HS574AS/883 Просмотр технического описания (PDF) - Signal Processing Technologies

Номер в каталоге

Компоненты Описание

производитель

HS574AS/883

12–Bit Sampling A/D Converters

Signal Processing Technologies 

signals between ground traces and cross digital

lines at right angles only.

Grounding Considerations

Any ground path from the analog and digital

ground should be as low resistance as possible to

accommodate the ground currents present with

this device.

The analog ground current is approximately 6mA

DC while the digital ground is 3mA DC. The

analog and digital common pins should be tied

together as close to the package as possible to

guarantee best performance. The code–depen-

dent currents flow through the VLOGIC and VCC

terminals and not through the analog and digital

common pins.

Power Supplies

The supply voltages for the SPx74A must be

kept as quiet as possible from noise pickup and

also regulated from transients or drops. Because

the part has 12–bit accuracy, voltage spikes on

the supply lines can cause several LSB devia-

tions on the output. Switching power supply

noise can be a problem. Careful filtering and

shielding should be employed to prevent the

noise from being picked up by the converter.

Capacitor bypass pairs are needed from each

supply pin to its respective ground to filter noise

and counter the problems caused by the varia-

tions in supply current. A 10µF tantalum and a

0.1µF ceramic type in parallel between VLOGIC

(pin 1) and digital common (pin15), and VCC (pin

7) and analog common (pin 9) is sufficient. VEE

is generated internally so pin 11 may be grounded

or connected to a negative supply if the SPx74A

is being used to upgrade an already existing

design.

CALIBRATION AND CONNECTION

PROCEDURES

Unipolar

The calibration procedure consists of adjusting

the converter’s most negative output to its ideal

value for offset adjustment, and then adjusting

the most positive output to its ideal value for gain

adjustment.

Starting with offset adjustment and referring to

Figure 4, the midpoint of the first LSB increment

should be positioned at the origin to get an output

code of all 0s. To do this, an input of +1⁄2 LSB or

+1.22mV for the 10V range and +2.44mV for the

20V range should be applied to the SPx74A.

Adjust the offset potentiometer R for code tran-

1

sition flickers between 0000 0000 0000 and

0000 0000 0001.

The gain adjustment should be done at positive

full scale. The ideal input corresponding to the

last code change is applied. This is 11⁄2LSB

below the nominal full scale which is +9.9963V

for the 10V range and +19.9927V for the 20V

range. Adjust the gain potentiometer R2 for flicker

between codes 1111 1111 1110 and 1111 1111

1111. If calibration is not necessary for the

intended

application,

replace

R

2

with

a

50Ω,

1%

metal film resistor and remove the network ana-

INPUT BUFFERS

12/8

CS

READ CONTROL

A0

R/C

CE

EOC8

CK

Q

D

Q

A0 LATCH

EOC12

H DQ

CK

R

Figure 6. SPx74A Control Logic

10

DELAY

NIBBLE B ZERO

OVERRIDE

NIBBLE A, B

NIBBLE C

STS

Share Link: