MIC3172YM

General Description
The MIC2172 and MIC3172YM 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 MIC3172YM 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 MIC3172YM is for applications that require on/off control of the regulator. The MIC3172YM is externally shutdown by applying a TTL low signal to EN (enable). When disabled, the MIC3172YM 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 VIN 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)

Feature