Application Information, cont’d.
However, if the DC/DC PWM Converter with the ENABLE input
circuit configuration was active HIGH, then the apparent choice
of the HV301 would result in the creation of a current path
through the protective diode clamp of the ENABLE input and the
PWRGD output MOSFET of the HV301. For this situation the
HV311 should be used as shown below in Application Circuit 2.
HV301/HV311
In some applications the PWRGD signal is used to activate load
circuitry on the isolated output side of the DC/DC PWM Con-
verter. In this situation an optocoupler is needed to provide the
required isolation as shown below in Application Circuit 3.
GND
R1
487kΩ
R2
6.81kΩ
R3
9.76kΩ
-48V
8
VDD
PWRGD
1
3 UV
2 OV
HV311
RAMP VEE
7
4
C1
10nF
SENSE GATE
5
6
R4
12.5mΩ
Q1
IRF530
+
Cload
-
ENABLE
+5V
DC/DC
PWM
CONVERTER
COM
Note: capacitor may be needed to slow PWRGD dv/dt if
oscillations are observed when VIN is close to OV.
Application Circuit 2
GND
R1
487kΩ
R2
6.81kΩ
R3
9.76kΩ
-48V
8
VDD
3 UV
2 OV
1
PWRGD
HV311
RAMP VEE SENSE GATE
7
4
5
6
C1
10nF
R4
12.5mΩ
Q1
IRF530
Optocoupler
Rload
ENABLE
+5V
Cload
DC/DC
PWM
COM
CONVERTER
Note: capacitor may be needed to slow PWRGD dv/dt if
oscillations are observed when VIN is close to OV.
11
Application Circuit 3