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APPLICATION INFORMATION
Current-Feedback Amplifiers
Independent Power Supplies
Power Supply Decoupling
Resistor Values
+
RF = 1 kW
VCC+
RI = 1 kW
RS = 50 W
RO = 10 W
RL
VI
VCC
TPA6120A2
SLOS431 – MARCH 2004
The
TPA6120A2
is
a
current-feedback
amplifier
with
differential
inputs
and
single-ended
outputs.
Current-feedback results in low voltage noise, high open-loop gain throughout a large frequency range, and low
distortion. It can be used in a similar fashion as voltage-feedback amplifiers. The low distortion of the
TPA6120A2 results in a signal-to-noise ratio of 120 dB as well as a dynamic range of 120 dB.
The TPA6120A2 consists of two independent high-fidelity amplifiers. Each amplifier has its own voltage supply.
This allows the user to leave one of the amplifiers off, saving power, and reducing the heat generated. It also
reduces crosstalk.
Although the power supplies are independent, there are some limitations. When both amplifiers are used, the
same voltage must be applied to each amplifier. For example, if the left channel amplifier is connected to a
±12-V
supply, the right channel amplifier must also be connected to a
±12-V supply. If it is connected to a different
supply voltage, the device may not operate properly and consistently.
When the use of only one amplifier is preferred, it must be the left amplifier. The voltage supply to the left
amplifier is also responsible for internal start-up and bias circuitry of the device. Regardless of whether one or
both amplifiers are used, the VCC- pins of both amplifiers must always be at the same potential.
To power down the right channel amplifier, disconnect the VCC+ pin from the power source.
The two independent power supplies can be tied together on the board to receive their power from the same
source.
As with any design, proper power supply decoupling is essential. It prevents noise from entering the device via
the power traces and provides the extra power the device can sometimes require in a rapid fashion. This
prevents the device from being momentarily current starved. Both of these functions serve to reduce distortion,
leaving a clean, uninterrupted signal at the output.
Bulk decoupling capacitors should be used where the main power is brought to the board. Smaller capacitors
should be placed as close as possible to the actual power pins of the device. Because the TPA6120A2 has four
power pins, use four surface mount capacitors. Both types of capacitors should be low ESR.
Figure 24. Single-Ended Input With a Noninverting Gain of 2 V/V
In the most basic configuration (see
Figure 24), four resistors must be considered, not including the load
impedance. The feedback and input resistors, RF and RI, respectively, determine the closed-loop gain of the
amplifier. RO is a series output resistor designed to protect the amplifier from any capacitance on the output path,
including board and load capacitance. RS is a series input resistor. Because the TPA6120A2 is a
current-feedback amplifier, take care when choosing the feedback resistor.
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