AAT2138

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Document overview

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Technical content

Features

•  Input Voltage Range: 2.7V to 5.5 V
• Output Voltage Range: Down to 3.0V
• Current-Limited Load Switch - ±10% High Precision - Programmable Current Limit Range: 500mA to 3A
• High-Current Step-Down Converter - Efficiency up to 95% - 85m Ω High-Side; 50mΩ Low-Side FETs - 2.8MHz Switching Frequency - 100% Low Dropout Operation - No External Compensation Required - PFM/PWM or forced PWM Modes - 1MHz to 3MHz External Clock Support
• Soft Start
• Independent Enable Pins for Switch and Converter
• Over-Temperature and Over Load Protection
• -40°C to +85°C Temperature Range
• Pb-Free, Low-Profile, 3mmx3mm 14-pin TDFN Package

Applications

• Wireless Modem Data Cards
• Portable Hard Drives
• Portable Memory Card Readers
• Barcode Scanners
• Credit Card Readers
• General USB Powered Devices Typical Application MODE ENREG REGIN SYSIN SW FB PGND AGND VIN 2.7V-5.5V AAT2138 1μF 22μF CIN COUT 274k Ω 59k Ω RSET ENSYS ON OFF PWM PFM/PWM 3.4V/3A 1μH OFF ON CIN 10μFBulk Capacitor RSET VOUT 0.1μF CIN

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 2 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Pin Descriptions Pin # Symbol Function 1, 2 PGND Power Ground. PGND is internally connected to the source of the low-side N-channel MOSFET. 3, 4 REGIN Input Power Supply for the Step-Down Regulator. Connect REGIN to the input power source. Bypass REGIN to PGND with a 4.7μF or greater ceramic capacitor. REGIN internally connects to the source of the load switch output and the step-down regulator’s high-side P-channel MOSFET (see the Functional Block Diagram).

5 ENREG

Step-Down Regulator Enable Input. A logic high enables the AAT2138 switching regulator. A logic low forces the AAT2138 into shutdown mode, placing the output into a high-impedance state and reducing the quiescent current to less than 1μA. Do NOT leave ENREG fl oating. 6 RSET Load Switch Current-Limit Adjustment. Connect a resistor between RSET and ground to set the input current limit threshold. 7 AGND Analog Ground. AGND is internally connected to the analog ground of the control circuitry. ENSYS Load Switch Enable. Active Low Input. A logic low enables the AAT2138 load switch. A logic high disables the AAT2138 load switch. Do NOT leave ENSYS fl oating. 9F B Feedback Input / Output Voltage Sense. FB senses the output voltage for regulation control. For adjustable output versions, connect a resistive divider network from the output to FB to GND to set the output voltage accordingly. The FB regulation threshold is 0.6V.

10 MODE

Regulator Operating Mode. Pull MODE high to force the regulator into forced PWM operation. Pull MODE low to allow automatic pulse-skipping under light-load operation. An external clock in the range of 1MHz to 3MHz can be connected into MODE as a synchronous clock signal for the step-down converter to bypass the internal oscillator. 11, 12 SYSIN System Load Switch Input. SYSIN connects to the source of the P-channel load switch that lim- its the system input supply current. Bias Input Supply for the System and Step-Down Regulator. SYSIN supplies power to the ana- log and logic control circuitry of the AAT2138. 13, 14 SW Inductor Switching Node. SW is internally connected to the source of the high-side P-Channel MOSFET and the drain of the low-side N-channel MOSFET. Externally connected to the power inductor as shown in the Typical Application Circuit. EP GND (EP) Exposed Pad. Connect directly to the ground plane to reduce the thermal impedance. Pin Configuration TDFN33-14 (Top View) 12REGIN ENREG AGND SW FB SYSIN RSET REGIN SYSIN PGND SW PGND MODE ENSYS

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 3 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Absolute Maximum Ratings1 Symbol Description Value Units VIN SYSIN, REGIN to PGND -0.3 to +6 V VSW SW to PGND -0.3 to (REGIN + 0.3) VFB FB to AGND -0.3 to (SYSIN + 0.3) VRSET RSET to AGND -0.3 to (VIN + 0.3) VEN ENSYS, ENREG to AGND -0.3 to (V IN + 0.3) ISYSIN Load Switch Maximum RMS Current Capability ±4.0 A VGND PGND to AGND -0.3 to +0.3 V TJ Operating Junction Temperature Range -40 to 150 °CTA Operating Ambient Temperature Range -40 to 85 TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 Thermal Characteristics Symbol Description Value Units ΘJA Maximum Thermal Resistance 60 °C/W PD Maximum Power Dissipation2, 3 1.67 W 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at co nditions other than the operating conditions specified is not implied. 2. Mounted on an FR4 board. 3. Derate 70mW/°C above 25°C.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 4 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Electrical Characteristics1 VSYSIN = 5.0V, ENREG = SYSIN, ENSYS = AGND = PGND, TA = -40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions Min Typ Max Units VSYSIN System Input Voltage Range SYSIN, REGIN 2.7 5.5 V VUVLO(SYSIN) System Input Under-Voltage Lockout SYSIN Rising 2.7 Hysteresis 0.2 VUVLO(REGIN) Regulator Input Under-Voltage Lockout REGIN Rising2 2.7 Hysteresis 0.2 VDIS(SYSIN) Regulator Input Discharge Threshold SYSIN Rising 3.15 Hysteresis 0.15 RDISCHRG Discharge MOSFET On-Resistance V SYSIN = VREGIN = 3.6V 8 Ω TSHDN Over-Temperature Shutdown Threshold Hysteresis = 15°C 150 °C IQ No Load Supply Current No Load Current; Not Switching 90 μAISHDN Shutdown Current ENREG = SW = GND, 1 System Input Load Switch RDS(ON) Load Switch On-Resistance V SYSIN = 5.0V, TA = 25°C 85 m Ω ΔISYSILIM Current Limit Accuracy RSET = 6.4kΩ, VREGIN < VUVLO(REGIN), TA = 20°C to 85°C -10 ±5 10 % Short-Circuit Current-Limit Threshold RSET = 6.4kΩ, VREGIN < VUVLO(REGIN), TA = 20°C to 85°C 400 mA Adjustable Current-Limit Range TA = 25°C 0.5 3 A tILIM Current-Limit Response Time 5 μs tSS(SYS) Load Switch Soft-Start Period 1.5 ms VIH_ENSYS ENSYS Input Logic Threshold High 1.5 VVIL_ENSYS ENSYS Input Logic Threshold Low 0.4 IENSYS ENSYS Input Current V EN = 0V or < VIN + 0.3V -1.0 1.0 μA Step-Down Regulator VOUT Output Voltage Range 3.0 V IN V IFB FB Leakage Current V FB = 0.65V 50 nA VFB FB Regulation Threshold3 10mA Load, TA = +25°C 588 600 612 mVNo Load, TA = -40°C to +85°C 582 600 618 ΔVOUT/IOUT Load Regulation I OUT = 0 to 2.5A, TA = 25°C 0.20 %/A ΔVOUT/VIN Line Regulation VIN = 3.6V to 5.5V, VOUT = 3.3V, TA = 25°C, IOUT = 10mA 0.10 0.30 %/V ILIMPK High-Side P-Channel MOSFET Current Limit 3.0 4.0 A RDS(ON)HI High-Side P-Channel MOSFET On- Resistance VREGIN = 3.6V 85 m Ω RDS(ON)LO Low-Side N-Channel MOSFET On- Resistance VREGIN = 3.6V 50 m Ω fOSC Internal Oscillator Frequency 2.4 2.8 MHz tSS(REG) Step-Down Regulator Soft-Start Period4 COUT = 100μF1 m s tOFF Minimum Off-time 50 ns VIH_ENREG ENREG Input Logic Threshold High 1.5 V VIL_ENREG ENREG Input Logic Threshold Low 0.4 V IENREG ENREG Input Current V EN = 0V or 5.5V < VIN + 0.3V -1.0 1.0 μA 1. The AAT2138 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assu red by design, characterization, and correla- tion with statistical process controls. 2. Also used for Load Switch Current-Limit Fold-back Threshold 3. The regulated feedback voltage is tested in an internal test mode that connects V FB to the output of the error amplifier. 4. This time period will keep the regulator start-up current around 300mA to 400mA.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 5 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Typical Characteristics VREGIN = 3.8V VREGIN = 4.2V VREGIN = 4.5V VREGIN = 4.8V VREGIN = 5.0V VREGIN = 5.5V 100 1 10 100 1000 10000 Step-Down Converter Efficiency (VOUT = 3.4V) Output Current (mA) Efficiency (%) 100 1 10 100 1000 10000 VIN = 4.2V VIN = 4.5V VIN = 4.8V VIN = 5.0V VIN = 5.2V VIN = 5.5V Step-Down Converter Efficiency (VOUT = 3.65V) Output Current (mA) Efficiency (%) 100 1 10 100 1000 10000 VREGIN = 4.2V VREGIN = 4.5V VREGIN = 4.8V VREGIN = 5.0V VREGIN = 5.2V VREGIN = 5.5V Step-Down Converter Efficiency (VOUT = 3.8V) Output Current (mA) Efficiency (%) -1.2 -0.8 -0.4 0.4 0.8 1.2 0 500 1000 1500 2000 2500 3000 VREGIN = 3.8V VREGIN = 4.2V VREGIN = 4.5V VREGIN = 4.8V VREGIN = 5.0V VREGIN = 5.5V Step-Down Converter Load Regulation (VOUT = 3.4V) Output Current (mA) Output Error (%) -1.2 -0.8 -0.4 0.4 0.8 1.2 0 500 1000 1500 2000 2500 3000 VREGIN = 4.2V VREGIN = 4.5V VREGIN = 4.8V VREGIN = 5.0V VREGIN = 5.2V VREGIN = 5.5V Step-Down Converter Load Regulation (VOUT = 3.8V) Output Current (mA) Output Error (%) -1.2 -0.8 -0.6 -0.4 -0.2 0.2 0.4 0.6 0.8 1.2 1mA 100mA 500mA 1000mA 1500mA 2000mA 2500mA Step-Down Converter Line Regulation (VOUT = 3.4V) Input Voltage (V) Output Error (%)

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 6 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Typical Characteristics -1.2 -0.8 -0.6 -0.4 -0.2 0.2 0.4 0.6 0.8 1.2 1mA 100mA 500mA 1000mA 1500mA 2000mA 2500mA Step-Down Converter Line Regulation (VOUT = 3.8V) Input Voltage (V) Output Error (%) 2.6 2.65 2.7 2.75 2.8 2.85 2.9 -40 -15 10 35 60 85 Frequency vs Temperature Temperature(°C) Frequency (MHz) 0.591 0.594 0.597 0.600 0.603 0.606 0.609 -40 -15 10 35 60 85 Feedback Voltage vs Temperature Temperature (ºC) VFB (V) 0.591 0.594 0.597 0.600 0.603 0.606 0.609 Feedback Voltage vs Input Voltage Input Voltage (V) VFB (V) 0.6 0.7 0.8 0.9 1.1 1.2 VENH VENL Step-Down Converter Enable Threshold vs Input Voltage Input Voltage (V) VENREG (V) 0.6 0.7 0.8 0.9 1.1 1.2 -40 -15 10 35 60 85 VENH VENL Step-Down Converter Enable Threshold vs Temperature Temperature (°C) VENREG (V)

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 7 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Typical Characteristics 100 110 120 85°C 25°C -40°C No Load Quiescent Current vs Input Voltage (Open Loop) Input Voltage (V) Quiescent Current (μA) 100 110 120 -40 -15 10 35 60 85 No Load Quiescent Current vs Temperature (Open Loop, VSYSIN = 5V) Temperature (°C) Quiescent Current (μA) 85°C 25°C -40°C No Load Quiescent Current vs Input Voltage (Close Loop, VOUT = 3.4V) Input Voltage (V) Quiescent Current (mA) -40 -15 10 35 60 85 No Load Quiescent Current vs Temperature (Close Loop, VSYSIN = 5V, VOUT = 3.4V) Temperature (°C) Quiescent Current (mA) 112 130 85°C 25°C -40°C Step-Down Converter P-Channel RDS(ON) vs Input Voltage Input Voltage (V) RDS(ON) (mΩ) 85°C 25°C -40°C Step-Down Converter N-Channel RDS(ON) vs Input Voltage Input Voltage (V) RDS(ON) (mΩ)

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 8 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Typical Characteristics VENREGIN 2V/div VOUT 2V/div IREGIN 1A/div Soft Start (VSYSIN = VREGIN = 5V, COUT = 22μF, L=1μH, VOUT = 3.4V, IOUT = 2.5A) Time 1ms/div Soft Start (VSYSIN = VREGIN = 5V, COUT = 22μF,VOUT = 3.4V, L = 1μH, IOUT = 0A) Time 1ms/div VENREGIN 2V/div VOUT 2V/div IREGIN 50mA/div Output Ripple (VSYSIN = VREGIN = 5V, PFM Mode, L=1μH, COUT = 22μF, CREGIN = 10μF + 0.1μF,VOUT = 3.4V,IOUT = 10mA) Time 400ns/div VSW 2V/div VOUT(AC) 10mV/div IIN 200mA/div VOUT(AC) 10mV/div IIN 200mA/div VSW 2V/div Output Ripple (VSYSIN = VREGIN = 5V, PWM Mode, L = 1μH, COUT = 22μF, CREGIN = 10μF + 0.1μF, VOUT= 3.4V, IOUT = 10mA) Time 400ns/div Output Ripple (VSYSIN = VREGIN = 5V, PWM Mode, L = 1μH, COUT = 22μF, CREGIN = 10μF + 0.1μF, VOUT = 3.4V, IOUT = 2A) Time 400ns/div VSW 2V/div IIN 1A/div VOUT(AC) 10mV/div 100mA Step-Down Converter Load Transient (VSYSIN = VREGIN = 5V, VOUT = 3.8V , CCOUT = 22μF, L = 1μH, CFF = 22pF, CREGIN = 10μF + 0.1μF) Time 100μs/div ILOAD 500mA/div VOUT(AC) 100mV/div

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 9 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Typical Characteristics 100 2.5A mA Step-Down Converter Load Transient (VSYSIN = VREGIN = 5V,VOUT = 3.8V, CCOUT = 22μF, L = 1μH, CFF = 22pF, CREGIN = 10μF + 0.1μF) Time 100μs/div VOUT(AC) 200mV/div ILOAD 1A/div 100mA Step-Down Converter Load Transient (VSYSIN = VREGIN = 5V, VOUT = 3.4V, CCOUT = 22μF, L = 1μH, CFF = 22pF, CREGIN = 10μF + 0.1μF) Time 100μs/div VOUT(AC) 100mV/div ILOAD 500mA/div Step-Down Converter LineTransient (IOUT = 100mA, VOUT = 3.8V, COUT = 22μF, L = 1μH, CFF = 22pF, CREGIN = 10μF + 0.1μF) Time 100μs/div VREGIN 1V/div 0V 0VVOUT(AC) 200mV/div 4.2V 0.6 0.7 0.8 0.9 1.1 1.2 VENH VENL Load Switch Enable Threshold vs Input Voltage Input Voltage (V) VENSYS (V) 4.2V Step-Down Converter LineTransient (IOUT = 100mA, VOUT = 3.4V, COUT = 22μF, L = 1μH, CFF = 22pF, CREGIN = 10μF + 0.1μF) Time 100μs/div VREGIN 1V/div VOUT(AC) 200mV/div 2.5A 100mA Step-Down Converter Load Transient (VSYSIN = VREGIN = 5V, VOUT = 3.4V, CCOUT = 22μF, L = 1μH, CFF = 22pF, CREGIN = 10μF + 0.1μF) Time 100μs/div VOUT(AC) 200mV/div ILOAD 1A/div

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 10 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Typical Characteristics 0.7 0.8 0.9 1.1 1.2 1.3 -40 -15 10 35 60 85 VENH VENL Load Switch Enable Threshold vs Temperature Temperature (°C) VENSYS (V) 100 120 140 85°C 25°C -40°C Load Switch RDS(ON) vs Input Voltage Input Voltage (V) RDS(ON) (mΩ) Load Switch Turn on (VSYSIN = 5V, CSYSIN = 1μF, CREGIN = 10μF + 0.1μF, RL = 100Ω) (VOUT = 3.4V) Time 400μS/div VOUT 2V/div IIN 500mA/div VENSYS 2V/div VREGIN 2V/div REGIN Discharge Function (VSYSIN from 5V to 3V, CSYSIN = 1μF, CREGIN = 10μF + 0.1μF) Time 400μs/div VSYSIN 2V/div VREGIN 2V/div Load Switch Turn On (VSYSIN = 5V, CSYSIN = 1μF, CREGIN = 10μF + 0.1μF + 680μF, RL = 100Ω) (VOUT = 3.4V) Time 2ms/div VOUT 2V/div IIN 500mA/div VENSYS 2V/div VREGIN 5V/div Load Switch Turn off (VSYSIN = 5V, CSYSIN = 1μF, CREGIN = 10μF + 0.1μF, RL = 100Ω) (VOUT = 3.4V) Time 1ms/div VOUT 2V/div IIN 50mA /div VENSYS 2V/div VREGIN 2V/div

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 11 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Functional Description The AAT2138 is a high performance, 2.8MHz, synchro- nous step-down converter with a high-precision, pro- grammable current limited P-channel load switch up to 3A. The P-channel load switch is adopted to limit the system input current. The current limit value is programmed by external resistor between RSET and GND. Its fast tran- sient response time makes it ideal to protect the system from input power surges. The AAT2138 employs internal error amplifier and com- pensation. It provides excellent transient response, load and line regulation. Its output voltage is programmed by an external resistor divider from 3.0V to converter input voltage. Soft start eliminates any output voltage over- shoot when the enable or input voltage is applied. Dropout mode makes the converter increase the switch duty cycle to 100% and the output voltage tracks the input voltage minus the R DS(ON) drop of the P-channel high-side MOSFET of the converter. The AAT2138's input voltage range is 2.7V to 5.5V. Two independent enable pins control the load switch and step-down converter separately. The converter efficiency has been optimized for a 1μH inductor. Control Scheme The AAT2138 uses a peak current-mode step-down con- trol scheme. The converter senses the current through the high-side P-channel MOSFET for current loop control as well as overload protection. A fixed slope compensa- tion signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The input current of the step-down converter is limited by the load switch. The feedback amplifier compares the FB voltage against the 0.6V reference voltage. The error amplifier’s trans- conductance output is internally compensated, and pro- grams the current-mode loop for the necessary peak switch current to force a constant output voltage over all load and line conditions. Enable/Soft Start AAT2138 has two independent enable pins: ENSYS and ENREG. When ENSYS is pulled high, the current limit load switch is turned off and REGIN drops to zero. When ENREG is pulled low, the step-down converter is forced into the low-power, no-switching, high impedance state. The total input current during shutdown is less than 1uA. When ENSYS is pulled low, the system will turn on the load switch in a soft start process. To avoid a big inrush current during the startup, the REGIN voltage will be charged from SYSIN with limited input current under 500mA. The startup time depends on the capacitance between REGIN and GND. When ENREG is pulled high, the step-down converter is Functional Block Diagram Step-Down Converter 600mV Reference FB SW PGNDENREG REGIN EN VP Load Switch Control SYSIN EN VP ENSYS 1.0V Ref. Current LimitRSET Current Limit MODE MODE AGND Discharge Control

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 12 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET active with soft start. When the REGIN voltage is above UVLO and reaches 95% of V SYSIN voltage, the reference voltage is charged from 0 to 0.6V slowly by an internal current source to avoid a large input inrush current. During the soft start, the output voltage increases with the reference voltage. The soft start time is about 1ms with a 100μF output capacitor. REGIN Discharge The voltage on the capacitor between REGIN and GND is discharged quickly when the power on SYSIN is removed quickly (unplugged adaptor). When ENSYS is pulled low and SYSIN is below 3.0V, AAT2138 automatically turns on the discharge MOSFET to discharge the REGIN capacitor storage. Discharge resistance is typical 8ohm and the specific discharge time depends on the capaci- tance between REGIN and GND. Input Under-Voltage Lockout Under-voltage lockout (UVLO) guarantees sufficient V REGIN bias and proper operation of all internal circuitry prior to activation. MODE Function When the MODE pin is pulled high, the part runs in forced PWM mode operation using the internal oscillator. When the MODE pin is pulled low, a light-load mode operation (PFM/PWM) is designed to reduce the domi- nant switching losses at low output voltage and light- load condition. The Step-Down converter can also be synchronized to an external clock signal fed into the MODE pin. In this case, the internal oscillator is bypassed. The frequency of the external clock must be in the range from 1MHz to 3MHz. Protection Circuitry The AAT2138 includes protection for overload and over- temperature conditions. The overload protection turns off the high-side switch when the inductor current exceeds the current-limit threshold (3A minimum). The AAT2138 includes thermal protection that disables the regulator and the load switch when the die tempera- ture reaches 150°C. The REGIN pin is maintained in a high-impendance state. It automatically restarts when the temperature drops by 15°C or more.

Application Information

The AAT2138's load switch current limit can be pro- grammed by an external resistor R SET from RSET to GND. In most applications, the variation in I LIM must be taken into account when determining R SET. The ILIM variation is due to processing variations from part to part, as well as variations in the voltages at SYSIN and REGIN, plus the operating temperature. Together, these three factors add up to a ±5% tolerance (see load switch I LIM specification in Electrical Characteristics section). Table 1 gives 1% standard metal film resistor example values for PMOS current limit programming. ILIM (A) R SET (kΩ) 0.4 13.3 0.482 10 0.51 9.53 0.553 8.88 0.613 8.06 0.798 6.34 0.908 5.6 1.01 5.1 1.078 4.75 1.245 4.02 1.538 3.16 2.07 2.2 2.48 1.74 2.64 1.6 2.9 1.4 3 1.3 Table 1: Examples of 1% Standard Resistor Value of RSET. 0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 RSET (kΩ) ILIMIT (A) Figure 1: Load Switch Current Limit vs R SET.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 13 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Dropout Voltage Dropout voltage is determined by RDS(ON) and the current passing through it. AAT2138 load switch typical RDS(ON) is 80mΩ for USB application. So, for a 750mA load switch current limit setting, the load switch dropout voltage can be calculated by: VDROPOUT_SWITCH = 750mA · 80mΩ = 60mV Step-Down Converter Inductor Selection The step-down converter uses peak current-mode con- trol 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 half the output volt- age 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 satura- tion 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. CREGIN Selection CREGIN is not only the load switch output capacitor but also the step-down converter input capacitor. It is designed to provide the additional input current and maintain the SYSOUT voltage for the step-down con- verter when load switch limits the input current from SYSIN. If the input voltage of the step-down converter is lower than the V OUT plus the dropout voltage, the AAT2138 enters dropout mode. C REGIN minimum value can be calculated by the following steps: First, calculate the allowed maximum delta voltage on CREGIN to keep VOUT in regulation: ΔVREGIN = VIN - VOUT - VDROPOUT_SWITCH - VDROPOUT_BUCK Second, calculate the required input current at SYSOUT for the step-down converter: IBUCKIN =

• IOUTVOUT η·VSYSIN - VDROPOUT_SWITCH Next, calculate the maximum current C REGIN should pro- vide: I CREGIN = IBUCKIN - ILIM Finally, derive the CSYSOUT at certain load on period T ON CREGIN_MIN =
• TONICREGIN ∆VREGIN Example: A 2A, 217Hz, 12.5% load pulse is applied on 3.8V VOUT in 5V VIN and 750mA load switch current limit, under the condition, V DROPOUT_SWITCH is 0.06V, VDROPOUT_BUCK is 0.17V. Therefore, considering the step-down converter at 2A, 3.8V, V OUT is 90%. ΔVREGIN = 5 - 3.8 - 0.06 - 0.17 = 0.970V IBUCKIN =
• 23.8 0.9·5 - 0.06 = 1.71A ICREGIN = 1.71 - 0.75 = 0.96A tON is 576μs for a 217Hz, 12.5% duty cycle load pulse. CREGIN_MIN =
• 5760.96 0.970 = 570μF IOUT 1A/div ISYSIN 1A/div VREGIN 2V/div VOUT 500mV/div 800μs/div Figure 2: AAT2138 Operation Waveform 2A, 577μs Load Pulse (Applied) VIN = 5V, VOUT = 3.8V.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 14 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Considering 20% capacitance tolerance, the minimum capacitance should be 684 μF. So select a 680 μF tanta- lum capacitor as C REGIN, as well as an additional 10 μF ceramic capacitor to closely filter the input voltage VREGIN of the step-down converter on the PCB board. Input Capacitor Selection Select a 1μF X7R or X5R ceramic capacitor for the sys- tem input. To estimate the required input capacitor size, determine the acceptable input ripple level and solve for C IN. The calculated value varies with input voltage and is a maximum when VIN is twice the output voltage. CIN = VOUT VIN 1 - VOUT VIN fS·VPP IOUT - ESR for VIN = 2 · VOUT, = · VOUT VIN 1 - VOUT VIN and CIN(MIN) = 1 4 · fS·VPP IOUT - ESR The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2138. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function due to their low ESR and ESL. To minimize stray parasitic inductance, place the capacitor as close 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 4). A laboratory test set-up typically consists of two long wires running from the bench power supply to the eval- uation 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 dur- ing load transients. Errors in the loop phase and gain measurements can also result. Feedback Resistor Selection The output voltage on the AAT2138 is adjustable 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 59kΩ. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensi- tive to external noise and interference. The maximum value of R1 should be below 1Mohm to keep reference voltage normal and avoid noise coupling. The external resistor R1, combined with an external capacitor up to 22pF feed-forward capacitor (C4 in Figure 3), 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 C31-C32 for stability. The external resistors set the out- put voltage according to the following equation: R1 = - 1 · R2 = VOUT VREF - 1 · R2 VOUT 0.6V Table 2 shows the standard 1% metal film resistor examples for different step-down ouput voltages VOUT (V) R2 = 59kΩ, R1 (kΩ) 3.3 267 3.4 274 3.6 294 3.8 316 Table 2: Resistor Selections for Different Output Voltage Settings.

1. Reliably solder the exposed pad (EP) to the GND

plane. A GND pad below EP is strongly recommended.

1. Keep the power traces, including the GND trace, the

nal lines under the inductor.

1. Connect the input capacitors (C1 and C21) as close as
2. Connect the input capacitor C23 as close as possible
3. Keep the switching node, SW away from the sensitive
4. Separate the feedback trace from any power trace and

high impedance feedback trace.

1. Minimize the resistance of the trace from the load

internal signal ground and the power ground. Figure 3. AAT2138 Evaluation Board Schematic.

Figure 4. AAT2138 Evaluation Board Layout Table 4: Recommended Capacitor Selection.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 17 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET

Ordering Information

Output Voltage Package Marking 1 Part Number (Tape and Reel) Adjustable ≥ 0.6V TDFN33-14 S6XYY AAT2138IWO-0.6-T12 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

3.000 ±± 0.050 Index Area 3.000 ±± 0.050 Detail "A" 1.650 ±± 0.050 2.500 ±± 0.050

0.203 REF

0.750 ±± 0.050 0.000 + 0.100 - 0.000 Detail "A" Side View 0.425 ±± 0.050 0.400 BSC0.180 ±± 0.050 Pin 1 Indicator (Optional) 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 c onnection.

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202006C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013 18 AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch DATA SHEET Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility fo r errors or omissions in these materials or the information contained herein. Sky- works may change its documentation, products, services, specifi cations or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for confl icts, incompatibilities, or other diffi culties arising from any future changes. No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided here- under, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale. THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, IN- CLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or en- vironmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper use or sale. Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifi cations as a result of design defects, errors, or operation of products outside of pub- lished parameters or design specifi cations. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifi cations or parameters. Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for identifi cation purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.