tk2070 Tripath Technology Inc., tk2070 Datasheet - Page 18

• Manufacturer Part Number: tk2070
• Description: Stereo 70w 4ohm Class-t Digital Audio Amplifier Driver Using Digital Power Processing Dpp Technology
• Manufacturer: Tripath Technology Inc.

T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
O V R L D B
The OVRLDB pin is a 5V logic output that is asserted just at the onset of clipping. When low, it
indicates that the level of the input signal has overloaded the amplifier resulting in increased distortion
at the output. The OVRLDB signal can be used to control a distortion indicator light or LED through a
transistor, as the OVRLDB cannot drive an LED directly. There is a 20K resistor on chip in series with
the OVRLDB output.
P e r f o r m a n c e M e a s u r e m e n t s o f t h e T K 2 0 7 0
The TK2070 operates by generating a high frequency switching signal based on the audio input. This
signal is sent through a low-pass filter (external to the Tripath amplifier) that recovers an amplified
version of the audio
input.
The frequency of the switching pattern is spread spectrum in nature and
typically varies between 100kHz and 1MHz, which is well above the 20Hz – 20kHz audio band. The
pattern itself does not alter or distort the audio input signal, but it does introduce some inaudible
components.
The measurements of certain performance parameters, particularly noise related specifications such
as THD+N, are significantly affected by the design of the low-pass filter used on the output as well as
the bandwidth setting of the measurement instrument used. Unless the filter has a very sharp roll-off
just beyond the audio band or the bandwidth of the measurement instrument is limited, some of the
inaudible noise components introduced by the TK2070 amplifier switching pattern will degrade the
measurement.
One feature of the TK2070 is that it does not require large multi-pole filters to achieve excellent
performance in listening tests, usually a more critical factor than performance measurements.
Though using a multi-pole filter may remove high-frequency noise and improve THD+N type
measurements (when they are made with wide-bandwidth measuring equipment), these same filters
degrade frequency response. The TK2070 Reference Board uses the Application/Test Circuit of this
data sheet, which has a simple two-pole output filter and excellent performance in listening tests.
Measurements in this data sheet were taken using this same circuit with a limited bandwidth setting in
the measurement instrument.
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TK2070 – MC/2.1/10-03