LTC1865 LINER [Linear Technology], LTC1865 Datasheet - Page 8

• Manufacturer Part Number: LTC1865
• Description: Ultra-Tiny, Differential, 16-Bit ADC with SPI Interface SPI Interface
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTC2452
The LTC2452 includes 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 in-
terface directly to the LTC2452. 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
Reference Voltage Range
The LTC2453 reference input range is 2.5V to V
simplest operation, REF can be shorted to V
Input Voltage Range
As mentioned in the Output Data Format section, the output
code is given as 32768•V
the output code is clamped at 65535 (all ones). For V
–V
The LTC2452 includes a proprietary system that can,
typically, digitize each input 8LSB above V
GND, if the differential input is within ±V
ample (Figure 3), if the user desires to measure a signal
slightly below ground, the user could set V
and V
approximately 32768. If V
the output code would be approximately 32760.
8
+
REF
and IN
, the output code is clamped at 0 (all zeroes).
REF
= 5V. If V
–
.
IN
+
Table 1. LTC2452 Output Data Format
DIFFERENTIAL INPUT
VOLTAGE V
≥V
V
0.5•V
0.5•V
0
–1LSB
–0.5•V
–0.5•V
≤ –V
= GND, the output code would be
REF
REF
IN
REF
– 1LSB
IN
REF
REF
/V
REF
REF
+
REF
– 1LSB
= GND – 8LSB = –1.22 mV,
– 1LSB
IN
+
+ 32768. For V
– V
IN
–
(MSB)
D15
REF
REF
1
1
1
1
1
0
0
0
0
CC
IN
. As an ex-
and below
CC
.
–
IN
D14
. For the
= GND,
1
1
1
0
0
1
1
0
0
≥ V
REF
IN
D13
≤
1
1
0
1
0
1
0
1
0
,
D12...D2
The total amount of overrange and underrange capability
is typically 31LSB for a given device. The 31LSB total
is distributed between the overrange and underrange
capability. For example, if the underrange capability is
8LSB, the overrange capability is typically 31 – 8 = 23LSB.
Output Data Format
The LTC2452 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).
Letting V
as 32768•V
LTC2452, D15, is the MSB, which is 1 for V
0 for V
significant bits (D14, D13...) until the LSB is output by the
LTC2452. Table 1 shows some example output codes.
1
1
0
1
0
1
0
1
0
IN
+
D1
IN
1
1
0
1
0
1
0
1
0
< V
Figure 3. Output Code vs V
IN
= (V
IN
–12
–16
–20
/V
(LSB)
20
16
12
–4
–8
–0.001
8
4
0
D0
–
1
0
0
1
0
1
0
1
0
REF
. This bit is followed by successively less
IN
+
–0.005
+ 32768. The first bit output by the
CORRESPONDING
DECIMAL VALUE
– V
65535
65534
49152
49151
32768
32767
16384
16383
IN
0
0
V
–
IN
SIGNALS
BELOW
GND
), the output code is given
+
/V
REF
0.005
+
IN
0.001
+
with V
2452 F03
0.0015
IN
IN
–
+
= 0
≥ V
IN
–
2452fc
and