-In
DRV604
R1
R 2
+
-
C3
R3
C1
C 2
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Component Selection
4
Component Selection
4.1
Charge Pump
The charge pump flying capacitors, C28 and C29, serves to transfer charge during the generation of the
negative supply voltage. The PVSS capacitors, C11 and C13, must be at least equal to the charge pump
capacitor in order to allow maximum charge transfer. Low ESR capacitors are an ideal selection, and a
value of 1µF is typical. Capacitor values smaller than 1µF can be used, but the maximum output can be
reduced, it is therefore recommended to validate the design with thorough testing.
4.2
Decoupling Capacitors
The DRV604 is a DirectPath™ Line Driver amplifier that requires adequate power supply decoupling to
ensure that the noise and total harmonic distortion (THD) are low. Good low equivalent-series-resistance
(ESR) ceramic capacitors, C3 and C4 typical 1µF, placed as close as possible to the device V
DD
leads
works best. Placing this decoupling capacitor close to the DRV604 is important for the performance of the
amplifier. For filtering lower frequency noise signals, a 10µF or greater capacitors placed near the audio
amplifier would also help, 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
DD
line, and an LC or RC filter may be needed if
noise-sensitive audio devices share the V
DD
supply.
4.3
Using the DRV604 as a 2
nd
Order Low-Pass Filter
Several audio DACs used today require an external low-pass filter to remove out of band noise. This is
possible with the DRV604 and the EVM is configured as a 50kHz 2
nd
order active Butterworth filter. The
topology chosen is the MFB with single ended input. Further the DRV604 needs an AC-coupling capacitor
to remove dc-content from the source.
Figure 3. 2
nd
Order Active Low-Pass Filter, SE Input
5
SLOU288 – February 2010
DRV604PWPEVM
Copyright © 2010, Texas Instruments Incorporated
