Datasheet

LM4782, LM4782TABD
www.ti.com SNAS231B –FEBRUARY 2004–REVISED MARCH 2013
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 LM4782 allows the user to drastically 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 circuitry allows the power supplies and their corresponding
capacitors to come up close to their full values before turning on the LM4782. Since the supplies have essentially
settled to their final value, no DC output spikes occur. At power down, the outputs of the LM4782 are forced to
ground before the power supply voltages fully decay preventing transients on the output.
OVER-VOLTAGE PROTECTION
The LM4782 contains over-voltage protection circuitry that limits the output current while also providing voltage
clamping. 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 alternately by sinking large current spikes.
SPiKe PROTECTION
The LM4782 is protected from instantaneous peak-temperature stressing of the power transistor array. The Safe
Operating graph in the Typical Performance Characteristics section shows the area of device operation where
SPiKe Protection Circuitry is not enabled. The SPiKe Protection Response waveform graph shows the waveform
distortion when SPiKe is enabled. Please refer to AN-898 (Literature Number SNAA008) for more detailed
information.
THERMAL PROTECTION
The LM4782 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 LM4782 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 between 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
understanding if optimum power output is to be obtained. An incorrect maximum power dissipation calculation
may result in inadequate heat sinking causing thermal shutdown and thus limiting the output power.
Equation 1 shows the theoretical maximum power dissipation point for each amplifier in a single-ended
configuration where V
CC
is the total supply voltage.
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