LTC2400CS8 datasheet(13/40 Pages) LINER

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LTC2400

Table 3. LTC2400 State Duration

State

Operating Mode

Duration

CONVERT

Internal Oscillator

FO = LOW

133ms

(60Hz Rejection)

FO = HIGH

160ms

(50Hz Rejection)

External Oscillator

FO = External Oscillator

20480/fEOSCs

with Frequency fEOSC kHz

(fEOSC/2560 Rejection)

SLEEP

As Long As CS = HIGH Until CS = 0 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)

APPLICATIONS INFORMATION

The selection of 50Hz or 60Hz rejection can also be made

by driving FO to an appropriate logic level. A selection

change during the sleep or data output states will not

disturb the converter operation. If the selection is made

during the conversion state, the result of the conversion in

progress may be outside specifications but the following

conversions will not be affected.

When a fundamental rejection frequency different from

50Hz or 60Hz is required or when the converter must be

synchronized with an outside source, the LTC2400 can

operate with an external conversion clock. The converter

automatically detects the presence of an external clock

signal at the FO pin and turns off the internal oscillator. The

frequency fEOSC of the external signal must be at least

2560Hz (1Hz notch frequency) to be detected. The exter-

nal clock signal duty cycle is not significant as long as the

minimum and maximum specifications for the high and

low periods tHEO and tLEO are observed.

While operating with an external conversion clock of a

frequency fEOSC, the LTC2400 provides better than 110dB

normal mode rejection in a frequency range fEOSC/2560

±4% and its harmonics. The normal mode rejection as a

function of the input frequency deviation from fEOSC/2560

is shown in Figure 4.

Whenever an external clock is not present at the FO pin, the

converter automatically activates its internal oscillator and

enters the Internal Conversion Clock mode. The LTC2400

INPUT FREQUENCY DEVIATION FROM NOTCH FREQUENCY (%)

–12

–8

–4

048

2400 G25

–60

–70

–80

–90

–100

–110

–120

–130

–140

Figure 4. LTC2400 Normal Mode Rejection When

Using an External Oscillator of Frequency fEOSC

operation will not be disturbed if the change of conversion

clock source occurs during the sleep state or during the

data output state while the converter uses an external

serial clock. If the change occurs during the conversion

state, the result of the conversion in progress may be

outside specifications but the following conversions will

not be affected. If the change occurs during the data output

state and the converter is in the Internal SCK mode, the

serial clock duty cycle may be affected but the serial data

stream will remain valid.

Table 3 summarizes the duration of each state as a

function of FO.

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