WM8985GEFLSLASHR datasheet(67/121 Pages) WOLFSON

67 / 121 page

Production Data

WM8985

PD, Rev 4.6, July 2009

Headphone Output using DC Blocking Capacitors

DC Coupled Headphone Output

Figure 26 Recommended Headphone Output Configurations

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

Ω load and C1, C2 = 220μF:

fc = 1 / 2

π RLC1 = 1 / (2π x 16Ω x 220μF) = 45 Hz

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

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

configurations should only be used with headphones.

WM8985GEFL/R Datasheet(PDF) 67 Page - Wolfson Microelectronics plc