Datasheet

LTC2433-1
11
24331fa
Simultaneous Frequency Rejection
The LTC2433-1 internal oscillator provides better than
87dB normal mode rejection over the range of 49Hz to
61.2Hz as shown in Figure 4. For this simultaneous 50Hz/
60Hz rejection, F
O
should be connected to GND.
When a fundamental rejection frequency different from
the range 49Hz to 61.2Hz is required or when the converter
must be sychronized with an outside source, the LTC2433-1
can operate with an external conversion clock. The conveter
automatically detects the presence of an external clock
signal at the F
O
pin and turns off the internal oscillator. The
frequency f
EOSC
of the external signal must be at least
Table 2. LTC2433-1 Output Data Format
Differential Input Voltage Bit 18 Bit 17 Bit 16 Bit 15 Bit 14 Bit 13 Bit 12 … Bit 0
V
IN
* EOC DMY SIG MSB
V
IN
* ≥ 0.5 • V
REF
** 00110 0 0…0
0.5 • V
REF
** – 1LSB 00101 1 1…1
0.25 • V
REF
** 00101 0 0…0
0.25 • V
REF
** – 1LSB 00100 1 1…1
0 00100 0 0…0
–1LSB 0 0011 1 1…1
–0.25 • V
REF
** 00011 0 0…0
–0.25 • V
REF
** – 1LSB 00010 1 1…1
–0.5 • V
REF
** 00010 0 0…0
V
IN
* < –0.5 • V
REF
** 00001 1 1…1
*The differential input voltage V
IN
= IN
+
– IN
–
.
**The differential reference voltage V
REF
= REF
+
– REF
–
.
Figure 4. LTC2433-1 Normal Mode
Rejection When Using an Internal Oscillator
48 50 52 54 56 58 60 62
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
NORMAL MODE REECTION RATIO (dB)
24361 F04
–80
–90
–100
–100
–120
–130
–140
2560Hz 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
HEO
and t
LEO
,
are observed.
While operating with an external conversion clock of a
frequency f
EOSC
, the LTC2433-1 provides better than 110dB
normal mode rejection in a frequency range f
EOSC
/2560
±4%. The normal mode rejection as a function of the input
frequency deviation from f
EOSC
/2560 is shown in Figure 5.
Whenever an external clock is not present at the F
O
pin the
converter automatically activates its internal oscillator and
enters the Internal Conversion Clock mode. The LTC2433-1
Figure 5. LTC2433-1 Normal Mode Rejection When
Using an External Oscillator of Frequency f
EOSC
DIFFERENTIAL INPUT SIGNAL FREQUENCY
DEVIATION FROM NOTCH FREQUENCY f
EOSC
/2560(%)
–12–8–404812
NORMAL MODE REJECTION (dB)
24361 F05
–80
–85
–90
–95
–100
–105
–110
–115
–120
–125
–130
–135
–140
APPLICATIO S I FOR ATIO
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