EUA2011 datasheet(12/16 Pages) EUTECH

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EUA2011

DS2011 Ver 1.1 Dec. 2007

Input Resistors (RI)

The input resistors (RI) set the gain of the amplifier

according to equation (1).

---------------------------------(1)

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 EUA2011 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 EUA2011 to operate at its

best, and keeps a high voltage at the input making the

inputs less susceptible to noise.

Decoupling Capacitor (CS)

The EUA2011 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 1µF, placed as close as possible to the device

VDD lead works best. Placing this decoupling capacitor

close to the EUA2011 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 10µF 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.

Input Capacitors (CI)

The EUA2011 does not require input coupling capacitors

if the design uses a differential source that is biased from

0.5 V to VDD – 0.8 V (shown in Figure 31). If the input

signal is not biased within the recommended common

−mode input range, if needing to use the input as a high

pass filter (shown in Figure 32), or if using a single-ended

source (shown in Figure 33), input coupling capacitors are

required.

The input capacitors and input resistors form a high-pass

filter with the corner frequency, fc, determined in equation

(2).

--------------------------------------------(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.

--------------------------------------------(3)

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.

Single-Ended Input Depop Function

In single-ended input application, there is an inherently

voltage difference in input pairs when shutdown is

released. In order to eliminate pop noise, the pop

cancellation circuit need to charge the input capacitor CI

until fully-differential inputs are balanced and output

power to load gradually.

The RC time constant should within the de-pop delay, if

150kΩ RI is chosen, the recommended CI should small

than 10nF for a good pop immunity.

Summing Input Signals

Most wireless phones or PDAs need to sum signals at the

audio power amplifier or just have two signal sources that

need separate gain. The EUA2011 makes it easy to sum

signals or use separate signal sources with different gains.

Many phones now use the same speaker for the earpiece

and ringer, where the wireless phone would require a

much lower gain for the phone earpiece than for the ringer.

PDAs and phones that have stereo headphones require

summing of the right and left channels to output the stereo

signal to the mono speaker.

ain

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