The MIC2172 and MIC3172 are complete 100 kHz 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 7 mA 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 shut down by applying a TTL-low signal to EN (enable). When disabled, the MIC3172 draws only leakage current (typically less than 1 μA). 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 that require two or more SMPS regulators that operate from the same input supply. The MIC2172 features a SYNC input that 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 ensure locking of the slave’s oscillators, the reference oscillator frequency must be higher than the slave. The master MIC2172’s oscillator frequency is increased up to 135 kHz by connecting a resistor from SYNC to ground (see Section 5.0, Applications Information). The MIC2172/3172 is available in an 8-pin plastic DIP or SOIC for –40°C to +85°C ambient temperature operation.