wm8903 Wolfson Microelectronics plc, wm8903 Datasheet - Page 33

• Manufacturer Part Number: wm8903
• Description: Ultra Low Power Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
w
MICROPHONE INSERTION / REMOVAL DETECTION
In a typical application, microphone insertion would be detected when the MICBIAS current exceeds
the Current Detect threshold set by MICDET_THR. In order to generate a MICBIAS Current Detect
interrupt from this event, MICDET_INV must be cleared to 0 (see “Interrupts”).
For detection of microphone removal, the MICDET_INV bit must be set to 1. In this case, a MICBIAS
Current Detect interrupt is generated when the MICBIAS current falls below the threshold set by
MICDET_THR.
MICROPHONE INSERTION / REMOVAL DE-BOUNCE AND FILTERING
The detection of these events is bandwidth limited for best noise rejection, and is subject to detection
delay time t
has been set appropriately, each insertion or removal event is guaranteed to be detected within the
delay time t
It is likely that the microphone socket contacts will have mechanical “bounce” when a microphone is
inserted or removed, and hence the resultant control signal will not be a clean logic level transition.
Since t
mechanical “bounce” has ceased. Hence after a mic insertion or removal has been detected, a time
delay should be applied before re-configuring the MICDET_INV bit. The maximum possible
mechanical bounce times for mic insertion and removal must be understood by the software
programmer.
Utilising a GPIO pin to monitor the steady state of the microphone detection function does not
change the timing of the detection mechanism, so there will also be a delay t
changes state. It may be desirable to implement de-bounce in the host processor when monitoring
the state of the GPIO signal.
To illustrate this, an example sequence including mic insertion detection is detailed in the
“Applications Information” section on page 154.
MICROPHONE INSERTION / REMOVAL CLOCKING REQUIREMENTS
A clock is required for the Current Detect circuit. This requires:
Any microphone insertion (or removal) event which happens while one or more of the above criteria
are not satisfied (for example during a low power mode where the CPU has disabled MCLK) will still
be detected, but only after the clocking conditions are met. An example is illustrated in Figure 27,
where the mic is inserted while MCLK is stopped.
Figure 26 MIC Detection events without MCLK
Mic insertion event
1.
2.
3.
DET
MCLK to be present
CLK_SYS_ENA = 1
WSMD_CLK_ENA = 1
DET
has a range of values, it is possible that the interrupt will be generated before the
DET
.
, as specified in the Electrical Characteristics. Provided that the MICDET_THR field
MCLK
GPIO
IRQ
happens at any time
(1) insertion event
during this period
t
DET
(2) insertion indicated t
after MCLK re-started
PP, Rev 3.1, August 2009
DET
before the signal
WM8903
DET
33