HCPL-5120 Datasheet, PDF (13/16 Pages) Agilent(Hewlett-Packard) – 2.0 Amp Output Current IGBT Gate Drive Optocoupler

+5 V
1
270 Ω
2
CONTROL
3
INPUT
74XXX
4
OPEN
COLLECTOR
8
0.1 µF
7
6
5
+_ ^{V CC = 15 V}
Rg
Q1
_ ^V EE ^{= -5 V}
+
Q2
+ HVDC
3-PHASE
AC
- HVDC
Figure 26. Typical Application Circuit with Negative IGBT Gate Drive
P_E Parameter Description
I_F
LED Current
V_F
LED On Voltage
Duty Cycle
Maximum LED
Duty Cycle
P_O Parameter Description
I_CC
Supply Current
V_CC
Positive Supply
Voltage
V_EE
Negative Supply
Voltage
E_SW (Rg, Qg)
Energy Dissipation in
the HCPL-5120 for
each IGBT Switching
Cycle (See Figure 27)
f
Switching Frequency
7
Qg = 100 nC
6
Qg = 250 nC
Qg = 500 nC
5
4
V_CC = 19 V
VEE = -9 V
3
2
1
0
0
20
40
60
80 100
Rg - GATE RESISTANCE - Ω
Figure 27. Energy Dissipated in the HCPL-5120
for Each IGBT Switching Cycle
LED Drive Circuit Considerations for
Ultra High CMR Performance.
Without a detector shield, the
dominant cause of optocoupler
CMR failure is capacitive
coupling from the input side of
the optocoupler, through the
package, to the detector IC as
shown in Figure 28. The HCPL-
5120 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
capacitive coupling between the
LED and optocoupler pins 5- 8
as shown in Figure 29. 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 transients. For example,
the recommended application
circuit (Figure 25), can achieve
10 kV/µs CMR while minimizing
component complexity.
Techniques to keep the LED in
the proper state are discussed
in the next two sections.
1
8
CLEDP
2
7
3
6
CLEDN
4
5
Figure 28. Optocoupler Input to Output Capaci-
tance Model for Unshielded Optocouplers.
1
C_LEDO1
8
CLEDP
2
7
CLEDO2
3
C_LEDN
6
4
5
SHIELD
Figure 29. Optocoupler Input to Output Capaci-
tance Model for Shielded Optocouplers.
13