MCP3201 timing notes

5.0 SERIAL COMMUNICATIONS

Communication with the device is done using a standard SPI-compatible serial interface. Initiating communication with the MCP3201 device begins with the CS going low. If the device was powered up with the CS pin low, it must be brought high and back low to initiate communication. The device will begin to sample the analog input on the first rising edge [of the clock pules] after CS goes low.

The sample period will end in the falling  edge of the second clock, at which time the device will output a low null bit. The next 12 clocks will output the result of the conversion with MSB first, as shown in Figure 5-1.

Data is always output from the device on the falling edge of the clock. If all 12 data bits have been transmitted and the device continues to receive clocks while the CS is held low, the device will output the conversion result LSB first, as shown in Figure 5-2. If more clocks are provided to the device while CS is still low (after the LSB first data has been transmitted), the device will clock out zeros indefinitely.



4.2 Reference Input

The reference input (VREF) determines the analog input voltage range and the LSB size, as shown below.

EQUATION 4-1:

LSB Size =  VREF / 4096


As the reference input is reduced, the LSB size is reduced accordingly. The theoretical digital output code produced by the A/D Converter is a function of the analog input signal and the reference input as shown below.

Digital Output Code = (4096 * VIN) / VREF

Where:

VIN = Analog Input Voltage = V(IN+) - V(IN-)

VREF = Reference Voltage

When using an external voltage reference device, the system designer should always refer to the manufacturer’s recommendations for circuit layout.

Any instability in the operation of the reference device will have a direct effect on the operation of the A/D Converter.

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