LTC2431 Linear Technology, LTC2431 Datasheet - Page 14

• Manufacturer Part Number: LTC2431
• Description: (LTC2430 / LTC2431) 20-Bit No Latency Delta-Sigma ADCs
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC2430/LTC2431
+FS, the conversion result is clamped to the value corre-
sponding to the +FS + 1LSB. For differential input voltages
below –FS, the conversion result is clamped to the value
corresponding to –FS – 1LSB.
Frequency Rejection Selection (F
The LTC2430/LTC2431 internal oscillator provides better
than 110dB normal mode rejection at the line frequency
and all its harmonics for 50Hz 2% or 60Hz 2%. For
60Hz rejection, F
50Hz rejection the F
The selection of 50Hz or 60Hz rejection can also be made
by driving F
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 LTC2430 or
LTC2431 can operate with an external conversion clock.
The converter automatically detects the presence of an
external clock signal at the F
oscillator. The frequency f
be at least 5kHz to be detected. The external clock signal
duty cycle is not significant as long as the minimum and
maximum specifications for the high and low periods t
and t
While operating with an external conversion clock of a
frequency f
than 110dB normal mode rejection in a frequency range
f
rejection as a function of the input frequency deviation
from f
Whenever an external clock is not present at the F
converter (LTC2430 or LTC2431) automatically activates
its internal oscillator and enters the Internal Conversion
Clock mode. Its 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 con-
verter uses an external serial clock. If the change occurs
during the conversion state, the result of the conversion in
14
EOSC
LEO
/2560 4% and its harmonics. The normal mode
EOSC
are observed.
/2560 is shown in Figure 4.
EOSC
O
to an appropriate logic level. A selection
, the LTC2430 or LTC2431 provides better
O
should be connected to GND while for
U
O
pin should be connected to V
U
EOSC
O
pin and turns off the internal
of the external signal must
O
W
)
U
O
pin, the
CC
HEO
.
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 and the
achievable output data rate as a function of F
SERIAL INTERFACE PINS
The LTC2430/LTC2431 transmit the conversion results
and receives the start of conversion command through a
synchronous 3-wire interface. During the conversion and
sleep states, this interface can be used to assess the
converter status and during the data output state it is used
to read the conversion result.
Serial Clock Input/Output (SCK)
The serial clock signal present on SCK is used to synchro-
nize the data transfer. Each bit of data is shifted out the
SDO pin on the falling edge of the serial clock.
In the Internal SCK mode of operation, the SCK pin is an
output and the converter (LTC2430 or LTC2431) 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 detected at the CS pin. If SCK
Figure 4. LTC2430/LTC2431 Normal Mode Rejection When
Using an External Oscillator of Frequency f
–100
–105
–110
–115
–120
–125
–130
–135
–140
–80
–85
–90
–95
DEVIATION FROM NOTCH FREQUENCY f
–12
DIFFERENTIAL INPUT SIGNAL FREQUENCY
–8
–4
0
4
EOSC
8
/2560(%)
2431 F04
EOSC
12
O
.
24301f