LTC2497 Linear Technology, LTC2497 Datasheet - Page 12

• Manufacturer Part Number: LTC2497
• Description: 16-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

www.DataSheet4U.com
LTC2497
APPLICATIONS INFORMATION
common mode reference (see the Automatic Differential
Input Current Cancellation section). This unique architec-
ture does not require on-chip buffers, thereby enabling
signals to swing beyond ground and V
cancellation does not interfere with the transparent offset
and full-scale auto-calibration and the absolute accuracy
(full scale + offset + linearity + drift) is maintained even
with external RC networks.
Power-Up Sequence
The LTC2497 automatically enters an internal reset state
when the power supply voltage V
mately 2.0V. This feature guarantees the integrity of the
conversion result and input channel selection.
When V
an internal power-on-reset (POR) signal with a duration
of approximately 4ms. The POR signal clears all internal
registers. The conversion immediately following a POR
cycle is performed on the input channel IN
CH1. The fi rst conversion following a POR cycle is accurate
within the specifi cation of the device if the power supply
voltage is restored to (2.7V to 5.5V) before the end of the
POR interval. A new input channel can be programmed into
the device during this fi rst data input/output cycle.
Reference Voltage Range
This converter accepts a truly differential, external reference
voltage. The absolute/common mode voltage range for
REF
the device (GND to V
V
The LTC2497 differential reference input range is 0.1V to
V
and REF
is determined by the thermal noise of the front end circuits.
Since the transition noise is well below 1LSB (0.02LSB), a
decrease in reference voltage will proportionally improve
the converter resolution and improve INL.
12
CC
REF
. For the simplest operation, REF
+
must be positive (REF
and REF
CC
–
can be shorted to GND. The converter output noise
rises above this threshold, the converter creates
–
pins covers the entire operating range of
CC
). For correct converter operation,
+
> REF
CC
+
–
drops below approxi-
can be shorted to V
).
CC
. Moreover, the
+
= CH0, IN
–
CC
=
Input Voltage Range
The analog inputs are truly differential with an absolute,
common mode range for the CH0-CH15 and COM input
pins extending from GND – 0.3V to V
these limits, the LTC2497 converts the bipolar differen-
tial input signal V
the selected input channels), from – FS = – 0.5 • V
to + FS = 0.5 • V
this range, the converter indicates the overrange or the
underrange condition using distinct output codes (see
Table 1).
Signals applied to the input (CH0-CH15, COM) may extend
300mV below ground and above V
any fault current due to input ESD leakage current, resis-
tors of up to 5k may be added in series with the input.
The effect of series resistance on the converter accuracy
can be evaluated from the curves presented in the Input
Current/Reference Current sections. In addition, series
resistors will introduce a temperature dependent error due
to input leakage current. A 1nA input leakage current will
develop a 1ppm offset error on a 5k resistor if V
This error has a very strong temperature dependency.
MUXOUT/ADCIN
The outputs of the multiplexer (MUXOUTP/MUXOUTN) and
the inputs to the ADC (ADCINP/ADCINN) can be used to
perform input signal conditioning on any of the selected
input channels or simply shorted together for direct
digitization. If an external amplifi er is used, the LTC2497
automatically calibrates both the offset and drift of this
circuit and the Easy Drive sampling scheme enables a
wide variety of amplifi ers to be used.
In order to achieve optimum performance, if an external
amplifi er is not used, short these pins directly together
(ADCINP to MUXOUTP and ADCINN to MUXOUTN) and
minimize their capacitance to ground.
REF
IN
= IN
where V
+
– IN
REF
–
(where IN
= REF
CC
. In order to limit
CC
+
- REF
+ 0.3V. Within
+
and IN
–
. Outside
REF
–
= 5V.
2497f
are
REF