HCPL-7840-300E Datasheet, PDF (14/19 Pages) AVAGO TECHNOLOGIES LIMITED – Isolation Amplifi er

Application Information
Power Supplies and Bypassing
The recommended supply con-nections are shown
in Figure 17. 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 current from
the existing floating supply. The voltage from the current
sensing resistor (Rsense) is applied to the input of the
HCPL-7840 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 -7840 is most often ob-
tained from the same supply used to power the power
transistor gate drive circuit. If a dedicated supply is re-
quired, 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
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
POWER
SUPPLY
–
R2
39 Ω
D1
5.1 V
MOTOR
•••
+ ^R1 –
R_SENSE
HV–
•••
C1
0.1 µF
C2
0.01 µF
HCPL-7840
Figure 17. Recommended supply and sense resistor connections.
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