ltc2435-1 Linear Technology Corporation, ltc2435-1 Datasheet - Page 16

• Manufacturer Part Number: ltc2435-1
• Description: 20-bit No Latency Delta Sigma Adcs With Differential Input And Differential Reference
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC2435/LTC2435-1
The LTC2435 internal oscillator provides better than 110dB
normal mode rejection at the line frequency and its harmon-
ics for 50Hz ±2% or 60Hz ±2%. For 60Hz rejection, F
should be connected to GND while for 50Hz rejection the F
pin should be connected to V
The selection of 50Hz or 60Hz rejection can also be made by
driving F
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 conver-
sions 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 LTC2435 can
operate with an external conversion clock. The converter
automatically detects the presence of an external clock
signal at the F
frequency f
to be detected. The external clock signal duty cycle is not
significant as long as the minimum and maximum specifi-
cations for the high and low periods t
observed.
While operating with an external conversion clock of a
frequency f
normal mode rejection in a frequency range f
±4% and its harmonics. The normal mode rejection as a
function of the input frequency deviation from f
is shown in Figure 7a.
Whenever an external clock is not present at the F
converter automatically activates its internal oscillator and
enters the Internal Conversion Clock mode. The LTC2435
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 speci-
fications but the following conversions will not be affected.
16
O
to an appropriate logic level. A selection change
EOSC
EOSC
O
pin and turns off the internal oscillator. The
, the LTC2435 provides better than 110dB
of the external signal must be at least 5kHz
U
U
CC
.
W
HEO
and t
EOSC
EOSC
U
O
LEO
pin, the
/2560
/2560
are
O
O
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 3a summarizes the duration of each state and the
achievable output data rate as a function of F
Frequency Rejection Selection LTC2435-1 (F
The LTC2435-1 internal oscillator provides better than
87dB normal mode rejection over the range of 49Hz to
61.2Hz as shown in Figure 7b. For simultaneous 50Hz/60Hz
rejection, F
In order to achieve 87dB normal mode rejection of 50Hz
±2% and 60Hz ±2%, two consecutive conversions must be
averaged. By performing a continuous running average of
the two most current results, both simultaneous rejection
is achieved and a nearly 2× increase in throughput is
realized relative to the LTC2430 (see Normal Mode Rejec-
tion, Ouput Rate and Running Averages sections of this
data sheet).
When a fundamental rejection frequency different from
the range 49Hz to 61.2Hz is required or when the converter
must be synchronized with an outside source, the
LTC2435-1 can operate with an external conversion clock.
The performance of the LTC2435-1 is the same as the
LTC2435 when driven by an external conversion clock at
the F
Table 3b summarizes the duration of each state and the
achievable output data rate as a function of F
Serial Interface Pins
The LTC2435/LTC2435-1 transmit the conversion results
and receive 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.
O
pin.
O
should be connected to GND.
O
O
.
.
O
)
24351fb