LTC2433-1CMS Linear Technology, LTC2433-1CMS Datasheet - Page 22

• Manufacturer Part Number: LTC2433-1CMS
• Description: IC ADC DIFF 16BIT 3WIRE 10-MSOP
• Manufacturer: Linear Technology

Specifications of LTC2433-1CMS

• Number Of Bits: 16
• Sampling Rate (per Second): 6.8
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC2433-1
APPLICATIO S I FOR ATIO
In addition to this gain error, an offset error term may also
appear. The offset error is proportional with the mismatch
between the source impedance driving the two input pins
IN
reference common mode voltages. While the input drive
circuit nonzero source impedance combined with the con-
verter average input current will not degrade the INL
performance, indirect distortion may result from the modu-
lation of the offset error by the common mode component
of the input signal. Thus, when using large C
values, it is advisable to carefully match the source imped-
ance seen by the IN
(internal oscillator and 50Hz/60Hz notch), every 180
mismatch in source impedance transforms a full-scale
common mode input signal into a differential mode input
signal of 1LSB. When F
with a frequency f
impedance transforms a full-scale common mode input
signal into a differential mode input signal of 3.7 • 10
• f
input common mode voltage for various values of source
resistance imbalance between the IN
large C
22
EOSC
+
and IN
LSB. Figure 18 shows the typical offset error due to
IN
Figure 18. Offset Error vs Common Mode Voltage
(V
Imbalance ( R
Large C
INCM
values are used.
–
–1
–2
–3
and with the difference between the input and
3
2
1
0
0
= IN
IN
A: R
B: R
C: R
D: R
C
D
G
A
B
E
F
0.5
Values (C
+
IN
IN
IN
IN
= IN
1
EOSC
= +400
= +200
= +100
= 0
U
IN
+
1.5
–
= R
) and Input Source Resistance
O
V
REF
REF
IN
F
T
R
C
and IN
, every 1
O
CC
A
SOURCEIN
IN
IN
is driven by an external oscillator
+
2
SOURCEIN
= GND
= 25 C
V
+
–
= IN
= 10 F
U
= 5V
INCM
= 5V
= GND
2.5
1 F)
–
= V
(V)
– = 500
–
3 3.5
INCM
+ – R
E: R
F: R
G: R
pins. When F
W
mismatch in source
IN
IN
IN
+
4
SOURCEIN
= –100
= –200
= –400
and IN
4.5
24331 F18
5
–) for
–
IN
U
pins when
O
capacitor
= LOW
–8
If possible, it is desirable to operate with the input signal
common mode voltage very close to the reference signal
common mode voltage as is the case in the ratiometric
measurement of a symmetric bridge. This configuration
eliminates the offset error caused by mismatched source
impedances.
The magnitude of the dynamic input current depends upon
the size of the very stable internal sampling capacitors and
upon the accuracy of the converter sampling clock. The
accuracy of the internal clock over the entire temperature
and power supply range is typically better than 0.5%. Such
a specification can also be easily achieved by an external
clock. When relatively stable resistors (50ppm/ C) are
used for the external source impedance seen by IN
IN
gain errors will be insignificant (about 1% of their respec-
tive values over the entire temperature and voltage range).
Even for the most stringent applications, a one-time
calibration operation may be sufficient.
In addition to the input sampling charge, the input ESD
protection diodes have a temperature dependent leakage
current. This current, nominally 1nA ( 10nA max), results
in a small offset shift. A 15k source resistance will create
a 0LSB typical and 1LSB maximum offset voltage.
Reference Current
In a similar fashion, the LTC2433-1 samples the differen-
tial reference pins REF
of charge to and from the external driving circuits thus
producing a dynamic reference current. This current does
not change the converter offset, but it may degrade the
gain and INL performance. The effect of this current can be
analyzed in the same two distinct situations.
For relatively small values of the external reference capaci-
tors (C
settles almost completely and relatively large values for
the source impedance result in only small errors. Such
values for C
gain performance without significant benefits of reference
filtering and the user is advised to avoid them.
–
, the expected drift of the dynamic current, offset and
REF
< 0.01 F), the voltage on the sampling capacitor
REF
will deteriorate the converter offset and
+
and REF
–
transfering small amount
+
24331fa
and