Vdd SW

IN-

IN+

GND

GND

OUT+

OUT-

VccOUT

VccIN

CIN

CIN

SD

SDa

GAIN

Digital

BaseBand

Analog

Baseband

or

CODEC

VIN

2.5Vto

5.5 V

Vref

BST

10 nF

1 F

m

4.7 H

m

10 F

m

10~20 W

10~22 H

m

10 F

m

0.1~2 F

m

1 F

m

R

L

SPK

R

C

ζ =

2

L

´

´

(4)

AUDMAX

SPK

1

=

2

R

C

´

´

´

f

p

(5)

AUDMAX

SPK

1

XC =

2 ×

×

× C

f

p

(6)

AUDMAX

XL = 2

L

f

p

´

´

´

(7)

(

)

2

2

Z =

R

+

XL

XC

-

(8)

OUTPEAK

CLASSDPEAK

V

I

=

Z

(9)

RESISTOR – SPEAKER LOAD CONFIGURATION

TPA2100P1

Figure 16. Application Schematic with Resistor – Speaker – Inductor Load Configuration

For the resistor – speaker – inductor load configuration, it is desired to make the output load configuration

overdamped (Zeta (

ζ) > 0.707). Use Equation 4 to calculate ζ:

If

ζ is greater than one, then the maximum audio frequency will be limited by the resistor – speaker capacitance

low pass filter as shown in Equation 5.

Calculate equivalent load impedance with Equation 6, through Equation 9.

To calculate the proper boost converter inductor required for this application, see the Inductor Selection section.

Note that an input low pass filter should be added before the audio amplifier in order to limit the audio frequency,

This load configuration is similar to the resistor – speaker – resistor load configuration. Apply the same equations

here to calculate the maximum audio frequency and maximum required current from the class-D audio amplifier.

Copyright © 2008, Texas Instruments Incorporated

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