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MAX97200BEWC+ Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX97200BEWC+ Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 13 page Low-Power, Low-Offset, Dual Mode, Class H DirectDrive Headphone Amplifier 9 Dual Mode Charge Pump The MAX97200’s Dual Mode, charge pump outputs either QPVIN/2 in high-efficiency mode or QPVIN in high- power mode, resulting in a power-supply differential of 1.8V or 3.6V. The charge-pump mode changes based on the level of the output signal needed. When the output voltage is small, the voltage rails are reduced to minimize power consumption. When the output voltage is large, the voltage rails are increased to accommodate the larger output need. High-power mode is similar to Maxim’s traditional DirectDrive architecture and is best suited for loads that require high voltage swing. High-efficiency mode improves power consumption by reducing the power- supply voltage across the amplifier’s output stage by half. The reduced power-supply voltage is good for idle conditions or low-signal level conditions into a head- phone. Class H Operation The MAX97200’s internal Class H amplifier uses a class AB output stage with multiple, discrete power supplies. This result’s in two power-supply differentials of 1.8V and 3.6V generated from a single 1.8V external supply. The PVIN/2 power-supply differential is used when the output voltage requirements are low, and the output is below VTH2 as seen in Figure 2. The higher supply differential is used when the output voltage exceeds the high threshold VTH2, maximizing output power and voltage swing. The transition time from high-efficiency mode to high-power mode occurs when the threshold is crossed. The switch from high-power mode to high-efficiency mode occurs 32ms (typ) after the threshold is crossed. Built-in hysteresis keeps the charge pump from erratic mode switching when the output voltage is near the high and low thresholds. Click-and-Pop Suppression In conventional single-supply audio amplifiers, the out- put-coupling capacitor contributes significantly to audi- ble clicks and pops. Upon startup, the amplifier charges the coupling capacitor to its bias voltage, typically half the supply. Likewise, on shutdown, the capacitor is dis- charged. This results in a DC shift across the capacitor, which appears as an audible transient at the speaker. Since the MAX97200 does not require output coupling capacitors, this problem does not arise. Additionally, the MAX97200 features extensive click-and-pop sup- pression that eliminates any audible transient sources internal to the device. Typically, the output of the device driving the MAX97200 has a DC bias of half the supply voltage. At startup, the input-coupling capacitor, CIN, is charged to the pream- plifier’s DC bias voltage through the MAX97200 input resistor, RIN. This DC shift across the capacitor results in an audible click-and-pop. The MAX97200 precharges the input capacitors when power is applied to ensure that no audible clicks or pops are heard when SHDN is pulled high. Shutdown The MAX97200 features a 1FA, low-power shutdown mode that reduces quiescent current consumption and extends battery life. Shutdown is controlled by the SHDN input. Driving the SHDN input low disables the drive amplifiers and charge pump and sets the headphone amplifier output resistance to 100I. Applications Information Component Selection Input-Coupling Capacitor The input capacitor (CIN), in conjunction with the ampli- fier input resistance (RIN_), forms a highpass filter that removes the DC bias from the 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- 2R C = π Figure 2. Inverting and Split Mode Transitions 10ms/div VPVDD VPVSS IN_ |
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