LM4732
External Components Description
(Figures 1-5)
Components
1
R
B
Functional Description
Prevents current from entering the amplifier’s non-inverting input. This current may pass through to the load
during system power down, because of the amplifier’s low input impedance when the undervoltage circuitry
is off. This phenomenon occurs when the V
+
and V
-
supply voltages are below 1.5V.
Inverting input resistance. Along with R
f
, sets AC gain.
Feedback resistance. Along with R
i
, sets AC gain.
Feedback resistance. Works with Cf and Rf creating a lowpass filter that lowers AC gain at high
frequencies. The -3dB point of the pole occurs when: (R
f
- R
i
)/2 = R
f
// [1/(2πf
c
C
f
) + R
f2
] for the
Non-Inverting configuration shown in
Compensation capacitor. Works with R
f
and R
f2
to reduce AC gain at higher frequencies.
Compensation capacitor. Reduces the gain at higher frequencies to avoid quasi-saturation oscillations of the
output transistor. Also suppresses external electromagnetic switching noise created from fluorescent lamps.
Feedback capacitor which ensures unity gain at DC. Along with R
i
also creates a highpass filter at f
c
=
1/(2πR
i
C
i
).
Provides power supply filtering and bypassing. Refer to the Supply Bypassing application section for proper
placement and selection of bypass capacitors.
Acts as a volume control by setting the input voltage level.
Sets the amplifier’s input terminals DC bias point when C
IN
is present in the circuit. Also works with C
IN
to
create a highpass filter at f
C
= 1/(2πR
IN
C
IN
). If the value of R
IN
is too large, oscillations may be observed on
the outputs when the inputs are floating. Recommended values are 10kΩ to 47kΩ. Refer to
Input capacitor. Prevents the input signal’s DC offsets from being passed onto the amplifier’s inputs.
Works with C
SN
to stabilize the output stage by creating a pole that reduces high frequency instabilities.
Works with R
SN
to stabilize the output stage by creating a pole that reduces high frequency instabilities. The
pole is set at f
C
= 1/(2πR
SN
C
SN
). Refer to
Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce
the Q of the series resonant circuit. Also provides a low impedance at low frequencies to short out R and
pass audio signals to the load. Refer to
Provides DC voltage biasing for the transistor Q1 in single supply operation.
Provides bias filtering for single supply operation.
Limits the voltage difference between the amplifier’s inputs for single supply operation. Refer to the
Clicks
and Pops
application section for a more detailed explanation of the function of R
INP
.
Provides input bias current for single supply operation. Refer to the
Clicks and Pops
application section for
a more detailed explanation of the function of R
BI
.
Establishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the
half-supply point along with C
A
.
Mute resistance set up to allow 0.5mA to be drawn from each MUTE pin to turn the muting function off.
→
R
M
is calculated using: R
M
≤
(|V
EE
| − 2.6V)/l where l
≥
0.5mA. Refer to the Mute Attenuation vs Mute
Current curves in the Typical Performance Characteristics section.
Mute capacitance set up to create a large time constant for turn-on and turn-off muting.
Mute switch. When open or switched to GND, the amplifier will be in mute mode.
Reduces current flow between outputs that are caused by Gain or DC offset differences between the
amplifiers.
2
3
4
R
i
R
f
R
f2
C
f
C
C
C
i
C
S
R
V
R
IN
C
IN
R
SN
C
SN
L (Note 15)
R (Note 15)
R
A
C
A
R
INP
R
BI
R
E
R
M
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
C
M
S
1
R
OUT
Note 15:
Optional components dependent upon specific design requirements.
www.national.com
8
NSC [ NATIONAL SEMICONDUCTOR ]
