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CM3706AGIM25 Datasheet(PDF) 6 Page - Champion Microelectronic Corp. |
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CM3706AGIM25 Datasheet(HTML) 6 Page - Champion Microelectronic Corp. |
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6 / 11 page  CM3706A 1.5MHz, 600mA Synchronous Step-Down Regulator 2008/03/07 Rev. 1.0 Champion Microelectronic Corporation Page 6 FUNCTIONAL DESCRIPTION Operation CM3706A is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope compensated current mode architecture. This Step-Down DC-DC Converter supplies 600mA output current at VIN = 3V with input voltage range from 2.5V to 6.5V. Current Mode PWM Control Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of the internal main switch (P-Ch MOSFET) and synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The current comparator, ICOMP, limitsthe peak inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present. Dropout Operation When the input voltage decreases toward the value of the output voltage, the CM3706A allows the main switch to remain on for more than one switching cycle and increases the duty cycle (Note 5) until it reaches 100%. The output voltage then is the input voltageminus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the IC. Idle Mode Operation At very light loads, the CM3706A automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. Maximum Load Current The CM3706A will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases. Note 5 : The duty cycle D of a step-down converter is defined as: % 100 % 100 × ≈ × × = IN OUT OSC ON V V f T D where TON is the main switch on time, and fOSC is the oscillator frequency (1.5Mhz). |
Similar Part No. - CM3706AGIM25 |
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Similar Description - CM3706AGIM25 |
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