HCNW3120 applications?as?shown?in??25.?Care?should?be?taken? Application Schematic

Avago Technologies

find HCNW3120 datasheet
HCNW3120 circuit
Applications Information
Eliminating Negative IGBT Gate Drive (Discussion applies 
to HCPL-3120 HCPL-J312  and HCNW3120
To  keep  the  IGBT  firmly  off,  the  HCPL-3120 has  a  very 
low maximum V
OL
 specification of 0.5 V. The HCPL-3120
realizes  this  very  low  V
OL
  by  using  a  DMOS  transistor 
with  1 Ω  (typical)  on  resistance  in  its  pull  down  circuit. 
When  the  HCPL-3120 is  in  the  low  state,  the  IGBT  gate 
is  shorted  to  the  emitter  by  Rg  +  1 Ω.  Minimizing  Rg 
and  the  lead  inductance  from  the  HCPL-3120 to  the 
IGBT gate and emitter (possibly by mounting the HCPL-
3120 on  a  small  PC  board  directly  above  the  IGBT) can 
eliminate the need for negative IGBT gate drive in many 
applications as shown in Figure 25. Care should be taken 
with such a PC board design to avoid routing the IGBT 
collector or emitter traces close to the HCPL-3120 input 
as  this  can  result  in  unwanted  coupling  of  transient 
signals into the HCPL-3120 and degrade performance. (If 
the IGBT drain must be routed near the HCPL-3120 input, 
then the LED should be reverse-biased when in the off 
state, to prevent the transient signals coupled from the 
IGBT drain from turning on the HCPL-3120.) 
+5 V
1
270
2
CONTROL
INPUT
74XXX
OPEN
COLLECTOR
8
0.1 µF
7
+
V
CC
= 18 V
+ HVDC
Rg
Q1
3
6
AC
4
5
Q2
- HVDC
Figure 25. Recommended LED drive and application circuit.
HCPL-3120 fig 25
18