CS43131 datasheet(40/156 Pages) CIRRUS

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DS1155F1

CS43131

4.5 Headphone Presence Detect and Output Load Detection

The interrupt status bits can be found in Section 7.6.1.

4.5.2

HP Load Detection

The CS43131 can measure the impedance of headphone DC load. Before taking measurements, the following criteria

must be met:

• The CS43131 is out of reset.

• XTAL is powered on, an external MCLK is provided or PLL mode is used to generate internal MCLK. MCLK_INT is

properly configured.

• The headphone output is powered down (PDN_HP = 1).

• The alternate headphone input is powered down (HP_IN_EN = 0).

• HPDETECT is high to indicate a headphone is plugged in.

• The HPLOAD_EN bit is set to turn on the impedance measurement subsystem. HPLOAD_ON_INT is unmasked

and there has been a long enough wait to confirm the subsystem is properly started.

• The HPLOAD_DC_DONE interrupt is unmasked.

Either Channel A or Channel B to be measured by setting HPLOAD_CHN_SEL. The measurement process by clearing

and setting the HPLOAD_DC_START bit. Once started, HPLOAD_DC_BUSY bit is set and a slowly ramping voltage is

asserted on the headphone load for a maximum of 200 ms, then holds constant for 100 ms. Fig. 4-11 shows the a

waveform of the impedance detection voltage.

Figure 4-11. Impedance Detection Voltage

Upon measurement completion, the following occurs:

1. The voltage asserted ramps down for 200 ms and is then removed.

2. The result of the measured resistance is reported in RL_DC_STAT.

3. HPLOAD_DC_DONE bit is set and the interrupt is triggered.

4. If HPLOAD_DC_ONCE bit has not been set, it is set. This bit is sticky until an HP unplug event has happened.

Once interrupted, the application processor services the interrupt by reading HPLOAD_DC_DONE_INT. At this point,

another measurement process can be initiated by clearing and setting the HPLOAD_DC_START bit. The impedance

measurement subsystem can also be turned off by clearing the HPLOAD_EN bit. HPLOAD_EN must be cleared (and

confirmed by unmasked HPLOAD_OFF_INT) before enabling the headphone output or the alternate headphone input.

During the impedance measurement process, the following conditions trigger the error interrupt bits:

• The headphone load is not present or is unplugged before the impedance measurement is complete (HPLOAD_

UNPLUG_INT).

• The headphone load is out of range, as specified in Table 3-7 (HPLOAD_OOR_INT).

• The headphone load measurement process is started without HP being properly turned off (HPLOAD_HPON_INT).

• The AC headphone load measurement process is initiated before the HPLOAD_DC_ONCE bit is set (HPLOAD_

NO_DC_INT).

Time

Voltage

200 ms

100 ms

200 ms

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