Datasheet
8
LTC1860L/LTC1861L
18601Lf
Load Circuit for t
dDO
, t
r
, t
f
, t
dis
and t
en
Voltage Waveforms for SDO Rise and Fall Times, t
r
, t
f
Voltage Waveforms for SDO Delay Times, t
dDO
and t
hDO
Voltage Waveforms for t
en
SDO
3k
20pF
TEST POINT
V
CC
t
dis
WAVEFORM 2, t
en
t
dis
WAVEFORM 1
1860 TC01
SCK
SDO
V
IL
t
dDO
t
hDO
V
OH
V
OL
1860 TC02
1860 TC03
CONV
SDO
t
en
SDO
t
r
t
f
1860 TC04
V
OH
V
OL
TEST CIRCUITS
Voltage Waveforms for t
dis
SDO
WAVEFORM 1
(SEE NOTE 1)
V
IH
t
dis
90%
10%
SDO
WAVEFORM 2
(SEE NOTE 2)
CONV
NOTE 1: WAVEFORM 1 IS FOR AN OUTPUT WITH INTERNAL CONDITIONS SUCH
THAT THE OUTPUT IS HIGH UNLESS DISABLED BY THE OUTPUT CONTROL
NOTE 2: WAVEFORM 2 IS FOR AN OUTPUT WITH INTERNAL CONDITIONS SUCH
THAT THE OUTPUT IS LOW UNLESS DISABLED BY THE OUTPUT CONTROL
1860 TC05
LTC1860L OPERATION
Operating Sequence
The LTC1860L conversion cycle begins with the rising
edge of CONV. After a period equal to t
CONV
, the conver-
sion is finished. If CONV is left high after this time, the
LTC1860L goes into sleep mode drawing only leakage
current. On the falling edge of CONV, the LTC1860L goes
into sample mode and SDO is enabled. SCK synchronizes
the data transfer with each bit being transmitted from SDO
on the falling SCK edge. The receiving system should
capture the data from SDO on the rising edge of SCK. After
completing the data transfer, if further SCK clocks are
applied with CONV low, SDO will output zeros indefinitely.
See Figure 1.
Analog Inputs
The LTC1860L has a unipolar differential analog input. The
converter will measure the voltage between the “IN
+
” and
“IN
–
” inputs. A zero code will occur when IN
+
minus IN
–
equals zero. Full scale occurs when IN
+
minus IN
–
equals
V
REF
minus 1LSB. See Figure 2. Both the “IN
+
” and
“IN
–
” inputs are sampled at the same time, so common
mode noise on the inputs is rejected by the ADC. If “IN
–
”
is grounded and V
REF
is tied to V
CC
, a rail-to-rail input span
will result on “IN
+
” as shown in Figure 3.
Reference Input
The voltage on the reference input of the LTC1860L (and
the LTC1861L MSOP package) defines the full-scale range
of the A/D converter. These ADCs can operate with refer-
ence voltages from V
CC
to 1V.
APPLICATIO S I FOR ATIO
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