As shown in Figure 17, 0.1
µF
bypass capacitors (C1, C2)
should be located as close as
possible to the pins of the
HCPL-7520. The bypass
capacitors are required because
of the high-speed digital nature
of the signals inside the HCPL-7520.
A 0.01
µF
bypass capacitor (C2) is
also recommended at the input due
to the switched-capacitor nature
of the input circuit. The input
bypass capacitor also forms part
of the anti-aliasing filter, which is
recommended to prevent high
frequency noise from aliasing down to
lower frequencies and interfering
with the input signal. The input filter
also performs an important
reliability function—it reduces
transient spikes from ESD events
flowing through the current
sensing resistor.
PC Board Layout
The design of the printed circuit
board (PCB) should follow good
layout practices, such as keeping
bypass capacitors close to the
supply pins, keeping output
signals away from input signals,
the use of ground and power
planes, etc. In addition, the
layout of the PCB can also affect
the isolation transient immunity
(CMTI) of the HCPL-7520,
due primarily to stray capacitive
coupling between the input and
the output circuits. To obtain
optimal CMTI performance, the
layout of the PC board should
minimize any stray coupling by
maintaining the maximum
possible distance between the
input and output sides of the
circuit and ensuring that any
ground or power plane on the
PC board does not pass directly
below or extend much wider than
the body of the HCPL-7520.
FLOATING
POSITIVE
SUPPLY
HV+
GATE DRIVE
CIRCUIT
U1
78L05
IN
C1
0.1 µF
OUT
C2
0.1 µF
R5
68
Ω
MOTOR
+ R1 -
R
SENSE
C3
0.01 µF
1 V
DD1
2 V
IN+
3 V
IN-
4 GND1
V
DD2
8
V
OUT
7
V
REF
6
GND2 5
C4
C5
C6
A/D
V
REF
GND
+5 V
µC
HCPL-7520
C6 = 150 pF
C4 = C5 = 0.1 µF
HV-
Figure 17. Recommended HCPL-7520 application circuit.
11
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
