USB interface card production, PCM2702 Application
Keywords: PCM2702, USB sound card circuit diagram
The article describes the use of a USB interface card, the effect is quite good, the circuit is very simple.
Circuit principle
The circuit schematic is shown in Figure 1.
PCM2702 (IC1) for the United States TI BB under the company's USB interface DAC chip. PCM2702 supports USB1.0 standard, may receive stereo or mono 16bit USB audio stream, the basic parameters as shown in Table 1. Integrated dual operational amplifier IC2 is used as an output buffer amplifier.
IC1 left the digital input section, the right for the analog output section, 2 feet PCM2702 required voltage of 3.3V, where skillfully with a red LED buck power indicator and serves simply plug it USB port It will light, and then R1 is to reduce the burden of the LED. R2 is a pull-up resistor, taking into account the large high-frequency ripple power provided by the computer, so the use of stronger filter measures. C3 ~ C11 and C18 are filtering and power supply decoupling capacitor, an inductor for filter plus analog section.
The audio output of the PCM2702 is biased from 1 to 2Vcc. It is not connected to the direct capacitor due to the subsequent buffer operation. IC2 constituting a direct magnification 1, AC magnification of the buffer amplifier 2, C16, C17, C19, C20 is a DC-blocking capacitor. Ignoring the resistance of the op amp output blocking capacitor capacity is calculated as follows:
C = 7 / (6πfLRL)
Wherein, as the lower limit frequency fL, RL is the load impedance, if the lower limit frequency is set to 40Hz, two headset in parallel, because a 32 ohm impedance is usually a common headset, then RL is 16Ω, is calculated to obtain 580.5 blocking capacitor uF, used here 680uF, and a 0.22uF capacitor CBB-frequency sound quality can be improved. Of course, since the output PCM2702 has a larger magnitude, as may be directly pushed TDA2282 power amplifier and other small, it can be changed to the op amp power amplifier, so that the output power will be bigger.
PCM2702 11 to 13 feet to the status flag pin. Manufacturers pointed out that the information given: 10 feet state when no audio signal is high, in the second frame header of the incoming audio data that is changed to a low level until the end of the second audio data frame header goes high before arrival level. As long as there is data input, it is 11 feet high. A first frame start pin 12 to the second data frame start is high, compared to a low level after the audio data signal input during the normal, continuous, or if the audio signal sampling period is zero 1024, then high. Figure 2 is a timing chart of these three pin states. Accordingly, the output signal can be applied to pin 10 on an inverter for driving the LED work instructions, as shown in FIG. However, during the playback music, the measurement found that 12 pins have been high levels during the input of the audio data stream, and the music will become low. Thus, pin 12 is also indicative of the signal driver circuit work, time, circuits, these two applications, relative to the latter, the former has 4 indicates strict sense, but power consumption is slightly larger.
Component selection
All electrolytic capacitor voltage value should be more than 6.3V, resistance power except R17 1 / 4W, be held, the remaining 1 / 16W can. C12, C15, C16, C17, C19, C20 greater impact on the sound quality should be used in high-quality capacitors. L1 can be made, about 10 turns of enameled wire can be used on a small thicker core (cylindrical, annular available). For convenience, in this circuit, the supply voltage directly from the USB 5V positive supply. Thus, the low pressure should be used op amp, preferably use a single power amplifier. This circuit design for both ease of use, if necessary, can be employed for this two chip peripheral power supply, the effect will be better. Figure 5 is a pin definition of the USB line A head socket on the computer.
This usb sound card no debugging, a fitted top. Where the operating system are not required to install drivers for more than 2000 computer Windows, the system can automatically identify. The disadvantage is that only the audio output without input.
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