47

edge can be used to read the data from the conver-

sion. Also, during conversion, the BUSY signal

puts the output data lines in Hi-Z states and inhibits

the input lines. This means that pulses on R/C are

ignored, so that new conversions cannot be initi-

ated during a conversion, either as a result of

spurious signals or to short-cycle the SP85XX

Series.

In the Read Mode, the input to R/C is kept nor-

mally LOW, and a HIGH pulse is used to read data

and initiate a conversion. In this mode, the rising

edge of R/C will enable the output data pins, and

the data from the previous conversion becomes

valid. The falling edge then puts the SP85XX

Series in a hold mode, and initiates a new conver-

sion.

The SP85XX Series will begin acquiring a new

sample just prior to the BUSY output rising, and

will track the input signal until the next conversion

is started.

Forusewithan8-bitbus,thedatacanbereadoutintwo

bytes under the control of HBE. With a LOW input

onHBE,attheendofaconversion,the8LSBsofdata

areloadedintotheoutputdriversonD

D

MSBs on D

forced LOW.

Analog Input Ranges

The SP85XX Series offers two standard bipolar

input ranges:

±10V and ±5V. If a ±10V range is

required, the analog input signal should be con-

nected to pin 2. A signal requiring a

±5V range

should be connected to pin 3. In either case, the

other pin of the two must be grounded or connected

to the adjustment circuits described in the section

on calibration.

Controlling The SP85XX Series

The SP85XX Series can be easily interfaced to most

microprocessor-based and other digital systems. The

microprocessor may take full control of each conver-

sion, or the SP85XX Series may operate in a stand-

alone mode, controlled only by the R/C input. Full

control consists of initiating the conversion and read-

ingtheoutputdataatusercommand,transmittingdata

either all 12-bits in one parallel word, or in two 8-bit

bytes.Thethreecontrolinputs(CS,R/CandHBE)are

FEATURES...

The SP85XX Series are specified at sampling

rates of 333kHz (SP8503), 200kHz (SP8505) or

100kHz (SP8510). Conversion times are factory

set for 2.70

µs, 4.7µs and 9.7µs maximum, re-

spectively,

over temperature, and the high-

speed sampling input stage insures a total acqui-

sition and conversion time of 3

µs, 5µs and 10µs

maximum, respectively, over temperature. Pre-

cision, laser-trimmed scaling resistors provide

industry–standard input ranges of

±5V or ±10V.

The 28-pin SP85XX Series are available in

narrow body plastic DIP, and SOIC packages

and it operates from a single +5V supply.

The SP85XX Series are available in grades

specified over the 0

°C to +70°C commercial

temperature ranges.

OPERATION

Basic Operation

Figure 1 shows the simple hookup circuit required

to operate the SP85XX Series in a

±10V range in

the Convert Mode. A convert command arriving

on R/C puts the SP85XX Series in the HOLD

mode, and a conversion is started. This pulse must

be LOW for a minimum of 40ns. Because this

pulse establishes the sampling instant of the A/D,

it must have very low jitter. BUSY will be held

LOW during the conversion, and rises only after

the conversion is completed and the data has been

transferred to the output drivers. Thus, the rising

Figure 1. Basic

±10V Operation

2

3

4

5

6

7

8

9

10

11

12

13

27

26

25

24

23

22

21

20

19

18

17

16

D0

(LSB)

Busy

Convert

Command

0.1µF

6.8µF +

+5V

+5V

+5V

N.C.

BUSY

CS

R/C

HBE

D0 (LSB)

D1

D2

D3

DGND

IN 1

IN 2

AGND

D11 (MSB)

D10

D9

D8

D7

D6

D5

D4

D11

(MSB)

Data

Out

Input

1

28

N.C.

N.C.

N.C.

N.C.

14

15