HCNW3120#300 Avago Technologies US Inc., HCNW3120#300 Datasheet - Page 21

• Manufacturer Part Number: HCNW3120#300
• Description: TRANSISTOR-STAGE-OUTPUT OPTOCOUPLER,1-CHANNEL,1.4KV ISOLATION,SO
• Manufacturer: Avago Technologies US Inc.

Specifications of HCNW3120#300

• Rohs Compliant: NO
• Voltage - Isolation: 5000Vrms
• Number Of Channels: 1, Unidirectional
• Current - Output / Channel: 2.5A
• Propagation Delay High - Low @ If: 300ns @ 7mA ~ 16mA
• Current - Dc Forward (if): 25mA
• Input Type: DC
• Output Type: Gate Driver
• Mounting Type: Surface Mount, Gull Wing
• Package / Case: 8-SMD (400 mil) Gull Wing
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

θ
LED Drive Circuit Considerations for Ultra High CMR Per-
formance. (Discussion applies to HCPL-3120, HCPL-J312,
and HCNW3120)
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 HCPL-3120
improves CMR perform-ance 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
Figure 28. Thermal model.
Figure 29. Optocoupler input to output capacitance model for unshielded
optocouplers.
21
LC
1
2
3
4
= 467 °C/W
C
C
LEDP
LEDN
HCPL-3120 fig 29
T
JE
θ
LD
= 442 °C/W
T
C
θ
CA
T
A
= 83 °C/W*
θ
T
DC
JD
= 126 °C/W
8
7
6
5
HCPL-3120 fig 28
T
T
T
q
q
q
q
*q
DC
LD
CA
JD
LC
JE
C
CA
= LED junction temperature
= detector IC junction temperature
= case temperature measured at the center of the package bottom
= LED-to-case thermal resistance
= LED-to-detector thermal resistance
= detector-to-case thermal resistance
= case-to-ambient thermal resistance
*θ
θ
θ
θ
θ
T
T
T
LC
LD
DC
CA
CA
will depend on the board design and the placement of the part.
JE
JD
C
= CASE TEMPERATURE MEASURED AT THE
= LED JUNCTION TEMPERATURE
= DETECTOR IC JUNCTION TEMPERATURE
= LED-TO-CASE THERMAL RESISTANCE
= LED-TO-DETECTOR THERMAL RESISTANCE
= DETECTOR-TO-CASE THERMAL RESISTANCE
= CASE-TO-AMBIENT THERMAL RESISTANCE
WILL DEPEND ON THE BOARD DESIGN AND
THE PLACEMENT OF THE PART.
CENTER OF THE PACKAGE BOTTOM
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
transients. For example, the recommended application
circuit (Figure 25), can achieve 25 kV/µs CMR while mini-
mizing component complexity.
Techniques to keep the LED in the proper state are
discussed in the next two sections.
Figure 30. Optocoupler input to output capacitance model for shielded
optocouplers.
1
2
3
4
C
C
LEDP
LEDN
HCPL-3120 fig 30
C
SHIELD
LEDO1
C
LEDO2
8
7
6
5