Schematic diagram of MCU SPI interface circuit

The SPI interface is a synchronous serial data transmission between the CPU and peripheral low-speed devices. Under the shift pulse of the master device, data is transmitted bit by bit, with the high bit first and the low bit last. It is full-duplex communication. The data transmission speed is generally faster than the I2C bus, and the speed can reach several Mbps.

For a 250μΩ shunt, the voltage signal across it at 40A is 250×40=10,000μV, or 10mVRMS, and the sampling signal is very small.

The channel gain should be set to the maximum, that is, 32 times. At this time, the maximum amplitude of the signal input is 26.25mVRMS. The actual maximum input signal is less than the maximum allowable input signal, and the shunt resistance value is selected reasonably.

As the SPI bus master, LPC9401 outputs a clock signal, and STPM01 communicates according to the clock signal of SCLNLC.

The following is a schematic diagram of the SPI interface and the microcontroller interface: