Datasheet

LM2876
www.ti.com SNAS088C –AUGUST 1995–REVISED MARCH 2013
APPLICATION INFORMATION
GENERAL FEATURES
Mute Function
The muting function of the LM2876 allows the user to mute the music going into the amplifier by drawing less
than 0.5 mA out of pin 8 of the device. This is accomplished as shown in the Typical Application Circuit where
the resistor R
M
is chosen with reference to your negative supply voltage and is used in conjuction with a switch.
The switch (when opened) cuts off the current flow from pin 8 to V
−
, thus placing the LM2876 into mute mode.
Refer to the Mute Attenuation vs Mute Current curves in the TYPICAL PERFORMANCE CHARACTERISTICS
section for values of attenuation per current out of pin 8. The resistance R
M
is calculated by the following
equation:
R
M
(|V
EE
| − 2.6V)/I8
where
• I8 ≥ 0.5 mA
Under-Voltage Protection
Upon system power-up the under-voltage protection circuitry allows the power supplies and their corresponding
caps to come up close to their full values before turning on the LM2876 such that no DC output spikes occur.
Upon turn-off, the output of the LM2876 is brought to ground before the power supplies such that no transients
occur at power-down.
Over-Voltage Protection
The LM2876 contains overvoltage protection circuitry that limits the output current to approximately 4Apeak while
also providing voltage clamping, though not through internal clamping diodes. The clamping effect is quite the
same, however, the output transistors are designed to work alternately by sinking large current spikes.
SPiKe Protection
The LM2876 is protected from instantaneous peak-temperature stressing by the power transistor array. The Safe
Operating Area graph in the TYPICAL PERFORMANCE CHARACTERISTICS section shows the area of device
operation where the SPiKe Protection Circuitry is not enabled. The waveform to the right of the SOA graph
exemplifies how the dynamic protection will cause waveform distortion when enabled.
Thermal Protection
The LM2876 has a sophisticated thermal protection scheme to prevent long-term thermal stress to the device.
When the temperature on the die reaches 165°C, the LM2876 shuts down. It starts operating again when the die
temperature drops to about 155°C, but if the temperature again begins to rise, shutdown will occur again at
165°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 165°C and 155°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, the heat sink should be chosen as discussed
in the THERMAL CONSIDERATIONS section, such that thermal shutdown will not be reached 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.
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