20
The primary functions of the
HCPL-x870 Digital Interface IC
are to derive a multi-bit output
signal by averaging the single-bit
modulator data, as well as to
provide a direct microcontroller
interface. The effective resolution
of the multi-bit output signal is a
function of the length of time
(measured in modulator clock
cycles) over which the average is
taken; averaging over longer
periods of time results in higher
resolution. The Digital Interface
IC can be configured for five
conversion modes which have
different combinations of speed
and resolution to achieve the
desired level of performance.
effective sampling time or reduce
conversion time to less than 1 µs,
a fast over-range detection circuit
that rapidly indicates when the
magnitude of the input signal is
beyond full-scale, an adjustable
threshold detection circuit that
indicates when the magnitude of
the input signal is above a user-
adjustable threshold level, an
offset calibration circuit, and a
second multiplexed input that
allows a second Isolated
Applications
Information
Product Description
The HCPL-7860/HCPL-786J
Isolated Modulator (optocoupler)
uses sigma-delta modulation to
convert an analog input signal
into a high-speed (10 MHz)
single-bit digital data stream; the
time average of the modulator’s
single-bit data is directly
proportional to the input signal.
The isolated modulator’s other
main function is to provide
galvanic isolation between the
analog input and the digital
output. An internal voltage
reference determines the full-
scale analog input range of the
modulator (approximately
± 320 mV); an input range of
± 200 mV is recommended to
achieve optimal performance.
Modulator to be used with a
single Digital Interface IC.
The digital output format of the
Isolated A/D Converter is 15 bits
of unsigned binary data. The
input full-scale range and code
assignment is shown in Table 1
below. Although the output con-
tains 15 bits of data, the effective
resolution is lower and is deter-
mined by selected conversion
mode as shown in Table 2 below.
Other functions of the HCPL-
x870 Digital Interface IC include
a Phase Locked Loop based pre-
trigger circuit that can either give
more precise control of the
Table 1. Input Full-Scale Range and Code Assignment.
Analog Input
Full Scale Range
Minimum Step Size
+Full Scale
Voltage Input
640 mV
Digital Output
32768 LSBs
20 µV
+320 mV
0 mV
1 LSB
111111111111111
100000000000000
000000000000000
Zero
-Full Scale
-320 mV
Table 2. Isolated A/D Converter Typical Performance Characteristics.
Conversion Time (µs)
Pre-Trigger Mode
Signal-to-
Noise Ratio
(dB)
Effective
Resolution
(bits)
Signal
Bandwidth
(kHz)
Signal
Delay
(µs)
103
52
20
11
6
Conversion
Mode
0
1
103
52
20
11
6
2
1
2
3
4
5
83
79
73
66
53
13.5
12.8
11.9
10.7
8.5
206
104
40
21
11
3.4
6.9
22
45
90
0.8
Note: Bold italic type indicates Default values.
ETC [ ETC ]
