LM3489

LM3489/LM3489Q Hysteretic PFET Buck Controller with Enable Pin June 23, 2008 LM3489/LM3489Q Hysteretic PFET Buck Controller with Enable Pin General Description The LM3489 is a high efficiency PFET switching regulator controller that can be used to quickly and easily develop a small, cost effective, switching buck regulator for a wide range of applications. The hysteretic control architecture provides for simple design without any control loop stability concerns using a wide variety of external components. The PFET architecture also allows for low component count as well as ultra-low dropout, 100% duty cycle operation. Another benefit is high efficiency operation at light loads without an increase in output ripple. A dedicated Enable Pin provides a shutdown mode drawing only 7µA. Leaving the Enable Pin unconnected defaults to on. Current limit protection can be implemented by measuring the voltage across the PFET’s RDS(ON), thus eliminating the need for a sense resistor. A sense resistor may be used to improve current limit accuracy if desired. The cycle-by-cycle current limit can be adjusted with a single resistor, ensuring safe operation over a range of output currents. ■ ■ ■ ■ ■ ■ ■ ■ ■ High efficiency 93% ±1.3% (±2% over temp) internal reference 100% duty cycle operation Maximum operation frequency > 1MHz Current limit protection Dedicated enable pin (on if unconnected) Shutdown mode draws only 7µA supply current MSOP-8 LM3489 is AEC-Q100 Grade 1 qualified Applications ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Set-Top Box DSL/Cable Modem PC/IA Auto PC TFT Monitor Battery Powered Portable Applications Distributed Power Systems Always On Power High Power LED Driver Automotive Features ■ ■ ■ ■ Easy to use control methodology No control loop compensation required Wide 4.5V to 35V input range 1.239V to VIN adjustable output range Typical Application Circuit 20186908 © 2008 National Semiconductor Corporation 201869 www.national.com LM3489/LM3489Q Connection Diagram Top View 20186909 8 Lead Plastic MSOP-8 NS package Number MUA08A Package Marking and Ordering Information Order Number LM3489MM LM3489MMX LM3489QMM LM3489QMMX Package Type MSOP-8 MSOP-8 MSOP-8 MSOP-8 Package Marking SKSB SKSB STEB STEB Supplied As: 1000 units on Tape and Reel 3500 units on Tape and Reel 1000 units on Tape and Reel 3000 units on Tape and Reel Automotive Grade* No No Grade 1 Grade 1 *Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including defect detection methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the AEC-Q100 standard. Automotive grade products are identified with the letter Q. For more information go to http://www.national.com/automotive. Pin Descriptions Pin # 1 2 3 4 5 Name ISENSE GND EN FB ADJ Description The current sense input pin. This pin should be connected to the PFET drain terminal directly or through a series resistor up to 600 ohm for 28V>Vin>35V. Signal ground. Enable pin. Connect EN pin to ground to shutdown the part or float to enable operation (Internally pulled high). This pin can also be used to perform UVLO function. The feedback input. Connect the FB to a resistor voltage divider between the output and GND for an adjustable output voltage. Current limit threshold adjustment. Connected to an internal 5.5µA current source. A resistor is connected between this pin and VIN. The voltage across this resistor is compared with the ISENSE pin voltage to determine if an over-current condition has occurred. Power ground. Gate Drive output for the external PFET. PGATE swings between VIN and VIN-5V. Power supply input pin. 6 7 8 PGND PGATE VIN www.national.com 2 LM3489/LM3489Q 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 Voltage PGATE Voltage FB Voltage ISENSE Voltage ADJ Voltage EN Voltage (Note 3) Maximum Junction Temp. Power Dissipation, TA = 25°C (Note 2) −0.3V to 36V −0.3V to 36V −0.3V to 5V −1.0V to 36V -1V (