LTC3613 FUNCTIONAL DIAGRAM VIN CIN PV SV IN IN INPUT SUPPLY IN CIN LDO OUT EN BO0ST UVLO D + B – 3.65V TG DRV MT C 4.2V B – R SW L SENSE VOUT EXTV 1.3μA CC + RUN + 0.75V 4.6V – – C 1.2V – START OUT LOGIC INTVCC CONTROL INTVCC VOUT ONE-SHOT STOP R TIMER FB2 CVCC BG DRV MB TIME RFB1 ADJUST PGND ICMP IREV – + – + CLOCK MODE/PLLIN CLOCK PLL DETECT SYSTEM SENSE+ SENSE– RT OSCILLATOR 1μA RT TRACK/SS + C + SS 0.6V INTVCC V + OSNS + 0.645V – + RPGD PGOOD OV EA DA – (g (A = 1) – m(EA) = 1.7mS) V – OSNS 3613 FD + UV– 0.555V VRNG ITH SGND INTVCC RITH R1 CITH1 R2 OPERATION (Refer to Functional Diagram)Main Control Loop In normal steady-state operation, the top MOSFET is turned on for a fixed time interval proportional to the delay in the The LTC3613 uses valley current mode control to regulate one-shot timer. The PLL system adjusts the delay in the the output voltage in a monolithic, all N-channel MOSFET one-shot timer until the top MOSFET turn-on is synchro- DC/DC step-down converter. Current control is achieved by nized either to the internal oscillator or the external clock sensing the inductor current across SENSE+ and SENSE–, input if provided. As the top MOSFET turns off, the bottom either by using an explicit resistor connected in series with MOSFET turns on with a small time delay (dead time) to the inductor or by implicitly sensing the inductor’s resis- avoid shoot-through current. The next switching cycle is tive (DCR) voltage drop through an RC filter connected initiated when the current comparator, I across the inductor. CMP, senses that inductor current has reached the valley threshold point 3613fa 10
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