TPA1517
www.ti.com
SLOS162D–MARCH 1997–REVISED FEBRUARY 2007
APPLICATION INFORMATION (continued)
COMPONENT SELECTION
Some of the general concerns for selection of capacitors are:
•
•
•
Leakage currents on aluminum electrolytic capacitors
ESR (equivalent series resistance)
Temperature ratings
LEAKAGE CURRENTS
Leakage currents on most ceramic, polystyrene, and paper capacitors are negligible for this application.
Leakage currents for aluminum electrolytic and tantalum tend to be higher. This is especially important on the
input terminals and the SVRR capacitor. These nodes encounter from 3 V to 7 V, and need to have leakage
currents less than 1 µA to keep from affecting the output power and noise performance.
EQUIVALENT SERIES RESISTANCE
ESR is mainly important on the output coupling capacitor, where even 1Ω of ESR in CO with an 8-Ω speaker can
reduce the output drive power by 12.5%. ESR should be considered across the frequency range of interest,
(i.e., 20 Hz to 20 kHz). The following equation calculates the amount of power lost in the coupling capacitor:
ESR
% Power in C
+
O
R
L
The power supply decoupling requires a low ESR as well to take advantage of the full output drive current.
TEMPERATURE RANGE
The temperature range of the capacitors are important. Many of the high-density capacitors perform differently at
different temperatures. When consistent high performance is required from the system overtemperature in terms
of low THD, maximum output power, and turn-on/off popping, then interactions of the coupling capacitors and
the SVRR capacitors need to be considered, as well as the change in ESR on the output capacitor with
temperature.
TURN-ON POP CONSIDERATION
To select the proper input coupling capacitor, the designer should select a capacitor large enough to allow the
lowest desired frequency pass and small enough that the time constant is shorter than the output RC time
constant to minimize turn-on popping. The input time constant for the TPA1517 is determined by the input 60-kΩ
resistance of the amplifier, and the input coupling capacitor according to the following generic equation:
1
T
+
C
2pRC
For example, 8-Ω speakers and 220-µF output coupling capacitors would yield a 90-Hz cut-off point for the
output RC network. The input network should be the same speed or faster ( > 90 Hz TC). A good choice would
be 180 Hz. As the input resistance is 60 kΩ, a 14-nF input coupling capacitor would do.
The bypass-capacitor time constant should be much larger (×5) than either the input coupling capacitor time
constant or the output coupling capacitor time constants. In the previous example with the 220-µF output
coupling capacitor, the designer should want the bypass capacitor, TC, to be in the order of 18 Hz or lower. To
get an 18-Hz time constant, CB is required to be 1 µF or larger because the resistance this capacitor sees is
7.5 kΩ.
In summary, follow one of the three simple relations presented below, depending on the tradeoffs between low
frequency response and turn-on pop.
1. If depop performance is the top priority, then follow:
7500 C u 5R C u 300000 C
B
L
O
I
2. If low frequency ac response is more important but depop is still a consideration then follow:
1
t 10 Hz
2p60000 C
I
14
Submit Documentation Feedback
TI [ TEXAS INSTRUMENTS ]
