ACPL-C870 查看數據表（PDF） - Avago Technologies
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ACPL-C870 Datasheet PDF : 14 Pages
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Power Supplies and Bypassing
A power supply of 5 V is required to power the ACPL-C87x
input side VDD1. In many motor drive DC bus voltage
sensing applications, this 5 V supply is most often obtained
from the same supply used to power the power transistor
gate drive circuit using an inexpensive 78L05 three-ter-
minal regulator. 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.
In some other applications a dedicated supply might be
required to supply the VDD1. These applications include
photovoltaic (PV) inverter voltage tracking and measure-
ment, temperature sensor signal isolation. In these 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 module.
As shown in Figure 22, 100 nF bypass capacitors (C2, C3)
should be located as close as possible to the pins of the
isolation amplifier. The bypass capacitors are required
because of the high-speed digital nature of the signals
inside the isolation amplifier. A 100 pF bypass capacitor
(Cin) is also recommended at the input pins due to the
switched-capacitor nature of the input circuit. The input
bypass capacitor Cin also forms part of the anti-aliasing
filter, which is recommended to prevent high-frequency
noise from aliasing down to lower frequencies and inter-
fering with the input signal. When R1 is far greater than R2,
the low-pass anti-aliasing filter corner frequency can be
calculated by 1/(2R2Cin). The input filter also performs
an important reliability function – it reduces transient
spikes from ESD events flowing through the high voltage
rails.
HV+
Floating
Positive Supply
Gate Drive
Circuit
HV -
R1
IN
C1
0.1μF
78L05
OUT
C2
0.1μF
VDD1
5V
VDD2
VIN
VOUT+
ACPL-C87A
C3
R2
Cin
SHDN
0.1nF
VOUT- 0.1μF
GND1
GND2
Figure 22. Recommended Power Supply and Bypassing
13
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