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LTM4607 Datasheet(PDF) 10 Page - Linear Technology |
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LTM4607 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 24 page  LTM4607 10 4607f locked loop comprised of an internal voltage controlled oscillator and a phase detector. This allows turning on the internal top MOSFET for locking to the rising edge of the external clock. A pulse detection circuit is used to detect a clock on the PLLIN pin to turn on the phase lock loop. The input pulse width of the clock has to be at least 400ns, and 2V in amplitude. The synchronized frequency ranges from 200kHz to 400kHz, corresponding to a DC voltage input from 0V to 2.4V at PLLFLTR. During the start up of the regulator, the phase-lock loop function is disabled. APPLICATIONS INFORMATION Figure 2. Frequency vs PLLFLTR Pin Voltage Low Current Operation To improve the efficiency at low current operation, LTM4607 provides three modes for both buck and boost operations by accepting a logic input on the FCB pin. Table 2 shows the different operation modes. Table 2. Different Operating Modes FCB PIN BUCK BOOST 0V to 0.75V Force Continuous Mode Force Continuous Mode 0.85V to 5V Skip-Cycle Mode Burst Mode Operation >5.3V DCM with Constant Freq DCM with Constant Freq When the FCB pin voltage is lower than 0.8V, the controller behaves as a continuous, PWM current mode synchronous switching regulator. When the FCB pin voltage is below VINTVCC – 1V, but greater than 0.8V, the controller enters Burst Mode operation in boost operation or enters skip- cycle mode in buck operation. During boost operation, Burst Mode operation is activated if the load current is lower than the preset minimum output current level. The MOSFETs will turn on for several cycles, followed by a variable “sleep” interval depending upon the load current. During buck operation, skip-cycle mode sets a minimum positive inductor current level. In this mode, some cycles will be skipped when the output load current drops below 1% of the maximum designed load in order to maintain the output voltage. When the FCB pin voltage is tied to the INTVCC pin, the controller enters constant frequency discontinuous current mode (DCM). For boost operation, if the output voltage is high enough, the controller can enter the continuous current buck mode for one cycle to discharge inductor current. In the following cycle, the controller will resume DCM boost operation. for buck operation, constant frequency discon- tinuous current mode is turned on if the preset minimum negative inductor current level is reached. At very light loads, this constant frequency operation is not as efficient as Burst Mode operation or skip-cycle, but does provide low noise, constant frequency operation. Input Capacitors In boost mode, since the input current is continuous, only minimum input capacitors are required. However, the input current is discontinuous in buck mode. So the selection of input capacitor CIN is driven by the need of filtering the input square wave current. For a buck converter, the switching duty-cycle can be estimated as: D V V OUT IN = Without considering the inductor current ripple, the RMS current of the input capacitor can be estimated as: I CIN(RMS) = I OUT(MAX) η •D • (1− D) In the above equation, η is the estimated efficiency of the power module. CIN can be a switcher-rated electrolytic aluminum capacitor, OS-CON capacitor or high volume ceramic capacitors. Note the capacitor ripple current rat- PLLFLTR PIN VOLTAGE (V) 0 0.5 2.0 450 400 350 300 250 200 150 100 50 0 4607 F02 1.0 1.5 2.5 |
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Similar Description - LTM4607 |
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