HCPL7800 datasheet(16/17 Pages) HP

16 / 17 page

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Figure 28. HCPL-7800 Block Diagram.

Figure 29. PC Board Trace Pattern and Loading Diagram Example.

VOLTAGE

REGULATOR

CLOCK

GENERATOR

Σ∆

MODULATOR

ENCODER

LED DRIVE

CIRCUIT

DETECTOR

CIRCUIT

DECODER

AND D/A

FILTER

ISO-AMP

OUTPUT

VOLTAGE

REGULATOR

ISO-AMP

INPUT

ISOLATION

BOUNDARY

conflicting considerations,

therefore, must be weighed

against each other in selecting an

appropriate sense resistor for a

particular application. To

maintain circuit accuracy, it is

recommended that the sense

resistor and the isolation amplifier

circuit be located as close as

possible to one another. Although

it is possible to buy current-

sensing resistors from established

vendors (e.g., the LVR-1, -3 and

-5 resistors from Dale), it is also

possible to make a sense resistor

using a short piece of wire or

even a trace on a PC board.

Figures 30 and 31 illustrate the

response of the overall isolation

amplifier circuit shown in Figure

26. Figure 30 shows the response

of the circuit to a

± 200 mV 20

kHz sine wave input and Figure

31 the response of the circuit to a

± 200 mV 20 kHz square wave

input. Both figures demonstrate

the fast, well-behaved response of

the HCPL-7800.

Figure 32 shows how quickly the

isolation amplifier recovers from

an overdrive condition generated

by a 2 kHz square wave swinging

between 0 and 500 mV (note that

the time scale is different from

the previous figures). The first

wave form is the output of the

application circuit with the filter

capacitors removed to show the

actual response of the isolation

amplifier. The second wave form

is the response of the same circuit

with the capacitors installed. The

recovery time and overshoot are

relatively independent of the

amplitude and polarity of the

overdrive signal, as well as its

duration.

For more information, refer to

Application Note 1059.

HCPL7800 Datasheet(PDF) 16 Page - Agilent(Hewlett-Packard)

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