LTC2414IGN datasheet(18/48 Pages) LINER

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LTC2414/LTC2418

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Table 5. LTC2414/LTC2418 State Duration

State

Operating Mode

Duration

CONVERT

Internal Oscillator

FO = LOW

133ms, Output Data Rate

≤ 7.5 Readings/s

(60Hz Rejection)

FO = HIGH

160ms, Output Data Rate

≤ 6.2 Readings/s

(50Hz 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/HIGH

As Long As CS = LOW But Not Longer Than 1.67ms

(Internal Oscillator)

(32 SCK cycles)

FO = External Oscillator with

As Long As CS = LOW But Not Longer Than 256/fEOSCms

Frequency fEOSC kHz

(32 SCK cycles)

External Serial Clock with

As Long As CS = LOW But Not Longer Than 32/fSCKms

Frequency fSCK kHz

(32 SCK cycles)

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.

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

output and the LTC2414/LTC2418 create their 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 detected at the CS pin. If SCK is HIGH or float-

ing at power-up or during this transition, the converter

enters the internal SCK mode. If SCK is LOW at power-up

or during this transition, 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.

When CS (Pin 16) is HIGH or the converter is in the con-

version state, the SDI input is ignored and may be driven

HIGH or LOW. When CS goes LOW and the conversion is

complete, SDO goes low and then SDI starts to shift in bits

on the rising edge of SCK.

Serial Data Output (SDO)

The serial data output pin, SDO (Pin 17), provides the

result of the last conversion as a serial bit stream (MSB

first) during the data output state. In addition, the SDO pin

is used as an end of conversion indicator during the

conversion and sleep states.

When CS (Pin 16) is HIGH, the SDO driver is switched to

a high impedance state. This allows sharing the serial

interface with other devices. If CS is LOW during the

convert or sleep state, SDO will output EOC. If CS is LOW

during the conversion phase, the EOC bit appears HIGH on

the SDO pin. Once the conversion is complete, EOC goes

LOW. The device remains in the sleep state until the first

rising edge of SCK occurs while CS = LOW.

Chip Select Input (CS)

The active LOW chip select, CS (Pin 16), is used to test the

conversion status and to enable the data input/output

transfer as described in the previous sections.

In addition, the CS signal can be used to trigger a new

conversion cycle before the entire serial data transfer has

been completed. The LTC2414/LTC2418 will abort any

serial data transfer in progress and start a new conversion

cycle anytime a LOW-to-HIGH transition is detected at the

CS pin after the converter has entered the data input/

output state (i.e., after the first rising edge of SCK occurs

with CS = LOW). If the device has not finished loading the

APPLICATIO S I FOR ATIO

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