6 output power limiter, 7 pwm control for performance improvement, Table 17 – NXP Semiconductors TFA9812 User Manual

Page 22: Tfa9812, Nxp semiconductors

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TFA9812_2

© NXP B.V. 2009. All rights reserved.

Preliminary data sheet

Rev. 02 — 22 January 2009

22 of 66

NXP Semiconductors

TFA9812

BTL stereo Class-D audio amplifier with I

2

S input

The I

2

C controls for selecting the +24 dB gain can be found in

Section 9.5.6

. The GAIN

pin has no function In I

2

C mode.

The TFA9812 features also specific gain settings which are related to < 0.5 %, 10 %, 20 %
or 30 % clipping at the output of the TFA9812. These clipping values are only valid under
the following conditions:

The volume control is set to 0 dB.

The gain boost is set to 0 dB.

A 0 dBFs I

2

S input signal is obtained.

The I

2

C controls for selecting a specific clip level can be found in

Section 9.5.6

. In Legacy

mode the clip level is set to 10 %.

8.5.6 Output power limiter

Output power can be limited to three discrete levels with respect to the maximum power.
The maximum power output value is determined by the value of the high voltage supply.
Clipping levels (see

Section 8.5.5

) still apply to the maximum levels of reduced output

voltage swings.

In I

2

C control mode the same output power limiting levels can be selected, see

Section 9.5.6

. In Legacy control mode two pins can be used to select the output power

limit level as shown in

Table 18

.

8.5.7 PWM control for performance improvement

The PWM switching frequency of the TFA9812 is dependent on:

The sampling frequency, f

s

.

The sampling frequency setting, f

s

(selected) (see

Section 9.5.7

).

The PWM switching frequency setting, f

sw

(selected) (see

Section 9.5.6

).

Equation 9

shows the relationship between these settings and the PWM carrier

frequency:

(9)

Table 17.

GAIN pin functionality

GAIN pin value

Function

0

0 dB gain

1

+24 dB gain

Table 18.

Legacy mode output power limiter control

Pin value

Function

ADSEL2/PLIM2

ADSEL1/PLIM1

0

0

Maximum power

0

1

Maximum power

1.5 dB

1

0

Maximum power

3.0 dB

1

1

Maximum power

4.5 dB

f

sw

f

s

f

s selected

)

(

)

----------------------------

f

sw selected

(

)

=

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