Datasheet

15
Analog Interfacing
Power Supplies and Bypassing
The recommended supply con-
nections are shown in Figure 26.
A floating power supply (which
in many applications could be
the same supply that is used to
drive the high-side power
transistor) is regulated to 5 V
using a simple zener diode (D1);
the value of resistor R4 should
be chosen to supply sufficient
Figure 25. Recommended applications circuit.
Figure 26. Recommended supply and sense resistor connections.
current from the existing
floating supply. The voltage from
the current sensing resistor
(Rsense) is applied to the input
of the HCPL-788J through an RC
anti-aliasing filter (R2 and C2).
Although the application
circuit is relatively simple, a
few recommendations should
be followed to ensure optimal
performance.
The power supply for the
HCPL-788J is most often obtained
from the same supply used to
power the power transistor gate
drive circuit. If a dedicated
supply is required, in many
cases it is possible to add an
additional winding on an
existing transformer. Otherwise,
some sort of simple isolated
supply can be used, such as a
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
LED1+
V
DD1
GND
1
R
SHUNT
0.02
Ω
ISOLATED +5 V
R3 4.7 k
Ω
R2
39
Ω
.01 µF
C3
0.1 µF
C1
0.1 µF
HCPL-788J
INPUT
CURRENT
+5 V
A/D
V
REF
GND
µC
TO OTHER
PHASE OUTPUTS
+
R1
C2
C6
0.1 µF
C4C8 C7 C5
C5 = C7 = C8 = 470 pF
C4 = 0.1 µF
16
15
14
13
12
11
10
9
5
1
2
8
7
3
4
6
GND
2
V
DD2
FAULT
ABSVAL
V
OUT
V
REF
V
DD2
GND
2
V
DD1
V
IN+
V
IN-
GND
1
V
DD1
C
H
C
L
V
LED+
R2
39 Ω
+
R4
C1
0.1 µF
C2
0.01 µF
FLOATING
POWER
SUPPLY
HV+
+
–
+
R1
R
SENSE
HV-
MOTOR
D1
5.1 V
GATE DRIVE
CIRCUIT
HCPL-788J