ACPL-7970-500E Avago Technologies US Inc., ACPL-7970-500E Datasheet - Page 17

• 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

Shunt Connections
The recommended method for connecting the isolated
modulator to the shunt resistor is shown in Figure 19. V
of the ACPL-7970 is connected to the positive terminal of
the shunt resistor, while V
power-supply return path functioning 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 connection 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 connec-
tion between the isolated modulator circuit and the gate
drive circuit should be the positive power supply line.
Figure 21. Schematic for three conductor shunt connection.
17
MOTOR
+
R
SENSE
–
IN
– is shorted to GND1, with the
HV+
HV–
CIRCUIT
DRIVE
GATE
R2a 2.2
R2b 2.2
FLOATING
POSITIVE SUPPLY
5.1 V
D1
IN
+
GND1
R1
C1a 1 F
C1b 0.1 F
In some applications, however, supply currents flowing
through the power-supply return path may cause offset
or noise problems. In this case, better performance may
be obtained by connecting V
the shunt resistor with two conductors, and connecting
GND1 to the shunt resistor with a third conductor for the
power-supply return path, as shown in Figure 21. When
connected this way, both input pins should be bypassed.
To minimize electromagnetic interference of the sense
signal, all of the conductors (whether two or three are
used) connecting the isolated modulator to the sense
resistor should be either twisted pair wire or closely
spaced traces on a PC board.
The resistor R2 in series with the input lead forms a low
pass anti-aliasing filter with the input bypass capacitor
C2. The resistor performs another important function
as well; it dampens any ringing which might be present
in the circuit formed by the shunt, the input bypass
capacitor, and the inductance of wires or traces connect-
ing the two. Undamped ringing of the input circuit near
the input sampling frequency can alias into the baseband
producing what might appear to be noise at the output
of the device.
C2
100nF
V
V
V
GND1
DD1
IN+
IN–
ISOLATION
ACPL-7970
BARRIER
MDAT
GND2
MCLK
V
DD2
IN
+ and V
ISOLATED
5 V/3.3 V
GND2
NON-
IN
C3a
0.1 F
– directly across
C3b
1 F