LM4990 PDF

It is capable of delivering 1. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement. The LM features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by either logic high or low depending on mode selection. Driving the shutdown mode pin either high or low enables the shutdown pin to be driven in a likewise manner to enable shutdown.

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It is capable of delivering 1. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components.

The LM does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement. The LM features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by either logic high or low depending on mode selection. Driving the shutdown mode pin either high or low enables the shutdown pin to be driven in a likewise manner to enable shutdown.

The LM is unity-gain stable and can be configured by external gain-setting resistors. MM Low 1. ITL Low 1. Shutdown occurs only with a low assertion. Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits.

Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. For the LM, see power derating curves for additional information.

Note 4: Human body model, pF discharged through a 1. Note 5: Machine Model, pF — pF discharged through all pins. Note 6: Typicals are measured at 25? C and represent the parametric norm. Exposure to direct sunlight will increase ISD by a maximum of 2? This value represents the parallel combination of the 10k?

If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is enabled when VDD is greater than 5. Operation above 6. Note Maximum power dissipation in the device PDMAX occurs at an output power level significantly below full output power. It may also be obtained from the power dissipation graphs.

Note All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. All bumps must be connected to achieve specified thermal resistance. Ri Ci Functional Description Inverting input resistance which sets the closed-loop gain in conjunction with Rf. Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Refer to the section, Proper Selection of External Components, for an explanation of how to determine the value of Ci.

Feedback resistance which sets the closed-loop gain in conjunction with Ri. Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for information concerning proper placement and selection of the supply bypass capacitor. Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External Components, for information concerning proper placement and selection of CB. Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of phase by ?.

Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage.

Four times the output power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or clipped.

A bridge configuration, such as the one used in LM, also creates a second advantage over single-ended amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load. This eliminates the need for an output coupling capacitor which is required in a single supply, single-ended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased internal IC power dissipation and also possible loudspeaker damage.

A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. Since the LM has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1.

Refer to the application information on the LM reference design board for an example of good heat sinking. C, then additional changes must be made. These changes can include reduced supply voltage, higher load impedance, or reduced ambient temperature. Internal power dissipation is a function of output power. Refer to the Typical Performance Characteristics curves for power dissipation information for different output powers and output loading.

The capacitor location on both the bypass and power supply pins should be as close to the device as possible. Typical applications employ a 5V regulator with 10? F tantalum or electrolytic capacitor and a ceramic bypass capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the LM The selection of a bypass capacitor, especially CB, is dependent upon PSRR requirements, click and pop performance as explained in the section, Proper Selection of External Components , system cost, and size constraints.

In addition, the LM contains a Shutdown Mode pin LD and MH packages only , allowing the designer to designate whether the part will be driven into shutdown with a high level logic signal or a low level logic signal. This allows the designer maximum flexibility in device use, as the Shutdown Mode pin may simply be tied permanently to either VDD or GND to set the LM as either a "shutdown-high" device or a "shutdown-low" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown pin to the same state as the Shutdown Mode pin.

The trigger point for either shutdown high or shutdown low is shown as a typical value in the Supply Current vs Shutdown Voltage graphs in the Typical Performance Characteristics section.

It is best to switch between ground and supply for maximum performance. While the device may be disabled with shutdown voltages in between ground and supply, the idle current may be greater than the typical value of 0. In either case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which provides a quick, smooth transition to shutdown.

Another solution is to use a single-throw switch in conjunction with an external pull-up resistor or pull-down, depending on shutdown high or low application. This scheme guarantees that the shutdown pin will not float, thus preventing unwanted state changes. While the LM is tolerant of 13 www. C is not exceeded. Additional copper foil can be added to any of the leads connected to the LM The LM is unity-gain stable which gives the designer maximum system flexibility.

Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1Vrms are available from sources such as audio codecs. Please refer to the section, Audio Power Amplifier Design, for a more complete explanation of proper gain selection. Besides gain, one of the major considerations is the closedloop bandwidth of the amplifier. To a large extent, the bandwidth is dictated by the choice of external components shown in Figure 1.

The input coupling capacitor, Ci, forms a first order high pass filter which limits low frequency response. This value should be chosen based on needed frequency response for a few distinct reasons.

Selection of Input Capacitor Size Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below Hz to Hz.

Thus, using a large input capacitor may not increase actual system performance. In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Ci. This charge comes from the output via the feedback and is apt to create pops upon device enable.

Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be minimized. Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value. Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the LM turns on.

Choosing CB equal to 1. F along with a small value of Ci in the range of 0. F , should produce a virtually clickless and popless shutdown function.

While the device will function properly, no oscillations or motorboating , with CB equal to 0. F, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 1. F is recommended in all but the most cost sensitive designs. A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating from the Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be easily found.

Extra supply voltage creates headroom that allows the LM to reproduce peaks in excess of 1W without producing audible distortion.

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