HCPL-7860 Datasheet, PDF (19/28 Pages) Agilent(Hewlett-Packard) – Isolated 15-bit A/D Converter

Applications
Information
Product Description
The HCPL-7860 Isolated Modula-
tor (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.
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.
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
Zero
-Full Scale
Voltage Input
640 mV
20 µV
+320 mV
0 mV
-320 mV
Digital Output
32768 LSBs
1 LSB
111111111111111
100000000000000
000000000000000
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
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.
Table 2. Isolated A/D Converter Typical Performance Characteristics.
Conversion
Mode
Signal-to-
Noise Ratio
(dB)
Effective
Resolution
(bits)
Conversion Time (µs)
Pre-Trigger Mode
0
1
2
Signal
Delay
(µs)
1
83
13.5
188
94
94
2
79
12.8
95
47
47
3
73
11.9
37
18
0.7
18
4
66
10.7
19
10
10
5
53
8.5
10
5
5
Note: Bold italic type indicates Default values.
Signal
Bandwidth
(kHz)
3.4
6.9
22
45
90
1-278