MCP3909 datasheet(21/40 Pages) MICROCHIP

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DS22025A-page 21

MCP3909

5.0

SERIAL INTERFACE

DESCRIPTION

5.1

Dual Functionality Pin And Serial

Interface Overview

The MCP3909 device contains three serial modes that

are accessible by changing the pin functionality of the

NEG, F2, F1, and F0 pins to SDO, SCK, SDI and CS,

respectively.

These modes are entered by giving the MCP3909

device a serial command on these pins during a time

window after device reset or POR. During this window

of time, F2 acts as SCK, F1 acts as SDI and F0 acts

as CS. Once a serial mode has been entered, the

device must be reset to disable mode functionality, or

change to another serial mode. This is done by using

MCLR pin or power on reset event.

During serial mode entry and the three serial modes,

data is clocked into the device on the rising edge of

SCK and out of the device on the falling edge of SCK.

The SPI data can be access at up to 20 MHz. This

speed enables quick data retrieval in between

conversion times. For 3-phase metering applications

with multiple ADCs, this fast communication is essen-

tial to allow for power calculation windows between

conversions, as shown in Figure 5-3.

After a serial mode has been entered, all blocks of the

MCP3909 device are still operational. The PGA, A/D

converters, HPF, multiplier, LPF, and other digital

sections are still functional, allowing the device to have

true dual functionality in energy metering systems.

FIGURE 5-1:

Dual Functionality Pins for

the MCP3909.

FIGURE 5-2:

Data Access between Data Ready Pulses using SPI Interface for a 3-phase System.

FOUT0

DGND

NEG / SDO

FOUT1

CLKOUT

CLKIN

DVDD

HPF

AVDD

CH0+

CHO-

CH1-

CH1+

HFOUT

MCLR

F0 / CS

REFIN / OUT

AGND

F1 / SDI

F2 / SCK

tSAMPLE

tLINE_CYC

SDO DR

Phase A,B,C I & V Data

16 bits

tSAMPLE

IRQ

x 6 ADCs

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