MIC2172_05 Datasheet, PDF (1/17 Pages) Micrel Semiconductor – 100kHz 1.25A Switching Regulators

MIC2172/3172
MIC2172/3172
Micrel, Inc.
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 syn-
chronization 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 desig-
nated 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 in-
creased 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)
Typical Applications
+5V
(4.75V min.)
L1
27µH
C1*
22µF
V_IN
D1
N/C SYNC
V_SW
MIC2172
1N5822
V_OUT
+12V, 0.14A
R1
10.7k
1%
R3
1k
COMP _GND FB
P1 P2 S
C3
1µF
C2
470µF
R2
1.24k
1%
* Locate near MIC2172 when supply leads > 2"
Figure 1.
MIC2172 5V to 12V Boost Converter
V_IN
4V to 6V
C1
R4*
22µF
Enable
Shutdown
R3
1k
V_IN
EN
V_SW
MIC3172
COMP _GND FB
P1 P2 S
C2
1µF
V_OUT
T1
5V, 0.25A
C3*
D2
1N5818
R1
C4 _3.74k
D1*
470µF _1%
1:1.25
L_PRI = 100µH
R2
1.24k
1%
* Optional voltage clipper (may be req’d if T1 leakage inductance too high)
Figure 2.
MIC3172 5V Flyback Converter
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com
April 2005
1
M9999-042205