Datasheet LTC3833 (Analog Devices) - 10

LTC3833
FUNCTIONAL DIAGRAM
VIN CIN VIN IN LDO OUT EN BO0ST UVLO D C + B B TG – 3.65V TG DRV MT 4.2V – SW L RSENSE VOUT EXTV 1.3µA CC RUN + + 0.75V – – 4.6V C 1.2V – START OUT LOGIC INTVCC CONTROL INTVCC VOUT ONE-SHOT STOP TIMER RFB2 CVCC BG TIME BG DRV MB RFB1 ADJUST PGND I I – CMP + – REV + CLOCK MODE/PLLIN CLOCK PLL DETECT SYSTEM SENSE+ SENSE– RT R OSCILLATOR 1µA T + TRACK/SS + C 0.6V SS INTVCC V + + 0.645V – + OSNS RPGD PGOOD OV EA DA – (g (A = 1) – m(EA) = 1.7mS) – VOSNS 3833 FD + –UV 0.555V VRNG ITH SGND INTVCC RITH R1 CITH1 R2
OPERATION (Refer to Functional Diagram) Main Control Loop
one-shot timer. The PLL system adjusts the delay in the The LTC3833 uses valley current mode control to regulate one-shot timer until the top MOSFET turn-on is synchro- the output voltage in an all N-channel MOSFET DC/DC step- nized either to the internal oscillator or the external clock down converter. Current control is achieved by sensing input if provided. As the top MOSFET turns off, the bottom the inductor current across SENSE+ and SENSE–, either MOSFET turns on with a small time delay (dead time) to by using an explicit resistor connected in series with the avoid shoot-through current. The next switching cycle is inductor or by implicitly sensing the inductor’s resistive initiated when the current comparator, ICMP , senses that (DCR) voltage drop through an RC filter connected across inductor current has reached the valley threshold point the inductor. and turns the bottom MOSFET off immediately and the top MOSFET on. Again in order to avoid shoot-through In normal steady-state operation, the top MOSFET is turned current there is a small dead-time delay before the top on for a fixed time interval proportional to the delay in the MOSFET turns on. 3833f 10