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MAX9722B Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX9722B Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 21 page Shutdown The MAX9722A/MAX9722B feature shutdown control allowing audio signals to be shut down or muted. Driving SHDN low disables the amplifiers and the charge pump, sets the amplifier output impedance to 10kΩ, and reduces the supply current. In shutdown mode, the supply current is reduced to 0.1µA. The charge pump is enabled once SHDN is driven high. Applications Information Power Dissipation Under normal operating conditions, linear power ampli- fiers can dissipate a significant amount of power. The maximum power dissipation for each package is given in the Absolute Maximum Ratings section under Continuous Power Dissipation or can be calculated by the following equation: where TJ(MAX) is +145°C, TA is the ambient tempera- ture, and θJA is the reciprocal of the derating factor in °C/W as specified in the Absolute Maximum Ratings section. For example, θJA of the thin QFN package is +63.8°C/W, and 99.3°C/W for the TSSOP package. The MAX9722A/MAX9722B have two power dissipation sources: the charge pump and two amplifiers. If power dissipation for a given application exceeds the maxi- mum allowed for a particular package, either reduce SVDD, increase load impedance, decrease the ambient temperature, or add heatsinking to the device. Large output, supply, and ground traces improve the maxi- mum power dissipation in the package. Thermal-overload protection limits total power dissipa- tion in the MAX9722A/MAX9722B. When the junction temperature exceeds +145°C, the thermal-protection circuitry disables the amplifier output stage. The ampli- fiers are enabled once the junction temperature cools by 5°C. This results in a pulsing output under continu- ous thermal-overload conditions. Output Power The device has been specified for the worst-case sce- nario—when both inputs are in-phase. Under this con- dition, the amplifiers simultaneously draw current from the charge pump, leading to a slight loss in SVSS head- room. In typical stereo audio applications, the left and right signals have differences in both magnitude and phase, subsequently leading to an increase in the max- imum attainable output power. Figure 6 shows the two extreme cases for in- and out-of-phase. In reality, the available power lies between these extremes. Powering Other Circuits from a Negative Supply An additional benefit of the MAX9722A/MAX9722B is the internally generated, negative supply voltage (PVSS). This voltage provides the ground-referenced output level. PVSS can, however, be used to power other devices within a design limit current drawn from PVSS to 5mA; exceeding this affects the headphone amplifier operation. A typical application is a negative supply to adjust the contrast of LCD modules. PVSS is roughly proportional to PVDD and is not a regulat- ed voltage. The charge-pump output impedance must be taken into account when powering other devices from PVSS. The charge-pump output impedance plot appears in the Typical Operating Characteristics. For best results, use 1µF charge-pump capacitors. UVLO The MAX9722A/MAX9722B feature an UVLO function that prevents the device from operating if the supply voltage is less than 2.2V (typ). This feature ensures proper operation during brownout conditions and pre- vents deep battery discharge. Once the supply voltage reaches the UVLO threshold, the MAX9722A/ MAX9722B charge pump is turned on and the ampli- fiers are powered. P T DISSPKG MAX J MAX JA () () = -TA θ 5V, Differential Input, DirectDrive, 130mW Stereo Headphone Amplifiers with Shutdown ______________________________________________________________________________________ 11 OUTPUT POWER vs. SUPPLY VOLTAGE SUPPLY VOLTAGE (V) 3.8 3.6 2.6 2.8 3.0 3.2 3.4 20 40 60 80 100 120 140 160 0 2.4 4.0 fIN = 1kHz RL = 32Ω THD+N = 10% INPUTS IN PHASE INPUTS 180° OUT OF PHASE Figure 6. Output Power vs. Supply Voltage With Inputs In/Out of Phase |
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