LTC1864LCMS8 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC1864LCMS8

µPower, 3V, 16-Bit, 150ksps 1- and 2-Channel ADCs in MSOP

Linear Technology 

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LTC1864L/LTC1865L

APPLICATIO S I FOR ATIO

LTC1865L OPERATION

Operating Sequence

The LTC1865L conversion cycle begins with the rising

edge of CONV. After a period equal to tCONV, the conver-

sion is finished. If CONV is left high after this time, the

LTC1865L goes into sleep mode drawing only leakage

current. The LTC1865L’s 2-bit data word is clocked into

the SDI input on the rising edge of SCK after CONV goes

low. Additional inputs on the SDI pin are then ignored until

the next CONV cycle. The shift clock (SCK) synchronizes

the data transfer with each bit being transmitted on the

falling SCK edge and captured on the rising SCK edge in

both transmitting and receiving systems. The data is

transmitted and received simultaneously (full duplex).

After completing the data transfer, if further SCK clocks

are applied with CONV low, SDO will output zeros indefi-

nitely. See Figure 4.

Analog Inputs

The two bits of the input word (SDI) assign the MUX

configuration for the next requested conversion. For a

given channel selection, the converter will measure the

voltage between the two channels indicated by the

“+” and “–” signs in the selected row of Table 1. In

single-ended mode, all input channels are measured with

respect to GND. A zero code will occur when the “+” input

minus the “–” input equals zero. Full scale occurs when

the “+” input minus the “–” input equals VREF minus

1LSB. See Figure 5. Both the “+” and “–” inputs are

sampled at the same time so common mode noise is

rejected. The input span in the SO-8 package is fixed at

VREF = VCC. If the “–” input in differential mode is

grounded, a rail-to-rail input span will result on the “+”

input.

Reference Input

The reference input of the LTC1865L SO-8 package is

internally tied to VCC. The span of the A/D converter is

therefore equal to VCC. The voltage on the reference input

of the LTC1865L MSOP package defines the span of the

A/D converter. The LTC1865L MSOP package can operate

with reference voltages from 1V to VCC.

Table 1. Multiplexer Channel Selection

SINGLE-ENDED

MUX MODE

DIFFERENTIAL

MUX MODE

MUX ADDRESS

SGL/DIFF ODD/SIGN

1

0

1

1

0

0

0

1

CHANNEL #

0

1

+

+

+

–

–

+

GND

–

–

1864 TBL1

CONV

SDI

SCK

SDO

tCONV

SLEEP MODE

DON’T CARE

DON'T CARE

tSMPL

S/D O/S

DON’T CARE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0*

Hi-Z

Hi-Z

*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER SCK CLOCKS ARE

APPLIED WITH CONV LOW, THE ADC WILL OUTPUT ZEROS INDEFINITELY

1864 F04

Figure 4. LTC1865L Operating Sequence

10

sn18645L 18645Lfs

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