Avago Technologies ACPL-224-500E - Manual (Page 56)

AV02-4387EN 53 Avago Technologies
Low Cost Isolated Phase Current Sensing with Analog Output
Motor Control Applications
Description
The HCPL-7840 Isolation Amplifier
can be used for isolating the motor
current sensing element from the
control circuit while at the same
time transmitting precision analog
signals. This circuit requires a low
cost shunt resistor for monitor-
ing the motor current. The voltage
across the sensing resistor is fed
to the HCPL-7840 input pins 2 and
3. A floating power supply (which
in many applications could be the
same one used to drive the high
side power transistors) is regulated
to 5 V using a simple three-terminal
voltage regulator, 78L05. The differ-
ential output from the HCPL-7840
isolation amplifier is converted to
a ground-referenced single-ended
output voltage with a simple differ-
ential amplifier circuit (MC34082A
and associated components).
Performance of Circuit
• Sense current: Up to 200 A
• Optocoupler bandwidth: Up to
100 kHz
• Optocoupler nonlinearity: 0.2%
• Optocoupler input offset voltage:
0.2 mV (typical)
• Optocoupler common­mode re-
jection: 15 kV/ µs
Benefits
• Small size and lower profile
circuit compared to Hall-Effect
device current sensing circuits.
• Industry standard low profile
components are used in this cir-
cuit.
• High precision measurement
while maintaining common
mode transient immunity.
Alternative Avago Parts
1) HCPL-7800A: 1% part-to-part
gain tolerance, HCPL-7800: 3%
part-to-part gain tolerance.
2) HCPL-788J: single ended output
isolation amplifier with integrat-
ed over current detection.
3) HCPL-7860 and HCPL-7870/
HCPL-0870: isolated 15 bit A/D
converter.
4) HCPL-786J: isolated 15 bit A/D
converter.
2.00 k Ω
10.0 k Ω
10.0 k Ω
2.00 k Ω
0.1 µF
0.1 µF
0.1 µF
0.1 µF
0.1 µF
0.01
µF
V OUT
R SENSE
M
IN OUT
78L05
HV+
+SUPPLY
39 Ω
1
2
3
4
8
8
7
6
5
4
7
150 pF
150 pF
6
5
HV–
+5 V
+5 V
-15 V
+15 V
+ –
–
+
MC34082A
HCPL-7840