PA3632

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

8 of 9

www.unisonic.com.tw

QW-R107-071.b



APPLICATION INFORMATION (Cont.)

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 1μF is typical. Capacitor values that are smaller than 1μF

can be used, but the maximum output voltage may be reduced and the device may not operate to specifications. If

connection.

DECOUPLING CAPACITORS

The UTC PA3632 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 close to the UTC PA3632 is important for the performance of the amplifier. For filtering lower-frequency

noise signals, a 10-μF 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.

USING THE UTC PA3632 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 UTC PA3632, as it can be used like a standard operational amplifier. Several filter topologies can be

implemented, both single-ended and differential. In Figure 2, 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 resistor values should have a low value for obtaining low noise, but should also have a high enough value to

get a small-size ac-coupling capacitor. With the proposed values of R1=15kΩ, R2=30kΩ, and R3=43kΩ, a dynamic

range (DYR) of 106dB can be achieved with a 1-μF input ac-coupling capacitor.

GAIN-SETTING RESISTORS

ensure maximum stability of the UTC PA3632.