Datasheet

NCL30081
http://onsemi.com
26
CS Pin Short Circuit Protection
Normally, if the CS pin or the sense resistor is shorted to
ground, the Driver will not be able to turn off, leading to
potential damage of the power supply. To avoid this, the
NCL30081 features a circuit to protect the power supply
against a short circuit of the CS pin. When the MOSFET is
on, if the CS voltage stays below V
CS(low)
after the adaptive
blanking timer has elapsed, the controller shuts down and
will attempt to restart on the next V
CC
hiccup.
+
−
CS
Q_drv
CS_short
S
R
Q
UVLO
BO_NOK
Adaptative
Blanking Time
Figure 54. CS Pin Short Circuit Protection Schematic
Q
V
CS(low)
V
VIN
Fault Management
OFF Mode
The circuit turns off whenever a major condition prevents
it from operating:
• Incorrect feeding of the circuit: “UVLO high”. The
UVLO signal becomes high when V
CC
drops below
V
CC(off)
and remains high until V
CC
exceeds V
CC(on)
.
• V
CC
OVP
• Output diode short circuit protection: “WOD_SCP
high”
• Output / Auxiliary winding Short circuit protection:
“Aux_SCP high”
• Die over temperature (TSD)
• Brown−Out: “BO_NOK” high
• Pin CS short circuited to GND: “CS_short high”
In this mode, the DRV pulses are stopped and the
controller turn−off some circuits to decrease the internal
consumption. V
CC
voltage decrease through the controller
own consumption (I
CC1
).
For the output diode short circuit protection, the output /
aux. winding short circuit protection and the V
CC
OVP, the
controller waits 4 seconds (auto−recovery timer) and then
initiates a startup sequence (V
CC
≥ V
CC(on)
) before
re−starting switching.
Latch Mode
This mode is activated by the output diode short−circuit
protection (WOD_SCP) and the Aux_SCP in version A
only.
In this mode, the DRV pulses are stopped and the
controller is latched. There are hiccups on V
CC
.
The circuit un−latches when V
CC
< V
CC(reset)
.