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Hardware Description
3.7.2
Headset Interface
This interface is single-ended, with both the input and output referenced to analog ground (AGND). The interface is intended
for headsets with an active condenser microphone and a 32Ω speaker. The HEADSET_INT_N interrupt line should be used to
detect that the headset is plugged in, and to ensure that the c18 selects the required audio path. HEADSET_INT_N is internally
pulled up (27 K), and should therefore be shorted to the ground when the headset is connected to the module.
An optional (normally closed) switch can be used for answering/ending (SEND/END) an incoming call from the headset. The
c18 monitors the HEADSET_MIC signal DC level, in order to define the state of the SEND/END switch. Be sure to pull down
the microphone input when the headset is unplugged from the c18. Figure 15 shows the headset interface:
The output power for the single-ended headset earpiece output is typically 8.8 mW for a full-scale +3dBm0 sine wave into a
32Ω speaker. The integrator should prepare a resistor in series with the headset earpiece (on HEADSET_SP line), in order to
provide a means for limiting the maximum output level and to ensure safety compliance.
3.7.3
Hands-free Audio (Auxiliary Audio) Interface
This single-ended interface is intended for car-kit-like applications. Because the audio output is used as an on/off signal (with
DC bias on it), an external capacitor should be used (1µF or more), as shown in Figure 16.
All maximum hands-free audio levels specified in this document refer to the 1kH sine wave with a 10kΩ load on the
AUDIO_OUT_ONOFF output and a volume set to audio level 3. This load represents input impedance of an amplifier typically
used in a car kit. There is no significant change in the audio levels for loads with an impedance higher than 10 kΩ. The module
is capable of driving lower impedances as well, down to 600 Ω, but at lower audio levels. For example, the output signal level
under the same conditions, but with a 600Ω load is around 300 mVp-p (instead of 1.06 Vp-p with a 10kΩ load).
Muting the external audio circuitry connected to the AUDIO_OUT_ONOFF signal is suggested, in order to reduce "pops" from
occurring due to the AUDIO_OUT_ONOFF transitions that occur when the ON/OFF switch is pressed or released. The
simplified way to do this is shown in Figure 16.
30
c18
MSM5100
2.2kΩ
MBIAS
0.1uF
MIC2P
MIC2N
0.1uF
AGND
SEND/END
SEND_END_DET
DETECT
22uF
EAR2
27kΩ
Figure 15. Headset Interface
OPTIONAL
SEND/END
SWITCH
N.C.
HEADSET_MIC
57
2.2kΩ
AGND
AGND
0-100Ω
HEADSET_SP
65
AGND
HEADSET_INT_N
55
AGND
59
AGND
98-08901C63-A
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