WM8737 datasheet(15/38 Pages) WOLFSON

15 / 38 page

Preliminary Technical Data

WM8737L

AI Rev 3.0 May 2004

DC MEASUREMENT

For dc measurements (battery voltage monitoring for example), the LINPUT1 and/or RINPUT1 pins

can be taken directly into the respective ADC, bypassing the microphone preamplifier and PGA.

In dc mode the ADC output is mid-scale for L/RINPUT1 voltage AGND and full-scale for L/RINPUT

voltage 1.7 x AVDD. Note that L/RINPUT1 must not exceed AVDD and so a voltage divider will be

required to bring the battery voltage into range.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

8:7

LINSEL

Left Channel Input Select

00: LINPUT1

01: LINPUT2

10: LINPUT3

11: dc measure on LINPUT1

6:5

LMICBOOST[1:0]

Left Channel Microphone Gain Boost

00: 13dB boost

01: 18dB boost

10: 28dB boost

11: 33dB boost

R2 (02h)

Analogue Audio

Path Control

(Left Channel)

LMBE

Left Channel Mic Boost Enable

0: Mic preamp disabled, bypass switch

is closed.

1: Mic preamp is enabled, bypass

switch is open.

8:7

RINSEL

Right Channel Input Select

00: RINPUT1

01: RINPUT2

10: RINPUT3

11: dc measure on RINPUT1

6:5

RMICBOOST[1:0]

Right Channel Microphone Gain Boost

Same as LMICBOOST

R3 (03h)

Analogue Audio

Path Control

(Right Channel)

RMBE

Right Channel Mic Boost Enable

Same as LMBE

Table 2 Input Software Control

The internal VREF input bias may cause unwanted loading of any potential divider connected to

L/RINPUT1 for the purpose of dc measurement. In this case, the internal bias sources can be

disabled by setting the appropriate bits of register R10 to zero.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

RINPUT1 dc

BIAS ENABLE

0: Disable dc bias to RINPUT1

1: Enable dc bias to RINPUT1

R10 (0Ah)

DC Measure

Control

LINPUT1 dc BIAS

ENABLE

0: Disable dc bias to LINPUT1

1: Enable dc bias to LINPUT1

Table 3 DC Measurement Bias Control

MICROPHONE PREAMPLIFER BYPASS AND BIAS CONTROL

When the Left or Right microphone preamplifier is disabled the user has two options for driving the

corresponding Left or Right PGA.

Default operation is to close a preamplifier bypass switch that connects the PGA input directly to the

L/RINPUT1/2/3 multiplexer output.

If the application has only a single left or right line level signal source and hence does not require the

multiplexer or microphone preamplifier, then better PGA gain accuracy and THD+N performance are

obtained by disabling the multiplexer and bypass switch and driving the PGA directly via the L/RACIN

pin. The multiplexer and switch are disabled by setting to zero the appropriate L/RBYPEN bit in

multiplexer is required (always required when the microphone preamplifier is enabled).

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