WM8962B datasheet(161/295 Pages) WOLFSON

161 / 295 page

WM8962

Rev 4.3

161

The compensation in internal loading capacitance (with respect to the default value) must be

configured on the XTI and XTO pins individually. The combined effect of the compensation is as per

series-connected capacitors; therefore, if the overall difference required is -1pF, then an adjustment of

-2pF must be made on each of the XTI and XTO pins. Note that this sum assumes that the difference

is the same for both pins.

To apply the capacitive correction, the combined difference (-2pF in the above example) should be

applied to XTI_CAP_SEL and XTO_CAP_SEL registers.

It is necessary to ensure that the values written to the XTI_CAP_SEL and XTO_CAP_SEL registers

do not cause internal limits to be exceeded; this requires the oscillator trim registers to be read, in

order to confirm the amount of calibration already configured to match the specified Electrical

Characteristics.

The value written to XTI_CAP_SEL, when summed with the trim value OSC_TRIM_XTI, must not

result in a value outside the limits of OSC_TRIM_XTI. The sum of the XTI_CAP_SEL and

OSC_TRIM_XTI settings must be between 8pF and 23.5pF.

The value written to XTO_CAP_SEL, when summed with the trim value OSC_TRIM_XTO, must not

result in a value outside the limits of OSC_TRIM_XTO. The sum of the XTO_CAP_SEL and

OSC_TRIM_XTO settings must be between 8pF and 23.5pF.

As an example, if the read value of OSC_TRIM_XTI is 21.5pF, then it is not possible to increase the

XTI capacitance by more than 2pF - a larger value would exceed the 23.5pF limit.

Note that the description provided here assumes that the difference in capacitance (with respect to the

recommended value) is the same for both pins (XTI and XTO).

The relevant registers are described in Table 106.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R115 (73h)

Oscillator

Trim (3)

4:0

OSC_TRIM_XTI

[4:0]

Trimmed Oscillator XTI capacitance

00h = 8pF

01h = 8.5pF

… 0.5pF steps

1Eh = 23pF

1Fh = 23.5pF

This field is for read-back only; it is set

automatically and cannot be adjusted.

see Table 107 for details.

R116 (74h)

Oscillator

Trim (4)

4:0

OSC_TRIM_XT

O [4:0]

Trimmed Oscillator XTO capacitance

00h = 8pF

01h = 8.5pF

… 0.5pF steps

1Eh = 23pF

1Fh = 23.5pF

This field is for read-back only; it is set

automatically and cannot be adjusted.

see Table 107 for details.

R119 (77h)

Oscillator

Trim (7)

7:4

XTO_CAP_SEL

[3:0]

0000

XTO load capacitance adjustment

Two’s complement format,

LSB = 0.5pF

Range is -4.0pF to +3.5pF

see Table 108 for details

3:0

XTI_CAP_SEL

[3:0]

0000

XTI load capacitance adjustment

Two’s complement format,

LSB = 0.5pF

Range is -4.0pF to +3.5pF

see Table 108 for details

Table 106 Oscillator Trim Control

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