ACPL-312U-000E Avago Technologies US Inc., ACPL-312U-000E Datasheet - Page 15

• Manufacturer Part Number: ACPL-312U-000E
• Description: OPTOCOUPLER IGBT 2.5A 8-DIP
• Manufacturer: Avago Technologies US Inc.

Specifications of ACPL-312U-000E

• No. Of Channels: 1
• Optocoupler Output Type: Gate Drive
• Input Current: 16mA
• Output Voltage: 30V
• Opto Case Style: DIP
• No. Of Pins: 8
• Output Current: 500mA
• Output Voltage Max: 27V
• Isolation Voltage: 3.75kV
• Forward Current If: 20mA
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LED Drive Circuit Considerations for Ultra High CMR Perfor-
mance.
Without a detector shield, the dominant cause of op-
tocoupler CMR failure is capacitive coupling from the
input side of the optocoupler, through the package, to
the detector IC as shown in Figure 29. The ACPL-312U
improves CMR performance by using a detector IC with
an optically transparent Faraday shield, which diverts the
capacitively coupled current away from the sensitive IC
circuitry. However, this shield does not eliminate the ca-
pacitive coupling between the LED and optocoupler pins
5-8 as shown in Figure 30. This capacitive coupling causes
perturbations in the LED current during common mode
transients and becomes the major source of CMR failures
for a shielded optocoupler. The main design objective of
a high CMR LED drive circuit becomes keeping the LED in
the proper state (on or off ) during common mode tran-
sients. For example, the recommended application circuit
(Figure 25), can achieve 25 kV/Ps CMR while minimizing
component complexity. Techniques to keep the LED in the
proper state are discussed in the next two sections.
Figure 29. Optocoupler input to output
capacitance model for unshielded opto-
couplers.
Figure 31. Equivalent circuit for figure 25 during common mode transient.
15
+5 V
1
2
3
4
C
C
LEDN
LEDP
V
+
–
SAT
* THE ARROWS INDICATE THE DIRECTION
OF CURRENT FLOW DURING –d V
1
2
3
4
C
C
I
LEDP
LEDP
LEDN
SHIELD
8
7
6
5
V
+
CM
–
Figure 30. Optocoupler input to output
capacitance model for shielded opto-
couplers.
CM
1
2
3
4
/dt.
8
7
6
5
C
C
LEDP
LEDN
C
SHIELD
LEDO1
0.1
μF
C
+
– V
LEDO2
Rg
CC
CMR with the LED On (CMRH).
A high CMR LED drive circuit must keep the LED on during
common mode transients. This is achieved by overdriv-
ing the LED current beyond the input threshold so that
it is not pulled below the threshold during a transient.
A minimum LED current of 10 mA provides adequate
margin over the maximum IFLH of 5 mA to achieve 25 kV/
μs CMR. CMR with the LED Off (CMRL). A high CMR LED
drive circuit must keep the LED off (V
common mode transients. For example, during a -dV
transient in Figure 31, the current flowing through C
also flows through the R
long as the low state voltage developed across the logic
gate is less than V
common mode failure will occur. The open collector drive
circuit, shown in Figure 32, cannot keep the LED off during
a +dV
C
mended for applications requiring ultra high CMRL per-
formance. Figure 33 is an alternative drive circuit which,
like the recommended application circuit (Figure 25), does
achieve ultra high CMR performance by shunting the LED
in the off state.
= 18 V
LEDN
8
7
6
5
cm
must be supplied by the LED, and it is not recom-
/dt transient, since all the current flowing through
Figure 33. Recommended LED drive circuit for ultra-high CMR.
+5 V
Figure 32. Not recommended open collector drive
circuit.
F(OFF)
+5 V
Q1
1
2
3
4
, the LED will remain off and no
SAT
C
C
and V
1
2
3
4
LEDP
LEDN
SHIELD
C
C
I
LEDP
LEDN
LEDN
SAT
SHIELD
of the logic gate. As
F
≤ V
F(OFF)
) during
8
7
6
5
cm
LEDP
8
7
6
5
/dt