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MAX4298 Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX4298 Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 14 page Ultra-High PSRR Stereo Drivers + Microphone Amp + 100mA Linear Regulator 8 _______________________________________________________________________________________ MAX4298 block diagram and Figure 2 is the MAX4299 block diagram. The amplifiers exhibit better than 115dB of DC power- supply rejection and 93dB at 20kHz. The output ampli- fiers are capable of driving a 1.5VRMS signal into 10kΩ load with 0.0008% distortion. They can also drive 32 Ω headphones to 1.2VRMS with 0.02% distortion. At +3.3V, the linear regulator can output 100mA of current. BIAS The common-mode bias point for the amplifiers is set to 2.25V by internal circuitry that has two functions. It pro- vides a clickless/popless power-up/power-down wave- form for the amplifiers. Also, it generates a ground- referenced bias voltage with ultra-high power-supply rejection ratio (PSRR). BIAS should be bypassed with 1µF to GND.The output impedance of the BIAS pin is 50k Ω. Clickless/Popless Function The MAX4298/MAX4299 are designed for high-fidelity audio performance into AC-coupled loads. Patented design techniques achieve a clickless/popless power-up sequence, and the use of a low-current standby supply (SVCC) or external Schottky diode/reservoir capacitor combination allows clickless/popless power-down. A clickless/popless mute function is also provided to main- tain a low impedance output when the input signal is switched off. Mute Function The MAX4298/MAX4299 have a MUTE pin that allows the user to mute the outputs of the device. This feature dis- connects the input signal from the power amplifiers when a logic high is present at the MUTE pin. To ensure proper functionality, the MUTE pin should always be tied to either VCC or GND. MUTE only affects the headphone driver outputs. REG, BIAS, and MICOUT are unaffected. OUT1 and OUT2 are muted, but remain in a low-impedance state to ensure clickless/popless operation. SVCC The MAX4298/MAX4299 provide a fully clickless power- down sequence. SVCC can either be connected to a low- current +5V power source or alternatively can be connected with a reservoir capacitor to ground and a Schottky diode to VCC. A reservoir capacitor of 220µF or higher provides enough charge for the clickless power- down sequence when CBIAS = 1µF. For larger values of CBIAS, increase the reservoir capacitor accordingly. Short to VCC if clickless power-down is not needed. Driver Amplifier The headphone driver amplifier is a class AB amplifier designed to drive 16 Ω loads. The amplifiers have innov- ative architectures for both the input and output stages to achieve ultra-high PSRR while maintaining rail-to-rail output drive capability. The output stage can drive high capacitive loads encountered when driving long cables used for desktop speakers or headphones. Microphone Preamplifier (MAX4299) The MAX4299 provides a microphone preamplifier that is a low-power version of the audio amplifier. It is intend- ed to be used for low-level signal amplification. This microphone preamplifier provides rail-to-rail output with very high PSRR. CBYPASS IN1 VCC SVCC OUT1 MUTE OUT2 GND MAX4298 IN2 BIAS + _ 50k Ω 2.25V _ + Figure 1. MAX4298 Block Diagram CBYPASS OUT1 MICIN GND MAX4299 MICOUT MUTE IN2 BIAS IN1 1.233V FB VCC SVCC REGON REG 18.4k Ω 11k Ω 50k Ω OUT2 N.C. _ + 2.25V + _ + _ + _ PGND Figure 2. MAX4299 Block Diagram |
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