ACPL-796J-060E 데이터 시트보기 (PDF) - Avago Technologies
부품명
상세내역
제조사
ACPL-796J-060E Datasheet PDF : 16 Pages
| |||
Table 11. Isotek (Isabellenhütte) four-terminal shunt summary.
Shunt Resistor
Part Number
PBV-R050-0.5
Shunt
Resistance
Tol.
m
%
50
0.5
Maximum
RMS Current
A
3
PBV-R020-0.5
20
0.5
7
PBV-R010-0.5
10
PBV-R005-0.5
5
0.5
14
0.5
25 [28]
PBV-R002-0.5
2
0.5
Note: Values in brackets are with a heatsink for the shunt.
39 [71]
Motor Power Range
120 VAC - 440 VAC
hp
0.8 - 3
2-7
4 - 14
7 - 25 [8 - 28]
11 - 39 [19 - 71]
kW
0.6 - 2
0.6 - 2
3 - 10
5 - 19 [6 - 21]
8 - 29 [14 - 53]
When laying out a PC board for the shunts, a couple of
points should be kept in mind. The Kelvin connections to
the shunt should be brought together under the body
of the shunt and then run very close to each other to the
input of the isolated modulator; this minimizes the loop
area of the connection and reduces the possibility of stray
magnetic fields from interfering with the measured signal.
If the shunt is not located on the same PC board as the
isolated modulator circuit, a tightly twisted pair of wires
can accomplish the same thing.
Also, multiple layers of the PC board can be used to increase
current carrying capacity. Numerous plated-through vias
should surround each non-Kelvin terminal of the shunt to
help distribute the current between the layers of the PC
board. The PC board should use 2 or 4 oz. copper for the
layers, resulting in a current carrying capacity in excess of
20 A. Making the current carrying traces on the PC board
fairly large can also improve the shunt’s power dissipa-
tion capability by acting as a heat sink. Liberal use of vias
where the load current enters and exits the PC board is
also recommended.
Shunt Connections
The recommended method for connecting the isolated
modulator to the shunt resistor is shown in Figure 17. VIN+
of the ACPL-796J is connected to the positive terminal of
the shunt resistor, while VIN– is shorted to GND1, with the
power-supply return path functioning as the sense line
to the negative terminal of the current shunt. This allows
a single pair of wires or PC board traces to connect the
isolated modulator circuit to the shunt resistor. By refer-
encing the input circuit to the negative side of the sense
resistor, any load current induced noise transients on the
shunt are seen as a common-mode signal and will not
interfere with the current-sense signal. This is important
because the large load currents flowing through the
motor drive, along with the parasitic inductances inherent
in the wiring of the circuit, can generate both noise
spikes and offsets that are relatively large compared
to the small voltages that are being measured across the
current shunt.
If the same power supply is used both for the gate
drive circuit and for the current sensing circuit, it is very
important that the connection from GND1 of the isolated
modulator to the sense resistor be the only return path
for supply current to the gate drive power supply in order
to eliminate potential ground loop problems. The only
direct connection between the isolated modulator circuit
and the gate drive circuit should be the positive power
supply line.
In some applications, however, supply currents flowing
through the power-supply return path may cause offset
or noise problems. In this case, better performance may
be obtained by connecting VIN+ and VIN– directly across
the shunt resistor with two conductors, and connecting
GND1 to the shunt resistor with a third conductor for the
power-supply return path, as shown in Figure 19. When
connected this way, both input pins should be bypassed.
To minimize electromagnetic interference of the sense
signal, all of the conductors (whether two or three are
used) connecting the isolated modulator to the sense
resistor should be either twisted pair wire or closely
spaced traces on a PC board.
The 39 resistor in series with the input lead (R2) forms
a low pass anti-aliasing filter with the 10 nF input bypass
capacitor (C2) with a 400 kHz bandwidth. The resistor
performs another important function as well; it dampens
any ringing which might be present in the circuit formed
by the shunt, the input bypass capacitor, and the induc-
tance of wires or traces connecting the two. Undamped
ringing of the input circuit near the input sampling
frequency can alias into the baseband producing what
might appear to be noise at the output of the device.
15
Share Link: 