NCS603
http://onsemi.com
11
Table 1. RECOMMENDED RESISTOR VALUES
Input Resistor Val-
ue, R
IN
Feedback Resistor Val-
ue, R
FB
Differential Input Gain Inverting Input Gain
Non Inverting Input
Gain
22 kW 22 kW
1.0 V/V –1.0 V/V 2.0 V/V
22 kW 33 kW
1.5 V/V –1.5 V/V 2.5 V/V
33 kW 68 kW
2.06 V/V –2.06 V/V 3.1 V/V
10 kW 100 kW
10.0 V/V –10.0 V/V 11.0 V/V
INPUT CAPACITOR
The input coupling capacitor blocks the DC voltage at the
amplifier input terminal. This capacitor creates a high−pass
filter with R
IN
. The size of the capacitor must be large
enough to couple at low frequencies without severe
attenuation in the audio bandwidth (20 Hz − 20 kHz).
The cut off frequency for the input high−pass filter is:
f
c
+
1
2pR
in
C
in
(eq. 12)
A f
c
< 20 Hz is recommended.
CHARGE PUMP CAPACITOR SELECTION
It is recommended to use ceramic capacitors with low
ESR for better performances. X5R or X7R capacitors are
recommended. The flying capacitor C
fly
(1 mF) serves to
transfer charge during the generation of the negative
voltage. The VSS reservoir capacitor C
VSS
must be equal at
least to the C
fly
capacitor to allow maximum charge transfer.
The 1 mF capacitors have to be connected as close as
possible to the corresponding pins.
Lower value capacitors can be used but the device may not
operate to specifications.
POWER SUPPLY DECOUPLING CAPACITORS
The NCS603 is a True Ground amplifier that requires an
adequate decoupling capacitor on VDD to reduce noise and
THD+N. Use a X5R / X7R ceramic capacitor and place it
close to the VDD pin. A value of 1mF is recommended. For
filtering lower frequency noise signals, a 10 mF or greater
capacitor placed near the audio power amplifier would also
help.
SHUTDOWN FUNCTION
The device enters shutdown mode when Enable signal is
low. During the shutdown mode, the internal charge pump
is shut down, and the DC quiescent current of the circuit does
not exceed 500 nA. The output is pulled to ground through
a low output impedance of about 40 ohms.
USING THE NCS603 AS A 2
nd
ORDER FILTER
Audio DACs can require an external low-pass filter to
remove out-of-band noise. This is possible with the
NCS603, which can be used as a standard Operational
Amplifier with the advantage of better performances
including “pop & click” noise behavior.
Single-ended and differential topologies can be
implemented. In Figures 25 and 26, a Multiple-FeedBack
(MFB) topoplogy, with differential inputs and single-ended
inputs is shown. The two topologies use AC-Coupling
capacitors (C
IN
) to block the DC-signal component coming
from the source; they contribute to reducing the output offset
voltage.
RIN
RIN
CIN
CIN
Vin−
Vin+
CDIFF
CINT
RFB
RFB
CINT
RINT
RINT
Vout
Figure 25. 2nd Order Active Low Pass Filter − Differential Input
