LTC2335-16 datasheet(34/40 Pages) LINER

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LTC2335-16

233516f

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applicaTions inForMaTion

Eachdatatransactionwindowisanopportunitytoprogram

thesequencerbyclockinginaseriesof8-bitcontrolwords

on SDI, each specifying a channel number and SoftSpan

range, as shown in Figures 17 and 18. To program the

sequencer with a series of up to 16 conversion configu-

rations, write in the corresponding control words in the

desired conversion order during a single data transaction.

Words beyond the 16th valid word will be ignored.

The control word format is as follows:

C[7]

C[6]

C[5]

C[4]

C[3]

C[2]

C[1]

C[0]

CH[2] CH[1] CH[0] SS[2] SS[1] SS[0]

The V bit (C[7]) controls whether the LTC2335-16 should

consider this a valid word. Any words which have V =

0 are considered invalid and are ignored (though valid

words will still be accepted after an invalid word). Words

which have V = 1 will be added to the sequencer in the

order provided. The C[6] bit is reserved for future use and

should be set to 0. The CH[2:0] (C[5:3]) bits are a binary

value 0 to 7 controlling the channel to be converted. The

SS[2:0] (C[2:0]) bits specify the desired SoftSpan range

for the conversion, as described in Table 1.

Sequencer programming is completed when the next

conversion is started. At this time, any incomplete words

are considered invalid and discarded. If one or more

valid words were provided, the sequencer is completely

overwritten with the new sequence, and the just-initiated

conversion employs the first provided configuration.

If no valid words were provided during the data transac-

tion window, the sequencer program is unchanged, and

the pointer advances to the next entry in the previously

programmed cycle to configure the next conversion.

Thus, once the sequencer has been programmed, simply

hold SDI low during subsequent data transactions to

cycle continually through the programmed sequence of

configurations.

Direct Per-Conversion Configuration

As a special case of the sequencer, the LTC2335-16

multiplexer and SoftSpan range can be directly controlled

every conversion with no latency and no additional set-

tling time or digital I/O overhead. To use the part in this

direct fashion, simply supply one control word on SDI

during a data transaction to specify the desired channel

number and SoftSpan range for the following conversion,

as shown in Figure 17.

If the desired channel and SoftSpan range for conversion

N+1 are known before seeing the result of conversion N,

specify the configuration by clocking in the corresponding

control word on SDI while clocking out the first 8 bits,

then hold SDI low. This particular use case is illustrated in

Figure 17. If the desired configuration is not known until

after the conversion data has been read, clock in 24 zeros

on SDI while the 24 bits of data are being read out; since

the V bits of those words are then 0, they are ignored.

Once the configuration has been determined, clock in 8

more bits on SDI which specify the desired configuration

for conversion N+1.

Serial LVDS I/O Mode

In LVDS I/O mode, information is transmitted using

positive and negative signal pairs (LVDS+/LVDS−) with bits

differentially encoded as (LVDS+ − LVDS−). These signals

are typically routed using differential transmission lines

with 100Ω characteristic impedance. Logical 1s and 0s

are nominally represented by differential +350mV and

−350mV,respectively.Forclarity,allLVDStimingdiagrams

and interface discussions adopt the logical rather than

physical convention.

As shown in Figure 19, in LVDS I/O mode the serial data

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

data differential input, SDI, serial clock differential output,

SCKO, and serial data differential output, SDO. Communi-

cation with the LTC2335-16 across this bus occurs during

predefined data transaction windows. Within a window,

the device accepts control words on SDI to configure the

SoftSpan range and channel for the next conversion and

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