ADS5281IPFPR datasheet(35/41 Pages) TI

35 / 41 page

www.ti.com

NOISE COUPLING ISSUES

ADS5281

ADS5282

SBAS397E – DECEMBER 2006 – REVISED JANUARY 2008

Table 7. State of Reference Voltages for Various Combinations of PD and INT/EXT

INTERNAL BUFFER STATE

INT/EXT

EXT_REF_VCM

REFT buffer

3-state

2.5V

3-state

2.5V(1)

1.5V + VCM/1.5V

Do not use

2.5V(1)

Do not use

REFB buffer

3-state

0.5V

3-state

0.5V(1)

1.5V – VCM/1.5V

Do not use

0.5V(1)

Do not use

VCM pin

1.5V

Force

Do not use

Force

Do not use

(1)

Weakly forced with reduced strength.

Smaller effective inductance of the supply and ground

pins leads to better noise suppression. For this

reason, multiple pins are used to drive each supply

High-speed mixed signals are sensitive to various

and ground. It is also critical to ensure that the

types of noise coupling. One primary source of noise

impedances of the supply and ground lines on the

is the switching noise from the serializer and the

board are kept to the minimum possible values. Use

output buffers. Maximum care is taken to isolate

of ground planes in the printed circuit board (PCB) as

these noise sources from the sensitive analog blocks.

well as large decoupling capacitors between the

As a starting point, the analog and digital domains of

supply and ground lines are necessary to obtain the

the device are clearly demarcated. AVDD and AVSS

best possible SNR performance from the device.

are used to denote the supplies for the analog

It is recommended that the isolation be maintained

sections, while LVDD and LVSS are used to denote

onboard by using separate supplies to drive AVDD

the digital supplies. Care is taken to ensure that there

and LVDD, as well as separate ground planes for

is minimal interaction between the supply sets within

AVSS and LVSS. The use of LVDS buffers reduces

the

device.

The

extent

noise

coupled

and

the injected noise considerably, compared to CMOS

transmitted from the digital to the analog sections

buffers.

The

current

the

LVDS

buffer

depends on:

independent of the direction of switching. Also, the

1. The effective inductances of each of the supply

low output swing as well as the differential nature of

and ground sets.

the LVDS buffer results in low-noise coupling.

2. The isolation between the digital and analog

supply and ground sets.

Submit Documentation Feedback

Product Folder Link(s): ADS5281 ADS5282

ADS5281IPFPR датащи(PDF) 35 Page - Texas Instruments

ADS5281IPFPR датащи(HTML) 35 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

датащи скачать

ссылки URL