CS43131 datasheet(41/156 Pages) CIRRUS

41 / 156 page

DS1155F1

CS43131

4.6 Clocking Architecture

The HPLOAD error interrupt bits are sticky. If any HPLOAD error interrupt bits are flagged, the RL_DC_STAT value should

be treated as invalid.

4.5.2.1 AC Load Detection

The CS43131 can also measure the headphone load impedance in the frequency range of 20 Hz to 20 kHz. The required

conditions before the measurement is similar to the low frequency load measurement, with one exception—HPLOAD_

MEAS_FREQ is set at the frequency of interest. Refer to Section 7.5.14 and Section 7.5.15 for details.

After HPLOAD_AC_START bit is cleared and set:

1. HPLOAD_AC_BUSY bit is set

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

3. HPLOAD_AC_DONE_INT is set and the interrupt is triggered.

For each headphone, the low-frequency load measurement must be performed (as indicated by the HPLOAD_DC_ONCE

bit) before any impedance is measured at other frequencies. If the low-frequency load measurement is not performed and

the process is initiated by pulsing the HPLOAD_AC_START bit low and high, the CS43131 can not generate a test signal

and sets the HPLOAD_NO_DC_INT error interrupt bit. Any RL_AC_STAT value should be treated as invalid.

Once the measurement begins, a tone at the specified frequency is applied on the headphone load. Because the test tone

is in the audio frequency range, it can be audible by the headphone user. It is recommended that the user system notify

the headphone user of the expected events before initiating this measurement.

For each frequency, the measurement completion time is affected by the frequency of interest. The lower the frequency,

the longer the measurement time. For the relationship between the frequency under test and the measurement time, the

following applies:

• For frequencies under test less than 6 kHz or when the CS43131 comes out of reset, 10 periods of the test tone is

the measurement time.

• For frequencies under test between 6 and 13 kHz, 20 periods of the test tone is the measurement time.

• For frequencies under test between 13 and 20 kHz, 30 periods of the test tone is the measurement time.

See Section 5.14.2 for example code of AC impedance measurement.

4.6 Clocking Architecture

4.6.1

Master Clock (MCLK) Sources

The MCLK is required by the CS43131 to operate any functionality associated with control, serial-port operation, or data

conversion. Depending on the setting of MCLK_SRC_SEL (see p. 114), the MCLK can be provided by one of following

methods:

• Sourced from a crystal oscillator between XTI/MCLK and XTO pins (see Fig. 4-12), then used directly as MCLK_INT

• Externally sourced through the XTI/MCLK input pin (see Fig. 4-13)

• PLL reference clock is provided through the XTI/MCLK input pin (see Fig. 4-13), then use internal PLL to convert

into MCLK_INT

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