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NCP2815AFCT2G Datasheet(PDF) 9 Page - ON Semiconductor |
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NCP2815AFCT2G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 11 page NCP2815 http://onsemi.com 9 DETAIL OPERATING DESCRIPTION Detailed Description The NCP2815 is a stereo headphone amplifier with NOCAP architecture. This architecture eliminates the need to use two big external capacitors required by conventional headphone amplifier. The structure of the NCP2815 is composed of two true ground amplifiers, a UVLO, a short circuit protection and a thermal shutdown circuit. Additionally, a special circuit is embedded to eliminate any pop and click noise that occurs during turn on and turn off time. Version A has an external gain selectable by two resistors, Version B has a gain of 1.5 V/V. NOCAP NOCAP is a patented architecture which requires only 2 small ceramic capacitors. It generates a symmetrical positive and negative voltage which it allows the output of the amplifiers to be biased to ground. LongPlay Architecture NCP2815 includes a LongPlay architecture which helps to save battery life by reducing the quiescent current. The charge pump frequency is reduced to 125 kHz for an output load < 500 mW. Current Limit Protection Circuit The NCP2815 contains protection circuitry against shorts to ground. The currrent is limited to 300 mA when an output is shorted to GND and a signal appears at the input. Thermal Overload Protection Internal amplifiers are switched off when the temperature exceeds 160 °C, and are switched back on when the temperature decreases below 140 °C. Under Voltage Lockout When the battery voltage decreases below 1.4 V, the amplifiers are turned off. The hysteresis required to turn back on the device is 100 mV. Pop and Click Suppression Circuitry The NCP2815 includes a special circuit to eliminate any pop and click noise during turn on and turn off time. The amplifier creates an offset during these transitions at the output which give a parasitic noise called “pop and click noise”. The NCP2815 eliminates this problem. Gain Setting Resistor Selection (Rin and Rf, A Version Only) Rin and Rf set the closed loop gain of the amplifier. A low gain configuration (close to 1) minimizes the THD + noise values and maximizes the signal to noise ratio. A closed loop gain in the range of 1 to 10 is recommended to optimize overall system performance. The formula to calculate the gain is: Av +* Rf Rin Input Capacitor Selection The input coupling capacitor blocks the DC voltage at the amplifier input terminal. This capacitor creates a high−pass filter with Rin (externally selectable for Version A, 20 kW for Version B). The size of the capacitor must be large enough to couple in the low frequencies without severe attenuation in the audio bandwith (20 Hz – 20 kHz). The cut off frequency for the input high−pass filter is : Fc + 1 2pRinCin A Fc < 20 Hz is recommended. Charge Pump Capacitor Selection Use a ceramic capacitor with low ESR for better performances. An X5R / X7R capacitor is recommended. The flying capacitor (C2) serves to transfer charge during the generation of the negative voltage. The PVM capacitor (C3) must be equal at least to the flying capacitor to allow maximum transfer charge. Table 1 suggests typical values and manufacturers: Table 1. Value Reference Package Manufac- turer 1 mF C1005X5R0J105K 0402 TDK 1 mF GRM155R60J105K19 0402 Murata Lower value capacitors can be used but the maximum output power is reduced and the device may not operate to specifications. Power Supply Decoupling Capacitor (C1) The NCP2815 is a True Ground amplifier which requires an adequate decoupling capacitor to reduce noise and THD + N. It is recommended to use an X5R / X7R ceramic capacitor with a value of 1 mF and place it as close as possible to the Vp pin. Shutdown Function The device enters in shutdown mode when the shutdown signal is low. During the shutdown mode, the DC quiescent current of the circuit does not exceed 1 mA. In this configuration, the output impedance is 20 k W on each output. Layout Recommendation Connect C1 as close as possible to the Vp pin. Connect C2 and C3 as close as possible to the NCP2815. Route the audio signal and SGND far away from Vp, CPP, CPM, PVM and PGND to avoid any perturbation due to the switching. |
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