51

R/C

BUSY

Converter

Mode

Data

BUS

Acquire

Convert

Acquire

Convert

Data Valid

Hi-Z State

Hi-Z State

Data Valid

t

W

t

B

Figure 5. Convert Mode Timing — R/C Pulse LOW, Outputs Enabled After Conversion

Series may draw excessive current. In normal

operation, this is not a problem because both pins

will be soldered together. However, during evalu-

ation, incoming inspection, repair, etc., where the

potential of a “Hot Socket” exists, care should be

taken to apply power to the SP85XX Series only

after it has been socketed.

Minimizing “Glitches”

Coupling of external transients into an analog-to-

digitalconvertercancauseerrorswhicharedifficultto

debug. In addition to the discussions earlier on layout

considerationsforsupplies,bypassingandgrounding,

there are several other useful steps that can be taken to

get the best analog performance out of a system using

the SP85XX Series. These potential system problem

sources are particularly important to consider when

developing a new system, and looking for the causes

of errors in breadboards.

First, care should be taken to avoid glitches during

critical times in the sampling and conversion process.

SincetheSP85XXSerieshasaninternalsample/hold

function, the signal that puts it into the hold state (R/C

going LOW) is critical, as it would be on any sample/

hold amplifier. The R/C falling edge should have a 5

to 10ns transition time, low jitter, and have minimal

ringing, especially during the 20ns after it falls.

R/C

BUSY

Converter

Mode

Data

BUS

Acquire

Convert

Acquire

Convert

Data

Valid

Hi-Z State

Hi-Z State

t

W

t

B

Data

Valid

Hi-Z State

Figure 6. Read Mode Timing — R/C Pulse HIGH, Outputs Enabled Only When R/C is High