IRMS = ILOAD

D(1-D)

CSS

PVIN

AVIN

EN

SS

SGND

PGND

SNS

SW

LM2852

+

VOUT = 1.8V

ILOAD = 0A to 2A

LO

CIN

VIN = 3.3V

Cf

Rf

CINX

CO

U1

12

LM2852

SNVS325E – JANUARY 2005 – REVISED JANUARY 2016

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Copyright © 2005–2016, Texas Instruments Incorporated

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 must

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM2852 is a DC-DC synchronous buck regulator capable of driving a maximum load current of 2A, with an

input range of 2.85 V to 5.5 V and a variable output range of 0.8 V to 3.3 V. Figure 13 is a schematic example of

a typical application.

8.2 Typical Application

Figure 13. LM2852 Example Circuit Schematic

8.2.1 Design Requirements

A typical application requires only four components: an input capacitor, a soft-start capacitor, an output filter

capacitor and an output filter inductor. To properly size the components for the application, the designer needs

the following parameters: input voltage range, output voltage, output current range, and required switching

frequency. These four main parameters affect the choices of component available to achieve a proper system

behavior.

8.2.2 Detailed Design Procedure

8.2.2.1 Input Capacitor (CIN)

Fast switching of large currents in the buck converter places a heavy demand on the voltage source supplying

PVIN. The input capacitor, CIN, supplies extra charge when the switcher needs to draw a burst of current from

the supply. The RMS current rating and the voltage rating of the CIN capacitor are therefore important in the

selection of CIN. The RMS current specification can be approximated by Equation 1:

where

•

D is the duty cycle, VOUT/VIN. CIN also provides filtering of the supply.

(1)

Trace resistance and inductance degrade the benefits of the input capacitor, so CIN must be placed very close to

PVIN in the layout. A 22-µF or 47-µF ceramic capacitor is typically sufficient for CIN. In parallel with the large

input capacitance a smaller capacitor may be added such as a 1-µF ceramic for higher frequency filtering.