LTC2445 datasheet(21/28 Pages) LINER

21 / 28 page

LTC2444/LTC2445/

LTC2448/LTC2449

sn2444589 2444589fs

APPLICATIO S I FOR ATIO

Figure 9. Internal Serial Clock, Continuous Operation

SCK

SDI

SDO

BUSY

2444 F10

CONVERSION

SLEEP

DATA OUTPUT

CONVERSION

MSB

BIT 28 BIT 27 BIT 26 BIT 25 BIT 24 BIT 23 BIT 22 BIT 21

BIT 20 BIT 19

BIT 0

LSB

SIG

BIT 29

“0”

BIT 30

EOC

BIT 31

SGL

OSR3

OSR2

OSR1

OSR0

TWOX

ODD

12345

DON'T CARE

VCC

REF+

REF–

CH0

CH7

CH8

CH15

COM

SCK

SDI

SDO

GND

1,4,5,6,31,32,33

REFERENCE

VOLTAGE

0.1V TO VCC

ANALOG

INPUTS

= EXTERNAL OSCILLATOR

= INTERNAL OSCILLATOR

1µF

2.7V TO 5.5V

LTC2448

4-WIRE

SPI INTERFACE

•

BUSY

Internal Serial Clock, 2-Wire I/O,

Continuous Conversion

This timing mode uses a 2-wire, all output (SCK and SDO)

interface. The conversion result is shifted out of the device

by an internally generated serial clock (SCK) signal, see

Figure 9. CS may be permanently tied to ground, simplify-

ing the user interface or isolation barrier. The internal

serial clock mode is selected by tying EXT HIGH.

During the conversion, the SCK and the serial data output

pin (SDO) are HIGH (EOC = 1) and BUSY = 1. Once the

conversion is complete, SCK, BUSY and SDO go LOW

(EOC = 0) indicating the conversion has finished and the

device has entered the low power sleep state. The part

remains in the sleep state a minimum amount of time

(≈500ns) then immediately begins outputting data. The

data output cycle begins on the first rising edge of SCK and

ends after the 32nd rising edge. Data is shifted out the SDO

pin on each falling edge of SCK. The internally generated

serial clock is output to the SCK pin. This signal may be

used to shift the conversion result into external circuitry.

EOC can be latched on the first rising edge of SCK and the

last bit of the conversion result can be latched on the 32nd

rising edge of SCK. After the 32nd rising edge, SDO goes

HIGH (EOC = 1) indicating a new conversion is in progress.

SCK remains HIGH during the conversion.

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