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4.2 Decoupling Capacitors

4.3 Using the DRV601 as a Second-Order Low-Pass Filter

R1 R3

Component Selection

The DRV601 is a DirectPath™ line driver amplifier that requires adequate power supply decoupling to

ensure that the noise and total harmonic distortion (THD) are low. A good low equivalent-series-resistance

(ESR) ceramic capacitor, C12, typical 1 µ F, placed as close as possible to the device V

leads works

best. Placing this decoupling capacitor close to the DRV601 is important for the performance of the

amplifier. For filtering lower frequency noise signals, a 10- µ F or greater capacitor placed near the audio

amplifier also helps, but is not required in most applications because of the high PSRR of this device.

The charge pump circuit does apply ripple current on the V

line, and a LC or RC filter may be needed if

noise-sensitive audio devices share the V

supply.

Many of the audio DACs used today require an external low-pass filter, to remove band noise. This is

possible with the DRV601, and the EVM is configured as a 40-kHz, second-order, active Butterworth filter.

The topology chosen is the MFB Single-Ended. Further, the DRV601 needs a ac-coupling capacitor to

remove dc-content from the source.

Figure 5. Second-Order, Active Low-Pass Filter

The component values can be calculated with the help of the TI FilterPro™ program available on:

http://focus.ti.com/docs/toolsw/folders/print/filterpro.html

In Table 3 , various proposals for the filter and gain settings can be found.

Table 3. DRV601EVM2 Specification

Gain High Pass Low Pass C1 C2 C3 R1 R2 R3

–1 V/V 16 Hz 40 kHz 100 pF 680 pF 1 µ F 10 kR 10 kR 24 kR

-1.5 V/V 19 Hz 40 kHz 68 pF 680 pF 1 µ F 8.2 kR 12 kR 30 kR

-2 V/V 11 Hz 40 kHz 33 pF 330 pF 1 µ F 15 kR 30 kR 47 kR

–2 V/V 11 Hz 30 kHz 47 pF 470 pF 1 µ F 15 kR 30 kR 43 kR

–3.33 V/V 12 Hz 40 kHz 33 pF 470 pF 1 µ F 13 kR 43 kR 43 kR

-10 V/V 15 Hz 30 kHz 22 pF 1 nF 2.2 µ F 4.7 kR 47 kR 27 kR

The resistor values should be low value to get low noise, but should be high value to get a small size

ac-coupling capacitor. With the proposed values, 15k, 30k, and47k, a DYR of 105 dB can be achieved

with a small 1- µ F input ac-coupling capacitor.

DRV601EVM2 6 SLOU217 – March 2008

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