an 85°C ambient temperature and a 120°C junction temperature with the TDFN 50°C/W package. PLOSS = IO12 · RDS(ON)H = 1.5A2 · 0.16Ω = 0.36W TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 360mW = 103°C The total losses are also investigated at the nominal lithium-ion battery voltage (3.6V). The simplified version of the RDS(ON) losses assumes that the N-channel and P-channel RDS(ON) are equal. PTOTAL = IO2 · RDS(ON) + (tsw · FS · IO + IQ) · VIN = 1.5A2 · 152mΩ + (5ns · 1.2MHz · 1.5A + 50μA) · 3.6V = 375mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 375mW = 104°C VOUT (V) Inductance (μH) Part Number Manufacturer Size (mm) 3.3 2.5 1.8 1.5 1.2 1.0 0.8 0.6 3.3 2.2 1.8 1.8 1.2 1.0 1.0 1.0 CDRH4D28 CDRH4D28 CDRH4D28 CDRH4D28 CDRH4D28 SD3114-1.0 SD3114-1.0 SD3114-1.0 Sumida Sumida Sumida Sumida Sumida Cooper Cooper Cooper 5x5x3 5x5x3 5x5x3 5x5x3 5x5x3 3.1x3.1x1.45 3.1x3.1x1.45 3.1x3.1x1.45 Rated Current (A) IRMS (A) ISAT (A) DCR () 2.07 2.07 2.07 36.4 23.2 20.4 20.4 17.5 0.042 0.042 0.042 1.57 2.04 2.2 2.2 2.56 1.67 1.67 1.67 Table 2: Surface Mount Inductors. Manufacturer Part Number Value Voltage Temp. Co. Case Murata Murata GRM21BR60J106KE19 GRM21BR60J226ME39 10μF 22μF 6.3V 6.3V X5R X5R 0805 0805 Table 3: Surface Mount Capacitors. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 17 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter Ordering Information Package Marking1 Part Number (Tape and Reel)2 TSOPJW-12 TDFN33-12 YVXYY SBXYY AAT1112ITP-0.6-T1 AAT1112IWP-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 TSOPJW-12 2.85 ± 0.20 2.40 ± 0.10 0.20 + 0.10 - 0.05 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 7° NOM 0.04 REF 0.055 ± 0.045 0.15 ± 0.05 + 0.10 1.00 - 0.065 0.9625 ± 0.0375 3.00 ± 0.10 4° ± 4° 0.45 ± 0.15 0.010 2.75 ± 0.25 All dimensions in millimeters. 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 DATA SHEET AAT1112 1.5A, 1.4MHz Step-Down Converter TDFN33-12 Index Area 0.43 ± 0.05 0.1 REF C0.3 0.45 ± 0.05 2.40 ± 0.05 3.00 ± 0.05 Detail "A" 3.00 ± 0.05 1.70 ± 0.05 Top View Bottom View 0.23 ± 0.05 Pin 1 Indicator (optional) 0.05 ± 0.05 0.23 ± 0.05 0.75 ± 0.05 Detail "A" Side View All dimensions in millimeters. Copyright © 2012, 2013 Skyworks Solutions, Inc. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201972B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 19