-4

200 Ps

-3

-2

-1

0

1

2

3

4

No Clipping

With Soft

Clipping

LM48520, LM48520TLBD

SNAS367C – FEBRUARY 2008 – REVISED APRIL 2013

www.ti.com

the input traces to prevent the noise from injecting into the input.

4. The power supply bypass capacitors, Cs1 and Cs2 should be placed as close to the LM48520 device as

possible.

GROUNDING GUIDELINES

There are three grounds on the LM48520, GND, SW_GND, and PGND. When laying out the PCB, it is critical to

connect the grounds as close to the device as possible. The simplest way to do that is to place vias close to the

GND, SW_GND, and PGND bumps and connect the GND, SW_GND, and PGND vias using a single ground

plane in an inner layer of the PCB.

Output Speaker Protection Function

The LM48520’s output voltage limiter can be used to set a minimum and maximum output voltage swing

magnitude. The voltage applied to the VLimit pin controls the limit on the output voltage level. The output level is

determined by the following equation:

Vout clipped = 8/3 * (PV1 — 2 * Vlimit)

(13)

where:

Vout clipped = the desired output level measured in Vpk

PV1 = Boost output voltage

Vlimit is the voltage applied the the Vlimit pin on the LM48520

or

Vout clipped = 1/2 * (PV1 — 3/8 * Vout clipped)

(14)

To disable the limiter, set Vlimit = 0V.

Figure 22 provides an example of how the output voltage limiter functions with VDD = 3.3V, AV = 6dB, PV1 = 5V,

Vlimit = 2V, RL = 8Ω, VIN = 2VP.

Figure 22. Soft Clipping vs No Clipping

Revision History

Rev

Date

Description

1.0

02/27/08

Initial release.

1.01

03/07/08

Added the Soft clipping vs No clipping curve.

1.02

03/12/08

Text edits.

C

04/05/13

Changed layout of National Data Sheet to TI format.

14

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