CS47L85 datasheet(239/370 Pages) CIRRUS

239 / 370 page

CS47L85

Rev 4.3

239

For correct operation, the respective output driver(s) must be disabled when headphone detection is commanded on

HPOUT1L or HPOUT1R. The required register settings are shown in Table 89.

See Table 71 for details of the HP1L_ENA and HP1R_ENA register bits. The applicable headphone output(s) configuration

must be maintained until after the headphone detection has completed.

DESCRIPTION

REQUIREMENT

HPOUT1L Impedance measurement

HP1L_ENA = 0

HPOUT1R Impedance measurement

HP1R_ENA = 0

Table 89 Output Configuration for Headphone Detect

When headphone detection is commanded, the CS47L85 uses an adjustable current source to determine the connected

impedance. A sweep of measurement currents is applied. The rate of this sweep can be adjusted using the HP_CLK_DIV

and HP_RATE registers.

The headphone detection process will typically comprise a number of separate measurements (for different impedance

ranges). Completion of each measurement is indicated by the HP_DONE register bit. When this bit is set, the measurement

result can be read from the HP_DACVAL and HP_DACVAL_DOWN fields, and subsequently decoded as described below.

C0 + (C1 × Offset)

(((HP_DACVAL + HP_DACVAL_DOWN) / 2) + 0.5)

C3 (1 + (C4 × Gradient))

Impedance (Ω) =

The associated parameters for decoding the measurement result are defined in Table 90. The applicable values are

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

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

Table 90 Headphone Measurement Decode parameters

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 ≤ 1019. (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), then it is

recommended to test initially with HP_IMPEDANCE_RANGE=00. If the resultant HP_DACVAL is < 169, then 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 the HP_POLL bit. Completion of each measurement is indicated by the

HP_DONE register bit. Note that, after the HP_DONE bit has been asserted, it will remain asserted until the next

measurement has been commanded.

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

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