HCPL-0870 datasheet(27/28 Pages) HP

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Table 9. Isotek (Isabellenhütte) Four-Terminal Shunt Summary.

Shunt

Maximum

Motor Power Range

Resistance

Tol.

RMS Current

120 Vac-440 Vac

Part Number

Ω

PBV-R050-0.5

0.5

0.8-3

0.6-2

PBV-R020-0.5

0.5

2-7

1.4-5

PBV-R010-0.5

0.5

4-14

3-10

PBV-R005-0.5

0.5

25 [28]

7-25 [8-28]

5-19 [6-21]

PBV-R002-0.5

0.5

39 [71]

11-39 [19-71]

8-29 [14-53]

Note: Values in brackets are with a heatsink for the shunt.

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 9; the

maximum current and motor

power range for each of the PBV-

series shunts are indicated. For

shunt resistances from 50 m

Ω

down to 10 m

Ω, the maximum

current is limited by the input

voltage range of the isolated

modulator. For the 5 m

Ω and

Ω 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 modula-

tor; 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

dissipation 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 modula-

tor to the shunt resistor is shown

in Figure 21. VIN+ (pin 2 of the

HPCL-7860) is connected to the

positive terminal of the shunt

resistor, while VIN- (pin 3) is

shorted to GND1 (pin 4), with the

power-supply return path func-

tioning 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

referencing 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 connec-

tion 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 con-

nection between the isolated

modulator circuit and the gate

drive circuit should be the

positive power supply line.

Shunt Resistor

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