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HCPL-7820 参数 Datasheet PDF下载

HCPL-7820图片预览
型号: HCPL-7820
PDF下载: 下载PDF文件 查看货源
内容描述: 高CMR模拟隔离放大器 [High CMR Analog Isolation Amplifiers]
分类和应用: 隔离放大器光电二极管分离技术隔离技术
文件页数/大小: 15 页 / 229 K
品牌: HP [ HEWLETT-PACKARD ]
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the HCPL-7820/7825 through an  
RC anti-aliasing filter (R5, C3).  
And finally, the differential output  
of the isolation amplifier is con-  
verted to a ground-referenced  
single-ended output voltage with a  
simple differential amplifier  
circuit (U3 and associated  
components). Although the  
application circuit is relatively  
simple, a few recommendations  
should be followed to ensure  
optimal performance.  
Inductive coupling between the  
input power-supply bypass  
capacitor and the input circuit,  
which includes the input bypass  
capacitor and the input leads of  
the HCPL-7820/7825, can  
induced voltage spikes which  
could adversely affect operation),  
and reasonable tolerance (to  
maintain overall circuit accuracy).  
The value of the shunt should be  
chosen as a compromise between  
minimizing power dissipation by  
making the shunt resistance  
introduce additional DC offset in  
the circuit. Several steps can be  
taken to minimize the mutual  
coupling between the two parts of  
the circuit, thereby improving the  
offset performance of the design.  
Separate the two bypass capaci-  
tors C2 and C3 as much as  
possible (even putting them on  
opposite sides of the PC board),  
while keeping the total lead  
lengths, including traces, of each  
bypass capacitor less than 20  
mm. PC board traces should be  
made as short as possible and  
placed close together or over  
ground plane to minimize loop  
area and pickup of stray magnetic  
fields. Avoid using sockets, as  
they will typically increase both  
loop area and inductance. And  
finally, using capacitors with  
small body size and orienting  
them perpendicular to each other  
on the PC board can also help.  
For more information concerning  
inductive coupling, see the  
smaller and improving circuit  
accuracy by making it larger and  
using more of the input range of  
the HCPL-7820/7825. Hewlett-  
Packard recommends 4 different  
shunts which can be used to sense  
average currents in motor drives  
up to 35 A and 35 hp. Table 1  
shows the maximum current and  
horsepower range for each of the  
LVR-series shunts from Dale.  
Even higher currents can be  
sensed with lower value shunts  
available from vendors such as  
Dale, IRC, and Isotek (Isabellen-  
huette). When sensing currents  
large enough to cause significant  
heating of the shunt, the tempera-  
ture coefficient of the shunt can  
introduce nonlinearity due to the  
amplitude dependent temperature  
rise of the shunt. Using a heat  
sink for the shunt or using a shunt  
with a lower tempco can help  
minimize this effect. The  
Supplies and Bypassing  
As mentioned above, an inexpen-  
sive 78L05 three-terminal regula-  
tor can be used to reduce the  
gate-drive power 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.  
As shown in Figure 24, 0.1 µF  
bypass capacitors (C2, C4) should  
be located as close as possible to  
the input and output power supply  
pins of the HCPL-7820/7825. The  
bypass capacitors are required  
because of the high-speed digital  
nature of the signals inside the  
isolation amplifier. A 0.01 µF  
bypass capacitor (C3) is also rec-  
ommended at the input pin(s) due  
to the switched-capacitor nature  
of the input circuit. The input  
bypass capacitor should be at  
least 1000 pF to maintain gain  
accuracy of the isolation amplifier.  
Application Note Designing with  
Hewlett-Packard Isolation  
Amplifiers.  
Application Note Designing with  
Hewlett-Packard Isolation  
Amplifiers contains additional  
information on designing with  
current shunts.  
Shunt Resistor Selection  
The current-sensing shunt resistor  
should have low resistance (to  
minimize power dissipation), low  
inductance (to minimize di/dt  
The recommended method for  
connecting the isolation amplifier  
to the shunt resistor is shown in  
Table 1. Current Shunt Summary  
Shunt Resistor  
Part Number  
Shunt  
Resistance  
Maximum  
Power Dissipation  
Maximum  
RMS Current  
Maximum  
Horsepower Range  
LVR-3.05-1%  
LVR-3.02-1%  
LVR-3.01-1%  
LVR-5.005-1%  
50 mΩ  
20 mΩ  
10 mΩ  
5 mΩ  
3 W  
3 W  
3 W  
5 W  
3 A  
8 A  
15 A  
35 A  
0.8-3.0 hp  
2.2-8.0 hp  
4.1-15 hp  
9.6-35 hp  
1-245