MIC2172 MICREL [Micrel Semiconductor], MIC2172 Datasheet
MIC2172
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MIC2172 Summary of contents
Page 1
... 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 ...
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... COMP *SYNC/ † 8-lead DIP (N) Pin Description Pin Number Pin Name 1 S GND 2 COMP (MIC2172) SYNC 4 (MIC3172 GND GND 1 Temperature Range – +85 C – +85 C – +85 C – +85 C † ...
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... MIC2172/3172 Absolute Maximum Ratings MIC2172 Input Voltage ................................................................. 40V Switch Voltage .............................................................. 65V Sync Current .............................................................. 50mA Feedback Voltage (Transient, 1ms) ........................... 15V Operating Temperature Range 8-pin PDIP ................................................. –40 to +85 C 8-pin SOIC ................................................ –40 to +85 C Electrical Characteristics MIC2172 Parameter Conditions Reference Section Pin 2 tied to pin 3 Feedback Voltage (V ...
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... MIC2172/3172 Parameter Conditions Oscillator Section Frequency ( Duty Cycle [ (max)] Sync Coupling Capacitor V PP Required for Frequency Lock V PP Peak-to-Peak Voltage C COUPLING Required for Frequency Lock Input Supply Voltage Section Minimum Operating Voltage Quiescent Current ( Supply Current Increase ( Bold type denotes specifications applicable to the full operating temperature range ...
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... MIC2172/3172 Parameter Conditions Error Amplifier Section Transconductance ( COMP FB COMP Voltage Gain ( 0.9V COMP FB Output Current V COMP Output Swing High Clamp, V Low Clamp, V Compensation Pin Duty Cycle = 0 Threshold Output Switch Section ON Resistance I SW Current Limit Duty Cycle = 50%, T Duty Cycle = 50%, T Duty Cycle = 80% Note 2 ...
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... MIC2172/3172 Typical Performance Characteristics MIC2172 Minimum Operating Voltage 2.9 2.8 2.7 2.6 Switch Current = 1A 2.5 2.4 2.3 -100 - 100 150 Temperature ( C) Supply Current D. D. Operating Voltage (V) IN Supply Current 90 50% 0 0.0 0.5 1.0 1.5 2.0 Switch Current (A) Supply Current ...
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... MIC2172/3172 Typical Performance Characteristics Error Amplifier Gain 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -100 - 100 150 Temperature ( C) Block Diagram MIC2172 V Reg SYNC Pin 4 FB Pin 3 1.24V Ref. S GND Pin 1 1997 Error Amplifier Gain 7000 6000 5000 4000 3000 2000 1000 100 1000 ...
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... Anti-Saturation The anti-saturation diode (D1) increases the usable duty cycle range of the MIC2172/3172 by eliminating the base to collector stored charge which would delay Q1’s turnoff. Compensation Loop stability compensation of the MIC2172/3172 can be ...
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... SYNC to ground. U2-SYNC and U3-SYNC are capacitively coupled to the master’s output (V slaves lock to the negative (falling edge) of U1’s output waveform. MIC3172 COMP Figure 7. External Synchronization R1 Care must be exercised to insure that the master MIC2172 is C1 always operating in continuous mode. 4- SYNC U1 ...
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... MIC2172/3172 Figure 7 shows how one or more MIC2172s can be locked to an external reference frequency. The slaves lock to the negative (falling edge) of the external reference waveform. Soft Start A diode-coupled capacitor from COMP to circuit ground slows the output voltage rise at turn on (figure 8 MIC2172/3172 ...
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... 1µF * Locate near MIC2172 when supply leads > 2 " Figure 11 12V Boost Converter The first step in designing a boost converter is determining whether inductor L1 will cause the converter to operate in either continuous or discontinuous mode. Discontinuous mode is preferred because the feedback control of the converter is simpler ...
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... A simple frequency compensation network consisting of R3 and C2 prevents output oscillations. High impedance output stages (transconductance type) in the MIC2172/3172 often permit simplified loop-stability solu- tions to be connected to circuit ground, although a more conventional technique of connecting the components from the error amplifier output to its inverting input is also possible. ...
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... The slightly higher duty cycle value is used to overcome circuit inefficiencies. A few iterations of equation (8) may be required if the duty cycle is found to be greater than 50%. Calculate the maximum transformer turns ratio that will guarantee safe operation of the MIC2172/ PRI SEC 3172 power switch – ...
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... Where output rectifier maximum peak BR reverse voltage rating V IN C1* 100µF * Locate near MIC2172/3172 when supply leads > 2 " † R3/R2 sets output voltage a = transformer turns ratio (0. Then 1N5817 will safely handle voltage and current require- ments in this example. ...
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... MIC2172/3172 50%, the MIC2172 (and MIC3172) has a maximum duty cycle capability of 90%. If 90% was required during operation (start-up and high load currents), a complete reset of the transformer during the off-time would require the voltage across the power switch to be ten times the input voltage. ...
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... MIC2172/3172 On/Off Control Especially important for battery powered applications, the lamp can be remotely or automatically turned off using the MIC3172’s EN pin. The entire circuit draws less than 1 A while shutdown 4.5V to 20V Enable (On) Shutdown (Off) Figure 15. LCD Backlight Fluorescent Lamp Supply ...