ACPL-7970-500E Avago Technologies US Inc., ACPL-7970-500E Datasheet - Page 16

• Manufacturer Part Number: ACPL-7970-500E
• Description: IsolatedSigmaDelta Mod, TR+IEC+LF
• Manufacturer: Avago Technologies US Inc.
• Series: -r
• Type: Sigma-Delta Modulatorr

Specifications of ACPL-7970-500E

• Operating Supply Voltage: 5.5 V
• Supply Current: 8 mA at 5 V
• Operating Temperature Range: - 40 C to + 105 C
• Mounting Style: SMD/SMT
• Package / Case: DIP-8 Gull Wing
• Input Voltage Range (max): + 200 mV
• Voltage - Isolation: 5000Vrms
• Input Type: DC
• Voltage - Supply: 3 V ~ 5.5 V, 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Lead Free Status / Rohs Status: Details

If the power dissipation in the shunt is too high, the resis-
tance of the shunt can be decreased below the maximum
value to decrease power dissipation. The minimum value
of the shunt is limited by precision and accuracy require-
ments of the design. As the shunt value is reduced, the
output voltage across the shunt is also reduced, which
means that the offset and noise, which are fixed, become
a larger percentage of the signal amplitude. The selected
value of the shunt will fall somewhere between the
minimum and maximum values, depending on the par-
ticular requirements of a specific design.
When sensing currents large enough to cause signifi-
cant heating of the shunt, the temperature coefficient
(tempco) of the shunt can introduce nonlinearity due to
the signal dependent temperature rise of the shunt. The
effect increases as the shunt-to-ambient thermal resis-
tance increases. This effect can be minimized either by
reducing the thermal resistance of the shunt or by using
a shunt with a lower tempco. Lowering the thermal resis-
tance can be accomplished by repositioning the shunt
on the PC board, by using larger PC board traces to carry
away more heat, or by using a heat sink.
For a two-terminal shunt, as the value of shunt resistance
decreases, the resistance of the leads becomes a signifi-
cant percentage of the total shunt resistance. This has two
primary effects on shunt accuracy. First, the effective resis-
tance of the shunt can become dependent on factors such
as how long the leads are, how they are bent, how far they
are inserted into the board, and how far solder wicks up
the lead during assembly (these issues will be discussed
in more detail shortly). Second, the leads are typically
made from a material such as copper, which has a much
higher tempco than the material from which the resistive
element itself is made, resulting in a higher tempco for the
shunt overall. Both of these effects are eliminated when a
four-terminal shunt is used. A four-terminal shunt has two
additional terminals that are Kelvin-connected directly
Table 11. Isotek (Isabellenhütte) four-terminal shunt summary.
Note: Values in brackets are a heatsink for the shunt.
16
Shunt Resistor
Part Number
PBV-R050-0.5
PBV-R020-0.5
PBV-R010-0.5
PBV-R005-0.5
PBV-R002-0.5
Shunt
Resistance
m:
50
20
10
5
2
Tol.
%
0.5
0.5
0.5
0.5
0.5
Maximum
RMS Current
A
3
7
14
25 (28)
39 (71)
across the resistive element itself; these two terminals are
used to monitor the voltage across the resistive element
while the other two terminals are used to carry the load
current. Because of the Kelvin connection, any voltage
drops across the leads carrying the load current should
have no impact on the measured voltage.
Several four-terminal shunts from Isotek (Isabellenhütte)
suitable for sensing currents in motor drives up to 71 Arms
(71 hp or 53 kW) are shown in Table 11; the maximum
current and motor power range for each of the PBV series
shunts are indicated. For shunt resistances from 50 m:
down to 10 m:, the maximum current is limited by the
input voltage range of the isolated modulator. For the 5
m: and 2 m: shunts, a heat sink may be required due to
the increased power dissipation at higher currents.
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.
Motor Power Range
120 V
hp
0.8-3
2-7
4-14
7-25 (8-28)
11-39 (19-71)
ac
– 440 V
ac
kW
0.6-2
1.4-5
3-10
5-19 (6-21)
8-29 (14-53)