LM4752TS National Semiconductor, LM4752TS Datasheet - Page 14

• Manufacturer Part Number: LM4752TS
• Description: IC, AMP, AUDIO, 11W, AB, 7TO263
• Manufacturer: National Semiconductor

Specifications of LM4752TS

• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 2-Channel Stereo
• Output Power (typ): 7x2@8OhmW
• 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: 7 +Tab
• Package Type: TO-263
• Amplifier Class: AB
• No. Of Channels: 2
• Output Power: 11W
• Supply Voltage Range: 9V To 32V
• Thd + N: 0.08% @ 1W, 8ohm, VCC=24V
• Load Impedance: 4ohm
• Operating Temperature Range: -40°C To +85°C
• Rohs Compliant: Yes
• Amplifier Case Style: TO-263
• Lead Free Status / RoHS Status: Not Compliant

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Application Information
CAPACITOR SELECTION AND FREQUENCY RESPONSE
With the LM4752, as in all single supply amplifiers, AC cou-
pling capacitors are used to isolate the DC voltage present at
the inputs (pins 2,6) and outputs (pins 1,7). 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
rolloff.
APPLICATION CIRCUIT WITH MUTE
With the addition of a few external components, a simple mute
circuit can be implemented, such as the one shown in Figure
3. This circuit works by externally pulling down the half supply
bias line (pin 5), effectively shutting down the input stage.
When using an external circuit to pull down the bias, care must
be taken to ensure that this line is not pulled down too quickly,
or output “pops” or signal feedthrough may result. 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 differential pair,
Power Dissipation vs Output Power
10003951
14
resulting in an output DC shift towards V
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 external mute circuitry, the voltage used to activate the
mute, the bias capacitor, the half-supply voltage, and internal
resistances used in the half-supply generator. Table 1 shows
a list of recommended values for the external mute circuitry.
OPERATING IN BRIDGE-MODE
Though designed for use as a single-ended amplifier, the
LM4752 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.
V
MUTE
5V
V
V
S
S
Power Dissipation vs Output Power
10 kΩ 10 kΩ 4.7 μF 360Ω 100 μF 21V–32V
20 kΩ 1.2 kΩ 4.7 μF 180Ω 100 μF 15V–32V
20 kΩ 910Ω 4.7 μF 180Ω
R1
TABLE 1. Values for Mute Circuit
R2
C1
R3
SUPPLY
47 μF
10003952
C
B
. An R-C timing
22V–32V
V
CC