92HD87 Datasheet, PDF (26/204 Pages) Integrated Device Technology – SINGLE CHIP PC AUDIO SYSTEM

92HD87
SINGLE CHIP PC AUDIO SYSTEM, CODEC+STEREO SPEAKER AMPLIFIER+CAPLESS HP+LDO
Internal
Headphone
Amp
SD/Mute
Internal BTL
Amp
SD/Mute
EAPD
EAPD PIN
Control
CODEC
VDD
SMU MUTE
OTHER
SD#
External
Power Amp
2.17. BTL Amplifier
An integrated class-AB stereo BTL amplifier is provided to directly drive 4 ohm speaker (2W @
4.75V) or 8 ohm speaker (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 prevents
unintentional power consumption when pausing audio playback. The amplifier may be controlled
using the EAPD pin (see EAPD section.)
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.
2.18. BTL Amplifier High-Pass Filter
Not available on TB revision.
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.
2.18.1. 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,
1KHz, or 2KHz. The high pass filter is enabled by default with a cut-off
frequency of 300Hz. The filter may be bypassed using the associated verb (processing state verb).
IDT CONFIDENTIAL
26
©2009 INTEGRATED DEVICE TECHNOLOGY, INC.
V 0.995 01/11
92HD87