MIC2172 Datasheet, PDF (1/16 Pages) Micrel Semiconductor – 100kHz 1.25A Switching Regulators Preliminary Information

MIC2172/3172
Micrel
MIC2172/3172
100kHz 1.25A Switching Regulators
Preliminary Information
General Description
slave’s. The master MIC2172’s oscillator frequency is in-
The MIC2172 and MIC3172 are complete 100kHz SMPS
current-mode controllers with internal 65V 1.25A power
creased up to 135kHz by connecting a resistor from SYNC to
ground (see applications information).
switches. The MIC2172 features external frequency syn- The MIC2172/3172 is available in an 8-pin plastic DIP or
chronization or frequency adjustment, while the MIC3172 SOIC for –40°C to +85°C operation.
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.
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
The MIC3172 is for applications that require on/off control of ^{• 7mA quiescent current (operating)}
the regulator. The MIC3172 is externally shutdown by ^{• <1µA quiescent current, shutdown mode (MIC3172)}
applying a TTL low signal to EN (enable). When disabled, the ^{• TTL shutdown compatibility (MIC3172)}
MIC3172 draws only leakage current (typically less than ^{• External frequency synchronization (MIC2172)}
4
1µA). EN must be high for normal operation. For applications ^{• External frequency trim (MIC2172)}
not requiring control, EN must be tied to V_IN or TTL high.
• Fits most LT1172 sockets (see applications info)
The MIC2172 is for applications requiring two or more SMPS ^Applications
regulators that operate from the same input supply. The • Laptop/palmtop computers
MIC2172 features a SYNC input which allows locking of its • Toys
internal oscillator to an external reference. This makes it • Hand-held instruments
possible to avoid the audible beat frequencies that result from • Off-line converter up to 50W
the unequal oscillator frequencies of independent SMPS
(requires external power switch)
regulators.
• Predriver for higher power capability
A reference signal can be supplied by one MIC2172 desig- ^{• Master/slave configurations (MIC2172)}
nated as a master. To insure locking of the slave’s oscillators,
the reference oscillator frequency must be higher than the
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
1997
4-13