1 Function description

LM4871 is a single bridge audio power amplifier 2

without output coupling capacitors. It can provide 3W continuous average capacitors or required buffer circuits to be stable. Power supply by 5V power supply (see notes). Go to WSON, VSSOP, SOIC or PDIP packaging can save the micro -power closing mode of electricity LM4871 in portable applications (IQ u003d 0.6 μA, external gain configuration capabilities when VDD applies to

pins compatible with LM4861 shutdown pinnacles .

The design of the BoOMER audio power amplifier specifically provides high -power, high -fidelity audio

Portable computer output. They only need a few external components

desktop computer at 2.0 V to 5.5V's low power supply voltage work. Because LM4871 does not require output coupling low -voltage audio system capacitors, self -lifting capacitors or buffer, it is very suitable for low -power portable key specification systems that require minimum volume and weight .

PO under 10%THD+N, 1kHz additional LM4871 function includes heat shutdown

-LM4871LD: 3 , 4 Unit's gain stability and external gain settings. 2.5 W (typical value)

Note: LM4871LD that has been properly installed -All other LM4871 packaging: 8 #8486 of the circuit board; load will provide 3W to 3 (10%1.5 w (typical) ThD). Other software packages of the LM4871 will

off the current off -current 0.6 μA (typical value) is 8 (10%THD) 1.5W. See application information. Part of the information power supply voltage range 2.0V to 5.5V about LM7148M, LM7148M, 1kHz, 1W continuous THD and LM4871N. The output power is 8 0.5%(maximum)

123]

These devices have limited built -in ESD protection. The wires should be shortened together, or the device is placed in the conductive foam during the storage or handling process to prevent static electricity from damaging the MOS door.

(1) Absolutely maximum rated value indicates the limit of damage to the device. The working rated value indicates that the device can work normally, but it cannot guarantee specific performance limit. AC Electric ensure the specifications under specific test conditions of specific performance limit. This assumes that the device is at the rated value of the operation. For parameters that are not given, the specifications cannot be guaranteed. However, the typical value is a good instructions.Equipment performance.

(2) If you need military/aerospace special equipment, please contact the Texas Instrument Sales Office/dealer to obtain standardization.

(3) The maximum power consumption must be reduced at high temperature, and the teaching assistant is determined by TJMAX, θJa and environmental temperature. The maximum allowable power consumption is PDMAX u003d (TJMAX -TA)/θJa or the given values u200bu200bgiven in the absolute maximum rated value. For LM4871, tjmax u003d 150 ° C. For θja of different packages, please refer to the application information part or the absolute maximum rated part.

(4) Human model, 100pf passes 1.5k resistance.

(5) Machine model, 220pf – 240pf Power electricity through all pins.

(6) Given θja is used in LM4871 packaged in NGN0008A, and the exposed-DAP welded to the 1IN2 regional circuit board copper printed by 1oz.

Electrical characteristics (1) (2)

The following specifications are applicable to VDD u003d 5V and RL u003d 8 , unless there are other regulations. The limit is suitable for TA u003d 25 ° C.

(1) Absolute maximum rated value indicates the limit of damage to the device. The work rated value indicates that the device can work normally, but cannot guarantee specific performance restrictions. DC and AC electrical states of electrical characteristics to ensure specifications under specific test conditions for specific performance limit. This assumes that the device is at the rated value. For parameters without restrictions, the specifications cannot be guaranteed, but the typical value is a good instruction equipment performance.

(2) Unless there are other regulations, all voltage is measured relative to the ground needle.

(3) At 25 ° C, the typical CAL is parameterized.

(4) Limit the AOQL (average shipment quality level) of TI.

Electrical characteristics (1) (2) (continued)

The following specifications are applicable to VDD u003d 5V and RL u003d 8 unless there are other regulations. Limited to TA u003d 25 ° C

(5) When loading from 5V power drive 3 or 4 Essence

Typical performance features

NGN feature

This curve shows the exposure of parts of the parts of the part of the part of the parts of the parts of the part of the parts of the welding at different environmental temperatures. On the plane of 1oz.cu, the labels of each plane are allGive an area curve. This label also specifies whether the plane is the same (top layer) as the chip, on the bottom, or on the two layers. This is the same as the conditions for infinite heat sinks and independence (radiator).

Drive 3 and 4 Matters

Load

The power of the load loss is a function of fluctuation between the voltage between the voltage between the load and the load impedance. As a decrease in load impedance, the load loss is increasingly dependent on the resistance between the interaction (PCB tracking and wire) amplifier output pins and the load connection. The cause of the residual trace resistance is dropped, causing the power supply to dissipate in the tracking instead of the requirements in the load. For example, 0.1 tracking resistance reduced the output power of 4 load consumption from 2.0W to 1.95W. This problem is to reduce load loss as the load impedance decreases. Therefore, maintaining the maximum load loss and the widest output voltage swing, the PCB tracking of the connected output pins to the load must be as wide as possible. Poor power adjustment has adversely affected the maximum output power. The supply voltage of poor supervision decreases with the increase of the load current. The reduction of the power supply voltage leads to the cutting signal tailoring of the air and the reduction of the output power. Even with strict supply, tracking resistance will also have an impact as poor supply control. Therefore, the power tracking of power as much as possible can help keep the output voltage full.

Bridge structure description

As shown in Figure 3, there are two computing amplifiers inside the LM4871, allowing several different amplifiers to configure. The gain of the first amplifier is external -configured; the second amplifier is fixed in the unified gain, and the reversal configuration. By selecting the radio frequency ratio, set the closed -loop gain of the first amplifier to RI, and the gain of the second amplifier is fixed by the two internal 40K the resistor is fixed. Figure 3 shows the input of the amplifier as the input of the amplifier 2. The signal generated by the two amplifiers is at the earthquake level, but the phase is 180 °. Therefore, the micro -scoring gain of IC is the average value u003d 2*(RF/RI) (1) The amplifier configuration is usually called the ""bridge mode"" by output VO1 and VO2 differential driving load. The bridge mode operation is different from the classic single -end amplifier's load connected to the ground configuration.

The design of the bridge amplifier has several obvious advantages compared with the single -end configuration, because it provides a differential driver to the load, which doubles the output swing to achieve the prescribed power supply voltage. Four times the output under the same conditions, compared with a single -end amplifier, power is possible. The realized growth output power assumes that the amplifier has no current limit or tailored. In order to select the closed loop gain of the amplifier without causing excessive tailoring, see the audio power amplifier design part. Different bridge outputAnother advantage is no load DC voltage. This is the result of the prejudice VO1 and VO2 under the same DC voltage, in this case, VDD/2. This eliminates the power supply of the coupled electric container, and the single -end amplifier needs. Eliminate the output coupling capacitance of the single -end structure to force the semi -power bias voltage of a single power amplifier to pass through the load. The current generated by the semi -power bias voltage increases the internal IC power consumption, and my permanent damage load is.

Power consumption

When the successful design of the design, whether it is a bridge connection or a bridge, the power consumption is a major problem of single -end. The direct consequence of the increase in the power transfer of the bridge to the load is to increase the internal power consumption. Formula 2 illustrates the maximum power consumption point amplifier of the bridge at a given power supply voltage and drives the specified output load. PDMAX u003d 4*(VDD) 2/(2π2RL) (2) Since the LM4871 has two computing amplifiers in one package, the maximum internal power consumption is double by 4 multiplied by a single -end Anders. Even if the power consumption increases significantly, LM4871 does not need to heat dissipation under most operating conditions and output loads. From Formula 2, assuming 5V power and 8 load, the maximum power consumption point is 625 mW. The maximum power consumption from equation 2 must not be greater than the formula 3: pdmax u003d (tjmax – TA)/θJa power consumption

For SOIC packaging, θja u003d 140 ° C/W; θja u003d 107 ° C/W; for VSSOP packaging, θja u003d 210 ° C/W, assuming free air running. For NGN packaging welded to the DAP pad, the DAP pad can be extended to the area of u200bu200b1.0in2 on PCB, and the θJa of LM4871 is 56 ° C/W. For LM4871, tjmax u003d 150 ° C. θja can reduce heat dissipation through some form. The θja will be the sum of θjc, θcs and θsa. θjc is a case connected to the package (or exposed DAP, such as the condition of the NGN package). θCS is the effect of the heat sinking heat and θsa on the heat sinks on the environmental thermal resistance. By adding additional copper area around SOIC and VSSOP, LM4871, θja can reduce packaging from its free air value. The results of the copper area around NGN from 1.0in2 to 2.0in2 area were reduced to 46 ° C/W. Based on the ambient temperature TA and θJa, Formula 3 can be used to calculate the maximum internal power consumption supported by IC packaging. If the result of Formula 2 is greater than that of 3, it is either lowering the power supply voltage, or increased load impedance, and the ambient temperature is reduced. For the typical application of 5V power supply, 8 load, and no additional heat dissipation, the maximum environmental temperature may not violate the maximum temperature. If the device runs near the maximum power, the knot temperature is about 61 ° C dissipation point and assumption surface paste. Package. For NGN packaging in the typical application of 5VPower, 4 load, 1.0in2 copper area welded to the exposed DAP pad, and the maximum environmental temperature was about 77 ° C, provided that the device was running near the maximum power consumption point. Internal power consumption is a function of the output power. If the typical operation does not dissipate near the maximum power, the ambient temperature can be increased. Refer to the typical performance characteristics of different output power and the power consumption information curve of the output load.

Power bypass

Like any amplifier, the correct power bypass is important to reject low noise performance and high power power supply. The position of the capacitors on the bypass and power pins should be as close to LM4871 as possible. The capacitors connected between the bypass and the ground improve the internal bias voltage stability and improve the PSRR. With the increase of PIN capacitors, the improvement of PSRR is also increasing. Typical applications use 5V regulator and 0.1 μF bypass electrical container, which helps the stability of the power supply. This does not eliminate the need to use 1 μF 钽 capacitor to bypass the power supply node of LM4871. The choice of bypass power container, especially the circuit breaker, depends on the power suppression ratio requirements. Click the pop -up performance as stated, the correct selection of external components, system cost and dimensional restrictions.

Shipping function

In order to reduce the power consumption when not in use, LM4871 contains a bias circuit for shutdown pin amplifier for external shutdown. When the logic high level is placed in a shutdown pin. The trigger point between the logic low level and the logic high level is usually semi -power supply. It is best to switch between the ground and the power to provide the maximum equipment performance. By switching the shutdown pin to the idle mode, the LM4871 power supply current consumption will minimize. When the device will be banned from the VDD, the typical value of the idle current may be greater than 0.6 μA In this case, the shutdown foot should be connected to a certain voltage to avoid unnecessary state changes. In many applications, the microcontroller is used to control or off the circuit to provide a fast and smooth transition to the shutdown state. Another solution is to connect to the external pull -up resistor using a single -pole -throw switch. When the switch is turned off, the stop is touched and the amplifier is activated. If the switch is turned off, the external pull -up resistor will disable LM4871. This scheme ensures that the closing pin does not float, thereby preventing unnecessary state changes.

Correctly select external components

In the application of integrated power amplifier, correct selection of external components is a key equipment and system performance for optimization. Although LM4871 can tolerate the combination of external components, the component value must be considered to maximize the overall quality of the system. LM4871 is a stable unit gain, which gives designers the biggest system flexibility. LM4871 should be used in a low -gain configuration to minimize the THD+N value and maximize the signal -to -noise ratio. Low -gain configuration requires a large input signal to get a given output power. Entering signal is equal to or greater than 1VRM to compile from audioObtain sources such as code. See the design of the ""Audio Power amplifier"" section in order to explain the correct gain choice more complete. In addition to gain, the closed bandwidth of the amplifier is also one of the main considerations. To a large extent, bandwidth depends on the choice of external components displayed in the design of the audio power amplifier. Enter the coupling capacitor CI to form a first -order high -pass filter to limit low -frequency response. This value should be selected based on some different reasons, according to the frequency of need.

Selection of the size of the input capacitor

For portable design, large input capacitors are both expensive and occupied by space. Obviously, a certain size capacitor needs to be coupled in the low frequency band without generating serious attenuation. However, in many cases, speakers are used for portable systems. Whether internally or outside, there is almost no ability to reproduce a signal of 150 Hz below 100Hz. Therefore, using large input capacitors may not improve the actual system performance. In addition to the system cost and size, the clicks and pop -up performance are also affected by the capacity of the input coupling, CI. The larger input coupling container requires more charge to achieve its static DC voltage (1/2 VDD in name). This charge comes from the output by feedback, and it is easy to produce persistent organic pollutants during the device enable. Therefore, the size of the minimized capacitor can be minimized by minimizing the capacitance on the basis of the necessary low -frequency response. In addition to the size of the minimum input capacitor, the value of the bypass container should also be considered carefully. Wingrser -packed container, CB, is the most critical component to reduce POP because it determines the opening of LM4871. The slower the volume of the output slope of the LM4871 to its static DC voltage (nominal 1/2 VDD), the slower the volume. Select CB equal to 1.0 μF and smaller CI values u200bu200b(from 0.1 μF to 0.39 μF), and there is no need to click and no POP shutdown function. When the device works correctly, (no oscillation or motorboat), when CB is equal to 0.1 μF, the device will be more likely to be opened and popped up. Therefore, in addition to the most sensitive products for costs, it is recommended that all products CB value is equal to 1.0 μF design

Audio power amplifier design

Design 1W/8 audio amplifier

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[ 123] In view of:

Power output 1 WRMS

Load impedance 8

Input level 1 vRMS

Input impedance 20 k

Bandwidth 100 HZ -20 KHz ± 0.25 DB designer must first determine the minimum power supply rail to obtain the specified output power. By inferring the typical performance characteristics of the output power and power supply voltage curve diagram, the power rail is easy to find. The second method to determine the minimum power supply track is to calculate the required voltage peak use equations 4, plus the inputOut of voltage. Using this method, the minimum power supply voltage is+(VODTOP+VODBOT), where Vodbot and Vottop are based on the typical performance characteristics.

In most applications, it is selected as a standard voltage of the power rail. The additional power supply voltage creates space, which enables LM4871 to reproduce the peak of more than 1W without generating it. At this time, the designer must ensure that the power selection and output impedance do not violate the conditions explained in the dispersion part. Once the power dissipation equation is resolved, the required micro -division gain can be determined according to Formula 5

According to Formula 5, the minimum AVD is 2.83; using AVD u003d 3. Since the required input impedance is 20K and the AVD impedance is 2, the ratio of RF is 1.5: 1 to RI results in the configuration of RI u003d 20K and RF u003d 30K The final design step is to meet the needs of bandwidth. It must be expressed as a pair of #8722; 3db frequency points. The distance between five times the -3DB point is 0.17DB band response to ± 0.25dB, which is better than specified.

FL u003d 100Hz/5 u003d 20Hz

100kHz*20KHz u003d 20kHz

As mentioned in the external component description, RI and CI create high -pass filter together. CI ≥ 1/(2π*20K *20Hz) u003d 0.397 μF; the use of 0.39μF high -frequency poles is determined by the product of the expected polar point FH and micro -divide gain, with average value. When AVD u003d 3 and FH u003d 100kHz, the GBWP u003d 150kHz obtained is GBWP, which is much 4MHz smaller than LM4871. This figure shows that if the designer needs to design a higher -differential amplifier, LM4871 can still be used without bandwidth limit.