MCP3909 datasheet(28/44 Pages) MICROCHIP

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MCP3909

DS22025B-page 28

5.4

Dual Channel Output Mode

This mode allows the user to retrieve the individual

channel information from the ADC outputs. The ADC

outputs of both channels are synchronized together

and their data ready is represented by the data ready

pulse on SDO. If the ADC output values are not clocked

out of the device, they will be over-written. A 32-bit data

word is given, each channel is 16 bits (15 bits + sign),

presented in 2's complement coding. Channel 1 comes

first then channel 0.

A data ready flag (DR) is output for every MCLK / 256

clock cycles and a new filter output value is ready. If the

dual channel output values are not clocked, and is not

clocked out of the device, they will be over-written.

The following formulas relate the channel input

voltages to their respective output code. The code

locks to +32767 on the positive side, and to -32768 on

the negative side.

5.5

High-Pass Filter Control

There are two options for the channel output data. The

first options collects the channel data pre-high pass

filter, or the output of the SINC filter of the delta sigma

modulator. The second option collects the channel data

post high pass filter. It is important to note that the

HPF pin controls the state of the high pass filter for this

second option. If the HPF pin is low, the post high pass

filter mode will output all zero's. This HPF pin must be

high to access the post HPF data in the channel output

mode.

FIGURE 5-5:

Dual Channel Output Mode.

Channel 1 Code

VIN+ VIN-

–

()

VREF

------------------------------------ 32768

8.06

0.47

0.66

-----------

⎝⎠

⎛⎞

Channel 0 Code

VIN+ VIN-

–

()

VREF

------------------------------------

⎝⎠

⎜⎟

⎛⎞

32768

8.06

0.66

0.47

-----------

⎝⎠

⎛⎞ PGA

TABLE 5-3:

CHANNEL OUTPUT MODE

CODING

Binary

Decimal

0 111 1111 1111 1111

+ 32,767

0 111 1111 1111 1110

+ 32,766

0 000 0000 0000 0000

1 111 1111 1111 1111

-1

1 000 0000 0000 0001

- 32,767

1 000 0000 0000 0000

- 32,768

D15 D14 D1

Hi-z

D16

D17

215

17 18

31 32

Hi-z

X 32

D30

D31

F1 / SDI

F2 / SCK

NEG / SDO

F0 / CS

X 16

Channel 1

Channel 0

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