AS3517H-ECTP datasheet(22/94 Pages) AMSCO

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AS3517 V17

Data Sheet, Confidential

www.austriamicrosystems.com

9.1.4

Headphone Output

General

The headphone output is designed to provide the audio signal with 2x40mW @ 16

Ω or 2x20mW @32Ω, which are typical values for

headphones. If the limiters (N20/N21) are disabled a maximum output of 2x60mW@16Ω or 2x30mW@32Ω can be achieved.

This output stage has an independent gain regulation for left and right channel with 32 steps @ 1.5dB each. The gain can be set from –

43.43dB to +1.07dB. A zero cross detection allows to control the actual execution of new gain settings.

Figure 8 Headphone Output

Headphones connected via decoupling capacitors

Headphones connected to Phantom Ground

(Common Mode)

Phantom Ground

There are 2 ways to connect a headphone to the AFE. In order to spare the bulky ac/dc decoupling capacitors at pins HPR/HPL a

buffered ground (Phantom Ground) is provided. This Common Mode Buffer needs to be switched on if utilized. If form factor

considerations are less stringent, the headphones can be conventionally connected via 2x100µF capacitors.

No-Pop Function

The output is automatically set to mute when the output stage is disabled.

To avoid Pop-Click noise during power-up and shut-down of the headphone amplifier, a charge/discharge control of HPGND (0V-1.45V-

0V) at pins HPR/HPL is incorporated into the AFE. The 100nF capacitor at pin HPGND is used to form the charge/discharge slope. Pls

observe that pin HPGND is a high impedance node which must not be connected to any other external device than the 100nF buffer

capacitor. To avoid Pop-Click noise one has to wait for 150ms in between a power-down (switch-off) and a power-up (switch-on) of the

headphone amplifier.

The output is automatically set to mute when the output stage is disabled.

Figure 9 HP POP-Click Suppression

HPGND [V]

70ms

AGND

MUTE OFF

HP Amps

powered down

Operation

Revision 1v3

- 93

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