WM8758CBGEFLSLASHV datasheet(53/90 Pages) WOLFSON

53 / 90 page

Production Data

WM8758B

PD, Rev 4.4, January 2012

When DC blocking capacitors are used, their capacitance and the load resistance together determine

the lower cut-off frequency of the output signal, fc. Increasing the capacitance lowers fc, improving the

bass response. Smaller capacitance values will diminish the bass response. Assuming a 16

 load

and C1, C2 = 220

F:

fc = 1 / 2 RLC1 = 1 / (2 x 16 x 220F) = 45 Hz

The AC coupling capacitor into the HP_COM feedback input requires to be a much smaller value,

typically 4.7uF as the internal resistance it is driving into is typically 22kohm.

In the DC coupled configuration, the headphone pseudo-ground is connected to the buffered midrail

reference pin (LOUT2 or ROUT2). The L/ROUT2 pins can be configured as a DC output driver by

setting the LOUT2MUTE and ROUT2MUTE register bits. The DC voltage on VMID in this

configuration is equal to the DC offset on the LOUT1 and ROUT1 pins therefore no DC blocking

capacitors are required. This saves space and material cost in portable applications.

It is not recommended to use DC-coupling to line inputs of another device. Although the built-in short

circuit protection on the headphone outputs would be tolerant of shorts to ground, such a connection

may be noisy, and may not function properly if the other device is grounded. DC-coupled

configurations should only be used with headphones.

COMMON MODE DEFAULT

The common mode feedback mode is enabled by writing a 1 to HP_COM or LINE_COM (reg 49 bits

7 and 8). Under normal operation these registers defaults 0 (common mode disabled). However the

polarity of these registers can be inverted by using 2-wire control interface mode and holding the

CSB_GPIO1 pin high. In this mode of operation HP_COM=0 enables HP common mode, and

HP_COM=1 disables HP common mode. Similarly LINE_COM=0 enables LINE common mode and

LINE_COM=1 disables LINE common mode. Note that if the CSB_GPIO1 is configured as a GPIO

the operation of HP_COM and LINE_COM revert back to non-inverted operation.

WM8758CBGEFL/V Datasheet(PDF) 53 Page - Wolfson Microelectronics plc