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MIC2172BM Datasheet(PDF) 1 Page - Micrel Semiconductor |
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MIC2172BM Datasheet(HTML) 1 Page - Micrel Semiconductor |
1 / 16 page 1997 4-13 MIC2172/3172 Micrel 4 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) •<1 µA 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) 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 1 µA). 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 MIC2172/3172 100kHz 1.25A Switching Regulators Preliminary Information Typical Applications C4 470µF D2 1N5818 C1 22µF C2 1µF R3 1k R4* VOUT 5V, 0.25A * Optional voltage clipper (may be req’d if T1 leakage inductance too high) C3* D1* R1 3.74k 1% R2 1.24k 1% VIN 4V to 6V T1 Enable Shutdown 1:1.25 LPRI = 100µH MIC3172 VIN VSW FB EN GND P1 P2 S COMP Figure 2. MIC3172 5V Flyback Converter +5V (4.75V min.) D1 1N5822 MIC2172 VIN VSW FB C1* 22µF R3 1k C3 1µF R1 10.7k 1% C2 470µF VOUT +12V, 0.14A L1 27µH * Locate near MIC2172 when supply leads > 2 " R2 1.24k 1% SYNC GND P1 P2 S N/C COMP Figure 1. MIC2172 5V to 12V Boost Converter |
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