Datasheet

cients, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as
ceramics, may result in an increase distortion at low
frequencies.
Other considerations when designing the input filter
include the constraints of the overall system, the actual
frequency band of interest and click-and-pop suppres-
sion. Although high-fidelity audio calls for a flat gain
response between 20Hz and 20kHz, portable voice-
reproduction devices such as cellular phones and two-
way radios need only concentrate on the frequency
range of the spoken human voice (typically 300Hz to
3.5kHz). In addition, speakers used in portable devices
typically have a poor response below 150Hz. Taking
these two factors into consideration, the input filter may
not need to be designed for a 20Hz to 20kHz response,
saving both board space and cost due to the use of
smaller capacitors.
BIAS Capacitor
The BIAS bypass capacitor, C
BIAS
, improves PSRR and
THD+N by reducing power-supply noise at the common-
mode bias node, and serves as the primary click-and-
pop suppression mechanism. C
BIAS
is fed from an
internal 25kΩ source, and controls the rate at which the
common-mode bias voltage rises at startup and falls
during shutdown. For optimum click-and-pop suppres-
sion, ensure that the input capacitor (C
IN
) is fully
charged (ten time constants) before C
BIAS
. The value of
C
BIAS
for best click-and-pop suppression is given by:
In addition, a larger C
BIAS
value yields higher PSRR.
C
CR
k
BIAS
IN IN
≥
⎡
⎣
⎢
⎤
⎦
⎥
10
25 Ω
MAX4364/MAX4365
1.4W and 1W, Ultra-Small, Audio Power
Amplifiers with Shutdown
______________________________________________________________________________________ 11
OUTPUT
POWER (W)
INTERNAL POWER
DISSIPATION (W)
EFFICIENCY (%)
0.25 0.55 31.4
0.50 0.63 44.4
0.75 0.63 54.4
1.00 0.59 62.8
1.25 0.53 70.2
1.40 0.48 74.3
V
CC
V
CC
C
IN
R
IN
R
F
C
F
C
BIAS
6
OUT-
IN+
BIAS
AUDIO INPUT
3
2
CLICKLESS/
POPLESS
SHUTDOWN
CONTROL
GND
SHDN
8
OUT+ 5
7
1
MAX4364
MAX4365
50k
Ω
50k
Ω
10k
Ω
10k
Ω
IN-4
Figure 2. High-Gain Configuration
Table 1. Efficiency in a 5V, 8Ω BTL System