Minimum System Board (5)-power supply and clock

 

Power Supply and clock are a key part of the entire system design. If the power supply is unstable or incorrect, the system is unstable when it is light, and the chip is burned out when it is heavy. If the clock signal is abnormal, then the "benchmark" of the entire digital system is broken.

1. Power Supply chip selection: in the past, because of the strict selection of power-on sequence, the chip selection is also a little troublesome. In the Development Board, you can directly select TI's tps767d301. As long as you select the appropriate capacitor and resistor according to the datasheet chip, everything is OK. Small details: this chip is TSSOP-28 encapsulated, but it has 29th pins, on the back of the chip, as bright as a mirror, need to open the "Skylight" on the PCB ", stick it to the ground plane: it is mainly used for heat dissipation, or the chip will be very hot. This process is called TI's thermal pad, which is easy to use.

2. Clock: Generally, two types of clock are used: Source crystal oscillator and passive crystal oscillator. The passive crystal oscillator is a crystal. It is easy to use and can be directly connected to the X1 and X2 pins of the DSP without external power supply, as shown in method 1. The internal clock oscillator circuit of the DSP is used. This method is easy to design, but the size of the Z crystal is generally relatively large, about 1 cm * 1cm, which accounts for a relatively high density of the device on the board, in addition, two additional decoupling capacitors are required.

 

Another method is to use an external source crystal oscillator. In Ti c2000dsp, 30 MHz is generally used, and then the internal PLL circuit of DSP is used to multiply to 150 MHz. This crystal oscillator generally has four corners: power supply, ground, clock output, and an empty pin, which are divided into two situations:

1) when the 3.3v external crystal oscillator is used, the power supply pin is connected to the 3.3 v vdd, and the clock signal is connected to the xclkin pin of the DSP. At this time, the X1 pin is grounded and the X2 pin is suspended. method 2 is shown.

2) When the 150 V External crystal oscillator is used (1.9v corresponds to the final MHz DSP clock, MHz c2000 DSP uses a V Crystal Oscillator), the clock signal output by the crystal oscillator can be directly connected to the X1 pin, at this time, the X2 pin is suspended and the xclkin pin is grounded. Method 3 is shown.

 

Through the serialization (1)-(5), the design attention at each sub-level is clearly explained. Next time, we will continue to discuss some supplementary issues and the subsequent hardware debugging process.