DATA SHEET AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch General Description Features The AAT2138 is a high current synchronous step-down Input Voltage Range: 2.7V to 5.5 V converter with an integrated current-limited load switch Output Voltage Range: Down to 3.0V designed for high precision current control applications. Current-Limited Load Switch By guarding against excessive input current, AAT2138 - 10% High Precision enables the system designer to maximize the output cur- - Programmable Current Limit Range: 500mA to 3A rent from the step-down converter while protecting the High-Current Step-Down Converter input supply. It is designed for protection of USB ports - Efficiency up to 95% from heavy load transient conditions commonly seen - 85m High-Side 50m Low-Side FETs with high data rate modem applications. - 2.8MHz Switching Frequency - 100% Low Dropout Operation AAT2138 integrates a high precision programmable cur- - No External Compensation Required rent limited P-channel MOSFET load switch to protect the - PFM/PWM or forced PWM Modes input supply against large currents which may cause the - 1MHz to 3MHz External Clock Support supply to fall out of regulation. The current limit thresh- Soft Start old is programmed up to 3A by an external resistor Independent Enable Pins for Switch and Converter between RSET and ground. Over-Temperature and Over Load Protection The AAT2138 is a 2.8MHz current mode step-down con- -40C to +85C Temperature Range verter. It utilizes a tiny 1H inductor and internal com- Pb-Free, Low-Profile, 3mmx3mm 14-pin TDFN Package pensation to enable it to have an extremely small foot print. The regulator supports 100% duty cycle operation Applications for dropout conditions. An external clock in the range of Wireless Modem Data Cards 1MHz to 3MHz can be fed into MODE as a synchronous Portable Hard Drives signal for the step-down regulator. This feature offers Portable Memory Card Readers the flexibility of fine tuning the switching frequency and Barcode Scanners optimizing performance in the application. Credit Card Readers AAT2138 is available in a Pb-free, low profile, 14-pin General USB Powered Devices 3mm x 3mm TDFN package. The product is rated over the -40C to 85C temperature range. Typical Application OFF V ENSYS IN SYSIN 2.7V-5.5V C R IN SET ON RSET 1F 1H REGIN V OUT SW C 3.4V/3A R1 IN Bulk Capacitor AAT2138 C IN 10F 274k 0.1F C OUT PGND 22F ON R2 ENREG FB 59k OFF PWM MODE AGND PFM/PWM Skyworks Solutions, Inc. Phone 781 376-3000 Fax 781 376-3100 sales skyworksinc.com www.skyworksinc.com 1 202006C Skyworks Proprietary Information Products and Product Information are Subject to Change Without Notice. March 18, 2013 DATA SHEET AAT2138 High Current Step-Down Converter with High-Precision Programmable Current Limited Load Switch Pin Descriptions Pin Symbol Function 1, 2 PGND Power Ground. PGND is internally connected to the source of the low-side N-channel MOSFET. Input Power Supply for the Step-Down Regulator. Connect REGIN to the input power source. Bypass REGIN to PGND with a 4.7F or greater ceramic capacitor. REGIN internally connects to 3, 4 REGIN the source of the load switch output and the step-down regulators high-side P-channel MOSFET (see the Functional Block Diagram). Step-Down Regulator Enable Input. A logic high enables the AAT2138 switching regulator. A 5 ENREG logic low forces the AAT2138 into shutdown mode, placing the output into a high-impedance state and reducing the quiescent current to less than 1A. Do NOT leave ENREG oating. Load Switch Current-Limit Adjustment. Connect a resistor between RSET and ground to set the 6 RSET input current limit threshold. 7 AGND Analog Ground. AGND is internally connected to the analog ground of the control circuitry. Load Switch Enable. Active Low Input. A logic low enables the AAT2138 load switch. A logic high 8 ENSYS disables the AAT2138 load switch. Do NOT leave ENSYS oating. Feedback Input / Output Voltage Sense. FB senses the output voltage for regulation control. For 9FB 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. 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 10 MODE 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. System Load Switch Input. SYSIN connects to the source of the P-channel load switch that lim- its the system input supply current. 11, 12 SYSIN Bias Input Supply for the System and Step-Down Regulator. SYSIN supplies power to the ana- log and logic control circuitry of the AAT2138. Inductor Switching Node. SW is internally connected to the source of the high-side P-Channel 13, 14 SW 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) 1 14 PGND SW 2 13 PGND SW 3 12 REGIN SYSIN 4 11 REGIN SYSIN 5 10 ENREG MODE 6 9 RSET FB AGND 7 8 ENSYS Skyworks Solutions, Inc. Phone 781 376-3000 Fax 781 376-3100 sales skyworksinc.com www.skyworksinc.com 2 202006C Skyworks Proprietary Information Products and Product Information are Subject to Change Without Notice. March 18, 2013