LM3487QMM

LM3487 High Efficiency High-Side N-Channel Controller for Switching Regulator February 19, 2008 LM3487 High Efficiency High-Side N-Channel Controller for Switching Regulator General Description The LM3487 is a high-side N-channel MOSFET switching regulator controller. It can be used in topologies requiring a high side MOSFET such as buck, inverting (buck-boost) and zeta regulators. The LM3487's internal push pull driver allows compatibility with a wide range of MOSFETs. A wide input voltage range and an adjustable current limit allow the LM3487 to be optimized for a wide variety of applications. The LM3487 has an adjustable switching frequency which can also be synchronized to an external clock. Current-mode control requires only a single resistor and capacitor for frequency compensation. The current mode architecture also yields superior line and load regulation and cycle-by-cycle current limiting. A 7µA shutdown state can be used for power savings and for power supply sequencing. Other features include external soft-start to reduce inrush current and output over voltage protection. Features ■ Adjustable/synchronizable switching frequency from ■ ■ ■ ■ ■ ■ ■ ■ ■ 100kHz to 1.4MHz Adjustable cycle by cycle current limit Wide 3V-35V input voltage range Thermal shutdown Frequency compensation optimized with a single capacitor and resistor External softstart Current mode operation Undervoltage lockout with hysteresis 10-lead Mini-SO10 (MSOP-10) package Automotive grade including AEC-Q100 is available Applications ■ ■ ■ ■ ■ ■ ■ ■ ■ ADSL Modems Local Voltage Regulation Distributed Power Notebook and Palmtop Computers Internet Appliances Printers and Office Automation Battery operated Devices Cable Modems Battery Chargers Typical Application Circuit 20049233 Typical High Efficiency Step-Down (Buck) Converter © 2008 National Semiconductor Corporation 200492 www.national.com LM3487 Connection Diagram 20049202 10-Lead Mini SO10 Package (MSOP-10 Package) Package Marking and Ordering Information Order Number LM3487MM LM3487MMX LM3487QMM LM3487QMMX For automotive grade including AEC-Q100 use ‘Q’ versions. Package Type Package Marking Supplied As: 1000 units on Tape and Reel 3500 units on Tape and Reel 1000 units on Tape and Reel 3500 units on Tape and Reel MSOP-10 S38B Pin Descriptions Pin Name ISEN SS/SD COMP FB GND FA/SYNC Pin Number 1 2 3 4 5 6 Description Current sense input pin. Voltage generated across an external sense resistor is fed into this pin. Soft-Start and Shutdown pin. Connect a capacitor from this pin to ground to achieve soft-start. Pull this pin below 0.7V (typical) to shutdown the device. Compensation pin. A resistor-capacitor combination connected to this pin provides compensation for the control loop. Feedback pin. The output voltage should be adjusted using a resistor divider to provide 1.260V (typical) at this pin. Ground pin. Frequency adjust and synchronization pin. Connect a resistor from this pin to ground to set the switching frequency. Connect a high impedance clock signal to this pin to synchronize the switching frequency with the rising edge of the clock. Switch Node. Source of the external MOSFET is connected to this node. Drive pin. The gate of the external MOSFET should be connected to this pin. Boot-strap pin. A capacitor must be connected between this pin and SW pin (pin 5) for proper operation. The voltage developed across this capacitor provides the gate drive for the external MOSFET. Power Supply Input pin. SW DR CB 7 8 9 VIN 10 www.national.com 2 LM3487 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN (Note 2) Peak Driver Output Current (