92HD81 Datasheet, PDF (31/279 Pages) Integrated Device Technology – SINGLE CHIP PC AUDIO SYSTEM

92HD81
SINGLE CHIP PC AUDIO SYSTEM, CODEC+SPEAKER AMPLIFIER+CAPLESS HP+LDO
Internal
Headphone
Amp
SD/Mute
Internal BTL
Amp
SD/Mute
EAPD
VDD
EAPD PIN
Control
CODEC
SMU MUTE
OTHER
SD#
External
Power Amp
2.18. BTL Amplifier
An integrated class-AB stereo BTL amplifier is provided to directly drive 4 ohm speakers (2W @
4.75V) or 8 ohm speakers (1W @ 4.75V). No external filter is needed for cable runs of 18” or less.
An internal DC blocking filter prevents distortion when the audio source has DC content, and pre-
vents unintentional power consumption when pausing audio playback. The amplifier may be con-
trolled using the EAPD pin (see EAPD section.)
Using a vendor specific verb, the BTL amplifier may be configured to support a mono speaker con-
nected to the L +/- pins. In this mode, the Left and Right audio is mixed and sent to the left output
only. The right channel is turned off to conserve power.
The BTL amplifier includes thermal management circuitry. When the CODEC reaches a temperature
of about 135 degrees, the output amplitude of the BTL amp is gradually lowered until the tempera-
ture falls below 135.
Maximum gain for the BTL amplifier is programmable. The following 4 gain settings relative to a
nominal line output are desired: +6.5dB, +9.5dB, +14.5dB and +16.5dB. Absolute gain may vary and
the suggested accuracy is +/-1.5dB. The gain is exposed in a vendor specific widget and is intended
to mimic the pin programmable gain implemented in discrete BTL amplifiers commonly used in note-
book computers.
2.19. BTL Amplifier High-Pass Filter
For mobile applications, speakers are often incapable of reproducing low frequency audio and
unable to handle the maximum output power of the BTL amplifier. A high-pass filter is implemented
in the DAC output path to reduce the amount of low frequency energy reaching speakers attached to
the BTL amplifier. This can prevent speaker failure.
2.19.1. Filter Description
The high-pass filter is derived from the common biquadratic filter and provides a 12dB/octave roll-off.
The filter may be programmed for a -3dB response at: 100Hz, 200Hz, 300Hz, 400Hz, 500Hz, 750Hz,
IDT CONFIDENTIAL
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©2009 INTEGRATED DEVICE TECHNOLOGY, INC.
V 0.995 01/11
92HD81