ltc2493 Linear Technology Corporation, ltc2493 Datasheet - Page 14

• Manufacturer Part Number: ltc2493
• Description: 24-bit 2-/4-channel Delta Sigma Adc With Easy Drive Input Current Cancellation And I2c Interface
• Manufacturer: Linear Technology Corporation

LTC2493
applicaTions inForMaTion
amplifiers. The remaining common mode input current
is eliminated by either balancing the differential input im-
pedances or setting the common mode input equal to the
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 LTC2493 automatically enters an internal reset state
when the power supply voltage, V
proximately 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 with simultaneous 50Hz/60Hz rejection and 1x output
rate. The first conversion following a POR cycle is accurate
within the specification 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, rejection mode, speed
mode, or temperature selection can be programmed into
the device during this first data input/output cycle.
Reference Voltage Range
This converter accepts a truly differential external reference
voltage. The absolute/common mode voltage range for the
REF
the device (GND to V
V
The LTC2493 differential reference input range is 0.1V to
V

REF
CC
. For the simplest operation, REF
+
must be positive (REF
and REF
CC
rises above this threshold, the converter creates
–
pins covers the entire operating range of
CC
). For correct converter operation,
+
> REF
–
CC
).
+
, drops below ap-
can be shorted to
CC
. Moreover, the
+
= CH0, IN
–
=
V
put noise is determined by the thermal noise of the front
end circuits and, as such, its value in nanovolts is nearly
constant with reference voltage. A decrease in reference
voltage will not significantly improve the converter’s effec-
tive resolution. On the other hand, a decreased reference
will improve the converter’s overall INL performance.
Input Voltage Range
The analog inputs are truly differential with an absolute,
common mode range for the CH0-CH3 and COM input pins
extending from GND – 0.3V to V
limits, the ESD protection devices begin to turn on and
the errors due to input leakage current increase rapidly.
Within these limits, the LTC2493 converts the bipolar
differential input signal V
IN
to +FS = 0.5 • V
this range, the converter indicates the overrange or the
underrange condition using distinct output codes (see
Table 1).
In order to limit any fault current, resistors of up to 5kW
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 Cur-
rent 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
strong temperature dependency.
I
The LTC2493 communicates through an I
I
multiple devices and multiple masters on a single bus. The
connected devices can only pull the data line (SDA) low
and can never drive it high. SDA is required to be externally
2
2
CC
C INTERFACE
C interface is a 2-wire open-drain interface supporting
–
are the selected input channels), from –FS = –0.5 • V
and REF
–
can be shorted to GND. The converter out-
REF
where V
IN
REF
= IN
REF
= 5V. This error has a very
CC
+
= REF
– IN
+ 0.3V. Outside these
–
+
2
(where IN
- REF
C interface. The
–
. Outside
+
2493fa
and
REF