RT9104 RICHTEK [Richtek Technology Corporation], RT9104 Datasheet - Page 8

• Manufacturer Part Number: RT9104
• Description: 3W Stereo Class-D Audio Power Amplifier with DC Volume Control
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9104
Application information
The RT9104 is a single-ended input and high efficiency
Class-D stereo audio amplifier featuring low resistance
internal power MOSFETs and over 85% power efficiency.
It requires only a few external components with small
footprints. The RT9104 also supports DC volume control
from −70dB to 20dB. Therefore, it is very suitable for
portable devices and LCD monitor applications. With a
filter-less modulation feature, the RT9104 can limit the
number of external components to a minimum.
DC Volume control
The voltage gain of RT9104 can be set by the external DC
voltage through the “VOLUME_IN” pin. There are a total
of 32 discrete gain steps of the amplifier with a range from
−70dB to 20dB for BTL operation.
A pictorial representation of the typical volume control
can be found in Figure 1.
www.richtek.com
8
-10
-30
-50
-70
Figure 1. Typical DC Voltage Control Operation
30
10
0.3
0.7
1.1
VOLUME_IN (V)
1.5
Gain Table
1.9
2.3
2.7
3.1
3.5
Fade In
For design flexibility, a fade mode is provided to slowly
ramp up the amplifier gain when coming out of shutdown
mode. This mode provides a smooth transition between
the active and shutdown states and virtually eliminates
any pops or clicks on the outputs.
Decoupling Capacitor
The RT9104 is a high performance Class-D audio amplifier
that requires adequate power supply decoupling to ensure
high efficiency and low total harmonic distortion (THD).
To filter out higher frequency transients, spikes, or digital
hash on the line, a low equivalent-series-resistance (ESR)
ceramic capacitor (typically 10μF), placed as close as
possible to the PVDD pins will achieve the best
performance. Placing this decoupling capacitor close to
the RT9104 is very important, since any resistance or
inductance in the trace between the device and the
capacitor can cause a loss in efficiency. For filtering out
lower frequency noise signals, a 10μF or greater capacitor
can be placed near the audio power amplifier.
Gain
(dB)
19.5
18.5
17.5
16.5
15.5
Table 1. VOLUME_IN Voltage for Gain Control
20
19
18
17
16
15
14
13
12
11
10
VOLUME_IN
(V)
3.4
3.3
3.2
3.1
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
1.9
3
2
Gain
(dB)
-19
-37
-70
-2
-4
-7
9
8
7
6
5
4
3
2
1
0
DS9104-01 April 2011
VOLUME_IN
(V)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
1