MCP3551-ESLASHMS datasheet(12/30 Pages) MICROCHIP

12 / 30 page

MCP3551/3

DS21950B-page 12

4.0

DEVICE OVERVIEW

The MCP3551/3 devices are 22-bit delta-sigma ADCs

that include fully differential analog inputs, a third-order

delta-sigma modulator, a fourth-order modified SINC

decimation filter, an on-chip, low-noise internal oscilla-

tor, a power supply monitoring circuit and an SPI 3-wire

digital interface. These devices can be easily used to

measure low-frequency, low-level signals such as

those found in pressure transducers, temperature,

strain gauge, industrial control or process control appli-

cations. The power supply range for this product family

is 2.7V to 5.5V; the temperature range is -40°C to

+125°C.

The

functional

block

diagram

for

the

MCP3551/3 devices is shown in Figure 4-1.

A Power-On Reset (POR) monitoring circuit is included

to ensure proper power supply voltages during the

conversion process. The clock source for the part is

internally generated to ±0.5% over the full-power

supply voltage range and industrial temperature range.

This stable clock source allows for superior conversion

repeatability and minimal drift across conversions.

The MCP3551/3 devices employ a delta-sigma conver-

sion technique to realize up to 22 bits of no missing

code performance with 21.9 Effective Number of Bits

(ENOB).

These

devices

provide

single-cycle

conversions with no digital filter settling time. Every

conversion includes an internal offset and gain

auto-calibration to reduce device error. These calibra-

tions are transparent to the user and are done in

real-time during the conversion. Therefore, these

devices do not require any additional time or

conversion to proceed, allowing easy usage of the

devices for multiplexed applications. The MCP3551/3

devices incorporate a fourth-order digital decimation

filter in order to allow superior averaging performance,

well

excellent

line

frequency

rejection

capabilities. The oversampling frequency also reduces

any external anti-aliasing filter requirements.

The MCP3551/3 devices communicate with a simple

3-wire SPI interface. The interface controls the

conversion start event, with an added feature of an

auto-conversion at system power-up by tying the CS

pin to logic-low. The device can communicate with bus

speeds of up to 5 MHz, with 50 pF capacitive loading.

The interface offers two conversion modes: Single

Conversion mode for multiplexed applications and a

Continuous Conversion mode for multiple conversions

in series. Every conversion is independent of each

other. That is, all internal registers are flushed between

conversions. When the device is not converting, it auto-

matically goes into Shutdown mode and, while in this

mode, consumes less than 1 µA.

FIGURE 4-1:

MCP3551/3

Functional Block Diagram.

Internal

Oscillator

Third-Order

ΔΣ

Modulator

Digital

Decimation

Filter (SINC4)

SPI™ 3-wire

Interface

Gain and

Offset

Calibration

Differential

Analog Input

Bitstream

Conversion

Code

Output

Code

Clock

Charge

Transfer

Reference

Input

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