LM3478MASLASHNOPB datasheet(16/43 Pages) TI2

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LM3478

SNVS085X – JULY 2000 – REVISED DECEMBER 2017

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM3478 may be operated in either the continuous conduction mode (CCM) or the discontinuous current

conduction mode (DCM). The following applications are designed for the CCM operation. This mode of operation

has higher efficiency and usually lower EMI characteristics than the DCM.

8.2 Typical Applications

8.2.1 Typical High Efficiency Step-Up (Boost) Converter

Figure 27. Typical High Efficiency Step-Up (Boost) Converter Schematic

The boost converter converts a low input voltage into a higher output voltage. The basic configuration for a boost

converter is shown in Figure 28. In the CCM (when the inductor current never reaches zero at steady state), the

boost regulator operates in two states. In the first state of operation, MOSFET Q is turned on and energy is

stored in the inductor. During this state, diode D is reverse biased and load current is supplied by the output

capacitor, COUT.

In the second state, MOSFET Q is off and the diode is forward biased. The energy stored in the inductor is

transferred to the load and the output capacitor. The ratio of the switch on time to the total period is the duty

cycle D as shown in Equation 8.

D = 1 - (Vin / Vout)

(8)

Including the voltage drop across the MOSFET and the diode the definition for the duty cycle is shown in

Equation 9.

D = 1 - ((Vin - Vq)/(Vout + Vd))

(9)

Vd is the forward voltage drop of the diode and Vq is the voltage drop across the MOSFET when it is on.

LM3478MA/NOPB Datasheet(PDF) 16 Page - Texas Instruments