Texas Instruments DRV602EVM2, Руководство пользователя, Страница: 5 / 18

4.2 Power-Supply Decoupling Capacitors
4.3 Using the DRV602 as a Second-Order, Low-Pass Filter in Single-Ended Input Mode
R
2
R
1
R
3
C
2
C
X
C
1
C
3
DRV602
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Component Selection
The DRV602 is a DirectPath™ line driver amplifier that requires adequate power-supply decoupling to
ensure that noise and total harmonic distortion (THD) are low. A good low ESR ceramic capacitor, C17
(1
µ
F typical), placed as close as possible to the device VDD leads is the best option. Placing this
decoupling capacitor close to the DRV602 device is important for amplifier performance. For filtering
lower-frequency noise signals, a 10-
µ
F or greater capacitor placed near the audio amplifier may also help,
but is not required in most applications because of the high PSRR of the DRV602.
The charge pump circuit does apply ripple current on the VDD line, and an LC or RC filter may be needed
if noise-sensitive audio devices share the VDD supply.
Several audio digital-to-audio converters (DACs) used in typical consumer applications require an external
low-pass filter to remove out-of-band noise. This function is also possible with the DRV602; the EVM is
configured as a 40-kHz, second-order active Butterworth filter to accomplish this filtering using an MFB
(Multiple Feed Back) topology. Furthermore, the DRV602 requires an ac-coupling capacitor to remove dc
content from the source.
The recommended component values can be calculated with the help of the TI FilterPro active filter design
program available at http://focus.ti.com/docs/toolsw/folders/print/filterpro.html on the TI web site. Figure 3
illustrates the circuit design for this configuration.
Figure 3. Second-Order, Active Low-Pass Filter
Figure 3 uses the component references also used in the FilterPro software. Various recommendation for
filter and gain settings are listed in Table 3 .
Table 3. DRV602EVM2 Filter Specifications
C1’ C2’ C3’ R1’ R2’ R3’
FilterPro
C23 C21 C13 R11 R15 R13
Gain High Pass Low Pass C24 C22 C14 R12 R16 R14
–1 V/V 16 Hz 40 kHz 100 pF 680 pF 1
µ
F 10 k
Ω
10 k
Ω
24 k
Ω
–1.5 V/V 19 Hz 40 kHz 68 pF 680 pF 1
µ
F 8.2 k
Ω
12 k
Ω
30 k
Ω
–2 V/V 11 Hz 40 kHz 15 pF 150 pF 1
µ
F 33 k
Ω
68 k
Ω
100 k
Ω
–2 V/V 11 Hz 30 kHz 47 pF 470 pF 1
µ
F 15 k
Ω
30 k
Ω
43 k
Ω
–3.33 V/V 12 Hz 40 kHz 33 pF 470 pF 1
µ
F 13 k
Ω
43 k
Ω
43 k
Ω
–10 V/V 15 Hz 30 kHz 22 pF 1 nF 2.2
µ
F 4.7 k
Ω
47k
Ω
27 k
Ω
SLOU248A – December 2008 – Revised January 2009 DRV602EVM2 5
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