PVDD
Enable
> 50
s
m
> 50
s
m
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On/Off Sequence
3
On/Off Sequence
For minimum click and pop interference during device power on and power off, the DRV632 Mute pin (pin
5) must be held low, primarily because of precharging of the ac-coupled input capacitors. The preferred
power-up/-down sequence is shown in
Figure 4
.
Figure 4. Power-Up/-Down Sequence
4
Component Selection
4.1
Charge Pump
The charge pump flying capacitor, C17, serves to transfer charge during the generation of the negative
supply voltage. The PVSS capacitor must be at least equal to the charge pump capacitor in order to allow
a maximum charge transfer. Low equivalent series resistance (ESR) capacitors are an ideal selection, with
a typical value of 1
m
F. Capacitor values less than 1
m
F can be used, but the maximum output can be
reduced. It is therefore recommended to validate the design with thorough testing.
4.2
Power-Supply Decoupling Capacitors
The DRV632 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, C15
(1
m
F typical), placed as close as possible to the device VDD leads is the best option. Placing this
decoupling capacitor close to the DRV632 device is important for amplifier performance. For filtering
lower-frequency noise signals, a 10-
m
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 DRV632.
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.
4.3
Using the DRV632 as a Second-Order, Low-Pass Filter in Single-Ended Input Mode
Several audio digital-to-audio converters (DAC) used in typical consumer applications require an external
low-pass filter to remove out-of-band noise. This function is also possible with the DRV632; the EVM is
configured as a 30-kHz, second-order active Butterworth filter to accomplish this filtering using an MFB
(multiple feedback) topology. Furthermore, the DRV632 requires an ac-coupling capacitor to remove dc
content from the source.
The active low-pass filter 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 5
illustrates the circuit design for this configuration.
5
SLOU301 – January 2010
DRV632EVM Evaluation Module
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