Datasheet

LM4780, LM4780TABD
www.ti.com SNAS193B –JULY 2003–REVISED APRIL 2013
External Components Description
(Figure 1 to Figure 6)
Components Functional Description
Prevents current from entering the amplifier's non-inverting input. This current may pass through to the load during
1 R
B
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.
2 R
i
Inverting input resistance. Along with R
f
, sets AC gain.
3 R
f
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 -
4 R
f2
(1)
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
Figure 6.
5 C
f
(1)
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
6 C
C
(1)
transistor. Also suppresses external electromagnetic switching noise created from fluorescent lamps.
7 C
i
(1)
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
8 C
S
placement and selection of bypass capacitors.
9 R
V
(1)
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
10 R
IN
(1)
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 Figure 6.
11 C
IN
(1)
Input capacitor. Prevents the input signal's DC offsets from being passed onto the amplifier's inputs.
12 R
SN
(1)
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
13 C
SN
(1)
set at f
C
= 1/(2πR
SN
C
SN
). Refer to Figure 6.
14 L
(1)
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
15 R
(1)
to the load. Refer to Figure 6.
16 R
A
Provides DC voltage biasing for the transistor Q1 in single supply operation.
17 C
A
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
18 R
INP
(1)
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
19 R
BI
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-
20 R
E
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.
21 R
M
→ R
M
is calculated using: R
M
≤ (|V
EE
| − 2.6V)/l where l ≥ 0.5mA. Refer to the Figure 21 curves in the Typical
Performance Characteristics section.
22 C
M
Mute capacitance set up to create a large time constant for turn-on and turn-off muting.
23 S
1
Mute switch. When open or switched to GND, the amplifier will be in mute mode.
24 R
OUT
Reduces current flow between outputs that are caused by Gain or DC offset differences between the amplifiers.
(1) Optional components dependent upon specific design requirements.
Optional External Component Interaction
The optional external components have specific desired functions. Their values are chosen to reduce the
bandwidth and eliminate unwanted high frequency oscillation. They may, however, cause certain undesirable
effects when they interact. Interaction may occur when the components produce reactions that are nearly equal
to one another. One example is the coupling capacitor, C
C
, and the compensation capacitor, C
f
. These two
components are low impedances at certain frequencies. They may couple signals from the input to the output.
Please take careful note of basic amplifier component functionality when selecting the value of these
components and their placement on a printed circuit board (PCB).
The optional external components shown in Figure 5 and Figure 6, and described above, are applicable in both
single and split supply voltage configurations.
Copyright © 2003–2013, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LM4780 LM4780TABD