LTC1861I データシートの表示（PDF） - Linear Technology

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LTC1861I

µPower, 12-Bit, 250ksps 1- and 2-Channel ADCs in MSOP

Linear Technology 

APPLICATIONS INFORMATION

CONV

SCK

tCONV

SLEEP MODE

LTC1860/LTC1861

tsuCONV

tSMPL

1 2 3 4 5 6 7 8 9 10 11 12

SDO

Hi-Z

B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0*

Hi-Z

*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER

Figure 1. LTC1860 Operating Sequence

111111111111

111111111110

•

•

•

000000000001

000000000000

*VIN = IN+ – IN–

1MF

VCC

VIN*

1860 F02

LTC1860

1 VREF

VIN = 0V TO VCC 2 IN+

3 IN–

VCC 8

SCK 7

SDO 6

4 GND CONV 5

1860 F03

SERIAL DATA LINK TO

ASIC, PLD, MPU, DSP

OR SHIFT REGISTERS

Figure 2. LTC1860 Transfer Curve

LTC1860 OPERATION

Operating Sequence

The LTC1860 conversion cycle begins with the rising edge

of CONV. After a period equal to tCONV, 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.

Figure 3. LTC1860 with Rail-to-Rail Input Span

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 VREF 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 VREF is tied to VCC, 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 VCC to 1V.

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11

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