LTC2335-16 datasheet(38/40 Pages) LINER

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LTC2335-16

233516f

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Thus, once the sequencer has been programmed, simply

hold SDI at an LVDS low level during subsequent data

transactionstocyclecontinuallythroughtheprogrammed

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 19.

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 at an LVDS low level. This particular use

case is illustrated in Figure 19. If the desired configura-

tion 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.

applicaTions inForMaTion

To obtain the best performance from the LTC2335-16, a

four-layer printed circuit board (PCB) is recommended.

Layout for the PCB should ensure the digital and analog

signal lines are separated as much as possible. In particu-

lar, care should be taken not to run any digital clocks or

signals alongside analog signals or underneath the ADC.

Also minimize the length of the REFBUF to GND (Pin 20)

bypass capacitor return loop, and avoid routing CNV near

signals which could potentially disturb its rising edge.

Supply bypass capacitors should be placed as close as

possible to the supply pins. Low impedance common re-

turns for these bypass capacitors are essential to the low

noise operation of the ADC. A single solid ground plane

is recommended for this purpose. When possible, screen

the analog input traces using ground.

Reference Design

For a detailed look at the reference design for this con-

verter, including schematics and PCB layout, please refer

to DC2412A, the evaluation kit for the LTC2335-16.

boarD layouT

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