CS51033

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6

Buck Regulator Operation

A block diagram of a typical buck regulator is shown in

Figure 4. If we assume that the output transistor is initially

off, and the system is in discontinuous operation, the

nominal value. The current drawn by the load is supplied by

below the threshold established by the feedback resistors R1

Q1 switches on and current flows through the inductor to the

output. The inductor current rises at a rate determined by

CS51033 is limited to 80%. If output voltage remains higher

does not turn on, skipping the pulse.

Figure 4. Buck Regulator Block Diagram

L

Feedback

Control

Charge Pump Circuit

(Refer to the CS51033 Application Diagram on page 2).

input voltage is below 5.0 V to ensure that there is suffifient

capacitors C1 and C2 will be charged to a diodes drop below

FET turns on, it’s drain voltage will be approximately equal

instantaneously, D2 is reverse biased and the anode voltage

rises to approximately 2.0

× 3.3 V − VD2. C1 transfers some

of its stored charge C2 via D3. After several cycles there is

sufficient gate drive voltage.