HCPL788J Datasheet, PDF (2/20 Pages) Agilent(Hewlett-Packard) – Isolation Amplifier with Short Circuit and Overload Detection

2
Description
The HCPL-788J isolation amplifier
is designed for current sensing in
electronic motor drives. In a
typical implementation, 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 con-
ISOLATION BOUNDARY
ditions on any of the motor
phases. The wire-OR-able rectified
output (ABSVAL), simplifies
measurement 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).
INPUT
+
CURRENT _RSHUNT
0.02 Ω
39 Ω
.01 µF
0.1 µF
ISOLATED +5 V
0.1 µF
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
Figure 1. Current Sensing Circuit.
Pin Descriptions
Symbol
Description
V_IN+ Positive input voltage (± 200 mV
recommended).
V_IN- Negative input voltage (normally
connected to GND₁).
C_H
C_L
V_DD1
Internal Bias Node. Connections to or
between C_H and C_L other than the re-
quired 0.1 µF capacitor shown, are not
recommended.
Supply voltage input (4.5 V to 5.5 V).
V_LED+
LED anode. This pin must be left uncon-
nected for guaranteed data sheet perfor-
mance. (For optical coupling testing only.)
V_DD1 Supply voltage input (4.5 V to 5.5 V).
GND₁ Ground input.
+5 V
Symbol
Description
GND₂
V_DD2
FAULT
Ground input.
Supply voltage input (4.5 V to 5.5 V).
Short circuit fault output. FAULT changes
from a high to low output voltage within
6 µs after V_IN exceeds the FAULT Detec-
tion 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
V_REF
Voltage output. Swings from 0 to V_REF.
The nominal gain is V_REF /504 mV.
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).
GND₂ Ground input.