Homemade TMS320F28335 Minimum System Board Power Supply and Clock

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Homemade TMS320F28335 Minimum System Board Power Supply and Clock [Copy link]

Power supply and clock are extremely critical links in the entire system design: if the power supply is unstable or incorrect, the system will work unstably at best, and the chip will be burned out at worst; if the clock signal is abnormal, the "benchmark" of the entire digital system will be broken. 1. Selection of power chip: In the design of the previous TMS320F2812 development board, the selection of chips was a bit troublesome because the power-on sequence and other options were strict. In the development board of TMS320F28335, TI's own TPS767D301 was directly selected. As long as the appropriate capacitors and resistors were selected according to the chip datasheet, everything was ok. A little detail: This chip is TSSOP-28 package, but it has a 29th pin, which is on the back of the chip, as bright as a mirror. It is necessary to open a "skylight" on the PCB and stick it to the ground plane: it is mainly used for heat dissipation, otherwise the chip will be very hot. This process is called TI's thermal pad, which is very convenient to use. 2. About the clock: Generally, there are two types of active crystal oscillators and passive crystal oscillators. Passive crystal oscillator is a crystal. Its usage is relatively simple. It does not require external power supply. It can be directly connected to the X1 and X2 pins of DSP. The connection method is shown in Figure 1. At this time, the clock oscillation circuit inside DSP is used. This method is simple to design, but the size of this quartz crystal is generally large, about 1cm*1cm, which takes up a lot of space when the device density on the board is high, and requires two additional decoupling capacitors. Another method is to use an external active crystal oscillator. In TI C2000DSP, 30MHz is generally enough, and then the PLL circuit inside DSP is used to multiply the frequency to 150MHz. This crystal oscillator generally has 4 corners, power supply, ground, clock output and an empty pin, which can be divided into two situations: 1) When using a 3.3V external crystal oscillator, the power pin is connected to 3.3V VDD, and the clock signal is connected to the XCLKIN pin of DSP; at this time, the X1 pin should be grounded and the X2 pin should be left floating; the connection method is shown in Figure 2. 2) When using a 1.9V external crystal oscillator (1.9V corresponds to the final 150MHz DSP clock, and a 100MHz C2000 DSP can use a 1.8V crystal oscillator), the clock signal output by the crystal oscillator can be directly connected to the X1 pin, while the X2 pin is left floating and the XCLKIN pin is grounded; the connection method is shown in Figure 3. Through the series (1)-(5), the design considerations of each sub-level are basically explained; next time, we will continue to talk about some supplementary issues and the subsequent hardware debugging process.