3-58
TELCOM SEMICONDUCTOR, INC.
5V PRECISION DATA ACQUISITION
SUBSYSTEMS
TC530
TC534
Figure 6. TC530/534 Typical Application
A0
A1
RESET
EOC
VCCD
VCCD
VDD
VDD
D
OUT
D
CLK
X1: 2MHz
R2
100k
R1
100k
100
1
μ
F
TC04
(1.25V V
REF
)
(1.03V)
D
IN
R/W
ACOM
OSC
IN
OSC
OUT
V
SS
DGND
C
AZ
C
AZ
0.22
μ
F
C
IN
0.33
μ
F
R
I
NT
100k
TC534
C
INT
Analog
Inputs
Channel
Control
C1
.01
μ
F
10
μ
F
MUX
IN1 +
IN1 –
IN2
+
IN2
–
IN3
+
IN3
–
IN4
+
IN4
–
+5V
+5V
–5V
(Optional)
BUF
V
REF
+
V
REF
–
+
C
REF
C
–
C
REF
0.22
μ
F
+
CAP
CAP
–
1
μ
F
+5V
INT
PROCESSOR
I/O
I/O
I/O
I/O
.01
μ
F
.01
μ
F
1
μ
F
3.
Calculate LOAD VALUE
LOAD VALUE = 256 – (t
INT
)(F
IN
)/1024 = [128]
10
[128]
10
= 80 hex
4.
Calculate R
INT
R
INT
(in M
) = V
INMAX
/20 = 2/20 = 100k
5.
Calculate C
INT
for maximum (4V) integrator out-
put swing
C
INT
(in
μ
F) = (t
INT
)(20 x 10
–6
)/ (V
S
– 0.9)
= (.066)(20 x 10
–6
)/(4.1)
= .32
μ
F (use closest value: 0.33
μ
F)
NOTE: TelCom recommended capacitor:
WIMA p/n: MK12 .33/63/10
6.
Choose C
REF
and C
AZ
based on conversion rate
Conversions/sec= 1/(t
AZ
+ t
INT
+ 2t
INT
+ 2msec)
= 1/(66msec + 66msec + 132msec
+ 2msec)
= 3.7 conversions/sec
from which C
AZ
= C
REF
= 0.22
μ
F (see Table 1)
NOTE: TelCom recommended capacitor:
WIMA p/n: MK12 .22/63/10
7.
Calculate V
REF
V
REF
(in Volts = (V
S
– 0.9)(C
INT
)(R
INT
)
2(t
INT
)
= (4.1)(0.33x10
–6
)(10
5
)/2(.066)
= 1.025V
Power Supply Sequencing
Improper sequencing of the power supply inputs (V
DD
vs. V
CCD
) can potentially cause an improper power-up
sequence to occur. See Circuit Design/Layout Consider-
ations below. Failing to insure a proper power-up sequence
can cause spurious operation.
Ciruit Design/Layout Considerations
(1) Separate ground return paths should be used for the
analog and digital circuitry. Use of ground planes and trace
fill on analog circuit sections is highly recommended
EXCEPTfor in and around the integrator section and
C
REF
, C
AZ
. (C
INT
, C
REF
, C
AZ
, R
INT
). Stray capacitance be-
tween these nodes and ground appears in parallel with the
components themselves and can affect measurement accu-
racy.