HCPL-788J Datasheet, PDF (2/20 Pages) AVAGO TECHNOLOGIES LIMITED – Isolation Amplifier with Short Circuit and Overload Detection SO-16 Package

Description
The HCPL-788J isolation ampli-fier is designed for cur-
rent sensing in electronic motor drives. In a typical
implementa-tion, motor currents flow through an ex-
ternal resistor and the resulting analog voltage drop is
sensed by the HCPL-788J. A larger analog output volt-
age is created on the other side of the HCPL-788J’s opti-
cal 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 of the motor phases. The wire-OR-able rectified
output (ABSVAL), simplifies measure-ment of motor load
since it performs polyphase rectification. Since the com-
mon-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).
INPUT
+
CURRENT _RSHUNT
0.02 Ω
39 Ω
.01 μF
0.1 μF
ISOLATED +5 V
0.1 μF
Figure 1. Current sensing circuit.
ISOLATION BOUNDARY
1 V_IN+
HCPL-788J
GND₂ 16
2 V_IN-
V_DD2 15
3 C_H
FAULT 14
4 C_L
ABSVAL 13
5 V_DD1
V_OUT 12
6 V_LED+
V_REF 11
7 V_DD1
V_DD2 10
8 GND₁
GND₂ 9
μC
0.1 μF
4.7 kΩ
TO OTHER
PHASE
OUTPUTS
A/D
V_REF
GND
+5 V
Pin Descriptions
Symbol
V
IN+
V
IN-
C
H
C
L
Description
Positive input voltage (±200 mV recommended).
Negative input voltage (normally connected to
GND ).
1
Internal Bias Node. Connections to or between C
H
and C other than the required 0.1 μF capacitor
L
shown, are not recommended.
V_DD1
V
LED+
V
DD1
GND
1
GND
2
V
DD2
Supply voltage input (4.5 V to 5.5 V).
LED anode. This pin must be left unconnected for
guaranteed data sheet performance. (For optical
coupling testing only.)
Supply voltage input (4.5 V to 5.5 V).
Ground input.
Ground input.
Supply voltage input (4.5 V to 5.5 V).
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 output. ABSVAL is 0 V
OUT
when V =0 and increases toward V as V
IN
REF
IN
approaches +256 mV or -256 mV. ABSVAL is
“wired-OR” able and is used for detecting
overloads.
V_OUT
V
REF
V
DD2
GND
2
Voltage output. Swings from 0 to V_REF.
The nominal gain is V /504 mV.
REF
Reference voltage input (4.0 V to V ). This
DD2
voltage establishes the full scale output ranges
and gains of V and ABSVAL.
OUT
Supply voltage input (4.5 V to 5.5 V).
Ground input.
2