Application Information
Power Supplies and Bypassing
The recommended supply connections are shown in
Figure 16. A floating power supply (which in many ap-
plications 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 current from the
existing floating supply. The voltage from the current
sensing resistor (Rsense) is applied to the input of the
HCPL-7520 through an RC anti-aliasing filter (R2 and
C2). Although the application circuit is relatively simple,
a few recom- mendations should be followed to ensure
optimal performance.
The power supply for the HCPL -7520 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 ad-
ditional winding on an existing transformer. Otherwise,
some sort of simple isolated supply can be used, such
as a line powered transformer or a high-frequency DC-
DC converter.
An inexpensive 78L05 three-terminal regulator can also
be used to reduce the floating supply voltage to 5 V. To
help attenuate high- frequency power supply noise or
ripple, a resistor or inductor can be used in series with
the input of the regulator to form a low-pass filter with
the regulator’s input bypass capacitor.
HV+
GATE DRIVE
CIRCUIT
+
FLOATING
POSITIVE
SUPPLY
-
R4
R2
MOTOR
39
Ω
+ R1 -
R
SENSE
D1
5.1 V
C1
0.1 µF
1 V
DD1
2 V
IN+
3 V
IN-
4 GND1
C2
0.01 µF
HCPL-7520
HV-
Figure 16. Recommended supply and sense resistor connections.
11
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
