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MIC2182 Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC2182 Datasheet(HTML) 10 Page - Micrel Semiconductor |
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10 / 28 page  MIC2182 Micrel M9999-042204 10 April 22, 2004 Functional Description See “Applications Information” following this section for com- ponent selection information and Figure 14 and Tables 1 through 5 for predesigned circuits. The MIC2182 is a BiCMOS, switched-mode, synchronous step-down (buck) converter controller. Current-mode control is used to achieve superior transient line and load regulation. An internal corrective ramp provides slope compensation for stable operation above a 50% duty cycle. The controller is optimized for high-efficiency, high-performance dc-dc con- verter applications. The MIC2182 block diagrams are shown in Figure 2a and Figure 2b. The MIC2182 controller is divided into 6 functions. • Control loop - PWM operation - Skip-mode operation • Current limit • Reference, enable, and UVLO • MOSFET gate drive • Oscillator and sync • Soft start Control Loop PWM and Skip Modes of Operation The MIC2182 operates in PWM (pulse-width-modulation) mode at heavier output load conditions. At lighter load condi- tions, the controller can be configured to automatically switch to a pulse-skipping mode to improve efficiency. The potential disadvantage of skip mode is the variable switching fre- quency that accompanies this mode of operation. The occur- rence of switching pulses depends on component values as well as line and load conditions. There is an external sync function that is disabled in skip mode. In PWM mode, the synchronous buck converter forces continuous current to flow in the inductor. In skip mode, current through the inductor can settle to zero, causing voltage ringing across the induc- tor. Pulling the PWM pin (pin 2) low will force the controller to operate in PWM mode for all load conditions, which will improve cross regulation of transformer-coupled, multiple output configurations. PWM Control Loop The MIC2182 uses current-mode control to regulate the output voltage. This method senses the output voltage (outer loop) and the inductor current (inner loop). It uses inductor current and output voltage to determine the duty cycle of the buck converter. Sampling the inductor current removes the inductor from the control loop, which simplifies compensa- tion. Current Sense Amp Error Amp VIN VDD CORRECTIVE RAMP PWM COMPARATOR RESET Reference Oscillator 11 14 10 16 15 13 12 8 9 7 3 COMP 100k MIC2182 [adj.] PWM Mode FB R2 R1 VOUT CSH VDD VBST CIN VIN HSD Q2 Q1 D1 D2 CBST COUT VIN VOUT L1 VSW LSD PGND CCOMP RCOMP 4.7 µF V 1.245V R1 R2 OUT =+ 1 S R Q CONTROL LOGIC AND PULSE-WIDTH MODULATOR RCS Gm = 0.2×10 -3 AV = 2 0.024V PWM Mode to Skip Mode LOW FORCES SKIP MODE Figure 3. PWM Operation |
Similar Part No. - MIC2182_04 |
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Similar Description - MIC2182_04 |
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