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Gain +

2 x 150 kW

R

I

V

V

(1)

fc +

1

2p R

I

C

I

(2)

C

I +

1

2p R

I

fc

(3)

TPA2006D1

SLOS498 – SEPTEMBER 2006

Resistor matching is very important in fully differential amplifiers. The balance of the output on the reference

voltage depends on matched ratios of the resistors. CMRR, PSRR, and cancellation of the second harmonic

distortion diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance resistors or

better to keep the performance optimized. Matching is more important than overall tolerance. Resistor arrays

with 1% matching can be used with a tolerance greater than 1%.

Place the input resistors very close to the TPA2006D1 to limit noise injection on the high-impedance nodes.

For optimal performance the gain should be set to 2 V/V or lower. Lower gain allows the TPA2006D1 to operate

at its best, and keeps a high voltage at the input making the inputs less susceptible to noise.

The TPA2006D1 is a high-performance class-D audio amplifier that requires adequate power supply decoupling

to ensure the efficiency is high and total harmonic distortion (THD) is low. For higher frequency transients,

spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically

1

µF, placed as close as possible to the device V

the TPA2006D1 is very important for the efficiency of the class-D amplifier, because any resistance or

inductance in the trace between the device and the capacitor can cause a loss in efficiency. For filtering

lower-frequency noise signals, a 10

µF or greater capacitor placed near the audio power amplifier would also

help, but it is not required in most applications because of the high PSRR of this device.

The TPA2006D1 does not require input coupling capacitors if the design uses a differential source that is biased

common-mode input range, if needing to use the input as a high pass filter (shown in Figure 22), or if using a

single-ended source (shown in Figure 23), input coupling capacitors are required.

Equation 2.

The value of the input capacitor is important to consider as it directly affects the bass (low frequency)

performance of the circuit. Speakers in wireless phones cannot usually respond well to low frequencies, so the

corner frequency can be set to block low frequencies in this application.

Equation 3 is reconfigured to solve for the input coupling capacitance.

If the corner frequency is within the audio band, the capacitors should have a tolerance of

±10% or better,

because any mismatch in capacitance causes an impedance mismatch at the corner frequency and below.

For a flat low-frequency response, use large input coupling capacitors (1

µF). However, in a GSM phone the

ground signal is fluctuating at 217 Hz, but the signal from the codec does not have the same 217-Hz fluctuation.

The difference between the two signals is amplified, sent to the speaker, and heard as a 217-Hz hum.

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