LTC2414 LINER [Linear Technology], LTC2414 Datasheet - Page 12

• Manufacturer Part Number: LTC2414
• Description: 8-/16-Channel 24-Bit No Latency TM ADCs
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC2414/LTC2418
first rising edge of SCK and depending on the control bits,
the converter updates its channel selection immediately
and is valid for the next conversion. The details of channel
selection control bits are described in the Input Data Mode
section. The output data is shifted out the SDO pin under
the control of the serial clock (SCK). The output data is
updated on the falling edge of SCK allowing the user to
reliably latch data on the rising edge of SCK (see Figure 3).
The data output state is concluded once 32 bits are read
out of the ADC or when CS is brought HIGH. The device
automatically initiates a new conversion and the cycle
repeats.
Through timing control of the CS and SCK pins, the
LTC2414/LTC2418 offer several flexible modes of opera-
tion (internal or external SCK and free-running conversion
modes). These various modes do not require program-
ming configuration registers; moreover, they do not dis-
turb the cyclic operation described above. These modes of
operation are described in detail in the Serial Interface
Timing Modes section.
Conversion Clock
A major advantage the delta-sigma converter offers over
conventional type converters is an on-chip digital filter
(commonly implemented as a Sinc or Comb filter). For
high resolution, low frequency applications, this filter is
typically designed to reject line frequencies of 50Hz or
12
Figure 2. LTC2414/LTC2418 State Transition Diagram
FALSE
U
IN
+
ADDRESS INPUT
DATA OUTPUT
= CH0, IN
POWER UP
CONVERT
CS = LOW
U
SCK
SLEEP
AND
TRUE
–
= CH1
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W
U
60Hz plus their harmonics. The filter rejection perfor-
mance is directly related to the accuracy of the converter
system clock. The LTC2414/LTC2418 incorporate a highly
accurate on-chip oscillator. This eliminates the need for
external frequency setting components such as crystals or
oscillators. Clocked by the on-chip oscillator, the LTC2414/
LTC2418 achieve a minimum of 110dB rejection at the line
frequency (50Hz or 60Hz ±2%).
Ease of Use
The LTC2414/LTC2418 data output has no latency, filter
settling delay or redundant data associated with the
conversion cycle. There is a one-to-one correspondence
between the conversion and the output data. Therefore,
multiplexing multiple analog voltages is easy.
The LTC2414/LTC2418 perform offset and full-scale cali-
brations in every conversion cycle. This calibration is trans-
parent to the user and has no effect on the cyclic operation
described above. The advantage of continuous calibration
is extreme stability of offset and full-scale readings with re-
spect to time, supply voltage change and temperature drift.
Power-Up Sequence
The LTC2414/LTC2418 automatically enter an internal
reset state when the power supply voltage V
below approximately 2V. This feature guarantees the
integrity of the conversion result and of the serial interface
mode selection. (See the 3-wire I/O sections in the Serial
Interface Timing Modes section.)
When the V
the converter creates an internal power-on-reset (POR)
signal with a typical duration of 1ms. The POR signal
clears all internal registers. Following the POR signal, the
LTC2414/LTC2418 start a normal conversion cycle and
follow the succession of states described above. The first
conversion result following POR is accurate within the
specifications of the device if the power supply voltage is
restored within the operating range (2.7V to 5.5V) before
the end of the POR time interval.
Reference Voltage Range
The LTC2414/LTC2418 accept a truly differential external
reference voltage. The absolute/common mode voltage
CC
voltage rises above this critical threshold,
CC
drops
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