Datasheet

2
Description
The HCPL-788J isolation ampli-
fier is designed for current
sensing in electronic motor
drives. In a typical implementa-
tion, motor currents flow
through an external resistor and
the resulting analog voltage drop
is sensed by the HCPL-788J. A
larger analog output voltage is
created on the other side of the
HCPL-788J’s optical isolation
barrier. The output voltage is
proportional to the motor
current and can be connected
directly to a single-supply A/D
converter. A digital over-range
output (FAULT) and an analog
rectified output (ABSVAL) are
also provided. The wire OR-able
over-range output (FAULT) is
useful for quick detection of
short circuit conditions on any
Figure 1. Current sensing circuit.
of the motor phases. The wire-
OR-able rectified output
(ABSVAL), simplifies measure-
ment of motor load since it
performs polyphase rectification.
Since the common-mode voltage
swings several hundred volts in
tens of nanoseconds in modern
electronic motor drives, the
HCPL-788J was designed to
ignore very high common-mode
transient slew rates (10 kV/µs).
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
GND
2
V
DD2
FAULT
ABSVAL
V
OUT
V
REF
V
DD2
GND
2
V
IN+
V
IN-
C
H
C
L
V
DD1
V
LED+
V
DD1
GND
1
R
SHUNT
0.02
Ω
ISOLATED +5 V
4.7 k
Ω
39
Ω
.01 µF
0.1 µF
0.1 µF
ISOLATION BOUNDARY
INPUT
CURRENT
+5 V
A/D
V
REF
GND
µC
TO OTHER
PHASE
OUTPUTS
+
0.1 µF
HCPL-788J
Symbol Description
FAULT Short circuit fault output. FAULT changes from a high
to low output voltage within 6 µs after V
IN
exceeds
the FAULT Detection Threshold. FAULT is an open
drain output which allows outputs from all the
HCPL-788Js in a circuit to be connected together
(“wired-OR”) forming a single fault signal for
interfacing directly to the micro-controller.
ABSVAL Absolute value of V
OUT
output. ABSVAL is 0 V
when V
IN
=0 and increases toward V
REF
as V
IN
approaches +256 mV or -256 mV. ABSVAL is
“wired-OR” able and is used for detecting
overloads.
V
OUT
Voltage output. Swings from 0 to V
REF
.
The nominal gain is V
REF
/504 mV.
V
REF
Reference voltage input (4.0 V to V
DD2
). This
voltage establishes the full scale output ranges
and gains of V
OUT
and ABSVAL.
V
DD2
Supply voltage input (4.5 V to 5.5 V).
GND
2
Ground input.
Symbol Description
V
IN+
Positive input voltage (±200 mV recommended).
V
IN-
Negative input voltage (normally connected to
GND
1
).
C
H
Internal Bias Node. Connections to or between C
H
C
L
and C
L
other than the required 0.1 µF capacitor
shown, are not recommended.
V
DD1
Supply voltage input (4.5 V to 5.5 V).
V
LED+
LED anode. This pin must be left unconnected for
guaranteed data sheet performance. (For optical
coupling testing only.)
V
DD1
Supply voltage input (4.5 V to 5.5 V).
GND
1
Ground input.
GND
2
Ground input.
V
DD2
Supply voltage input (4.5 V to 5.5 V).
Pin Descriptions