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LM4961 Arkusz danych(PDF) 9 Page - Texas Instruments |
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LM4961 Arkusz danych(HTML) 9 Page - Texas Instruments |
9 / 24 page LM4961, LM4961LQBD www.ti.com SNAS242K – AUGUST 2004 – REVISED MAY 2013 For the NJB0028A, θJA = 66°C/W. TJMAX = 125°C for the LM4961. Depending on the ambient temperature, TA, of the system surroundings, Equation 6 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 5 is greater than that of Equation 6, then either the supply voltage must be increased, the load impedance increased or TA reduced. For the typical application of a 4.2V power supply, with a 2uF+30 Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 109°C provided that device operation is around the maximum power dissipation point. Thus, for typical applications, power dissipation is not an issue. Power dissipation is a function of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient temperature may be increased accordingly. Refer to the Typical Performance Characteristics curves for power dissipation information for lower output levels. EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS The LM4961’s exposed-DAP (die attach paddle) package (NJB) provides a low thermal resistance between the die and the PCB to which the part is mounted and soldered. The low thermal resistance allows rapid heat transfer from the die to the surrounding PCB copper traces, ground plane, and surrounding air. The NJB package should have its DAP soldered to a copper pad on the PCB. The DAP’s PCB copper pad may be connected to a large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink, and radiation area. Further detailed and specific information concerning PCB layout, fabrication, and mounting an NJB (WQFN) package is found in Texas Instruments Package Engineering Group under application note AN-1187 (Literature Number SNOA401). SHUTDOWN FUNCTION In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry to provide a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch connected between VDD and Shutdown pins. BAND SWITCH FUNCTION The LM4961 features a Band Switch function which allows the user to use one amplifier for both receiver (earpiece) mode and ringer/loudspeaker mode. When a logic high (VDD) is applied to the Band-SW pin (pin 19) the amplifier is in ringer mode. This enables the boost converter and sets the externally configurable closed loop gain selection to BW1. If the Band-SW pin has a logic low (GND) applied to its terminal then the device is in receiver mode. In this mode the boost converter is disabled and the gain selection is switched to BW2. This allows the amplifier to be powered directly from the battery minus the voltage drop across the Schottky diode. REDUCING TRANSIENT CURRENT SPIKE Due to the quick turn-on time of the Boost Converter, a transient supply current spike is observed on shutdown release. To reduce the rise time of the output voltage (V1), thus reducing the value of the supply current spike, please refer to application circuit in Figure 20. Using this configuration will allow the user to reduce the transient supply current spike without the Boost Converter experiencing any stability issues. Copyright © 2004–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM4961 LM4961LQBD |
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