LTC1860 Datasheet, PDF (8/12 Pages) Linear Technology – mPower, 12-Bit, 250ksps 1- and 2-Channel ADCs in MSOP

LTC1860/LTC1861
TEST CIRCUITS
Load Circuit for t_dDO, t_r, t_f, t_dis and t_en
TEST POINT
3k
SDO
20pF
V_CC t_dis WAVEFORM 2, t_en
t_dis WAVEFORM 1
1860 TC01
Voltage Waveforms for t_en
CONV
SDO
1860 TC03
t_en
Voltage Waveforms for SDO Delay Times, t_dDO and t_hDO
SCK
V_IL
t_dDO
t_hDO
SDO
V_OH
V_OL
1860 TC02
Voltage Waveforms for SDO Rise and Fall Times, t_r, t_f
SDO
t_r
V_OH
V_OL
t_f
1860 TC04
Voltage Waveforms for t_dis
CONV
V_IH
SDO
WAVEFORM 1
(SEE NOTE 1)
90%
t_dis
SDO
WAVEFORM 2
(SEE NOTE 2)
10%
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
APPLICATIO S I FOR ATIO
LTC1860 OPERATION
Operating Sequence
The LTC1860 conversion cycle begins with the rising edge
of CONV. After a period equal to t_CONV, the conversion is
finished. If CONV is left high after this time, the LTC1860
goes into sleep mode drawing only leakage current. On the
falling edge of CONV, the LTC1860 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.
8
Analog Inputs
The LTC1860 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 LTC1860 (and the
LTC1861 MSOP package) defines the full-scale range of
the A/D converter. These ADCs can operate with reference
voltages from V_CC to 1V.
18601f