ISC300 Datasheet, PDF (5/11 Pages) Burr-Brown (TI) – Universal Precision Isolated MEASUREMENT CHANNEL

PGA
The programmable gain amplifier allows the user to digitally
select device gains of 0.5 and 50, allowing input ranges of
±0.1V or, ±10V full scale. When used in conjunction with
the 0.1V, 10V and common references, channel calibration
can be performed.
Isolated Supplies
Two 13V isolated supplies, capable of supplying 5mA each,
are available to power signal conditioning circuitry.
OUTPUT SECTION
The output section passes power across the isolation barrier
to provide the isolated supplies, and demodulates the signal
transmitted back across the isolation barrier.
ABOUT THE BARRIER
For any isolation product, barrier integrity is of paramount
importance in achieving high reliability. The ISC300 uses
miniature transformers designed to give maximum isolation
performance when encapsulated in a high dielectric strength
material. The device is designed so that the barrier is located
at the center of the package.
HIGH VOLTAGE TESTING
Burr-Brown Corporation has adopted a partial discharge test
criterion that conforms to the German VDE0884 Opto-
coupler Standards. This method requires the measurement of
minute current pulses (< 5pC) while applying 800Vrms,
60Hz high-voltage stress across every device isolation
barrier. During a two second test partial discharge must
occur five times on five separate half cycles of 60Hz,
and each time occurrence must not be separated by a line
period of more than four half cycles in order to produce a
partial discharge fail. This confirms transient overvoltage
(1.6 x V_rated) protection without damage. Life-test results
verify the absence of failure under continuous rated voltage
and maximum temperature.
This new test method represents the “state-of-the-art” for
nondestructive high voltage reliability testing. It is based on
the effects of non-uniform fields existing in heterogeneous
dielectric material during barrier degradation. In the case of
void non-uniformities, electric field stress begins to ionize
the void region before bridging the entire high voltage
barrier.
The transient conduction of charge during and after the
ionization can be detected externally as a burst of 0.01µs –
0.1µs current pulses that repeat on each AC voltage cycle.
The minimum AC barrier voltage that initiates partial dis-
charge is defined as the “inception voltage.” Decreasing the
barrier voltage to a lower level is required before partial
discharge ceases and is defined as the “extinction voltage.”
We have designed and characterized the package to yield an
inception voltage in excess of 800Vrms so that transient
overvoltages below this level will not cause any damage.
The extinction voltage is above 500Vrms so that even
overvoltage-induced partial discharge will cease once the
barrier voltage is reduced to the rated level. Older high
voltage test methods relied on applying a large enough
overvoltage (above rating) to catastrophically break down
marginal parts, but not so high as to damage good ones. Our
new partial discharge testing gives us more confidence in
barrier reliability than breakdown/no breakdown criteria.
BASIC OPERATION
SIGNAL AND SUPPLY CONNECTIONS
As with any mixed signal analog and digital signal compo-
nent, correct decoupling and signal routing precautions must
be observed to optimize performance. The ISC300 has an
internal 0.1µF decoupling capacitor at V_CC, so additional
V_CC decoupling will not be necessary. However, a ground
plane will minimize potential noise problems. If a low
impedance ground plane is not used, Com 2 should be tied
directly to the ground at the supply. It is not necessary to
connect DCom 2 and Com 2 at the device. Layout practices
associated with isolation signal conditioners are very impor-
tant. The capacitance associated with the barrier and series
resistance in the signal and reference leads must be mini-
mized. Any capacitance across the barrier will increase AC
leakage, and in conjunction with ground line resistance, may
degrade high frequency IMR, see Figure 2.
INPUT CONFIGURATION
The ISC300 allows easy configuration for temperature mea-
surement using an RTD. Figure 3 shows the basic connec-
tions for RTD operation. The two reference currents excite
the resistance transducer and a current-to-voltage conver-
sion is made corresponding to the resistance value of the
transducer. If a gain of 50 is selected, a 10Ω resistance value
results in a (10 • 200µA) • 50 = 0.1V output; the 500Ω full
scale value gives a (500 • 200µA) • 50 = 5V output. The
connection of the sense line allows open circuit sensor
detection. An open circuit will give a corresponding > 5.1V
output. A short circuit will give a corresponding < 0.1V
output. See the Applications section under Fault Conditions
for more information.
Com 1
C_INT
Com 2
C_EXT
R
V_ISO
FIGURE 2. Barrier Capacitance.
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ISC300