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MAX98310EWL Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX98310EWL Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 14 page ���������������������������������������������������������������� Maxim Integrated Products 11 MAX98309/MAX98310 Mono 1.4W Class AB Audio Amplifiers The increase in power delivered by the BTL configuration directly results in an increase in internal power dissipa- tion over the single-ended configuration. The maximum internal power dissipation for a given VDD and load is given by the following equation: 2 DD D(MAX) 2 L 2V P R = π If the internal power dissipation for a given application exceeds the maximum allowed for a given package, reduce power dissipation by increasing the ground plane heatsinking capability and the size of the traces to the device. See the Layout and Grounding section. Other methods for reducing power dissipation are to reduce VDD, increase load impedance, decrease ambient temperature, reduce gain, or reduce input signal. Thermal-overload protection limits total power dissipation in the MAX98309/MAX98310. When the junction temper- ature exceeds +160NC, the thermal protection circuitry disables the amplifier. Operation returns to normal once the die cools by 15NC. Amplifier Gain Fixed Differential Gain (MAX98310) The MAX98310 features four internally fixed differential gain options selectable by GAIN (Table 1). This simplifies design, decreases required application footprint size, and eliminates external gain-setting resistors. External Differential Gain (MAX98309) The MAX98309 features an external gain option. Resistors RF and RIN. See the Simplified Block Diagram and set the gain of the amplifier as follows: F V IN R A R = where AV is the desired voltage gain. Hence, an RIN of 10kI and an RF of 20kI yields a gain of 2V/V or 6dB. RF can be either fixed or variable, allowing the use of a digitally controlled potentiometer to alter the gain under software control. Input Filter The fully differential amplifier inputs can be biased at voltages other than midsupply. The common-mode feedback circuit adjusts for input bias, ensuring the out- puts are still biased at midsupply. Input capacitors are not required as long as the input voltage is within the specified common-mode range listed in the Electrical Characteristics table. If input capacitors are used, input capacitor CIN, in con- junction with the input resistor RIN, forms a highpass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to bias the sig- nal to an optimum DC level. Assuming zero-source imped- ance, the -3dB point of the highpass filter is given by: 3dB IN IN 1 f 2 R C − = π Setting f-3dB too high affects the low-frequency response of the amplifier. Use capacitors with adequately low volt- age coefficients, such as X7R ceramic capacitors with a high voltage rating. Capacitors with higher voltage coef- ficients result in increased distortion at low frequencies. BIAS Capacitor BIAS is the output of the internally generated VDD/2 bias voltage. The BIAS bypass capacitor, CBIAS, improves PSRR and THD+N by reducing power supply and other noise sources at the common-mode bias node, and also generates the clickless/popless startup DC bias wave- form for the speaker amplifiers. Bypass BIAS with a 0.1FF capacitor to GND. Larger values of CBIAS (up to 1FF) improve PSRR. Supply Bypassing Proper power-supply bypassing ensures low-noise, low- distortion performance. Connect a 1FF ceramic capacitor from VDD to GND. Add additional bulk capacitance as required by the application. Locate the bypass capacitor as close as possible to the device. Layout and Grounding Good PCB layout is essential for optimizing performance. Use large traces for the power-supply inputs and amplifier outputs to minimize losses due to parasitic trace resis- tance and route heat away from the device. Good ground- ing improves audio performance, and prevents any digital switching noise from coupling into the audio signal. Table1.FixedDifferentialGain GAINCONNECTION GAIN(dB) VDD 0 GND 3 Unconnected 6 BIAS 9 |
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