Avago Technologies ACPL-224-500E - Manual (Page 58)

AV02-4387EN 55 Avago Technologies
Low Cost Isolated Phase Current Sensing with Analog Output and Over Current Detection
Motor Control Applications
Description
The HCPL-788J can be used for iso-
lating the motor current sensing
element from the control circuit
while at the same time transmit-
ting precision analog signals and
over current fault signal. This circuit
requires a high precision-sensing
resistor for monitoring the motor
current. The voltage across the
sensing resistor is fed to the HCPL-
788J input pins 2 and 3. The single-
ended output allows it to interface
directly with the A/D port of the
micro-controller. The sensing resis-
tor is available from several suppli-
ers, which are listed in the “Inverter
Design using Gate Drive and Current
Sense Optocoupler” section.
Performance of Circuit
• Overcurrent fault response: 3 µs
typical
• Sense current up to 100 A or
more
• Bandwidth: 30 kHz typical
• Nonlinearity: 0.06% typical
• Input offset voltage: 3 mV max.
over temp.
• Common­mode rejection: 10 kV/
µs@V
CM
= 15 kV min.
Benefits
• No additional fault detection cir-
cuitry needed
• Direct interface with micro­con-
troller
• Smaller size and lower profile
compared to Hall-Effect device
based current sensing circuits
• High precision measurement
while at the same time maintain-
ing transient immunity
5
FLOATING
POSITIVE
SUPPLY
1
2
8
7
3
4
6
16
15
14
C8
13
12
11
10
9
GND 2
V DD2
FAULT
ABSVAL
V OUT
V REF
V DD2
GND 2
V DD1
V IN+
V IN–
GND 1
V DD1
C H
C L
V LED+
A/D
TO OTHER
PHASE
OUTPUTS
GATE DRIVE
CIRCUIT
C4 C7 C5
R3 4.7 k Ω
C6
0.1 µF
+5 V
GND
C5 = C7 = C8 = 470 pF
C4 = 0.1 µF
V REF
µC
HCPL-788J
C1
0.1 µF
C2
0.1 µF
D1
5.1 V
R2
39 Ω
R1
HV +
+ +
R SENSE
MOTOR
HV +
+
–
R4