Datasheet

LTC2460/LTC2462
9
24602fa
between the conversion and the output data. Therefore,
multiplexing multiple analog input voltages requires no
special actions.
The LTC2460/LTC2462 perform offset calibrations every
conversion. This calibration is transparent to the user and
has no effect upon the cyclic operation described previously.
The advantage of continuous calibration is stability of the
ADC performance with respect to time and temperature.
The LTC2460/LTC2462 include a proprietary input sampling
scheme that reduces the average input current by several
orders of magnitude when compared to traditional delta-
sigma architectures. This allows external filter networks
to interface directly to the LTC2460/LTC2462. Since the
average input sampling current is 50nA, an external RC
lowpass filter using 1kΩ and 0.1µF results in <1LSB
additional error. Additionally, there is negligible leakage
current between IN
+
and IN
–
.
Input Voltage Range (LTC2460)
Ignoring offset and full-scale errors, the LTC2460 will
theoretically output an “all zero” digital result when the
input is at ground (a zero scale input) and an “all one”
digital result when the input is at V
REF
(V
REFOUT
= 1.25V).
In an under-range condition, for all input voltages below
zero scale, the converter will generate the output code 0. In
an over-range condition, for all input voltages greater than
V
REF
, the converter will generate the output code 65535.
For applications that require an input range greater than
0V to 1.25V, please refer to the LTC2450.
Input Voltage Range (LTC2462)
As mentioned in the Output Data Format section, the output
code is given as 32768 • (V
IN
+
– V
IN
–
)/V
REF
+ 32768. For
(V
IN
+
– V
IN
–
) ≥ V
REF
, the output code is clamped at 65535
(all ones). For (V
IN
+
– V
IN
–
) ≤ –V
REF
, the output code is
clamped at 0 (all zeroes).
The LTC2462 includes a proprietary architecture that
can, typically, digitize each input up to 8 LSBs above V
REF
and below GND, if the differential input is within ±V
REF
.
As an example (Figure 3), if the user desires to measure
a signal slightly below ground, the user could set V
IN
–
= GND, and V
REF
= 1.25V. If V
IN
+
= GND, the output code
would be approximately 32768. If V
IN
+
= GND – 8LSB =
–0.305mV, the output code would be approximately 32760.
For applications that require an input range greater than
±1.25V, please refer to the LTC2452.
Output Data Format
The LTC2460/LTC2462 generates a 16-bit direct binary
encoded result. It is provided as a 16-bit serial stream
through the SDO output pin under the control of the SCK
input pin (see Figure 4).
The LTC2462 (differential input) output code is given by
32768 • (V
IN
+
– V
IN
–
)/V
REF
+ 32768. The first bit output
by the LTC2462, D15, is the MSB, which is 1 for V
IN
+
≥
V
IN
–
and 0 for V
IN
+
< V
IN
–
. This bit is followed by succes-
sively less significant bits (D14, D13, …) until the LSB is
output by the LTC2462, see Table 1.
D
15
LSB
SDO
SCK
D
14
D
13
D
12
D
11
D
10
D
9
D
8
D
7
D
6
D
5
D
4
D
3
D
2
D
0
D
1
24602 F04
t
1
t
3
t
KQ
t
lSCK
t
hSCK
t
2
CS
MSB
SDI
EN2 SPD*
*SPD IS A DON’T CARE BIT FOR THE LTC2462
SLP
DON’T CARE
t
5
t
6
EN1
applicaTions inForMaTion
Figure 4. Data Input/Output Timing