Datasheet

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Single Ended Output Capacitor, C

Output Filter and Frequency Response

LOUT /ROUT

filter

LOUT

filter

ROUT

TPA3122D2

SLOS527A – DECEMBER 2007 – REVISED DECEMBER 2007

in high gain applications. For this reason, a low-leakage tantalum or ceramic capacitor is the best choice. When

polarized capacitors are used, the positive side of the capacitor should face the amplifier input in most

applications as the dc level there is held at 2 V, which is likely higher than the source dc level. Note that it is

important to confirm the capacitor polarity in the application. Additionally, lead-free solder can create dc offset

voltages and it is important to ensure that boards are cleaned properly.

In single ended (SE) applications, the DC blocking capacitor forms a high pass filter with speaker impedance.

The frequency response rolls of with decreasing frequency at a rate of 20dB/decade. The cutoff frequency is

determined by

fc = 1/2 × π C

Table 2 shows some common component values and the associated cutoff frequencies:

Table 2. Common Filter Responses

– DC Blocking Capacitor ( µ F)

Speaker Impedance ( Ω )

= 60 Hz f

= 40 Hz f

= 20 Hz

4 680 1000 2200

8 330 470 1000

For the best frequency response, a flat passband output filter (second order Butterworth) may be used. The

output filter components consist of the series inductor and capacitor to ground at the LOUT and ROUT pins.

There are several possible configurations depending on the speaker impedance and whether the output

configuration is Single Ended (SE) or Bridge Tied Load (BTL). Table 3 list several possible arrangements.

Table 3. Recommended Filter Output Components

Output Configuration Speaker Impedance ( Ω ) Filter Inductor ( µ H) Filter Capacitor (nF)

4 22 680

Single Ended (SE)

8 47 390

4 10 1500

Bridge Tied Load

8 22 680

Figure 26. BTL Filter Configuration Figure 27. SE Filter Configuration

Product Folder Link(s) :TPA3122D2