ISC300 Datasheet, PDF (4/11 Pages) Burr-Brown (TI) – Universal Precision Isolated MEASUREMENT CHANNEL

THEORY OF OPERATION
The ISC300 has no galvanic connection between the input
and output sections. The differential input signal is multi-
plied by the programmable gain amplifier and accurately
transferred across the isolation barrier to the output. The
output section demodulates the signal transferred from the
input section and transfers power to the input section.
ISC300 DESIGN
The ISC300 consists of:
• A filtered differential high impedance input.
• Precision matched current sources.
• Fault detect bias resistors.
• Digitally selectable internal calibration references.
• Digitally selectable gain.
• Isolation of all digital and analog signals.
• Isolated DC/DC converter.
• Synchronizable internal oscillator.
• Two isolated power supplies available for external cir-
cuitry.
• Externally available 10V reference.
INPUT SECTION
Filter
Since the ISC300 is designed to measure slowly changing
processes, the input filter is set for a cut off frequency of
2Hz. This gives good noise rejection at power frequencies of
50Hz and 60Hz.
Sense Lines
The two sense lines can be configured to detect short or open
circuits e.g. transducer burn out. This would be indicated by
an out of range output (see Input Configuration in Applica-
tions section).
Multiplexer
The multiplexer is used to route either the measurement
channel or the precision voltage references (used in system
calibration) to the programmable gain amplifier.
Isolation Barrier
The isolation barrier consists of two transformers and three
opto couplers. One transformer transmits the signal from the
input side to the output side. The other transmits power from
the output side to the input side. The opto-couplers are used
to isolate the logic used for mux select, gain and reference
voltage control.
Voltage Reference
The voltage reference provides 10V, 0.1V and 0V references
for channel calibration. The 10V reference is also available
externally.
Current References
Two matched 200µA current references are available for the
excitation of RTDs or for use in external signal conditioning
circuitry.
9 +V_ISO
2 –V_ISO
8 Sense 2
5
+I_P
6
–I_P
3 Sense 1
1
V_REF
4
I_REF1
7
I_REF2
10 Com 1
20M
+V_ISO
Filter
Channel 1 Out
20M
–V_ISO
Ref
10.0V
MUX
Channel 2
99R
0.100V
Channel 3
Current
Reference
–V_ISO
R
Com₁
Channel 4
A₁
A₀
PGA
FIGURE 1. ISC300 Block Diagram.
Input Side
Barrier
Modulate
Demod
Rectify
Power
Com 1
O
P
T
O
Com 2
C
O
L
U
P
A
T
L
C
E
H
Output Side
Out
28
V_CC (+15) 25
CKI
26
Com 2 27
V_DD (+5) 18
CLK
22
G
19
A₀
20
A₁
21
RST
23
DCom 2 24
®
ISC300
4