7

®

ISO166/ISO176

ISO176 can also be synchronized to a 400kHz to 700kHz

Square-Wave External Clock since an internal clamp and

filter provide signal conditioning. A square-wave signal of

25% to 75% duty cycle, and

±3V to ±20V level can be used

to directly drive the ISO176.

With the addition of the signal conditioning circuit shown in

Figure 2, any 10% to 90% duty-cycle square-wave signal

can be used to drive the ISO166 and ISO176 Ext Osc pin.

With the values shown, the circuit can be driven by a

4Vp-p TTL signal. For a higher or lower voltage input,

increase or decrease the 1k

Ω resistor, R

e.g. for a

±4V square-wave (8Vp-p) R

to 2k

Ω. The value of C

30pF for ISO176 and 680pF for ISO166.

When periodic noise from external sources such as system

clocks and DC/DC converters are a problem, ISO166 and

ISO176 can be used to reject this noise. The amplifier can be

synchronized to an external frequency source, f

the amplifier response curve at one of the frequency and

amplitude nulls indicated in the “Signal Response vs Carrier

Frequency” performance curve.

ISOLATION MODE VOLTAGE

Isolation Mode Voltage (IMV) is the voltage appearing

between isolated grounds GND1 and GND2. The IMV can

induce error at the output as indicated by the plots of IMV

versus Frequency. It should be noted that if the IMV fre-

puts in a manner similar to that described above, and the

amplifier response will be identical to that shown in the

“Signal Response vs Carrier Frequency” performance curve.

This occurs because IMV-induced errors behave like input-

referred error signals. To predict the total IMR, divide the

isolation voltage by the IMR shown in “IMR vs Frequency”

performance curve and compute the amplifier response to

this input-referred error signal from the data given in the

“Signal Response vs Carrier Frequency” performance curve.

Due to effects of very high-frequency signals, typical IMV

performance can be achieved only when dV/dT of the

isolation mode voltage falls below 1000V/

µs. For conve-

nience, this is plotted in the typical performance curves for

the ISO166 and ISO176 as a function of voltage and fre-

quency for sinusoidal voltages. When dV/dT exceeds

1000V/

µs but falls below 20kV/µs, performance may be

degraded. At rates of change above 20kV/

µs, the amplifier

may be damaged, but the barrier retains its full integrity.

Lowering the power supply voltages below

±15V may

decrease the dV/dT to 500V/

µs for typical performance, but

the maximum dV/dT of 20kV/

µs remains unchanged.

Leakage current is determined solely by the impedance of

the barrier capacitance and is plotted in the “Isolation Leak-

age Current vs Frequency” curve.

ISOLATION VOLTAGE RATINGS

Because a long-term test is impractical in a manufacturing

situation, the generally accepted practice is to perform a

production test at a higher voltage for some shorter time.

The relationship between actual test voltage and the continu-

ous derated maximum specification is an important one.

Historically, Burr-Brown has chosen a deliberately conser-

vative one: VTEST = (2 x ACrms continuous rating) +

1000V for 10 seconds, followed by a test at rated ACrms

voltage for one minute. This choice was appropriate for

conditions where system transients are not well defined.

Recent improvements in high-voltage stress testing have

produced a more meaningful test for determining maximum

permissible voltage ratings, and Burr-Brown has chosen to

apply this new technology in the manufacture and testing of

the ISO166 and ISO176.

CARRIER FREQUENCY CONSIDERATIONS

ISO166 and ISO176 amplifiers transmit the signal across the

ISO-barrier by a duty-cycle modulation technique. This

system works like any linear amplifier for input signals

For signal frequencies above f

more complex. The Signal Response versus Carrier Fre-

quency performance curve describes this behavior graphi-

cally. The upper curve illustrates the response for input

signals varying from DC to f

that varies in both amplitude and frequency, as shown by the

lower curve. The lower horizontal scale shows the periodic

variation in the frequency of the output component. Note

that at the carrier frequency and its harmonics, both the

frequency and amplitude of the response go to zero. These

characteristics can be exploited in certain applications.

It should be noted that for the ISO176, the carrier frequency

is nominally 500kHz and the –3dB point of the amplifier is

60kHz. Spurious signals at the output are not significant

under these circumstances unless the input signal contains

significant components above 250kHz.

For the ISO166, the carrier frequency is nominally 110kHz

and the –3dB point of the amplifier is 6kHz.

FIGURE 2. Square-Wave to Triangle Wave Signal Condi-

tioner for Driving ISO166/176 Ext Osc Pin.

10k

Ω

C

X

OPA602

R

X

1k

Ω

1µF

Square-Wave In

Triangle Out

to ISO166/176

Ext Osc