Digital Current Sensing
Circuit
shunt resistance, any range of
current can be monitored, from
less than 1 A to more than 100 A.
than 1 µs, the fast over-range
detector for quickly detecting
short circuits, different conversion
modes giving various resolution/
speed trade-offs, offset calibra-
tion mode to eliminate initial
offset from measurements, and
an adjustable threshold detector
for detecting non-short circuit
overload conditions.
As shown in Figure 1, using the
Isolated 2-chip A/D converter to
sense current can be as simple as
connecting a current-sensing
resistor, or shunt, to the input
and reading output data through
the 3-wire serial output interface.
By choosing the appropriate
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
NON-ISOLATED
+ 5 V
ISOLATED
+ 5 V
CCLK
CLAT
V
DD
CHAN
+
V
V
V
V
CDAT
MCLK1
MDAT1
MCLK2
MDAT2
GND
SCLK
SDAT
CS
DD1
IN+
IN-
DD2
INPUT
CURRENT
3-WIRE
SERIAL
INTERFACE
MCLK
MDAT
R
SHUNT
0.02
C1
0.1 µF
+
THR1
OVR1
RESET
C2
0.1 µF
GND1 GND2
HCPL-7860
C3
10 µF
HCPL-x870
Figure 1: Typical Application Circuit.
®
that is compatible with SPI ,
low-bandwidth analog input into
a high-speed one-bit data stream
by means of a sigma-delta ( ∆)
Product Overview
Description
®
®
QSPI , and Microwire proto-
cols, allowing direct connection
to a microcontroller. The Digital
Interface IC is available in two
package styles: the HCPL-7870 is
in a 16-pin DIP package and the
HCPL-0870 is in a 300-mil wide
SO-16 surface-mount package.
Features of the Digital Interface
IC include five different conver-
sion modes, three different pre-
trigger modes, offset calibration,
fast over-range detection, and
adjustable threshold detection.
Programmable features are con-
figured via the Serial Configura-
tion port. A second multiplexed
input is available to allow
∑
The HCPL-7860 Isolated Modu-
lator and the HCPL-x870 Digital
Interface IC together form an
isolated programmable two-chip
analog-to-digital converter. The
isolated modulator allows direct
measurement of motor phase
currents in power inverters while
the digital interface IC can be
programmed to optimize the
conversion speed and resolution
trade-off.
oversampling modulator. This
modulation provides for high
noise margins and excellent
immunity against isolation-mode
transients. The modulator data
and on-chip sampling clock are
encoded and transmitted across
the isolation boundary where they
are recovered and decoded into
separate high-speed clock and
data channels.
The Digital Interface IC converts
the single-bit data stream from
the Isolated Modulator into
fifteen-bit output words and
provides a serial output interface
In operation, the HCPL-7860
Isolated Modulator (optocoupler
with 3750 V
dielectric with-
RMS
stand voltage rating) converts a
measurements with a second
1-261
HP [ HEWLETT-PACKARD ]
