TA0105A Datasheet, PDF (18/29 Pages) Tripath Technology Inc. – STEREO CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM ) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
The feedback resistors, R_FB, can be calculated using the following formula:
RFB = ^{1.0k Ω * VPP} − 1.0k Ω
4.5
The above equation assumes that VPP=|VNN|.
The gain of the modulator can be calculated using the following formula:
AV - MODULATOR ≈ ^{(R FB + 1.0k Ω ) * 2.02} + 1
1020
For example, in a system with VPP_MAX=185V and VNN_MAX=-185V,
R_FB = 40.11kΩ, use 39.2kΩ, 1%
The resultant modulator gain is:
AV - MODULATOR ≈ ^{40.2k Ω * 2.02} + 1 = 80.61V/V
1020
MUTE
When a logic high signal is supplied to MUTE, both amplifier channels are muted (both high- and low-side
transistors are turned off). When a logic level low is supplied to MUTE, both amplifiers are fully
operational. There is a delay of approximately 200 milliseconds between the de-assertion of MUTE and
the un-muting of the TA0105A. Please note that when the amplifier is in mute, the outputs are in a high
impedance state and thus, the feedback resistors will set the output at approximately 2.5V without a load
connected.
To ensure proper device operation, including minimization of turn on/off transients that can result in
undesirable audio artifacts, Tripath recommends that the TA0105A device be muted prior to power up or
power down of the 5V supply. The “sensing” of the V5 supply can be easily accomplished by using a
“microcontroller supervisor” or equivalent to drive the TA0105A mute pin high when the V5 voltage is
below 4.5V. This will ensure proper operation of the TA0105A input circuitry. A micro-controller
supervisor such as the MCP101-450 from Microchip Corporation has been used by Tripath to implement
clean power up/down operation.
HMUTE
The HMUTE pin is a 5V logic output that indicates various fault conditions within the device. These
conditions include: over-current, overvoltage and undervoltage. The HMUTE output is capable of directly
driving an LED through a series 2kΩ resistor.
TURN-ON & TURN-OFF NOISE
If turn-on or turn-off noise is present in a TA0105A amplifier, the cause is frequently due to other circuitry
external to the TA0105A. While the TA0105A has circuitry to suppress turn-on and turn-off transients, the
combination of the power supply and other audio circuitry with the TA0105A in a particular application
may exhibit audible transients. In addition, a non-trimmed output offset will created an audible click on
turn-on and turnoff. One solution that will completely eliminate turn-on and turn-off pops and clicks
(assuming a nulled output offset) is to use a relay to connect/disconnect the amplifier from the speakers
with the appropriate timing at power on/off. The relay can also be used to protect the speakers from a
component failure (e.g. shorted output MOSFET). “DC protection” circuitry would need to be
implemented external to the TA0105A detect such failures.
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TA0105A – RW/ Rev. 2.2/05.05