August 1999 1 LM2574
LM2574 Micrel
Ordering Information
Part Number Temp. Range Package
LM2574BN –40°C to +85°C 8-pin Plastic DIP
LM2574BWM –40°C to +85°C 14-pin Wide SOIC
LM2574-3.3BN –40°C to +85°C 8-pin Plastic DIP
LM2574-3.3BWM –40°C to +85°C 14-pin Wide SOIC
LM2574-5.0BN –40°C to +85°C 8-pin Plastic DIP
LM2574-5.0BWM –40°C to +85°C 14-pin Wide SOIC
LM2574-12BN –40°C to +85°C 8-pin Plastic DIP
LM2574-12BWM –40°C to +85°C 14-pin Wide SOIC
LM2574
52kHz Simple 0.5A Buck Regulator
Final Information
Features
• 3.3V, 5V, 12V, and Adjustable Output Versions
• Adjustable Version Output 1.23V to 37V ±4% Max. over
Line and Load Conditions.
• Guaranteed 0.5A Output Current
• Wide Input Voltage, up to 40V
• Thermal Shutdown and Current Limit Protection
• Requires only 4 external Components.
• Shutdown Capability (Standby Mode)
• Low Power Standby Mode < 200µA Typical
• High Efficiency
• 52kHz Fixed Frequency Internal Oscillator
• Uses Standard Inductors
Applications
• Simple High-efficiency Step-down (Buck) Regulator
• Efficient Pre-Regulator for Linear Regulators
• On-card Switching Regulators
• Positive to Negative Converter (Buck-Boost)
General Description
The LM2574 family is a series of easy to use fixed and
adjustable switching voltage regulators. The LM2574 con-
tains all of the active circuitry necessary to construct a
stepdown (buck) switching regulator and requires a minimum
of external components.
The LM2574 is available in 3.3V, 5V, and 12V fixed output
versions, or an adjustable version with an output voltage
range of 1.23V to 37V. Output voltage is guaranteed to ±4%
for specified input and load conditions.
The LM2574 can supply 0.5A while maintaining excellent line
and load regulation. The output switch includes cycle-by-
cycle current limiting, as well as thermal shutdown for full
protection under fault conditions.
An external shutdown connection selects operating or standby
modes. Standby current is less than 200µA.
Heat sinks are generally unnecessary due the regulator’s
high efficiency. Adequate heat transfer is usually provided by
soldering all package pins to a printed circuit board.
The LM2574 includes internal frequency compensation and
an internal 52kHz fixed frequency oscillator guaranteed to
±10% of the frequency.
Circuits constructed around the LM2574 use a standard
series of inductors which are available from several different
manufacturers.
Pin Configuration
8-pin DIP (N)
FB 1
SIG GND 2
ON/OFF 3
PWR GND 4
8*
7 OUTPUT
6*
5V
IN
14-pin SOIC (WM)
*1
*2
FB 3
SIG GND 4
ON/OFF 5
PWR GND 6
*7
14 *
13 *
12 OUTPUT
11 *
10 VIN
9*
8*
* NC: solder to printed circuit for
maximum heat transfer
Figure 1. Fixed Output Regulator Circuit
V
IN
PWR
GND SIG
GND ON/
OFF
OUT
FB
LM2574
C
IN
22µF
40V MAX
UNREGULATED
DC IN REGULATED
OUTPUT
0.5A
11DQ05 C
OUT
220µF
330µH
Typical Application
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com