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LM4809
The LM4809 output does not require a bootstrap capacitor or buffer network, and is packaged in MSOP and SOP.
LM4809 Overview:
The LM4809 is a Class AB, dual-channel audio power amplifier. Each channel can provide an average power of 105mW (5V operating voltage, 16Ω load, THD+N=0.1%), and the total harmonic distortion + noise in the audio range is less than 0.1% (20Hz ~ 20KHz).
The application circuit of LM4809 is simple and requires very few peripheral devices. The output of LM4809 does not require bootstrap capacitance or buffer network, and adopts MSOP and SOP package to save circuit area, which is very suitable for low voltage and low power application solutions such as mobile phones and various mobile devices. The LM4809 can be controlled to enter sleep mode to reduce power consumption. The LM4809 has an internal thermal shutdown protection mechanism.
The LM4809 operates stably, has a gain bandwidth product of up to 2.5MHz, and is stable per unit gain. The feedback resistor is external, and the gain is configured using the external gain configuration resistor for easy application.
LM4809 Features:
High supply voltage rejection ratio (PSRR), up to 70dB at 217Hz and 1KHz
Noise and harmonic distortion (THD+N) < 0.1% (f=1KHz) at 16Ω load with output power of 105mW
Noise + harmonic distortion (THD+N)< 0.1% (f=1KHz) at 32 loads with output power of 70mW
Power down mode Leakage current is small, typical value is 0.4μA
Small package, MSOP, SOP package, save circuit area
The "crackling" sound of power-on and power-off has good suppression ability
Wide operating voltage range 2.0V-6V
No bootstrap capacitance required
Unit gain stabilization
LM4809 Application:
Earphone power amplifier
Personal mobile terminal PDA
Karaoke microphone
Microphone preamplifier
LM4809 schematic diagram:
LM4809 Order Information:.png)
LM4809 Typical application circuit:
LM4809 Pin distribution diagram:
LM4809 Pin Description:
LM4809 Application Description:
LM4809 Micro power off function
When switching off pin /SD to GND, the 4809 power supply current is minimized in off mode. When the device is turned off and the turn-off pin voltage is greater than 0.2V DD, the turn-off current may be greater than the typical value of 0.4μA. In addition, the off pin should be connected to a certain potential, because the off pin dangling can cause the amplifier to operate unpredictably.
In many applications, a microcontroller or microprocessor is used to control the turn-off circuit in order to make the circuit turn off quickly and smoothly. Another method is to use a single-pole single-throw switch with an external pull-up resistor. When the switch is closed, the pin /SD is connected to the ground to disable the amplifier. If the switch is not closed, the external pull-up resistor will enable 4809. This scheme ensures that the shutdown pin will not be suspended to avoid unpredictable state changes.
Power consumption is one of the key indicators for the amplifier, the maximum self-power consumption of the differential output amplifier is:
PDMAX = 4× (V DD) 2 / (2×Π 2× R L)
It must be noted that the self-consumption is a function of the output power.
In the circuit design, the internal temperature of the chip can not be higher than T JMAX (150℃). According to the thermal resistance of the chip JA, the heat dissipation performance can be increased by cooling copper platinum by itself.
If the chip still does not meet the requirements, it is necessary to increase the load resistance, reduce the power supply voltage or reduce the ambient temperature to solve the problem.
LM4809 Power bypass
In the application of amplifier, the bypass design of the power supply is very important, especially for the noise performance of the application scheme and the power supply voltage suppression performance. In the design, the bypass capacitor is required to be as close to the chip and power pin as possible. A typical capacitance is an electrolytic capacitor of 10μF and a ceramic capacitor of 0.1μF.
In the LM4809 application circuit, another capacitor C B (connected to BYP pin) is also very critical, affecting PSRR, switching/switching noise performance. For details, see the Bypass Capacitor Selection section below.
Selection of LM4809 peripheral components
The correct selection of peripheral components can ensure the performance of the chip, although the LM4809 can have a large margin to guarantee performance, but in order to ensure the overall performance, it is also required to correctly select peripheral components.
The overall gain of the LM4809 is stable, giving designers maximum flexibility. The LM4809 should be used in low gain configurations to minimize the THD+N value and to minimize the signal-to-noise ratio. Low gain configurations require large input signals to obtain a given output power, with input signals from, for example, audio codecs equal to or greater than 1Vrms. Refer to the Audio Power Amplifier Design section for a more complete explanation of the correct gain selection.
In addition to gain, a major design consideration is the closed-loop bandwidth of the amplifier, which for a large range is determined by selecting the external components in Figure 1. The input coupling capacitance Ci and the output coupling capacitance Co form the first-stage high-pass filter, which limits the low-frequency response. These values should be selected based on the need for frequency response.
The LM4809 is stable in unit gain, so it can be used in a wide range. Unit-gain amplification is usually applied to reduce THD+N and maximize the signal-to-noise ratio. However, this requires maximum input voltage, and a typical CODEC can have a voltage output of 1V rms. In addition, the closed-loop bandwidth must be guaranteed, and the input coupling capacitance Ci (forming a first-order high-pass) determines the low-frequency response.
LM4809 Select the input coupling capacitor
Too large input capacitance increases the cost and increases the area, which is very unfavorable for applications where the cost and area are tight. Obviously, it is important to determine how much capacitance to use to complete the coupling. In fact, in many applications, the Speaker cannot reproduce low-frequency speech below 100Hz-150Hz, so the use of large capacitors can not improve the performance of the system.
In addition to the cost and size of the system, noise performance is affected by the size of the input coupling capacitance. A large input coupling capacitance requires more charge to reach the static DC voltage (usually the midpoint voltage of the power supply, i.e. 1/2V DD). These charges come from the feedback output, which often produces noise when the device is enabled. Thus, the opening noise can be minimized based on the minimization of the input capacitance based on the required low frequency response.
In addition to minimizing the input/output capacitance size, the size of the bypass capacitor should also be considered in detail. The bypass capacitor C B is the most important component to minimize the opening noise, which determines the speed of LM4809 opening. The slower the LM4809 output reaches the static DC voltage (usually the midpoint voltage of the power supply, that is, 1/2V DD) (see Table 8), the smaller the opening noise. Choosing a 1.0μF C B and a small Ci(in the range of 0.1μF to 0.39μF) will achieve a virtually noise-free switching function. When the device is functioning normally (no oscillations or crackles) and the CB is 0.1μF, the device will be more affected by the on-noise. Therefore, 1.0μF or larger C B is recommended in all but the most cost-sensitive designs.
LM4809 Package size
MSOP8:
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