LTC6945 datasheet(21/24 Pages) LINER

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2271f

LTC2271

APPLICATIONS INFORMATION

GROUNDING AND BYPASSING

The LTC2271 require a printed circuit board with a clean

unbroken ground plane. A multilayer board with an in-

ternal ground plane in the ﬁrst layer beneath the ADC 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, VREF, REFH and REFL pins. Bypass

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

Size 0402 ceramic capacitors are recommended. The traces

connecting the pins and bypass capacitors must be kept

short and should be made as wide as possible.

Of particular importance is the capacitor between REFH

and REFL. This capacitor should be on the same side of

the circuit board as the A/D, and as close to the device

as possible.

The analog inputs, encode signals, and digital outputs

should not be routed next to each other. Ground ﬁll and

grounded vias should be used as barriers to isolate these

signals from each other.

HEAT TRANSFER

Most of the heat generated by the LTC2271 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 must

be soldered to a large grounded pad on the PC board. This

pad should be connected to the internal ground planes by

an array of vias.

TYPICAL APPLICATIONS

LTC2271

VCM1

GND

AIN1+

AIN1–

GND

REFH

REFL

REFH

REFL

PAR/SER

AIN2+

AIN2–

GND

VCM2

OUT1C+

OUT1C–

OUT1D+

OUT1D–

DCO+

DCO–

OVDD

OGND

FR+

FR–

OUT2A+

OUT2A–

OUT2B+

OUT2B–

–

CN1

1μF

C29

1μF

2.2μF

1μF

C16 0.1μF

2271 TA02

OVDD

DIGITAL

OUTPUTS

C37

1μF

0.1μF

VDD

SENSE

SDO

VDD

ENCODE

INPUT

SPI

PORT

PAR/SER

AIN1+

AIN1–

AIN2+

AIN2–

CN1: 2.2μF LOW INDUCTANCE

INTERDIGITATED CAPACITOR

TDK CLLE1AX7S0G225M

MURATA LLA219C70G225M

AVX W2L14Z225M

OR EQUIVALENT

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