MIC2172/3172 100kHz 1.25A Switching Regulators General Description Features The MIC2172 and MIC3172 are complete 100kHz SMPS 1.25A, 65V internal switch rating current-mode controllers with internal 65V 1.25A power 3V to 40V input voltage range switches. The MIC2172 features external frequency Current-mode operation synchronization or frequency adjustment, while the Internal cycle-by-cycle current limit MIC3172 features an enable/shutdown control input. Thermal shutdown Although primarily intended for voltage step-up Low external parts count applications, the floating switch architecture of the MIC2172/3172 makes it practical for step-down, inverting, Operates in most switching topologies and Cuk configurations as well as isolated topologies. 7mA quiescent current (operating) Operating from 3V to 40V, the MIC2172/3172 draws only <1A quiescent current, shutdown mode (MIC3172) 7mA of quiescent current making it attractive for battery TTL shutdown compatibility (MIC3172) operated supplies. External frequency synchronization (MIC2172) The MIC3172 is for applications that require on/off control External frequency trim (MIC2172) of the regulator. The MIC3172 is externally shutdown by applying a TTL low signal to EN (enable). When disabled, Fits most LT1172 sockets (see applications info) the MIC3172 draws only leakage current (typically less than 1A). EN must be high for normal operation. For Applications applications not requiring control, EN must be tied to VIN or Laptop/palmtop computers TTL high. Toys The MIC2172 is for applications requiring two or more SMPS regulators that operate from the same input supply. Hand-held instruments The MIC2172 features a SYNC input which allows locking Off-line converter up to 50W (requires external power of its internal oscillator to an external reference. This switch) makes it possible to avoid the audible beat frequencies Predriver for higher power capability that result from the unequal oscillator frequencies of Master/slave configurations (MIC2172) independent SMPS regulators. A reference signal can be supplied by one MIC2172 designated as a master. To insure locking of the slaves oscillators, the reference oscillator frequency must be higher than the slaves. The master MIC2172s 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 40C to +85C operation. Micrel Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel +1 (408) 944-0800 fax + 1 (408) 474-1000 Micrel MIC2172/3172 Typical Applications Figure 1. MIC2172 5V to 12V Boost Converter Figure 2. MIC3172 Flyback Converter Ordering Information Part Number Junction Temp. Range Package Standard Pb-Free MIC2172BN MIC2172YN 40C to +85C 8-pin plastic DIP MIC2172BM MIC2172YM 40C to +85C 8-pin SOIC MIC3172BN MIC3172YN 40C to +85C 8-pin plastic DIP MIC3172BM MIC3172YM 40C to +85C 8-pin SOIC Note: 1. Other Voltage available. Contact Micrel for details. Pin Configuration 8-pin DIP (N) 8-pin SOIC (M) M9999-041806 April 2006 2 (408) 955-1690