LM2745MTC Integrated Circuit Chip microchips and integrated circuits

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LM2745/8

Synchronous Buck Controller with Pre-bias Startup, and Optional Clock Synchronization

General Description

The LM2745/8 are high-speed synchronous buck regulator controllers with an accurate feedback voltage accuracy of ±1.5%. It can provide simple down conversion to output voltages as low as 0.6V. Though the control sections of the IC are rated for 3 to 6V, the driver sections are designed to accept input supply rails as high as 14V.

The use of adaptive non-overlapping MOSFET gate drivers helps avoid potential shoot-through problems while maintaining high efficiency. The IC is designed for the more cost-effective option of driving only N-channel MOSFETs in both the high-side and low-side positions. It senses the low-side switch voltage drop for providing a simple, adjustable current limit.

The LM2745/8 features a fixed-frequency voltage-mode PWM control architecture which is adjustable from 50 kHz to 1 MHz with one external resistor. In addition, the LM2745 also allows the switching frequency to be synchronized to an external clock signal over the range of 250 kHz to 1 MHz. This wide range of switching frequency gives the power supply designer the flexibility to make better tradeoffs between component size, cost and efficiency.

Features include the ability to startup with a pre-biased load on the output, soft-start, input undervoltage lockout (UVLO) and Power Good (based on both undervoltage and overvoltage detection). In addition, the shutdown pin of the IC can be used for providing startup delay, and the soft-start pin can be used for implementing precise tracking, for the purpose of sequencing with respect to an external rail.

Features

• Switching frequency from 50 kHz to 1 MHz
• Switching frequency synchronize range 250 kHz to 1 MHz (LM2745 Only)
• Startup with a pre-biased output load
• Power stage input voltage from 1V to 14V
• Control stage input voltage from 3V to 6V
• Output voltage adjustable down to 0.6V
• Power Good flag and shutdown
• Output overvoltage and undervoltage detection
• ±1.5% feedback voltage accuracy over temperature
• Low-side adjustable current sensing
• Adjustable soft-start
• Tracking and sequencing with shutdown and soft start pins
• TSSOP-14 package

Applications

• Down Conversion from 3.3V
• Cable Modem, DSL and ADSL
• Laser Jet and Ink Jet Printers
• Low Voltage Power Modules
• DSP, ASIC, Core and I/O

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

V_CC                                                                                      -0.3 to 7V

BOOT Voltage                                                                    -0.3 to 18V

I_SEN                                                                                    -0.3 to 14V

FREQ/SYNC Voltage                                               -0.5 to V_CC + 0.3V

All other pins                                                            -0.3 to V_CC + 0.3V

Junction Temperature                                                                 150˚C

Storage Temperature                                                   −65˚C to 150˚C

Soldering Information

  Lead Temperature (soldering, 10sec)                                       260˚C

  Infrared or Convection (20sec)                                                  235˚C

ESD Rating (Note 3)                                                                       2kV

Operating Ratings

Supply Voltage Range, V_CC (Note 2)                                        3V to 6V

BOOT Voltage Range                                                             1V to 17V

Junction Temperature Range (T_J)                                −40˚C to +125˚C

Thermal Resistance (θ_JA)                                                          155˚C/W

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device operates correctly. Operating Ratings do not imply guaranteed performance limits.

Note 2: The power MOSFETs can run on a separate 1V to 14V rail (Input voltage, VIN). Practical lower limit of VIN depends on selection of the external MOSFET. See the MOSFET GATE DRIVERS section under Application Information for further details.

Note 3: ESD using the human body model which is a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Typical Application

Connection Diagrams

Physical Dimensions inches (millimeters) unless otherwise noted

TSSOP-14 Pin Package

NS Package Number MTC14