ncp1083 ON Semiconductor, ncp1083 Datasheet - Page 14

• Manufacturer Part Number: ncp1083
• Description: Integrated High Power Poe-pd Interface & Dc-dc Converter Controller With 9v Auxiliary Supply Support
• Manufacturer: ON Semiconductor

the AUX pin to VPORTN
below 13.5 V (but above 9 V), calculate the voltage dividers
Raux1, Raux3 and Raux2, Rdet1, Rdet2 to divide the input
voltage to at least 2 V at the UVLO pin and 2 V at the AUX
pin, using the following formulas. Note the maximum
voltage is 3.3 V.
With
Vd is the voltage drop over the rectifiers and masking diodes
(typical 0.6 V), and
When the auxiliary input supply is above 13.5 V, connect
R
R
R
aux3
aux2
aux1
+
+
+ 20 KW
V
845
V
V
aux
VPORTNx
aux
t
R
1,2
*
aux1
Figure 14. Current Limitation Configuration (Inrush & Ilim1 Pins)
* V
* V
Vds_pgood
. When the auxiliary supply is
1 V / 9.2 V
V
threshold
aux
dp
dp
*
V
* V
* V
V
24 K
ILIM1 /
INRUSH
Figure 15. Inrush and Ilim1 Selection Mechanism
t
dp
VPORTNx
*
t
d
V
* V
VDS_PGOOD
d
*
VDDA1
V
t
t
Inrush
Ilim1
Vbg1
http://onsemi.com
0
1
&
detector
14
VDDA1
NCP1083
Vdp = 0.5 V the forward voltage drop of the NCP1083
internal diode, and
Vt is the desired voltage at the AUX pin.
PoE interface (detection and classification) is disabled and
does not allow the PD device to be powered from the
Ethernet until the auxiliary supply is removed.
Ethernet cable before the auxiliary supply is connected, the
power will continue to be supplied from the Ethernet cable
unless the voltage of the auxiliary supply is higher than the
Ethernet supply voltage.
are programmed individually by an external Rinrush and
Rilim1 resistors respectively connected between INRUSH
and VPORTN
shown in Figure 14.
Inrush and Operational Current Limitations
Current_limit_ON
Note that as soon as the auxiliary supply is connected the
If the PoE PD device was drawing the current from the
The inrush current limit and the operational current limit
VDDA1
NCP1083
VDDA1
1,2
, and between ILIM1 and VPORTN
Pass Switch
2 V
I_pass_switch
Ilim_ref
VDDA1
RTN
1,2
as