ncp1082 ON Semiconductor, ncp1082 Datasheet - Page 12

• Manufacturer Part Number: ncp1082
• Description: Integrated Poe-pd & Dc-dc Converter Controller With 9v Auxiliary Supply Support
• Manufacturer: ON Semiconductor

Auxiliary Supply Support
networks and minimize the bill of materials, the NCP1082
supports drawing power from an external supply. The
NCP1082 supports the IEEE 802.3af standard when the PoE
capability is available and acts as a regular DC-DC converter
when there is no power source on the Ethernet cable as
shown in Figure 11.
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
To support applications connected to non PoE enabled
When the auxiliary input supply is above 13.5 V, connect
Figure 11. Front and Rear Auxiliary Supply Input with Support for Very Low Input Voltages
R
R
R
VPORT
aux3
aux2
aux1
+
+
+ 20 KW
V
845
V
V
aux
aux
POE(+)
t
for very low
VAUX(−)
VAUX only
POE(−)
R
Optional −
1,2.
*
aux1
Figure 12. Current Limitation Configuration (Inrush & Ilim1 Pins)
* V
* V
. When the auxiliary supply is
V
VAUX(+)
aux
dp
dp
*
V
* V
* V
V
24 K
ILIM1 /
INRUSH
t
dp
VPORTNx
*
t
Raux1
Raux3
d
Or
Raux2
V
* V
d
*
to VPORTN1,2 (Front AUX Configuration)
to RTN (Rear AUX Configuration)
V
t
t
Rdet2
Rdet1
D1
D2
Vbg1
http://onsemi.com
12
VDDA1
VPORTN1,2
ways depending on where the auxiliary supply is injected.
The front, rear and direct auxiliary supply configurations are
explained in more detail in the application note “NCP1082-3
PoE Auxiliary Supply Applications”.
UVLO
AUX
Vdp = 0.5 V the forward voltage drop of the NCP1082
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 12.
VPORTP
Inrush and Operational Current Limitations
Auxiliary supply support can be implemented in three
Note that as soon 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
NCP1082
NCP1082
Switch
VDDA1
Pass
RTN
1,2
, and between ILIM1 and VPORTN
DC−DC Stage
Ilim_ref
Cpd
1,2
as