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LM4734 Datasheet(PDF) 14 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. LM4734
Description  3 Channel 20W Audio Power Amplifier with Mute and Standby
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Manufacturer  NSC [National Semiconductor (TI)]
Direct Link  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM4734 Datasheet(HTML) 14 Page - National Semiconductor (TI)

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Typical Performance Characteristics (Continued)
Output Power vs Supply Voltage
Chs1&3in Parallel Mode (Note 16)
f = 1kHz, R
L =4
Ω, 80kHz BW
Output Power vs Supply Voltage
All Chs in Parallel Mode (Note 16)
f = 1kHz, R
L =2
Ω, 80kHz BW
200898J6
200898J5
Note 15: Bridge mode graphs were taken using the demo board and inverting the signal to the channel 3 input.
Note 16: Parallel mode graphs were taken using the demo board connecting each output through a 0.1
Ω/3W resistor to the load.
Application Information
MUTE MODE
By placing a logic-high voltage on the mute pins, the signal
going into the amplifiers will be muted. If the mute pins are
connected to a logic-low voltage, the amplifiers will be in a
non-muted state. There are three mute pins, one for each
amplifier, so that one channel can be muted without muting
the other if the application requires such a configuration.
Refer to the Typical Performance Characteristics section
for curves concerning Mute Attenuation vs Mute Pin Voltage.
STANDBY MODE
The standby mode of the LM4734 allows the user to drasti-
cally reduce power consumption when the amplifiers are
idle. By placing a logic-high voltage on the standby pins, the
amplifiers will go into Standby Mode. In this mode, the
current drawn from the V
CC supply is typically less than 30µA
total for all amplifiers. The current drawn from the V
EE supply
is typically 8mA. Clearly, there is a significant reduction in
idle power consumption when using the standby mode.
There are three Standby pins, so that one channel can be
put in standby mode without putting the other amplifier in
standby if the application requires such flexibility. Refer to
the Typical Performance Characteristics section for
curves showing Supply Current vs. Standby Pin Voltage for
both supplies.
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection cir-
cuitry allows the power supplies and their corresponding
capacitors to come up close to their full values before turning
on the LM4734. Since the supplies have essentially settled
to their final value, no DC output spikes occur. At power
down, the outputs of the LM4734 are forced to ground before
the power supply voltages fully decay preventing transients
on the output.
OVER-VOLTAGE PROTECTION
The LM4734 contains over-voltage protection circuitry that
limits the output current while also providing voltage clamp-
ing. The clamp does not, however, use internal clamping
diodes. The clamping effect is quite the same as diodes
because the output transistors are designed to work alter-
nately by sinking large current spikes.
THERMAL PROTECTION
The LM4734 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die exceeds 150˚C, the LM4734 shuts
down. It starts operating again when the die temperature
drops to about 145˚C, but if the temperature again begins to
rise, shutdown will occur again above 150˚C. Therefore, the
device is allowed to heat up to a relatively high temperature
if the fault condition is temporary, but a sustained fault will
cause the device to cycle in a Schmitt Trigger fashion be-
tween the thermal shutdown temperature limits of 150˚C and
145˚C. This greatly reduces the stress imposed on the IC by
thermal cycling, which in turn improves its reliability under
sustained fault conditions.
Since the die temperature is directly dependent upon the
heat sink used, the heat sink should be chosen so that
thermal shutdown is not activated during normal operation.
Using the best heat sink possible within the cost and space
constraints of the system will improve the long-term reliability
of any power semiconductor device, as discussed in the
Determining the Correct Heat Sink section.
DETERMlNlNG MAXIMUM POWER DISSIPATION
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understand-
ing if optimum power output is to be obtained. An incorrect
maximum power dissipation calculation may result in inad-
equate heat sinking causing thermal shutdown and thus
limiting the output power.
Equation (1) shows the theoretical maximum power dissipa-
tion point for each amplifier in a single-ended configuration
where V
CC is the total supply voltage.
www.national.com
14


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