WM8750CLSEFLSLASHR datasheet(21/65 Pages) WOLFSON

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Production Data

WM8750L

PD, Rev 4.4, August 2012

The internal MICBIAS circuitry is shown below. Note that the is a maximum source current capability

for MICBIAS is 3mA. The external biasing resistors therefore must be large enough to limit the

MICBIAS current to 3mA.

AGND

MICBIAS

= 1.8 x VMID

= 0.9 X AVDD

VMID

internal

resistor

internal

resistor

MICB

Figure 8 Microphone Bias Schematic

PGA CONTROL

The PGA matches the input signal level to the ADC input range. The PGA gain is logarithmically

adjustable from +30dB to –17.25dB in 0.75dB steps. Each PGA can be controlled either by the user

or by the ALC function (see Automatic Level Control). When ALC is enabled for one or both channels,

then writing to the corresponding PGA control register has no effect.

The gain is independently adjustable on both Right and Left Line Inputs. Additionally, by controlling

the register bits LIVU and RIVU, the left and right gain settings can be simultaneously updated.

Setting the LIZC and RIZC bits enables a zero-cross detector which ensures that PGA gain changes

only occur when the signal is at zero, eliminating any zipper noise. If zero cross is enabled a timeout

is also available to update the gain if a zero cross does not occur. This function may be enabled by

setting TOEN in register R23 (17h).

The inputs can also be muted in the analogue domain under software control. The software control

registers are shown in Table 9. If zero crossing is enabled, it is necessary to enable zero cross

timeout to un-mute the input PGAs. This is because their outputs will not cross zero when muted.

Alternatively, zero cross can be disabled before sending the un-mute command.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R0 (00h)

Left Channel

PGA

LIVU

Left Volume Update

0 = Store LINVOL in intermediate

latch (no gain change)

1 = Update left and right channel

gains (left = LINVOL, right =

intermediate latch)

LINMUTE

Left Channel Input Analogue Mute

1 = Enable Mute

0 = Disable Mute

Note: LIVU must be set to un-mute.

LIZC

Left Channel Zero Cross Detector

1 = Change gain on zero cross only

0 = Change gain immediately

5:0

LINVOL

[5:0]

010111

( 0dB )

Left Channel Input Volume Control

111111 = +30dB

111110 = +29.25dB

. . 0.75dB steps down to

000000 = -17.25dB

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