ACPL-796J-500E Avago Technologies US Inc., ACPL-796J-500E Datasheet - Page 13

• Manufacturer Part Number: ACPL-796J-500E
• Description: Isolated Sigma-Delta Mod, T/R+LF
• Manufacturer: Avago Technologies US Inc.

Specifications of ACPL-796J-500E

• Amplifier Type: Isolation
• Number Of Circuits: 1
• Current - Input Bias: 500nA
• Voltage - Input Offset: 3000µV
• Current - Supply: 14mA
• Voltage - Supply, Single/dual (±): 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Current - Output / Channel: -
• -3db Bandwidth: -
• Slew Rate: -
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application Information
Digital Current Sensing Circuit
Figure 18 shows a typical application circuit for motor control phase current sensing. By choosing the appropriate shunt
resistance, any range of current can be monitored, from less than 1 A to more than 100 A.
Figure 18. Typical application circuit for motor phase current sensing.
Power Supplies and Bypassing
As shown in Figure 18, a floating power supply (which in
many applications could be the same supply that is used
to drive the high-side power transistor) is regulated to 5
V using a simple zener diode (D1); the value of resistor
R1 should be chosen to supply sufficient current from
the existing floating supply. The voltage from the current
sensing resistor or shunt (R
the ACPL-796J through an RC anti-aliasing filter (R2 and
C2). And finally, a clock is connected to the ACPL-796J and
data are connected to the digital filter. Although the appli-
cation circuit is relatively simple, a few recommendations
should be followed to ensure optimal performance.
The power supply for the isolated modulator is most
often obtained from the same supply used to power the
power transistor gate drive circuit. If a dedicated supply
is required, in many cases it is possible to add an addi-
tional winding on an existing transformer. Otherwise,
some sort of simple isolated supply can be used, such as
a line powered transformer or a high-frequency DC-DC
converter.
An inexpensive 78L05 three terminal regulator can also be
used to reduce the floating supply voltage to 5 V. To help
attenuate high-frequency power supply noise or ripple, a
resistor or inductor can be used in series with the input of
the regulator to form a low-pass filter with the regulator’s
input bypass capacitor.
13
MOTOR
+
R
SENSE
–
HV+
HV–
SENSE
) is applied to the input of
CIRCUIT
DRIVE
GATE
R2 39 :
FLOATING
POSITIVE SUPPLY
5.1 V
D1
10 nF
C2
R1
C1
0.1 PF
As shown in Figure 18, 0.1 PF bypass capacitors (C1 and
C3) should be located as close as possible to the input and
output power-supply pins of the isolated modulator. The
bypass capacitors are required because of the high-speed
digital nature of the signals inside the isolated modulator.
A 10 nF bypass capacitor (C2) is also recommended at the
input due to the switched-capacitor nature of the input
circuit. The input bypass capacitor also forms part of the
anti-aliasing filter, which is recommended to prevent high
frequency noise from aliasing down to lower frequencies
and interfering with the input signal.
PC Board Layout
The design of the printed circuit board (PCB) should follow
good layout practices, such as keeping bypass capacitors
close to the supply pins, keeping output signals away from
input signals, the use of ground and power planes, etc. In
addition, the layout of the PCB can also affect the isolation
transient immunity (CMR) of the isolated modulator, due
primarily to stray capacitive coupling between the input
and the output circuits. To obtain optimal CMR perfor-
mance, the layout of the PC board should minimize any
stray coupling by maintaining the maximum possible
distance between the input and output sides of the circuit
and ensuring that any ground or power plane on the PC
board does not pass directly below or extend much wider
than the body of the isolated modulator.
V
V
V
GND1
DD1
IN
IN
+
–
ISOLATION
ACPL-796J
BARRIER
MCLKIN
MDAT
GND2
V
DD2
ISOLATED
5 V/3.3 V
NON-
C3
0.1 PF