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LM2840-Q1, LM2841-Q1, LM2842-Q1

SNVSBE5 – APRIL 2019

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Product Folder Links: LM2840-Q1 LM2841-Q1 LM2842-Q1

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7.4 Device Functional Modes

7.4.1 Continuous Conduction Mode

The LM284x-Q1 contain a current-mode, PWM buck regulator. A buck regulator steps the input voltage down to

a lower output voltage. In continuous conduction mode (when the inductor current never reaches zero at steady-

state operation), the buck regulator operates in two cycles. The power switch is connected between VIN and SW.

In the first cycle of operation the transistor is closed and the diode is reverse biased. Energy is collected in the

inductor and the load current is supplied by COUT and the rising current through the inductor. During the second

cycle the transistor is open and the diode is forward biased due to the fact that the inductor current cannot

instantaneously change direction. The energy stored in the inductor is transferred to the load and output

capacitor. The ratio of these two cycles determines the output voltage. The output voltage is defined

approximately as shown in Equation 1.

D = VOUT / VIN

(1)

D’ = (1 – D)

where

•

D is the duty cycle of the switch

(2)

D and D' are required for design calculations.