LM3886
SNAS091C –MAY 1999–REVISED MARCH 2013
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(excluding active protection circuitry)
External Components Description
(See Figure 1 and Figure 3)
Components
Functional Description
1.
2.
3.
4.
5.
RIN
RA
CA
C
Acts as a volume control by setting the voltage level allowed to the amplifier's input terminals.
Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.
Provides bias filtering.
Provides AC coupling at the input and output of the amplifier for single supply operation.
RB
Prevents currents from entering the amplifier's non-inverting input which may be passed through to the load upon power-
down of the system due to the low input impedance of the circuitry when the under-voltage circuitry is off. This
phenomenon occurs when the supply voltages are below 1.5V.
(1)
6.
CC
Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of the output
transistor. The capacitor also suppresses external electromagnetic switching noise created from fluorescent lamps.
7.
8.
Ri
Ci
Inverting input resistance to provide AC Gain in conjunction with Rf1.
Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:
fc = 1/(2πRi Ci)
(1)
(1)
9.
Rf1
Rf2
Feedback resistance to provide AC Gain in conjunction with Ri.
10.
At higher frequencies feedback resistance works with Cf to provide lower AC Gain in conjunction with Rf1 and Ri. A high
frequency pole (lowpass roll-off) exists at:
fc = [Rf1 Rf2 (s + 1/Rf2Cf)]/[(Rf1 + Rf2)(s + 1/Cf(Rf1 + Rf2))]
11.
12.
Cf(1)
RM
Compensation capacitor that works with Rf1 and Rf2 to reduce the AC Gain at higher frequencies.
Mute resistance set up to allow 0.5 mA to be drawn from pin 8 to turn the muting function off.
→RM is calculated using: RM ≤ (|VEE| − 2.6V)/I8 where I8 ≥ 0.5 mA. Refer to the Figure 44 and Figure 45 in Typical
Performance Characteristics.
13.
14.
15.
CM
Mute capacitance set up to create a large time constant for turn-on and turn-off muting.
(1)
RSN
CSN
Works with CSN to stabilize the output stage by creating a pole that eliminates high frequency oscillations.
Works with RSN to stabilize the output stage by creating a pole that eliminates high frequency oscillations.
(1)
fc = 1/(2πRSNCSN
)
(1)
16.
17.
L
Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the Q of the
series resonant circuit due to capacitive load. Also provides a low impedance at low frequencies to short out R and pass
audio signals to the load.
(1)
R
18.
19.
CS
S1
Provides power supply filtering and bypassing.
Mute switch that mutes the music going into the amplifier when opened.
(1) Optional components dependent upon specific design requirements. Refer to Application Information for more information.
OPTIONAL EXTERNAL COMPONENT INTERACTION
Although the optional external components have specific desired functions that are designed to reduce the
bandwidth and eliminate unwanted high frequency oscillations they may cause certain undesirable effects when
they interact. Interaction may occur for components whose reactances are in close proximity to one another. One
example would be the coupling capacitor, CC, and the compensation capacitor, Cf. These two components act as
low impedances to certain frequencies which will couple signals from the input to the output. Please take careful
note of basic amplifier component functionality when designing in these components.
The optional external components shown in Figure 3 and described above are applicable in both single and split
voltage supply configurations.
8
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