LTC2295 datasheet(18/24 Pages) LINER

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LTC2295

2295fa

APPLICATIO S I FOR ATIO

Digital Output Multiplexer

The digital outputs of the LTC2295 can be multiplexed onto

a single data bus. The MUX pin is a digital input that swaps

the two data busses. If MUX is High, Channel A comes out

on DA0-DA13, OFA; Channel B comes out on DB0-DB13,

OFB. If MUX is Low, the output busses are swapped and

Channel A comes out on DB0-DB13, OFB; Channel B comes

out on DA0-DA13, OFA. To multiplex both channels onto

a single output bus, connect MUX, CLKA and CLKB together

(see the Timing Diagram for the multiplexed mode). The

multiplexed data is available on either data bus—the un-

used data bus can be disabled with its OE pin.

Grounding and Bypassing

The LTC2295 requires a printed circuit board with a clean,

unbroken ground plane. A multilayer board with an inter-

nal ground plane is recommended. Layout for the printed

circuit board should ensure that digital and analog signal

lines are separated as much as possible. In particular, care

should be taken not to run any digital track alongside an

analog signal track or underneath the ADC.

High quality ceramic bypass capacitors should be used

at the VDD, OVDD, VCM, REFH, and REFL pins. Bypass

capacitors must be located as close to the pins as possible.

Of particular importance is the 0.1

µF capacitor between

REFH and REFL. This capacitor should be placed as close

to the device as possible (1.5mm or less). A size 0402

ceramic capacitor is recommended. The large 2.2

µF

capacitor between REFH and REFL can be somewhat

further away. The traces connecting the pins and bypass

capacitors must be kept short and should be made as wide

as possible.

The LTC2295 differential inputs should run parallel and

close to each other. The input traces should be as short as

possible to minimize capacitance and to minimize noise

pickup.

Heat Transfer

Most of the heat generated by the LTC2295 is transferred

from the die through the bottom-side exposed pad and

package leads onto the printed circuit board. For good

electrical and thermal performance, the exposed pad

should be soldered to a large grounded pad on the PC

board. It is critical that all ground pins are connected to a

ground plane of sufficient area.

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