DRV632
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SLOS681 –JANUARY 2011
CHARGE-PUMP FLYING CAPACITOR AND PVSS CAPACITOR
The charge-pump flying capacitor 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 maximum charge
transfer. Low-ESR capacitors are an ideal selection, and a value of 1 mF is typical. Capacitor values that are
smaller than 1 mF can be used, but the maximum output voltage may be reduced and the device may not
operate to specifications. If the DRV632 is used in highly noise-sensitive circuits, it is recommended to add a
small LC filter on the VDD connection.
DECOUPLING CAPACITORS
The DRV632 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, typically 1 mF, placed as close as possible to the device VDD lead works best. Placing this decoupling
capacitor close to the DRV632 is important for the performance of the amplifier. For filtering lower-frequency
noise signals, a 10-mF or greater capacitor placed near the audio power amplifier would also help, but it is not
required in most applications because of the high PSRR of this device.
GAIN-SETTING RESISTOR RANGES
The gain-setting resistors, RIN and Rfb, must be chosen so that noise, stability, and input capacitor size of the
DRV632 are kept within acceptable limits. Voltage gain is defined as Rfb divided by RIN.
Selecting values that are too low demands a large input ac-coupling capacitor, CIN. Selecting values that are too
high increases the noise of the amplifier. Table 1 lists the recommended resistor values for different
inverting-input gain settings.
Table 1. Recommended Resistor Values
GAIN
–1 V/V
INPUT RESISTOR VALUE, RIN
FEEDBACK RESISTOR VALUE, Rfb
10 kΩ
8.2 kΩ
15 kΩ
4.7 kΩ
10 kΩ
12 kΩ
30 kΩ
47 kΩ
–1.5 V/V
–2 V/V
–10 V/V
USING THE DRV632 AS A SECOND-ORDER FILTER
Several audio DACs used today require an external low-pass filter to remove out-of-band noise. This is possible
with the DRV632, as it can be used like a standard operational amplifier. Several filter topologies can be
implemented, both single-ended and differential. In Figure 7, multi-feedback (MFB) with differential input and
single-ended input are shown.
An ac-coupling capacitor to remove dc content from the source is shown; it serves to block any dc content from
the source and lowers the dc gain to 1, helping to reduce the output dc offset to a minimum.
The component values can be calculated with the help of the TI FilterPro™ program available on the TI Web site
at:
http://focus.ti.com/docs/toolsw/folders/print/filterpro.html.
Copyright © 2011, Texas Instruments Incorporated
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