MCP3201-CISLASHMS datasheet(22/36 Pages) MICROCHIP

22 / 36 page

MCP3201

DS21290E-page 22

6.2

Maintaining Minimum Clock Speed

When the MCP3201 initiates the sample period, charge

is stored on the sample capacitor. When the sample

period is complete, the device converts one bit for each

clock that is received. It is important for the user to note

that a slow clock rate will allow charge to bleed off the

sample cap while the conversion is taking place. At

85°C (worst case condition), the part will maintain

proper charge on the sample capacitor for at least

1.2 ms after the sample period has ended. This means

that the time between the end of the sample period and

the time that all 12 data bits have been clocked out

must not exceed 1.2 ms (effective clock frequency of

10 kHz). Failure to meet this criteria may induce

linearity errors into the conversion outside the rated

specifications. It should be noted that during the entire

conversion cycle, the A/D Converter does not require a

constant clock speed or duty cycle, as long as all timing

specifications are met.

6.3

Buffering/Filtering the Analog

Inputs

If the signal source for the A/D Converter is not a low

impedance source, it will have to be buffered

or inaccurate

conversion

results

may

occur.

See Figure 4-2. It is also recommended that a filter be

used to eliminate any signals that may be aliased back

into the conversion results. This is illustrated in

Figure 6-3 where an op amp is used to drive the analog

input of the MCP3201 device. This amplifier provides a

low impedance source for the converter input and a

low-pass filter, which eliminates unwanted high-

frequency noise.

Low-pass (anti-aliasing) filters can be designed using

Microchip’s interactive FilterLab® software. FilterLab

will calculate capacitor and resistor values, as well as

determine the number of poles that are required for the

application. For more information on filtering signals,

see the application note AN699 “Anti-Aliasing Analog

Filters for Data Acquisition Systems.”

FIGURE 6-3:

The MCP601 Operational

Amplifier is used to implement a 2nd order anti-

aliasing filter for the signal being converted by

the MCP3201 device.

MCP3201

VDD

10 µF

IN-

IN+

VIN

VREF

4.096V

Reference

1µF

10 µF

0.1 µF

MCP601

MCP1541

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