The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ω load and 38W into 8Ω with 0.1% (THD + N) from 20 Hz±20 kHz.. The LM3886 maintains an excellent Signal-to-Noise Ratio of greater than 92 dB with a typical low noise floor of 2.0 mV. It exhibits extremely low (THD + N) values of 0.03% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

Figure 1. LM3886 68W High End Power Amplifier Double Supply

Figure 2. LM3886 68W High End Power Amplifier Single Supply

68W cont. avg. output power into 4Ω at V_CC ±28V
38W cont. avg. output power into 8Ω at V_CC ±28V
50W cont. avg. output power into 8Ω at V_CC ±35V

Component Description

R_IN  : Acts as a volume control by setting the voltage level allowed to the amplifier's input terminals.

R_A   : Provides DC voltage biasing for the single supply operation and bias current for the positive input
terminal.

C_A   : Provides bias filtering.

C     :  Provides AC coupling at the input and output of the amplifier for single supply operation.

R_B   : Prevents currents from entering the amplifier's non-inverting input which may be passed through to the load upon power-down of the system due to the low input impedance of the circuitry when the under-voltage circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.

*C_C  : Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of the output transistor. The capacitor also suppresses external electromagnetic switching noise created from fluorescent lamps.

R_i     :  Inverting input resistance to provide AC Gain in conjunction with R_f1.

C_i     : Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:
f_c = 1/(2π R_i C_i)

R_f1   : Feedback resistance to provide AC Gain in conjunction with R_i.

*R_f2 : At higher frequencies feedback resistance works with Cf to provide lower AC Gain in conjunction
with R_f1 and R_i. A high frequency pole (lowpass roll-off) exists at: f_c = [R_f1 R_f2 (s + 1/R_f2C_f)]/[(R_f1 + R_f2)(s + 1/C_f(R_f1 + R_f2))]

*C_f    : Compensation capacitor that works with R_f1 and R_f2 to reduce the AC Gain at higher frequencies.

R_M    : Mute resistance set up to allow 0.5 mA to be drawn from pin 8 to turn the muting function off.
RM is calculated using: RM ≤ (lVEEl - 2.6V)/I8 where I8 ≥ 0.5 mA. Refer to the Mute

C_M    : Mute capacitance set up to create a large time constant for turn-on and turn-off muting.

*R_SN : Works with C_SN to stabilize the output stage by creating a pole that eliminates high frequency
oscillations.

*C_SN : Works with R_SN to stabilize the output stage by creating a pole that eliminates high frequency oscillations. f_c = 1/(2πR_SNC_SN)

*L     : Provides high impedance at high frequecies so that R may decouple a highly capacitive load

*R    : and reduce the Q of the series resonant circuit due to capacitive load. Also provides a low
impedance at low frequencies to short out R and pass audio signals to the load.

C_S   : Provides power supply filtering and bypassing.

S₁   : Mute switch that mutes the music going into the amplifier when opened.

GENERAL FEATURES

Mute Function: The muting function of the LM3886 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 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_b, thus placing the LM3886 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 RM is calculated by the following equation:
RM (lVEEl - 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 LM3886 such that no DC output spikes occur. Upon turn-off, the output of the LM3886 is brought to ground before the power supplies such that no transients occur at power-down.

Over-Voltage Protection : The LM3886 contains overvoltage protection circuitry that limits the output current to approximately 11Apeak 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 LM3886 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 LM3886 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 LM3886 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 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.