LM3477AMMX

LM3477 www.ti.com SNVS141K – OCTOBER 2000 – REVISED MARCH 2013 LM3477 High Efficiency High-Side N-Channel Controller for Switching Regulator Check for Samples: LM3477 FEATURES DESCRIPTION • • • • • The LM3477/A 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 LM3477/A's internal push pull driver allows compatibility with a wide range of MOSFETs. This, the wide input voltage range, use of discrete power components and adjustable current limit allows the LM3477/A to be optimized for a wide variety of applications. 1 2 • • • • 500kHz Switching Frequency Adjustable Current Limit 1.5% Reference Thermal Shutdown Frequency Compensation Optimized with a Single Capacitor and Resistor Internal Softstart Current Mode Operation Undervoltage Lockout with Hysteresis 8-lead (VSSOP-8) Package APPLICATIONS • • • • • • • • Local Voltage Regulation Distributed Power Notebook and Palmtop Computers Internet Appliances Printers and Office Automation Battery operated Devices Cable Modems Battery Chargers The LM3477/A uses a high switching frequency of 500kHz to reduce the overall solution size. Currentmode 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 5µA shutdown state can be used for power savings and for power supply sequencing. Other features include internal soft-start and output over voltage protection. The internal soft-start reduces inrush current. Over voltage protection is a safety feature to ensure that the output voltage stays within regulation. The LM3477A is similar to the LM3477. The primary difference between the two is the point at which the device transitions into hysteretic mode. The hysteretic threshold of the LM3477A is one-third of the LM3477. Hysteretic Threshold (1) (1) LM3477 ≊ 36% of programmed current limit LM3477A ≊ 12% of programmed current limit See Hysteretic Threshold and PROGRAMMING THE CURRENT LIMIT/HYSTERETIC THRESHOLD for more information. 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2000–2013, Texas Instruments Incorporated LM3477 SNVS141K – OCTOBER 2000 – REVISED MARCH 2013 www.ti.com Typical Application Circuit L 3.3PH Q1 FDC653N RSN 0.02: CSN 0.1PF D 30BG100 6 1 VIN 4.5V - 5.5V CBYP 0.1PF CIN 120PF/20V RFB1 20.5k COUT 47PF ceramic FB DR VOUT 2.5V, 3A RFB2 20.0k 3 7 CB LM3477 2 8 VIN COMP/SD 5 4 SW GND ISEN CBOOT 0.1PF RC 510 CC1 47nF * *RFB1 = RFB2 (Vout - 1.26)/1.26 Figure 1. Typical High Efficiency Step-Down (Buck) Converter Connection Diagram ISEN COMP/SD VIN LM3477 CB FB DR GND SW Figure 2. 8 Lead (VSSOP-8 Package) PIN DESCRIPTION Pin Name Pin Number ISEN 1 Current sense input pin. Voltage generated across an external sense resistor is fed into this pin. Description COMP/SD 2 Compensation pin. A resistor-capacitor combination connected to this pin provides compensation for the control loop. Pull this pin below 0.65V to shutdown. FB 3 Feedback pin. The output voltage should be adjusted using a resistor divider to provide 1.270V at this pin. GND 4 Ground pin. SW 5 Switch Node. Source of the external MOSFET is connected to this node. DR 6 Drive pin. The gate of the external MOSFET should be connected to this pin. CB 7 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. VIN 8 Power Supply Input pin. These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 2 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated Product Folder Links: LM3477 LM3477 www.ti.com SNVS141K – OCTOBER 2000 – REVISED MARCH 2013 Absolute Maximum Ratings (1) (2) Input Voltage 36V Peak Driver Output Current (