LTC2420IS8#TR Linear Technology, LTC2420IS8#TR Datasheet - Page 11

• Manufacturer Part Number: LTC2420IS8#TR
• Description: IC ADC 20BIT MICROPOWER 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC2420IS8#TR

• Number Of Bits: 20
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
not disturb 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 delta-sigma converters offer over
conventional type converters is an on-chip digital filter
(commonly known as Sinc or Comb filter). For high
resolution, low frequency applications, this filter is typi-
cally designed to reject line frequencies of 50Hz or 60Hz
plus their harmonics. In order to reject these frequencies
in excess of 110dB, a highly accurate conversion clock is
required. The LTC2420 incorporates an on-chip highly
accurate oscillator. This eliminates the need for external
frequency setting components such as crystals or oscilla-
tors. Clocked by the on-chip oscillator, the LTC2420
rejects line frequencies (50Hz or 60Hz 2%) a minimum
of 110dB.
Ease of Use
The LTC2420 data output has no latency, filter settling or
redundant data associated with the conversion cycle.
There is a one-to-one correspondence between the
conversion and the output data. Therefore, multiplexing
an analog input voltage is easy.
The LTC2420 performs offset and full-scale calibrations
every conversion cycle. This calibration is transparent to
the user and has no effect on the cyclic operation de-
scribed 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 LTC2420 automatically enters an internal reset state
when the power supply voltage V
mately 2.2V. This feature guarantees the integrity of the
conversion result and of the serial interface mode selec-
tion which is performed at the initial power-up. (See the
2-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 duration of approximately 0.5ms. The POR
CC
voltage rises above this critical threshold,
U
U
CC
drops below approxi-
W
U
signal clears all internal registers. Following the POR
signal, the LTC2420 starts a normal conversion cycle and
follows the normal succession of states described above.
The first conversion result following POR is accurate
within the specifications of the device.
Reference Voltage Range
The LTC2420 can accept a reference voltage from 0V to
V
thermal noise of the front-end circuits, and as such, its
value in microvolts is nearly constant with reference
voltage. A decrease in reference voltage will not signifi-
cantly improve the converter’s effective resolution. On the
other hand, a reduced reference voltage will improve the
overall converter INL performance. The recommended
range for the LTC2420 voltage reference is 100mV to V
Input Voltage Range
The converter is able to accommodate system level offset
and gain errors as well as system level overrange situa-
tions due to its extended input range, see Figure 3. The
LTC2420 converts input signals within the extended input
range of – 0.125 • V
For large values of V
absolute maximum voltage range of – 0.3V to (V
Beyond this range, the input ESD protection devices begin
to turn on and the errors due to the input leakage current
increase rapidly.
Input signals applied to V
– 300mV and above V
CC
. The converter output noise is determined by the
V
CC
–1/8V
9/8V
1/2V
+ 0.3V
–0.3V
V
REF
REF
REF
REF
0
Figure 3. LTC2420 Input Range
NORMAL
RANGE
INPUT
REF
CC
REF
to 1.125 • V
by 300mV. In order to limit any
IN
, this range is limited by the
EXTENDED
may extend below ground by
RANGE
INPUT
REF
ABSOLUTE
MAXIMUM
RANGE
INPUT
.
2420 F03
LTC2420
CC
+ 0.3V).
11
CC
.