LTC2439-1IGN datasheet(13/28 Pages) LINER

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LTC2439-1

24391f

APPLICATIO S I FOR ATIO

Table 3. LTC2439-1 Output Data Format

Differential Input Voltage

Bit 18

Bit 17

Bit 16

Bit 15

Bit 14

Bit 13

Bit 12

…

Bit 0

VIN*

EOC

DMY

SIG

MSB

VIN* ≥ 0.5 • VREF**

0110

…

0.5 • VREF** – 1LSB

0101

…

0.25 • VREF**

0101

…

0.25 • VREF** – 1LSB

0100

…

0100

…

–1LSB

0011

…

– 0.25 • VREF**

0011

…

– 0.25 • VREF** – 1LSB

0010

…

– 0.5 • VREF**

0010

…

VIN* < –0.5 • VREF**

0001

…

*The differential input voltage VIN = IN+ – IN–.

**The differential reference voltage VREF = REF+ – REF–.

Table 4. LTC2439-1 State Duration

State

Operating Mode

Duration

CONVERT

Internal Oscillator

FO = LOW

147ms, Output Data Rate

≤ 6.8 Readings/s

Simultaneous 50Hz/60Hz Rejection

External Oscillator

FO = External Oscillator

20510/fEOSCs, Output Data Rate ≤ fEOSC/20510 Readings/s

with Frequency fEOSC kHz

(fEOSC/2560 Rejection)

SLEEP

As Long As CS = HIGH Until CS = LOW and SCK

DATA OUTPUT

Internal Serial Clock

FO = LOW

As Long As CS = LOW But Not Longer Than 1.09ms

(Internal Oscillator)

(19 SCK cycles)

FO = External Oscillator with

As Long As CS = LOW But Not Longer Than 152/fEOSCms

Frequency fEOSC kHz

(19 SCK cycles)

External Serial Clock with

As Long As CS = LOW But Not Longer Than 19/fSCKms

Frequency fSCK kHz

(19 SCK cycles)

In the Internal SCK mode of operation, the SCK pin is an

output and the LTC2439-1 creates its own serial clock by

dividing the internal conversion clock by 8. In the External

SCK mode of operation, the SCK pin is used as input. The

Internal or External SCK mode is selected on power-up and

then reselected every time a HIGH-to-LOW transition is de-

tected at the CS pin. If SCK is HIGH or floating at power-

up or during this transition, the converter enters the internal

SCK mode. If SCK is LOW at power-up or during this tran-

sition, the converter enters the external SCK mode.

Serial Data Input (SDI)

The serial data input pin, SDI (Pin 20), is used to shift in the

channel control bits during the data output state to prepare

the channel selection for the following conversion.

SERIAL INTERFACE PINS

The LTC2439-1 transmits the conversion results and re-

ceives the start of conversion command through a syn-

chronous 4-wire interface. During the conversion and sleep

states, this interface can be used to assess the converter

status and during the data I/O state it is used to read the

conversion result and write in channel selection bits.

Serial Clock Input/Output (SCK)

The serial clock signal present on SCK (Pin 18) is used to

synchronize the data transfer. Each bit of data is shifted out

the SDO pin on the falling edge of the serial clock and each

input bit is shifted in the SDI pin on the rising edge of the

serial clock.

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