Pre-Production
WM8985
CLASS D / CLASS AB HEADPHONE OUTPUTS (LOUT2 AND ROUT2)
The outputs LOUT2 and ROUT2 are designed to drive two headphone loads of 16Ω or 32Ω or line
outputs (See Headphone Output and Line Output sections, respectively). Each output has an
individual volume control PGA, a mute and an enable control bit as shown in Figure 27. LOUT2 and
ROUT2 output the left and right channel mixer outputs respectively.
REGISTER
ADDRESS
BIT
LABEL
DCLKDIV
DEFAULT
DESCRIPTION
R7 (07h)
7:4
1000
Controls clock division from
SYSCLK to generate suitable class
D clock.
Recommended class D clock
frequency = 1.4MHz.
0000 = divide by 1
0010 = divide by 2
0011 = divide by 3
0100 = divide by 4
0101 = divide by 5.5
0110 = divide by 6
1000 = divide by 8
1001 = divide by 12
1010 = divide by 16
R23 (17h)
8
CLASSDEN
0
Enable signal for class D mode on
LOUT2 and ROUT2
0 = Class AB mode
1 = Class D mode
Table 35 Class D Control Registers
When driving headphones using class D outputs it is necessary to use appropriate filtering, placed
close to the device, to minimise EMI emissions from the headphone cable (Refer to "Applications
Information" for more information). This filtering does not prevent class AB mode operation.
Figure 27 LOUT2 and ROUT2 Class D Headphone Configuration
PP, Rev 3.4, October 2006
67
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
