TK2070 Datasheet, PDF (15/21 Pages) Tripath Technology Inc. – STEREO 70W (4Ohm) CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPP) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
Mute Control
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 TK2070.
To ensure proper device operation, including minimization of turn on/off transients that can result in
undesirable audio artifacts, Tripath recommends that the TK2070 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 TC2001 mute pin high when the V5 voltage is
below 4.5V. This will ensure proper operation of the TK2070 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.
If turn-on and/or turn-off noise is still present with a TK2070 amplifier, the cause may be other
circuitry external to the TK2070. While the TK2070 has circuitry to suppress turn-on and turn-off
transients, the combination of power supply and other audio circuitry with the TK2070 in a particular
application may exhibit audible transients. One solution that will completely eliminate turn-on and
turn-off pops and clicks is to use a relay to connect/disconnect that amplifier from the speakers with
the appropriate timing during power on/off.
TK2070 Output Capability
The TK2070 can drive two 4 Ohm loads with 70 Watts 10% THD+N. The maximum sustained
amplifier output power will be determined by a number of factors including the TC2001/TPS1035
junction temperatures, the load impedance and the power supply voltage.
Tripath does not recommend driving loads below 4 Ohms bridged as the amplifier efficiency will be
reduced and the amplifier will reach it’s current limit at relatively low power output levels. With the
outputs connected in parallel, however, the TK2070 is capable of driving single channel loads down
to 2 Ohms with very high power capability. Please refer to the RB-TK2070 datasheet for parallel
mode operation of the TK2070.
Output Voltage Offset
The TK2070 does not have internal compensation for DC offset. The output offset voltage must be
trimmed with a potentiometer at the INV1/INV2 pins of the TC2001. If the output offset voltage is not
trimmed the efficiency of the TK2070 will be significantly reduced and the idle current will be
significantly increased.
Output Filter Design
Tripath amplifiers generally have a higher switching frequency than PWM implementations, allowing
the use of higher cutoff frequency filters and reducing the load dependent peaking/drooping in the
20kHz audio band. This is especially important for applications where the end customer may attach
any speaker to the amplifier (as opposed to a system where speakers are shipped with the amplifier),
since speakers are not purely resistive loads and the impedance they present changes over
frequency and from speaker model to speaker model. An RC network, or “Zobel” (R_Z, C_Z) should be
placed at the filter output to control the impedance “seen” by the TP2051 when not attached to a
speaker load. The TK2070 works well with a 2^nd order, 80kHz LC filter with L_O = 10uH and C_O =
0.47uF and R_Z = 10 Ohm/1W and C_Z = 0.47uF.
Output inductor selection is a critical design step. The core material and geometry of the output filter
inductor affects the TK2070 distortion levels, efficiency, power dissipation and EMI output.
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TK2070 – MC/2.1/10-03