MIPSZ2012D2R2 datasheet(35/48 Pages) STMICROELECTRONICS

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TS4621B

Application information

Doc ID 022194 Rev 2

35/48

Therefore, in most cases, Rin should be set to 4 dB to calculate the minimum input capacitor

Cin.

Example:

At maximum gain G = 4 dB, Rindiff/2 = k

Ω/2 = 17 kΩ. However, to take into consideration

the worst case, one has to use Rindiff/2 = 25 k

Ω/2 = 12.5 kΩ.

In this case and for a -3 dB cutoff frequency of 20 Hz, Cin = 0.64 µF. The closest normalized

value is 0.68 µF but a 1 µF capacitor is more suitable to take into consideration the capacitor

tolerance +/-20 %.

If the aim is to have the 20 Hz at -1 dB, the capacitor has to be multiplied by 1.96. As such,

Cin = 0.64 x 1.96 = 1.25 µF. The closest normalized value would be 1.5 µF or 2.2 µF.

4.4.6

Low-pass output filter (Rout and Cout) and IEC 61000-4-2 ESD

protection

The TS4621B is designed to operate with a passive first-order low-pass filter (as shown in

Figure 1.). This low-pass filter is mandatory to ensure correct operation of the TS4621B over

the volume range and output capacitance range vs. load.

Rout must have a value of 12

Ω minimum and Cout a value of 0.8 nF minimum up to 100 nF

maximum. Values of 12

Ω and 1 nF are a good starting point for a design to be able to drive

a classic headphone (16

Ω, 32 Ω, 60 Ω) and the line-in of any Hi-fi system or sound card.

The cutoff frequency of this filter (12

Ω and 1 nF) is approximately 13 MHz and clearly

above the audio band.

However, this output RC filter is also a part of the IEC 61000-4-2 ESD protection. In most

cases, this RC filter is designed with transient absorbers and the final solution can be a

discrete solution or an integrated solution. ST Microelectronics’ portfolio has many

integrated solutions for ESD, but one dedicated to headphone amplifiers in particular:

IPAD(a) reference EMIF02-AV01F3.

To fit the IEC 61000-4-2 standard, this audio line IPAD can be added to the output of the

TS4621B as shown in Figure 78.

MIPSZ2012D2R2 Datasheet(PDF) 35 Page - STMicroelectronics