DirectPath Headphone Amplifier

Voice Bypass Mode

HEADPHONE AMPLIFIER GAIN

VOLUME CONTROL

TPA2051D3

Table 1. Class-D Amplifier Gain Levels

CLASS-D GAIN

NOMINAL GAIN

REGISTER BYTE:

SPK_GAIN

0

+6 dB

1

+12 dB

Set the HPL_Enable bit (Register 1, Bit 3) to logic high to enable the headphone left output and the HPR_Enable

bit (Register 1, Bit 2) to logic high to enable the headphone right output. The headphone amplifier draws 4.1 mA

of typical supply current with both left and right outputs active and less than 1

µA when deactivated.

Set the VM_Bypass bit (Register 1, Bit 0) to logic high to the bypass mode from BYPASS+ and BYPASS–to the

speaker pins (OUT+ and OUT-pins). This will automatically disable the Class-D speaker amplifier.

The Headphone amplifier gain can be differentiated from the default volume control gain. Register 6, bits 7 to 5

and register 5 bit 6 can be used to attenuate the gain on the headphone amplifier. This function is useful to

differentiate the channel gain of the speaker amplifier from the channel gain of the headphone amplifier. So for

the same input signal different output voltage levels for the speaker and the headphone amplifier can be

selected. The following table shows the gain values. This feature is required since the headphone does not

require the same output voltage level as the speaker amplifier.

Table 2. Headphone Amplifier Gain Levels

HEADPHONE GAIN

HEADPHONE GAIN

REGISTER BYTE:

NOMINAL GAIN

REGISTER BYTE:

NOMINAL GAIN

HP_0dB, HP_GAIN[2:0]

HP_0DB, HP_GAIN[2:0]

0000

-12 dB

0101

-4.5 dB

0001

-10.5 dB

0110

-3 dB

0010

-9 dB

0111

-1.5 dB

0011

-7.5 dB

1xxx

0 dB

0100

-6 dB

The TPA2051D3 has three independent volume controls: One for the mono input configurations (Mode 0), one

for the STEREO1 input pair (INL1 and INR1, when in Mode 1, 3, 5, and 6), and one for the STEREO2 input pair

(INL2 and INR2, when in Mode 2 and 4). Each have 5-bit (32-step) resolution and are audio tapered; gain step

changes become smaller at higher gain settings. All volume controls range from –66 dB to +18 dB.

The Class-D speaker amplifier gain can be selected between 6 dB and 12 dB on top of the volume control. Thus

the total gain for the speaker channel (volume control plus Class-D amplifier) range is from –60 dB to +30 dB.

The headphone amplifiers have a secondary volume control (see Headphone Amplifier Gain section) besides the

main volume control. The secondary volume control ranges from –12 dB to 0 dB in 1.5 dB steps. Thus the total

gain for the headphone channel (volume control plus headphone amplifier) range is from –78 dB to +18 dB.

The Mono Input volume control byte is located in Register 4, Bits 4 to 0. The Stereo Input 1 volume control byte

is located at Register 5, Bits 4 to 0, and the Stereo Input 2 volume control byte is at Register 6, Bits 4 to 0. Gain

matching between the left and right channels for STEREO1 and STEREO2 is presented in the operating

characteristics table.

The input impedance to the TPA2051D3 changes as gain changes. See the Operating Characteristics section for

specifications. Values listed in Table 3 are nominal values.

attack time (volume decrease) and the release time (volume increase).

Copyright © 2009, Texas Instruments Incorporated

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