MIC4574 Micrel
4-92 April 1998•
MIC4574
200kHz Simple 0.5A Buck Voltage Regulator
General Description
The MIC4574 is a series of easy to use fixed and adjustable
BiCMOS step-down (buck) switch-mode voltage regulators.
The 200kHz MIC4574 duplicates the pinout and function of
the 52kHz LM2574. The higher switching frequency may
allow up to a 2:1 reduction in output filter inductor size.
The MIC4574 is available in 3.3V, and 5V fixed output
versions or a 1.23V to 20V adjustable output version. Both
versions are capable of driving a 0.5A load with excellent line
and load regulation.
The feedback voltage is guaranteed to ±2% tolerance for
adjustable versions, and the output voltage is guaranteed to
±3% for fixed versions, within specified voltages and load
conditions. The oscillator frequency is guaranteed to ±10%.
In shutdown mode, the regulator draws less than 200µA
standby current. The regulator performs cycle-by-cycle
current limiting and thermal shutdown for protection under
fault conditions.
This series of simple switch-mode regulators requires a
minimum number of external components and can operate
using a standard series of inductors. Frequency compensa-
tion is provided internally.
The MIC4574 is available in DIP (N) and SOIC (WM) pack-
ages for the industrial temperature range.
Typical Applications
C1
47µF
35V
D1
1N5819
C2
220µF
16V
L1
100µH
SGND
FB
SW
MIC4574-5.0BN
SHDN
8V to 24V
5.0V/0.5A
V
IN
PGND
24
1
73
5
Shutdown
Enable
Fixed Regulator
C1
10µF
35V
D1
C2
330µF
6.3V
L1
100µH
SGND
FB
SW
MIC4574BWM
SHDN
6V to 24V
3.3V/0.5A
V
IN
R2
2.49k
1%
R1
1.50k
1%
PGND
3
12
64
10
5
C3
3300pF
MBRS130LT3
Shutdown
Enable
Adjustable Regulator
Features
• Fixed 200kHz operation
• 3.3V, 5V, and adjustable output versions
• Voltage over specified line and load conditions:
Fixed version: ±3% max. output voltage
Adjustable version: ±2% max. feedback voltage
• Guaranteed 0.5A switch current
• Wide 4V to 24V input voltage range
• Wide 1.23V to 20V output voltage range
• Requires minimum external components
• < 200µA typical shutdown mode
• 75% efficiency (adjustable version > 75% typ.)
• Standard inductors and capacitors are
25% of typical LM2574 values
• Thermal shutdown
• Overcurrent protection
• 100% electrical thermal limit burn-in
Applications
• Simple high-efficiency step-down (buck) regulator
• Efficient preregulator for linear regulators
• On-card switching regulators
• Positive-to-negative converter (inverting buck-boost)
• Isolated flyback converter using minimum external
components
• Negative boost converter
