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NCP2890AFCT2 Datasheet(PDF) 11 Page - ON Semiconductor |
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NCP2890AFCT2 Datasheet(HTML) 11 Page - ON Semiconductor |
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11 / 16 page  NCP2890, NCV2890 http://onsemi.com 11 APPLICATION INFORMATION Detailed Description The NCP2890 audio amplifier can operate under 2.6 V until 5.5 V power supply. It delivers 320 mW rms output power to 4.0 W load (Vp = 2.6 V) and 1.0 W rms output power to 8.0 W load (Vp = 5.0 V). The structure of the NCP2890 is basically composed of two identical internal power amplifiers; the first one is externally configurable with gain−setting resistors Rin and Rf (the closed−loop gain is fixed by the ratios of these resistors) and the second is internally fixed in an inverting unity−gain configuration by two resistors of 20 k W. So the load is driven differentially through OUTA and OUTB outputs. This configuration eliminates the need for an output coupling capacitor. Internal Power Amplifier The output PMOS and NMOS transistors of the amplifier were designed to deliver the output power of the specifications without clipping. The channel resistance (Ron) of the NMOS and PMOS transistors does not exceed 0.6 W when they drive current. The structure of the internal power amplifier is composed of three symmetrical gain stages, first and medium gain stages are transconductance gain stages to obtain maximum bandwidth and DC gain. Turn−On and Turn−Off Transitions A cycle with a turn−on and turn−off transition is illustrated with plots that show both single ended signals on the previous page. In order to eliminate “pop and click” noises during transitions, output power in the load must be slowly established or cut. When logic high is applied to the shutdown pin, the bypass voltage begins to rise exponentially and once the output DC level is around the common mode voltage, the gain is established slowly (50 ms). This way to turn−on the device is optimized in terms of rejection of “pop and click” noises. The device has the same behavior when it is turned−off by a logic low on the shutdown pin. During the shutdown mode, amplifier outputs are connected to the ground. When a shutdown low level is applied, it takes 350 ms before the DC output level is tied to Ground. However, as shown on Figure 30, the turn off time of the audio signal is 40 ms. A theoretical value of turn−on time at 25 °C is given by the following formula. Cby: bypass capacitor R: internal 300 k resistor with a 25% accuracy Ton = 0.95 * R * Cby (285 ms with Cby = 1 mF) If a faster turn on time is required then a lower bypass capacitor can be used. The other option is to use NCP2892 which offers 100 ms with 1 mF bypass capacitor. Shutdown Function The device enters shutdown mode when shutdown signal is low. During the shutdown mode, the DC quiescent current of the circuit does not exceed 100 nA. Current Limit Circuit The maximum output power of the circuit (Porms = 1.0 W, Vp = 5.0 V, RL = 8.0 W) requires a peak current in the load of 500 mA. In order to limit the excessive power dissipation in the load when a short−circuit occurs, the current limit in the load is fixed to 800 mA. The current in the four output MOS transistors are real−time controlled, and when one current exceeds 800 mA, the gate voltage of the MOS transistor is clipped and no more current can be delivered. Thermal Overload Protection Internal amplifiers are switched off when the temperature exceeds 160 °C, and will be switched on again only when the temperature decreases fewer than 140 °C. The NCP2890 is unity−gain stable and requires no external components besides gain−setting resistors, an input coupling capacitor and a proper bypassing capacitor in the typical application. The first amplifier is externally configurable (Rf and Rin), while the second is fixed in an inverting unity gain configuration. The differential−ended amplifier presents two major advantages: − The possible output power is four times larger (the output swing is doubled) as compared to a single−ended amplifier under the same conditions. − Output pins (OUTA and OUTB) are biased at the same potential Vp/2, this eliminates the need for an output coupling capacitor required with a single−ended amplifier configuration. The differential closed loop−gain of the amplifier is given by Avd + 2* Rf Rin + Vorms Vinrms . Output power delivered to the load is given by Porms + (Vopeak)2 2* RL (Vopeak is the peak differential output voltage). When choosing gain configuration to obtain the desired output power, check that the amplifier is not current limited or clipped. The maximum current which can be delivered to the load is 500 mA Iopeak + Vopeak RL . |
Similar Part No. - NCP2890AFCT2 |
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Similar Description - NCP2890AFCT2 |
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