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APA2012QBI-TRG Datasheet(PDF) 10 Page - Anpec Electronics Coropration |
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APA2012QBI-TRG Datasheet(HTML) 10 Page - Anpec Electronics Coropration |
10 / 19 page Copyright © ANPEC Electronics Corp. Rev. A.3 - Oct., 2013 www.anpec.com.tw 10 APA2012 Application Information Figure 1. APA2012 Output waveform (Voltage& Current) Fully Differential Amplifier The APA2012 is a fully differential amplifier with differen- tial inputs and outputs. The fully differential has some advantages versus traditional amplifier. First, there is no need for the input coupling capacitors, because the com- mon-mode feedback will compensate the input bias. The inputs can biased from 0.5V~V DD-0.5V, and the outputs still be biased at mid-supply of APA2012. If the inputs are biased out of the input range, the coupling capacitors are required. Second, No need the mid-supply capacitor (C B), this is because any shift of the mid-supply of APA2012, will have the same affect both positive & negative channel, and will cancel at the differential outputs. Third, The fully differential amplifier will cancel the GSM RF transmitter’s signal (217Hz). Class-D Operation Shutdown Function In order to reduce power consumption while not in use, the APA2012 contains a shutdown function to externally turn off the amplifier bias circuitry. This shutdown feature turns the amplifier off when logic low is placed on the SD pin for APA2012. The trigger point between a logic high and logic low level is typically 0.4VDD. It is best to switch between ground and the supply voltage VDD to provide maximum device performance. By switching the SD pin to low level, the amplifier enters a low-consumption- cur- rent state,I DD for APA2012 is in shutdown mode. On nor- mal operating, APA2012’s SD pin should pull to high level to keeping the IC out of the shutdown mode. The SD pin should be tied to a definite voltage to avoid unwanted state changes. The APA2012 modulation scheme is show in figure 1, The outputs V OP and VON are in phase with each other when no input signals. When output > 0V the duty cycle of VOP is greater than 50% and V ON is less than 50%, and when output <0V, the duty cycle of VOP is less than 50% and V ON is greater than 50%. This method reduces the switching current across the load, and reduces the I2R losses in the load that improve the amplifier’s efficiency. This modulation scheme has very short pulses across the load, this making the small ripple current and very little loss on the load, and the LC filter can be eliminate in most applications. Added the LC filter can increase the efficiency by filter the ripple current. VOUTP VOUTN VOUT (VOUTP-VOUTN) IOUT Output = 0 Output > 0 Output < 0 VOUTP VOUTN VOUT (VOUTP-VOUTN) IOUT VOUTP VOUTN VOUT (VOUTP-VOUTN) IOUT Square Wave Into the Speaker Apply the square wave into the speaker may cause the voice coil of speaker jump out the air gap and deface the voice coil. But this depend on the amplitude of square wave is high enough and the bandwidth of speaker is high than the square wave¡¦s frequency. For 250KHz switching frequency, this is not issue for the speaker, because the frequency is beyond the audio band, and can¡¦t significantly move the voice coil, as cone movement is proportional to 1/f 2 for frequency out of audio band. |
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