LM2678 SIMPLE SWITCHER High Efficiency 5-A Step-Down Voltage Regulator
1 Features
- Efficiency Up to 92%
- Simple and Easy to Design Using Off-the-Shelf External Components
- 120-mΩ DMOS Output Switch
- 3.3-V, 5-V, and 12-V Fixed Output and Adjustable (1.2 V to 37 V) Versions
- 50-μA Standby Current When Switched OFF
- ±2% Maximum Output Tolerance Over Full Line and Load Conditions
- Wide Input Voltage Range: 8 V to 40 V
- 260-kHz Fixed Frequency Internal Oscillator
- −40 to 125°C Operating Junction Temperature Range
- Create a Custom Design Using the LM2678 With the WEBENCH® Power Designer
2 Applications
- Simple-to-Design, High Efficiency (>90%) Step-Down Switching Regulators
- Efficient System Preregulator for Linear Voltage Regulators
- Battery Chargers
3 Description
The LM2678 series of regulators are monolithic integrated circuits which provide all of the active functions for a step-down (buck) switching regulator capable of driving up to 5-A loads with excellent line and load regulation characteristics. High efficiency (>90%) is obtained through the use of a low ON-resistance DMOS power switch. The series consists of fixed output voltages of 3.3 V, 5 V, and 12 V and an adjustable output version.
The SIMPLE SWITCHER® concept provides for a complete design using a minimum number of external components. A high fixed frequency oscillator
(260 kHz) allows the use of physically smaller sized components. A family of standard inductors for use with the LM2678 are available from several manufacturers to greatly simplify the design process.
The LM2678 series also has built-in thermal shutdown, current limiting, and an ON/OFF control input that can power down the regulator to a low 50-μA quiescent current standby condition. The output voltage is ensured to a ±2% tolerance. The clock frequency is controlled to within a ±11% tolerance.
Device Information(1)
| PART NUMBER | PACKAGE | BODY SIZE (NOM) |
|---|---|---|
| LM2678 | TO-263 (7) | 10.10 mm × 8.89 mm |
| TO-220 (7) | 14.986 mm × 10.16 mm | |
| VSON (14) | 6.00 mm × 5.00 mm |
- For all available packages, see the orderable addendum at the end of the data sheet.
Typical Application
4 Revision History
Changes from J Revision (June 2016) to K Revision
- Deleted RADJ = 5.6 kΩGo
- Deleted and updated with new values for Min, Typ and Max Go
- Deleted and updated with new values for Min and Max Go
- Changed soft-start pin to ON/OFF pinGo
- Changed to 200 µA from 1.5 mAGo
- Changed typ and max values to 16 and 15 mAGo
Changes from I Revision (April 2013) to J Revision
- Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section.Go
- Removed all references to Computer Design Software LM267X Made Simple (Version 6.0)Go
Changes from H Revision (April 2013) to I Revision
- Changed layout of National Data Sheet to TI formatGo
5 Pin Configuration and Functions
Pin Functions
| PIN | I/O | DESCRIPTION | ||
|---|---|---|---|---|
| NAME | TO-263, TO-220 | VSON | ||
| Switch output | 1 | 12, 13, 14 | O | Source pin of the internal high-side FET. This is a switching node. Attached this pin to an inductor and the cathode of the external diode. |
| Input | 2 | 2, 3 | I | Supply input pin to collector pin of high-side FET. Connect to power supply and input bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN and GND must be as short as possible. |
| CB | 3 | 4 | I | Boot-strap capacitor connection for high-side driver. Connect a high-quality 100-nF capacitor from CB to VSW Pin. |
| GND | 4 | 9 | — | Power ground pins. Connect to system ground. Ground pins of CIN and COUT. Path to CIN must be as short as possible. |
| FB | 6 | 7 | I | Feedback sense input pin. Connect to the midpoint of feedback divider to set VOUT for ADJ version or connect this pin directly to the output capacitor for a fixed output version. |
| ON/OFF | 7 | 8 | I | Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin high or float to enable the regulator. |
| NC | 5 | 1, 5, 6, 10, 11 | — | No connect pins. |
