AS3515_08 datasheet(11/67 Pages) AMSCO

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AS3515 V15

austriamicrosystems

Data Sheet, Confidential

www.austriamicrosystems.com

Revision 3.1

- 66

6.2

Headphone Output

6.2.1

General

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

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

headphones.

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. The maximum output power of 40mW @ 16

Ω is achieved, by setting the mixer output to 1Vp and using the gain of

1.07dB.

Figure 3 Headphone-Output

6.2.2

Phantom Ground

HPCM pin is the buffered HPGND output. It can be used to drive the loads without external blocking capacitors between HPL / HPR and

HPCM. If the load is between HPR / HPL and BVSS, 100uF of de-coupling capacitors are needed. The phantom ground can be switched

off to save power if not needed.

6.2.3

No-Pop Function

To avoiding click and pop noise during power-up and shutdown, the output is automatically set to mute when the output stage is disabled.

HPGND pin, which needs a 100nF capacitor outside, gets charged on power-up with 2uA to AGND=1.45V. After start-up the DC level of

the following pins are the same: HPR=HPL=HPCM=HPGND=AGND=1.45V. The Start-up time before releasing mute is about 90ms. To

avoid pop-noise 150ms discharging time of HPGND after a shutdown, have to be waited before starting up again.

6.2.4

Over-current Protection

This output stage has an over-current protection, which disables the output for 256ms or 512ms. This value can be set in the headphone

registers. The over-current protection limit of HPR and HPL pin is typical 145mA while HPCM pin has a 210mA threshold. If needed, the

over-current condition can also be signalled via an interrupt to the controlling microprocessor.

6.2.5

Headphone Detection

With a control bit the headphone detection can be enabled. The detection is only working as long as the headphone stage is in power

down mode and the load is applied between HPR / HPL and HPCM. the headphone detection can also trigger a corresponding interrupt.

6.2.6

Power Save Options

To save power, especially when driving 32 Ohm loads, a reduction of the bias current can be selected. Together with switching off the

phantom ground this gives 4 possible operating modes.

Table 7

Headphone Power-Save Options

HPCM_OFF

IBR_HPH

IDD_HPH (typ.)

Load

2.2mA

16 Ohm

1.5mA

16 Ohm

1.5mA

32 Ohm

1.0mA

32 Ohm

BVDD = 3.3V, TA= 25oC unless otherwise mentioned

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