SNAS545C May 2004 – May 2017 LM386
PRODUCTION DATA.
Refer to the PDF data sheet for device specific package drawings
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
Below are shown different setups that show how the LM386 can be implemented in a variety of applications.
Figure 10 shows the minimum part count application that can be implemented using LM386. Its gain is internally set to 20.
Figure 10. LM386 with Gain = 20 To make the LM386 a more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8 open the 1.35-kΩ resistor sets the gain at 20 (26 dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35-kΩ resistor, the gain will go up to 200 (46 dB). If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done by capacitively coupling a resistor (or FET) from pin 1 to ground.
Additional external components can be placed in parallel with the internal feedback resistors to tailor the gain and frequency response for individual applications. For example, we can compensate poor speaker bass response by frequency shaping the feedback path. This is done with a series RC from pin 1 to 5 (paralleling the internal
15-kΩ resistor). For 6 dB effective bass boost: R ~= 15 kΩ, the lowest value for good stable operation is R = 10 kΩ if pin 8 is open. If pins 1 and 8 are bypassed then R as low as 2 kΩ can be used. This restriction is because the amplifier is only compensated for closed-loop gains greater than 9.
The schematic shows that both inputs are biased to ground with a 50 kΩ resistor. The base current of the input transistors is about 250 nA, so the inputs are at about 12.5 mV when left open. If the dc source resistance driving the LM386 is higher than 250 kΩ it will contribute very little additional offset (about 2.5 mV at the input, 50 mV at the output). If the dc source resistance is less than 10 kΩ, then shorting the unused input to ground will keep the offset low (about 2.5 mV at the input, 50 mV at the output). For dc source resistances between these values we can eliminate excess offset by putting a resistor from the unused input to ground, equal in value to the dc source resistance. Of course all offset problems are eliminated if the input is capacitively coupled.
When using the LM386 with higher gains (bypassing the 1.35 kΩ resistor between pins 1 and 8) it is necessary to bypass the unused input, preventing degradation of gain and possible instabilities. This is done with a 0.1 μF capacitor or a short to ground depending on the dc source resistance on the driven input.
Figure 12. LM386 with Gain = 200 The Detailed Design Procedure can be found in the Detailed Design Procedure section.
Figure 14. LM386 with Gain = 50 The Detailed Design Procedure can be found in the Detailed Design Procedure section.
Figure 16. Low Distortion Power Wienbridge Oscillator The Detailed Design Procedure can be found in the Detailed Design Procedure section.
Figure 18. LM386 with Bass Boost The Detailed Design Procedure can be found in the Detailed Design Procedure section.
Figure 20. Square Wave Oscillator | DESIGN PARAMETER | EXAMPLE VALUE |
|---|---|
| Load Impedance | 4 Ω to 32 Ω |
| Supply Voltage | 5 V to 12 V |
The Detailed Design Procedure can be found in the Detailed Design Procedure section.
Figure 22. AM Radio Power Amplifier The Detailed Design Procedure can be found in the Detailed Design Procedure section.