SP574B Datasheet, PDF (8/15 Pages) Sipex Corporation – 12-Bit Sampling A/D Converters

The gain adjustment should be done at positive full
scale. The ideal input corresponding to the last
code change is applied. This is 1¹â„ LSB below the
2
nominal full scale which is +9.9963V for the 10V
range and +19.9927V for the 20V range. Adjust
the gain potentiometer R for flicker between
2
codes 1111 1111 1110 and 1111 1111 1111. If
calibration is not necessary for the intended appli-
cation, replace R₂ with a 50Ω, 1% metal film
resistor and remove the network analog input to
pin 13 for the 0V to 10V range or to pin 14 for the
0V to 20V range.
Bipolar
The gain and offset errors listed in the specifica-
tions may be adjusted to zero using the potentiom-
eters R₁ and R₂ (See Figure 3). If adjustment is not
needed, either or both pots may be replaced by a
50Ω, 1% metal film resistor.
To calibrate, connect the analog input signal to pin
13 for a ±5V range or to pin 14 for a ±10V range.
First apply a DC input voltage ¹â„ LSB above
2
negative full scale which is –4.9988V for the ±5V
range or –9.9976V for the ±10V range. Adjust the
offset potentiometer R₁ for flicker between output
codes 0000 0000 0000 and 0000 0000 0001. Next,
apply a DC input voltage 1¹â„₂ LSB below positive
full scale which is +4.9963V for the ±5 range or
+9.9927V for the ±10V range. Adjust the gain
potentiometer R₂ for flicker between codes 1111
1110 and 1111 1111 1111.
Alternative
The
100Ω
potentiometer
R
2
provides
gain
adjust
for 10V and 20V ranges. In some applications, a
full scale of 10.24V (for and LSB of 2.5mV) or
20.48 (for an LSB of 5.0mV) is more convenient.
For these, replace R₂ by a 50Ω, 1% metal film
resistor. Then to provide gain adjust for the 10.24
range, add a 200Ω potentiometer in series with pin
13. For the 20.48V range, add a 1000Ω potentiom-
eter in series with pin 14.
CONTROLLING THE SPx74B
The SPx74B can be operated by most micropro-
cessor systems due to the control input pins and
on–chip logic. It may also be operated in the
“stand–alone” mode and enabled by the R/C
input pin. Full microprocessor control consists
of selecting an 8– or 12–bit conversion cycle,
initiating the conversion, and reading the output
data when ready. The output read has the options
of choosing either 12–bits at once or 8–bits fol-
lowed by 4–bits in a left–justified format. All five
control inputs are TTL/CMOS compatible and
include 12/8, CS, A₀, R/C and CE. The use of these
inputs in controlling the converter’s operation is
OUTPUT BITS
2
12/8
3
CS
A0 ⁴
R/C ⁵
CE ⁶
MSB _{27 26 25 24 23 22 21 20 19 18 17 16} LSB
CONTROL
LOGIC
NIBBLE A
NIBBLE B
NIBBLE C
THREE–STATE BUFFERS AND CONTROL
12–BITS
OSCILLATOR
12–BIT SAR
ANALOG
INPUTS
±5V
±10V
10V
IN 13
20V
IN 14
BIP
OFF 12
12–BITS
SAMPLE/HOLD
MSB
STROBE
CDAC
LSB
COMP
28
STS
1 VLOGIC ^+5V
+
10µF
0.1µF
15 DGND
100Ω
R1
VREF
OUT 8
REF
AMP
REF
OFFSET/GAIN
TRIM NETWORK
100Ω
R2
10
VREF
IN
VCC 7 ₊
10µF
+15V
VEE 11
0.1µF
9
AGND
N.C.
Figure 3. Bipolar Input Connections
SP574B/674B/1674B/774B
12–Bit Sampling A/D Converters
8
© Copyright 2000 Sipex Corporation