MCP3565R datasheet(42/108 Pages) MICROCHIP

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MCP3565R

DS20006401C-page 42



2020-2021 Microchip Technology Inc.

The resolution (number of possible output codes

expressed in powers of two or in bits) of the digital

filter is 24-bit maximum for any OSR = OSR3 x OSR1

and data format choice. The resolution only depends

on the OSR through the OSR[3:0] bits setting in the

CONFIG1 register per Table 5-6. Once the OSR is

chosen, the resolution is fixed and the output code of

the ADC is encoded with the data format defined by

the DATA_FORMAT[1:0] bits setting in the CONFIG3

The transfer function of this filter has a unity gain at

each multiple of DMCLK. A proper anti-aliasing filter

must be placed at the ADC inputs. This will attenuate

the frequency contents around each multiple of

DMCLK and keep the desired accuracy over the base-

band of the converter. This anti-aliasing filter can be a

simple first-order RC network with low time constant to

provide a high rejection at DMCLK frequency.

The conversion time is a function of the OSR settings

and the DMCLK frequency.

EQUATION 5-4:

CONVERSION TIME FOR

OSR = OSR3 x OSR1

In One-Shot mode, each conversion is launched

individually, so the maximum data rate is effectively

1/TCONV if each conversion is launched with no delay.

The digital filter is reset in between each conversion.

However, due to the nature of the digital filter (which

memorizes the sum of the incoming bit stream), the

data rate at the filter output can be maximized if the

filter is never reset. Because of the internal resampling

of the digital filter, the output data rate can be equal to

DMCLK/OSR = DRCLK; this is the case in Continuous

mode. In this case, the first conversion still happens in

the TCONV time, as this is the settling time of the filter.

The subsequent conversions are pipelined and give

their output at a data rate of DRCLK. The Continuous

Conversion mode can optimize the data rate, while

consuming the same power as One-Shot mode, which

is advantageous in applications that require a

continuous sampling of the analog inputs. The

Continuous mode is not compatible with multiplexing

the inputs (see

Section 5.15 “Scan Mode” for more

details about the Conversion mode settings in MUX

and Scan modes).

Figure 5-5 shows the fundamental difference between

One-Shot mode and Continuous mode in a simplified

diagram.

FIGURE 5-5:

One-Shot Mode vs. Continuous Mode.

TCONV

3 OSR3







OSR1 1

–





OSR3







DMCLK



TCONV

One-shot mode

Conversions are Serialized,

Filter is Reset after Each Conversion

Group Delay: TCONV

Data Rate: 1/(TCONV)

Conversion1

TCONV

Continuous mode

Conversions are Pipelined,

Filter is Never Reset

Group Delay: TCONV

Data Rate: DRCLK

TCONV

Conversion2

TCONV

Conversion3

1/DRCLK

TCONV

Analog Input

Signal

Conversion1

Conversion2

TCONV= Settling Time

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