LM4755TS National Semiconductor, LM4755TS Datasheet - Page 14

• Manufacturer Part Number: LM4755TS
• Description: IC,Audio Amplifier,DUAL,BIPOLAR,SIP,9PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM4755TS

• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 2-Channel Stereo
• Output Power (typ): 11x2@4OhmW
• Audio Amplifier Function: Speaker
• Total Harmonic Distortion: 0.08@8Ohm@2W%
• Single Supply Voltage (typ): 12/15/18/24/28V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Power Dissipation: 62.5W
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 50dB
• Single Supply Voltage (min): 9V
• Single Supply Voltage (max): 32V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 9 +Tab
• Package Type: TO-263
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Application Information
The LM4755 contains circuitry to pull down the bias line in-
ternally, effectively shutting down the input stage. An external
R-C should be used to adjust the timing of the pull-down. If
the bias line is pulled down too quickly, currents induced in
the internal bias resistors will cause a momentary DC voltage
to appear across the inputs of each amplifier's internal differ-
ential pair, resulting in an output DC shift towards Vsupply.
An R-C timing circuit should be used to limit the pull-down
time such that output “pops” and signal feedthroughs will be
minimized. The pull-down timing is a function of a number of
factors, including the internal mute circuitry, the voltage used
to activate the mute, the bias capacitor, the half-supply volt-
age, and internal resistances used in the half-supply genera-
tor. Table 1 shows a list of recommended values for the
external R-C.
CAPACITOR SELECTION AND FREQUENCY RESPONSE
With the LM4755, as in all single supply amplifiers, AC cou-
pling capacitors are used to isolate the DC voltage present at
TABLE 1. Recommended Values for Mute Circuit
V
MUTE
5V
5V
5V
5V
5V
5V
Power Dissipation vs Output Power
12V
15V
20V
24V
28V
30V
V
CC
8.2 kΩ
8.2 kΩ
18 kΩ
18 kΩ
12 kΩ
12 kΩ
Rm
10005960
10 µF
10 µF
10 µF
10 µF
10 µF
10 µF
Cm
14
the inputs (pins 3, 7) and outputs (pins 1, 8). As mentioned
earlier in the External Components section these capacitors
create high-pass filters with their corresponding input/output
impedances. The Typical Application Circuit shown in Fig-
ure 1 shows input and output capacitors of 0.1 µF and 1,000
µF respectively. At the input, with an 83 kΩ typical input re-
sistance, the result is a high pass 3 dB point occurring at 19
Hz. There is another high pass filter at 39.8 Hz created with
the output load resistance of 4Ω. Careful selection of these
components is necessary to ensure that the desired frequen-
cy response is obtained. The Frequency Response curves in
the Typical Performance Characteristics section show how
different output coupling capacitors affect the low frequency
roll-off.
OPERATING IN BRIDGE-MODE
Though designed for use as a single-ended amplifier, the
LM4755 can be used to drive a load differentially (bridge-
mode). Due to the low pin count of the package, only the non-
inverting inputs are available. An inverted signal must be
provided to one of the inputs. This can easily be done with the
use of an inexpensive op-amp configured as a standard in-
verting amplifier. An LF353 is a good low-cost choice. Care
must be taken, however, for a bridge-mode amplifier must
theoretically dissipate four times the power of a single-ended
type. The load seen by each amplifier is effectively half that
of the actual load being used, thus an amplifier designed to
drive a 4Ω load in single-ended mode should drive an 8Ω load
when operating in bridge-mode.
Power Dissipation vs Output Power
10005961