®

ISC300

5

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

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 0.01

µs –

0.1

µs 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 0.1

µF decoupling capacitor at V

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 10

Ω resistance value

results in a (10 • 200

µA) • 50 = 0.1V output; the 500Ω full

scale value gives a (500 • 200

µA) • 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.

FIGURE 2. Barrier Capacitance.

C

INT

C

EXT

Com 2

Com 1

V

ISO

R