L

PVDD

PVDD

I

= I

VBAT

0.8

æ

ö

´ ç

÷

´

è

ø

L

BOOST

VBAT

(PVDD

VBAT)

L =

I

PVDD

´

-

´

´

f

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Operation

NOTE:

The TPA2025D1 has an auto pass-through mode. Under normal operation (EN = HIGH), the

boost converter automatically turns off if no audio signal is present at one of the inputs (IN+

or IN-).

2.2

Boost Settings

The default voltage for the boost converter is 5.9 V (unloaded) and cannot be changed. If no audio signal

is present, the boost converter is automatically disabled. Once the audio signal is present at IN+ and IN-,

the boost converter enables automatically, when the output signal exceeds 2 V

2.2.1

Boost Terms

The following is a list of terms and definitions:

C

MIN

Minimum boost capacitance required for a given ripple voltage on PVOUT (PVDD)

L

Boost inductor

f

boost

Switching frequency of the boost converter

I

PVDD

Current pulled by the class-D amplifier from the boost converter

I

PVDD

Current pulled by the class-D amplifier from the boost converter

I

L

Current through the boost inductor.

PVDD (PVOUT)

Supply voltage for the class-D amplifier (Voltage generated by the boost converter

output)

VBAT (VDD)

Supply voltage to the TPA2025D1 (Supply voltage to the EVM).

ΔI

L

Ripple current through the inductor.

ΔV

Ripple voltage on PVOUT (PVDD) due to capacitance

2.2.2

Changing the Boost Inductor

Working inductance decreases as inductor current increases. If the drop in working inductance is severe

enough, it may cause the boost converter to become unstable, or cause the TPA2025D1 to reach its

current limit at a lower output power than expected. Inductor vendors specify currents at which inductor

values decrease by a specific percentage. This can vary by 10% to 35%. Inductance is also affected by dc

current and temperature.

Inductor current rating is determined by the requirements of the load. The inductance is determined by two

factors: the minimum value required for stability and the maximum ripple current permitted in the

application.

Use Equation 1 to determine the required current rating. Equation 1 shows the approximate relationship

between the average inductor current, I

PVOUT, and VBAT, respectively.) Insert I

inductor must maintain at least 90% of its initial inductance value at this current.

(1)

The minimum working inductance is 1.3

μH. A lower value may cause instability.

Ripple current,

ΔI

in the inductor as well as the potential for EMI. Use Equation 2 to determine the value of the inductor, L.

Equation 2 shows the relationships among inductance L, VBAT, PVDD, the switching frequency, f

ΔI

(2)

3

SLOU310

– September 2011

TPA2025D1 Audio Power Amplifier Evaluation Module

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