MIC2172/3172
100kHz 1.25A Switching Regulators
General Description
The MIC2172 and MIC3172 are complete 100kHz SMPS
current-mode controllers with internal 65V 1.25A power
switches. The MIC2172 features external frequency
synchronization or frequency adjustment, while the
MIC3172 features an enable/shutdown control input.
Although primarily intended for voltage step-up
applications, the floating switch architecture of the
MIC2172/3172 makes it practical for step-down, inverting,
and Cuk configurations as well as isolated topologies.
Operating from 3V to 40V, the MIC2172/3172 draws only
7mA of quiescent current making it attractive for battery
operated supplies.
The MIC3172 is for applications that require on/off control
of the regulator. The MIC3172 is externally shutdown by
applying a TTL low signal to EN (enable). When disabled,
the MIC3172 draws only leakage current (typically less
than 1µA). EN must be high for normal operation. For
applications not requiring control, EN must be tied to V
IN
or
TTL high.
The MIC2172 is for applications requiring two or more
SMPS regulators that operate from the same input supply.
The MIC2172 features a SYNC input which allows locking
of its internal oscillator to an external reference. This
makes it possible to avoid the audible beat frequencies
that result from the unequal oscillator frequencies of
independent SMPS regulators.
A reference signal can be supplied by one MIC2172
designated as a master. To insure locking of the slave’s
oscillators, the reference oscillator frequency must be
higher than the slave’s. The master MIC2172’s oscillator
frequency is increased up to 135kHz by connecting a
resistor from SYNC to ground (see applications
information).
The MIC2172/3172 is available in an 8-pin plastic DIP or
SOIC for –40°C to +85°C operation.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
1.25A, 65V internal switch rating
3V to 40V input voltage range
Current-mode operation
Internal cycle-by-cycle current limit
Thermal shutdown
Low external parts count
Operates in most switching topologies
7mA quiescent current (operating)
<1µA quiescent current, shutdown mode (MIC3172)
TTL shutdown compatibility (MIC3172)
External frequency synchronization (MIC2172)
External frequency trim (MIC2172)
Fits most LT1172 sockets (see applications info)
Applications
Laptop/palmtop computers
Toys
Hand-held instruments
Off-line converter up to 50W (requires external power
switch)
•
Predriver for higher power capability
•
Master/slave configurations (MIC2172)
•
•
•
•
___________________________________________________________________________________________________________
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2006
M9999-041806
(408) 955-1690
MICREL [ MICREL SEMICONDUCTOR ]
