MIC2172/3172 Micrel, Inc. MIC2172/3172 100kHz 1.25A Switching Regulators slaves. The master MIC2172s oscillator frequency is in- General Description creased up to 135kHz by connecting a resistor from SYNC to The MIC2172 and MIC3172 are complete 100kHz SMPS ground (see applications information). current-mode controllers with internal 65V 1.25A power The MIC2172/3172 is available in an 8-pin plastic DIP or switches. The MIC2172 features external frequency syn- SOIC for 40C to +85C operation. chronization or frequency adjustment, while the MIC3172 features an enable/shutdown control input. Features Although primarily intended for voltage step-up applications, 1.25A, 65V internal switch rating the floating switch architecture of the MIC2172/3172 makes 3V to 40V input voltage range it practical for step-down, inverting, and Cuk configurations Current-mode operation as well as isolated topologies. Internal cycle-by-cycle current limit Operating from 3V to 40V, the MIC2172/3172 draws only Thermal shutdown 7mA of quiescent current making it attractive for battery Low external parts count operated supplies. Operates in most switching topologies 7mA quiescent current (operating) The MIC3172 is for applications that require on/off control of <1A quiescent current, shutdown mode (MIC3172) the regulator. The MIC3172 is externally shutdown by TTL shutdown compatibility (MIC3172) applying a TTL low signal to EN (enable). When disabled, the External frequency synchronization (MIC2172) MIC3172 draws only leakage current (typically less than External frequency trim (MIC2172) 1A). EN must be high for normal operation. For applications Fits most LT1172 sockets (see applications info) not requiring control, EN must be tied to V or TTL high. IN Applications The MIC2172 is for applications requiring two or more SMPS 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 Master/slave configurations (MIC2172) A reference signal can be supplied by one MIC2172 desig- nated as a master. To insure locking of the slaves oscillators, the reference oscillator frequency must be higher than the Typical Applications V OUT V IN +5V 5V, 0.25A T1 4V to 6V (4.75V min.) D2 C1 R4* C3* C1* L1 1N5818 22F 22F R1 27H C4 3.74k V OUT 470F 1% D1* V D1 IN V +12V, 0.14A IN Enable V N/C SYNC SW EN V SW Shutdown R1 1:1.25 1N5822 MIC2172 10.7k L = 100H PRI MIC3172 1% COMP FB COMP FB GND R2 GND R3 R2 C2 P1 P2 S R3 1.24k P1 P2 S 1k 1.24k 470F 1k 1% C3 1% C2 1F 1F * Locate near MIC2172 when supply leads > 2 * Optional voltage clipper (may be reqd if T1 leakage inductance too high) Figure 1. Figure 2. MIC2172 5V to 12V Boost Converter MIC3172 5V Flyback Converter Micrel, Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 MIC2172/3172 Micrel, Inc. Ordering Information Part Number Temperature Standard Pb-Free Range Package MIC2172BN MIC2172YN 40C to +85C 8-pin plastic DIP MIC2172BM MIC2172YM 40C to +85C 8-lead SOIC MIC3172BN MIC3172YN 40C to +85C 8-pin plastic DIP MIC3172BM MIC3172YM 40C to +85C 8-lead SOIC Pin Configuration MIC2172*/3172 MIC2172*/3172 S GND 1 8 P GND 1 S GND 1 8 P GND 1 COMP 2 7 V COMP 2 7 V SW SW FB 3 6 P GND 2 FB 3 6 P GND 2 *SYNC/ EN 4 5 V *SYNC/ EN 4 5 V IN IN 8-pin DIP (N) 8-lead SOIC (M) Pin Description Pin Number Pin Name Pin Function 1S GND Signal Ground: Internal analog circuit ground. Connect directly to the input filter capacitor for proper operation (see applications info). Keep separate from power grounds. 2 COMP Frequency Compensation: Output of transconductance type error amplifier. Primary function is for loop stabilization. Can also be used for output voltage soft-start and current limit tailoring. 3FB Feedback: Inverting input of error amplifier. Connect to external resistive divider to set power supply output voltage. 4 (MIC2172) SYNC Synchronization/Frequency Adjust: Capacitively coupled input signal greater than devices free running frequency (up to 135kHz) will lock devices oscillator on falling edge. Oscillator frequency can be trimmed up to 135kHz by adding a resistor to ground. If unused, pin must float (no connection). 4 (MIC3172) EN Enable: Apply TTL high or connect to V to enable the regulator. Apply IN TTL low or connect to ground to disable the regulator. Device draws only leakage current (<1A) when disabled. 5V Supply Voltage: 3.0V to 40V IN 6P GND 2 Power Ground 2: One of two NPN power switch emitters with 0.3 current sense resistor in series. Required. Connect to external inductor or input voltage ground depending on circuit topology. 7V Power Switch Collector: Collector of NPN switch. Connect to external SW inductor or input voltage depending on circuit topology. 8P GND 1 Power Ground 1: One of two NPN power switch emitters with 0.3 current sense resistor in series. Optional. For maximum power capability connect to P GND 2. Floating pin reduces current limit by a factor of two. M9999-042205 2 April 2005