HCPL-0872-000E Datasheet, PDF (6/12 Pages) AVAGO TECHNOLOGIES LIMITED – Digital Interface IC

Applications Information
Digital Current Sensing
As shown in Figure 1, using the Isolated 2-chip A/D
converter to sense current can be as simple as connect-
ing a current-sensing resistor, or shunt, to the input and
reading output data through the 3-wire serial output
interface. By choosing the appropriate shunt resistance,
any range of current can be monitored, from less than 1
A to more than 100 A.
Even better performance can be achieved by fully
utilizing the more advanced features of the Isolated
A/D converter, such as the pre-trigger circuit, which
can reduce conversion time to less than 1µs, the fast
over-range detector for quickly detecting short circuits,
different conversion modes giving various resolution/
speed trade-offs, offset calibration mode to eliminate
initial offset from measurements, and an adjustable
threshold detector for detecting non-short circuit
overload conditions.
Product Description
The Digital Interface IC, HCPL-0872 converts the single-
bit data stream from the Isolated Modulator (such as
HCPL-7860/786J/7560) into fifteen-bit output words and
provides a serial output interface that is compatible with
SPI^®, QSPI^®, and Microwire^® protocols, allowing direct con-
nection to a microcontroller. A second multiplexed input
is available to allow measurements with a second isolated
modulator without additional hardware.
The Digital Interface IC, HCPL-0872 can used together
with Isolated Modulator, HCPL-7860/786J/7560 to form
an isolated programmable two-chip analog-to-digital
converter. The primary functions of the HCPL-0872 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 resolu-
tion to achieve the desired level of performance. Other
functions of the HCPL-0872 Digital Interface IC include
a Phase Locked Loop based pre-trigger circuit that can
either give more precise control of the effective sampling
time or reduce conversion time to less than 1µs, 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 adjust-
able 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.
NON-ISOLATED
+5V
INPUT
CURRENT
+
R _SHUNT
0.02
ISOLATED
+5V
C1
0.1 µF
V _DD1
V _IN+
V _IN-
GND1
V _DD2
MCLK
MDAT
GND2
HCPL-7860
HCPL-786J
HCPL-7560
Figure 1. Typical Application Circuit.

C2
0.1 µF
CCLK
CLAT
CDAT
MCLK1
MDAT1
MCLK2
MDAT2
GND
V _DD
CHAN
SCLK
SDAT
CS
THR1
OVR1
RESET
HCPL-0872
3-WIRE
SERIAL
INTERFACE
+
C3
10 µF