AS3525-A/-B C22O22
Data Sheet, Confidential
7.4.6
Headphone Output
7.4.6.1 General
The headphone output is designed to provide the audio signal with 2x40mW @ 16Ω 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 @ 16Ω is achieved, by setting the mixer output to 1Vp and using the gain of 1.07dB.
Figure 50 Headphone Output
Headphones connected via decoupling capacitors
Headphones connected to Phantom Ground
(Common Mode)
7.4.6.2 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.
7.4.6.3 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.
7.4.6.4 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.
7.4.6.5 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.
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