CS47L35 datasheet(160/300 Pages) CIRRUS

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DS1085F3

CS47L35

4.12 External Accessory Detection

Equation 4-2. Headphone Impedance Calculation

The associated parameters for decoding the measurement result are defined Table 4-79. The applicable values are

dependent on the HP_IMPEDANCE_RANGE setting in each case. The Offset and Gradient values are derived from

Note that, to achieve the specified measurement accuracy, the above equation must be calculated to an accuracy of at

least 5 decimal places throughout.

The impedance measurement result is valid when 169  HP_DACVAL  1017. (In case of any contradiction with the HP_

IMPEDANCE_RANGE description, the HP_DACVAL validity takes precedence.)

If the external impedance is entirely unknown (i.e., it could lie in any of the HP_IMPEDANCE_RANGE regions), it is

recommended to test initially with HP_IMPEDANCE_RANGE = 00. If the resultant HP_DACVAL is < 169, the impedance

is higher than the selected measurement range, so the test should be scheduled again, after incrementing HP_

IMPEDANCE_RANGE.

Each measurement is triggered by writing 1 to HP_POLL. Completion of each measurement is indicated by HP_DONE.

Note that, after HP_DONE has been asserted, it remains asserted until the next measurement has been commanded.

Note: A simpler, but less accurate, procedure for headphone impedance measurement is also supported, using the HP_

LVL field. When the HP_DONE bit is set, indicating completion of a measurement, the impedance can be read

directly from the HP_LVL field, provided that the value lies within the range of the applicable HP_IMPEDANCE_

RANGE setting.

Note that, for detection using one of the MICDETn pins, the HP_LVL field is the only supported measurement

output option. The HP_IMPEDANCE_RANGE field is not valid for detection on the MICDETn pins. See

Table 4-80 for further description of the HP_LVL field.

The headphone detection function is an input to the interrupt control circuit and can be used to trigger an interrupt event

on completion of the headphone detection; see Section 4.15.

The fields associated with headphone detection are described in Table 4-80. The external circuit configuration is shown

Fig. 4-61.

Note that 32-bit register addressing is used from R12888 (0x3000) upwards; 16-bit format is used otherwise. The registers

noted in Table 4-80 contain a mixture of 16- and 32-bit register addresses.

Table 4-79. Headphone Measurement Decode Parameters

Parameter

HP_IMPEDANCE_

RANGE = 00

HP_IMPEDANCE_

RANGE = 01

HP_IMPEDANCE_

RANGE = 10

HP_IMPEDANCE_

RANGE = 11

1.007

9.696

100.684

–0.0072

–0.0795

–0.9494

4003

7975

7300

69.3

69.6

62.9

63.2

0.0055

0.25

Offset

HP_OFFSET_00

HP_OFFSET_01

HP_OFFSET_10

HP_OFFSET_11

Gradient

HP_GRADIENT_0X

HP_GRADIENT_1X

Impedance





C1 Offset





HP_DACVAL

HP_DACVAL_DOWN

 2



 0.5



--------------------------------------------------------------------------------------------------------------

C3 1C4 Gradient





-------------------------------------------------------

–

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- C

–

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