LTC2756 datasheet(32/40 Pages) LINER

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LTC2345-18

234518f

For more information www.linear.com/LTC2345-18

applicaTions inForMaTion

throughput. Together, these I/O interface options enable

the LTC2345-18 to communicate equally well with legacy

microcontrollers and modern FPGAs.

Serial CMOS I/O Mode

As shown in Figure 17, in CMOS I/O mode the serial data

bus consists of a serial clock input, SCKI, serial data

input, SDI, serial clock output, SCKO, and eight lanes of

serial data output, SDO0 to SDO7. Communication with

the LTC2345-18 across this bus occurs during predefined

data transaction windows. Within a window, the device

accepts 24-bit SoftSpan configuration words for the next

conversion on SDI and outputs 24-bit packets containing

conversion results and channel configuration information

from the previous conversion on SDO0 to SDO7. New

data transaction windows open 10ms after powering up

or resetting the LTC2345-18, and at the end of each con-

version on the falling edge of BUSY. In the recommended

use case, the data transaction should be completed with

a minimum tQUIET time of 20ns prior to the start of the

next conversion, as shown in Figure 17. New SoftSpan

configuration words are only accepted within this recom-

mended data transaction window, but SoftSpan changes

take effect immediately with no additional analog input

settling time required before starting the next conversion.

It is still possible to read conversion data after starting the

nextconversion,butthiswilldegradeconversionaccuracy

and therefore is not recommended.

Just prior to the falling edge of BUSY and the opening of

a new data transaction window, SCKO is forced low and

SDO0 to SDO7 are updated with the latest conversion

results from analog input channels 0 to 7, respectively.

Rising edges on SCKI serially clock conversion results

and analog input channel configuration information out

on SDO0 to SDO7 and trigger transitions on SCKO that are

skew-matched to the data on SDO0 to SDO7. The resulting

C2 C1 C0

S23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

S22 S21 S20 S19 S18 S17 S16 S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5

D17

D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

SS1

SS2

SS0 D17

CNV

CS = PD = 0

DON’T CARE

tACQ

BUSY

SDO7

SCKO

SDO0

SCKI

SDI

DON’T CARE

SAMPLE N

RECOMMENDED DATA TRANSACTION WINDOW

SAMPLE N + 1

SOFTSPAN CONFIGURATION WORD FOR CONVERSION N + 1

CHANNEL 0

24-BIT PACKET

CONVERSION N

CHANNEL 1

24-BIT PACKET

CONVERSION N

CHANNEL 7

24-BIT PACKET

CONVERSION N

CHANNEL 0

24-BIT PACKET

CONVERSION N

234518 TD01

CONVERSION RESULT

CHANNEL ID SOFTSPAN

CONVERSIONRESULT

D17

D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

SS1

SS2

SS0 D17

DON’T CARE

CONVERSION RESULT

CHANNEL ID SOFTSPAN

CONVERSIONRESULT

tSCKI

tSCKIH

tBUSYLH

tSCKIL

tHSDOSCKI

tDSDOSCKI

tSSDISCKI

tQUIET

tHSDISCKI

tDSDOBUSYL

tCNVH

tSKEW

tCONV

tCNVL

tCYC

Figure 17. Serial CMOS I/O Mode

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