ncp1081 ON Semiconductor, ncp1081 Datasheet - Page 14

• Manufacturer Part Number: ncp1081
• Description: Integrated High Power Poe-pd Interface & Dc-dc Converter Controller
• Manufacturer: ON Semiconductor

capacitor is charged with the INRUSH current (in order to
limit the internal power dissipation of the pass−switch).
Once the Cpd capacitor is fully charged, the current limit
switches from the inrush current to the current limit level
(ilim1) as shown in Figure 12. This transition occurs when
both following conditions are satisfied:
Vds_pgood is true (meaning that RTN−VPORTN
below the high level of Vds_pgood). This mechanism allows
a current level transition without any current spike in the
pass−switch because the operational current limit (ilim1) is
enabled once the pass−switch is not limiting the current
anymore, meaning that the Cpd capacitor is fully charged.
When VPORT reaches the UVLO_on level, the Cpd
The operational current limit will stay selected as long as
1. The VDS of the pass−switch is below the
2. The pass−switch is no longer in current limit
Vds_pgood low level (1 V typical).
mode, meaning the gate of the pass−switch is
“high” (above 2 V typical).
VPORTNx
Figure 11. Current Limitation Configuration (Inrush & Ilim1 Pins)
Vds_pgood
1V / 9.2V
threshold
ILIM1 /
INRUSH
VPORTNx
Figure 12. Inrush and Ilim1 Selection Mechanism
VDDA1
VDS_PGOOD
Inrush
Ilim1
Vbg1
http://onsemi.com
1,2
0
1
VDDA1
&
is
detector
14
Current_limit_ON
NCP1081
Thermal Shutdown
down the device in case of high power dissipation. Once the
thermal shutdown (TSD) threshold is exceeded, following
blocks are turned off:
•
•
•
•
voltage is still above the UVLO level, the NCP1081
automatically restarts with the current limit set in the inrush
state, the DC−DC controller is disabled and the Css
(soft−start capacitor) discharged. The DC−DC controller
becomes operational as soon as capacitor Cpd is fully
charged.
The NCP1081 includes thermal protection which shuts
When the TSD error disappears and if the input line
DC−DC controller
Pass−switch
VDDH and VDDL regulators
CLASS regulator
NCP1081
VDDA1
VDDA1
2V
Ilim_ref
Switch
Pass
I_pass_switch
RTN